Understanding HVDC/FACTS Controller’s Sustainable Development & Comparative Analyses of GTO, GCT, IGBT, MTO, ETO, MCT and MOSFET Operations

Published by Badr Mesned Alshammari1, Tariq Masood2, Muhammad Tajammal Chughtai1, Samer Karim3, University of Hail, Hail, Saudi Arabia (1), Dukhan Operations, Qatar Petroleum (2), Maintenance Department QAFAC (3)

Abstract. This article presents a comparative study through analyses regarding a number of power electronics devices. Power Electronic devices have innovative contribution to control the electrical power operations with a degree of precision. The GTO normally are not equipped with amplifying gates. The Asymmetric GTOs are inherently equipped with fast recovery diodes across each GTO, for reverse operations based on the that reverse voltage capability is not required for GTOs operations. This also provide techno economic benefits high voltage, voltage drop and current ratings capability. It can sustain against, short and long-time overcurrent.

Streszczenie. W artykule przedstawiono analize porównawczą różnych elementów elektronicznych stosowanych w energoelektronice. Analizowano także wpływ właściwości tych elementów na prtacę urządzeń energetyki, takich jak np. sterowniki wysokonapięciowe FACTS. Analiza wpływu właściwości elementów elektronicznych na pracę układów energoelektroniki, takich jak sterownik FACTS.

Keywords: diode, transistor, thyristor, FACTS Devices
Słowa kluczowe: elementy elektroniczne, układy energoelektroniki

Introduction

Electrical power system operations never been ideal, as the load vary the power utilities will use its maximum capability to manage the operating scenarios requirements as occurred. We are very much conversant as the load increases; the power utilities will use their maximum facilities to meet the requirements. The innovation of GTO Thyristors led toward development of power transmission Operational control that provide flexible controllability for the power transmission network with a degree of precision. Herewith, we have simulated 400 Mvar 400 kV TCSC (Thyristor Control Series Capacitor) and +200Mvar, 220 kV STATCOM (static synchronous compensator) which have been introduced in UPFC control mechanism at the GCC Power grid [1].

a) Diode

This is a two layers device which conduct unidirectional operations, this device also operates forward direction from Anode to Cathode. The diode device did not equip with gate to control the forward conduction. The diode did not conduct in reverse direction when diode polarity is reversed, the cathode become positive against the anode polarity.

b) Transistor

This is three layers device (electrodes) and it conducts in forward direction when collector (electrode) is biased positive with respect to emitter. The transistor will start functioning, when current or voltage signal is applied to the device, this is called the base part of the Transistor.

c) Thyristor

This device contains four layers, it conducts fully in forward direction when anode is at positive potential against the cathode. The turn on signal of voltage or current applied to operate the third electrode known as gate. There are two types of Thyristor, firstly symmetrical device equipped to block both forward and reverse directions and the other symmetrical device which blocks only the forward direction. Thyristor is an essential device for the FACTS Controllers.

Power Electronics application

a) GTO Operations

The Power Electronic devices have innovative contribution to control electrical power operations and control it with a degree of precision. In order to turn on a GTO gate it required 3-4% current of 1000A GTO device for a time of 10Sec. However, for the GTO turn off operation, it required 30-40% current pulse for an interval of 20- 35Sec. In order to drive high current, pulse required low voltage from 10-15 Volts and this pulse remained in operations up to 20-40Sec. It indicates that the GTO turn off operations required very small energy. But large losses and significant cooling factors are economical limitation for the GTO operations. For the GTO to turn-off it required 10- 15% energy as compared to GTO turn on energy required 10-15 for the Thyristor device. The GTO did not equip with amplifying gates. The Asymmetric GTOs inherently are equipped with fast recovery diode connected across each GTO. For reverse operations which is based on reverse voltage capability is not required for GTOs operations. This also provide techno economic benefits such as high voltage, voltage drop and current ratings capability. It can sustain against, short and long-time overcurrent [2].

b) Turn on and Turn off Operations

As discussed above the GTOs inherently acquired high switching losses and stress during turn on and turn off processes with associated device. During turn-on process the current pulse of 3-4% is applied to the load current for 10 microseconds with a fast increase gate-circuit inherently in-built inductance which is pertained from gate to cathodecircuit to start the operations. There is small delay before the cathode and anode circuit current operations to rise and voltage begins to fall immediately. The GTO turn-off process is executed by reverse conducting diode operations, this is another valve like situation in the same operational phase. This is important to learn that during GTO turn on operations, large reverse leakage current of the diode can be anticipated. Therefore, on turn-on operations it is very important and to consider some current from 0.2-45% to be maintained to prevent unlatching of the GTO. This is also known back porch current. As demonstrated below in Figure 1(a) the GTO can be turned off by –ve and turn on by +ve gate signal. Sometimes the Thyristor gate did not properly go off and lose their control. In order to switch off properly, a special technique is used this is also known commutation. Due to commutation, this device is not viable economically. Therefore, the GTO is technically and economically being justified. In the diode symbol, there are two arrows the forward arrow shows positive signal to turn on the GTO and backward arrow shows negative signal to turn-off the GTO. Figure 1(b) shows the two transistor PNP and NPN back to back analogy, it becomes as a GTO connection. The PNP transistor acquired low gain value, the Thyristor is switched on when positive gate supply is provided. When current is flowing from Anode this is known emitter current (IE1) and (IB1) and collector current (IC1) this flows through NPN transistor. When G1 gate is activated with +ve pulse current the current start flowing from anode to the cathode, and a current pulse flows from G1 to cathode. When –ve current pulse is applied at G1 the collector current would not reduce but will remain the same and oppose the IB2 based current and the GTO will be turned off. This high-performance device used for FACTS/HVDC devices in particularly for reactive power compensation and adjustable frequency inverter [3,4].

Fig. 1: GTO (Gate Turn off Thyristor Analogy)

MTO Operations

MOS Turn-on Thyristor device which is developed as a combination of MOSFET and GTO devices. In order to address conventional GTO operational issue, the MTO is the solution to address the limitation of GTO application as given below.

Snubber circuit, dv/dt and Gate drive power requirements.

The MTO gives more significant performance, it required very small power to drive the gate and also reduced turn off time from 20-30µsec to 1-2µsec, leading to reduction of device system cost. It also reduced the losses because of eliminated storage time which demonstrates high dv/dt at small snubber capacitors and eradicated snubber resistance in the MTO circuit. This is combination of MOSFET and GTO devices.

ETO Operations

ETO Operations contain two Gates, one gate is used to turn on and other is in series to (MOSFET) and is used for turn-off. The Turn-off voltage applied at the N-MOSFET, transfers all the current from the cathode via MOSFET into the base. It occurred the fast turn-off and stopping the regenerating latched state. This is also imperative, the MOSFET did not see high voltage, no matter how high ETO voltage occurred. The ETO contains following merit and demerit as listed below.

• The main advantage of the series MOSFET gate is that the current transfer from cathode is wide-ranging and swift.

• The MOSFET carry the main GTO current, leading to increase the voltage drop and corresponding losses. In fact the MOSFET is low voltage control device from 0.3 to 0.5V, whereas, this is not significant.

GCT and IGCT Operations

GCT (Gate commutated Thyristor) is hard switched GTO which contains high large and swift current pulse which allow the full rated flow of current. To reduce the inductance of the Gate circuit to a lowest possible value, a fast-rising high gate current pulse is applied by incorporating special efforts of the GCT (IGCT), as required for the ETO and MTO to the possible extent. Key element is that GCT is being achieved by fast gate drive response and this is attained by applying coaxial cathode-gate which is feed through a multi-layered gate derive circuit.

IGBT Operations

This is combination of BJT and PMOSFET having high input impedance and low on state power loss as it happens in case of a BJT. This device is also known as metal oxide insulated gate transistor (MOSIGT) and it conductively modulated field effect transistor (COMFET), gain modulation FET(GEMFET) and insulated gate transistor (IGT). Figure 2(a) depicts when Vcc is supplied, it will pass to collector also known as IC (collector current). If there is zero voltage at VG (gate voltage) then VCE (collector emitter voltage) and VCC will be equal. When VG (Gate Voltage) is provided it will produce VGE (gate emitter voltage) as soon as it increases the VCE will reduce against the Vcc this point is called the breakdown point and IGBT starts conducting. Figure 2(b) represents the VGE against the Ic (collector current) as the VGE voltage increases the Ic will increases the VGEt is called the (gate threshold voltage) as Ic starts flowing at its maximum value [5].

Fig. 2: IGBT operations

Fig. 3: IGBT operational characteristics

Figure 3 presents the IGBT characteristics, this depicts a graph between Ic (collector current) and Vce (Collector Emitter Voltage). When VGE is equal to zero as given, IGBT will remain in off position or cut-off condition during that time whatever current flows this is called the leakage current. As the VG supply increases the VGE1 will increase and reach its breakdown point where IGBT starts conducting, as soon as the base voltage increases the VGE2, VGE3, VGE4, and VGE5 will also increases, under this condition the IC will reach at its active state and stabilize, this is conduction state of the IGBT. In the graph, red line represents the load line when IGBT will be on the VCE (Collector Emitter Voltage) and it is zero and IC will be at its maximum. As soon as the collector current stabilizes this is known as active line of the IGBT operations [7,8].

MCT Operations

This device incorporates the MOSFET structure for both turn-on and turn-off operations and also gives fast turn-off and turn-on operations with low switching losses. The required power and energy for this operation is very small or negligible. It also contains characteristic of delay time (storage time). Secondly as latching device operations it contains low on state voltage drop with precision as for Thyristor.

Main advantage of this device compared to other turnoff devices. The MOS gate both turn-on and off operation is very close to the distributed cathode, this may lead to incur low switching losses at fast switching operations for Thyristor device. This device also demonstrates ultimate Thyristor operations with low on-state switching losses.

MOSFET Operations

This type of transistor can carry the fast switching speed and low switching losses and also controlled by applying voltage rather than current. This is extensively used for low power devices application but unsuitable for high power devices. This device required low energy to operate and comprises with very fast switching speed and low switching losses.

This is an ideal for gate amplifying device because it has high forward on-state resistance as well as high on-state losses. Therefore, this device is not suitable for power devices operations.

FACTS/HVDC Technology development where it is today

First HVDC project commission in 1954 at Gotland with 100 kV and carry only 20-Megawatt DC power. Recently, due to technological developments the HVDC voltage reached at 800 kV and power transferable capacity approached up to 8000 MW. In fact, the innovation of Thyristor valve replaced the mercury arc valve in 1960. The Thyristor based HVDC converter and inverter-based station was commissioned in 1972. The Thyristor based HVDC control topology was simple as compared to mercury arc control valve. Secondly, maintenance and operating cost was nominal as compared to mercury arc control valve. As discussed earlier, the Thyristor has a drawback that is it has only turn-on capability but not turn-off. This is not possible to leave the device in none-conducting mode. In fact, noneconducting mode is managed and control by the network grid electrical flow which leads the device to respond to a reverse bias operation and this cannot be controlled directly.

Thyristor was used first time in 1970 and many innovative developments have been witnessed and is still being used predominantly in the World by large. This device is well reputed and matured for its application in large power transmission generation and transmission network from hundreds to thousands of megawatts. Whereas, the IGBT has an advanced level of Thyristor based control in HVDC/FCTS controllers.

The major difference in IGBT and Thyristor is that IGBT has a turn-on and turn-off capability from external control signal. It has acquired advance and independent operational control and has no relation to network grid power flow. As far as the installation is concerned it has very small footprint which is easy to accommodate and power flow from/to offshore power generation facilities. This is superior device compare to Thyristor but with limited power flow capabilities. This is new device, still lot of innovation is required to fit in HVDC/FACTS devices purposefully. As we have discussed earlier the IGBT based HVDC has been developed and implemented up to 1000 megawatt per pole and Thyristor based HVDC has reached at 8000 megawatts[9].

Table 1: Abbreviation and Synonyms

.
Study Comparative Analyses of Thyristor and Transistor Operations

The transistor devices principally have an excellent switching performance, its fast switching conduction operations and lower switching losses. But Thyristor has low switching losses and it can handle higher power capability as compared to the Transistor control and switching operations. Further development is in progress to achieve best of both Thyristor control and on-state operations having low switching losses and to handle higher power capability.

Conclusion

This paper presents the promising operational impact of GTOs to enhance the performance of the FACTS devices (UPFC, STATCOM, SSSC) Controller on Multiple Bus system on the power grid which is assessed by using Matlab modeling and simulation. The Matlab tool is very much expedient to identify and determine the GTOs behavioural characteristic performance. These GTOs have versatile capability and capacity. EMTP is used to validate the Matlab model credibility. TNA has confirmed GCC network operational credibility of the approximation and developed new power system operational technique. The Matlab codes are provided and developed step by step to perform fast pragmatic operational studies to Assess UPFC suitability and application on the GCC Power grid.

REFERENCES

1. Wollard K., Uno lamm: inventor and activist, IEEE Sectrume., 25(1988), nr 3, 43-45
2. Kimbark E.W., Direct Current Transmission. New York: Wiley, vol.1,1971.
3. Siemens _High Voltage DC transmission system (HVDC), (2017), http://www.energy.siemens.com/hq/en/powertransmission/hbdc/
4. Okeke T., Zaher R., Flexible AC Transmission Systems (FACTS) published IEEE Conference, (2013)
5. Bocovich M., Mohan N., Overview of Series Connected Flexible AC Transmission Systems (FACTS), IEEE Conference ( 2013)
6. X.Y Zhou X. Y., Aggarwal R. K., Detailed modelling and simulation of UPFC using EMTP, IEEE Conference ( 2014)
7. Yadav M., Soni A., Improvement of power flow and voltage stability using unified power flow controller, ICEEOT (2016).
8. Masood T., Qureshi S.A., FACTS Control Devices (STATCOM, SSSC and UPFC) Re-Configuration Techniques By PSIM/MATLAB, IEEE-ICEE (2007) Lahore, Pakistan
9. U. Lamm A. U., The peculiarties of high-voltage dc power transmission, IEEE Spectrum., 3(1966), nr.8, 76-84.

Authors: Dr. Badr Mesned Alshammari, Associate Professor, Department of Electrical Engineering, College of Engineering, University of Hail, Hail, KSA. E-mail: bms.alshammari@uoh.edu.sa; Dr. Tariq Masood, Dukhan Operations, Qatar Petroleum, Qatar. E-mail: t.masood.dr@bath.edu; Prof. Dr. Muhammad Tajammal Chughtai, Department of Electrical Engineering, College of Engineering, University of Hail, Hail, KSA. Email: chughta@yahoo.com; Samer Karim, Maintenance Department, QAFAC, Qatar. E-mail: samerk@qafac.com.qa .

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 96 NR 3/2020. doi:10.15199/48.2020.03.25

ADALINE Harmonics Extraction Algorithm applied to a Shunt Active Power Filter based on an Adaptive Fuzzy Hysteresis Current Control and a Fuzzy DC Voltage Controller

Published by Noureddine KHENFAR, Abdelhafid SEMMAH, Mohamed KADEM, Djillali Liabes University of Sidi Bel Abbes, Algeria.

Abstract. This paper deals with the use of an adaptive linear (ADALINE) neural network in a harmonic extraction algorithm based on the calculation of instantaneous active and reactive powers. This technique, called “ANN-PQ”, is developed in order to achieve an effective separation between the fundamental and harmonic components of the instantaneous powers, which used as reference variables in the control of the shunt active power filter (SAPF). In order to further increase the filtering performances of the SAPF, fuzzy logic theory is used in two parts of the SAPF control system. The first concerns the modulation technique where the hysteresis band of the current control strategy will be generated by a fuzzy inference system. In the second part, the fuzzy logic will be integrated into the external control loop of the SAPF to maintain the DC voltage at its reference value. The numerical simulation results, given at the end of this paper, clearly show the effectiveness of the proposed control techniques.

Streszczenie. W artykule omówiono zastosowanie adaptacyjnej liniowej sieci neuronowej (ADALINE) w algorytmie ekstrakcji harmonicznych opartym na obliczaniu chwilowych mocy czynnych i biernych. Technika ta, zwana „ANN-PQ”, została opracowana w celu uzyskania skutecznego oddzielenia składowych podstawowych i harmonicznych mocy chwilowych, które są wykorzystywane jako zmienne odniesienia w sterowaniu bocznikowym filtrem mocy czynnej (SAPF). W celu dalszego zwiększenia wydajności filtrowania SAPF, w dwóch częściach systemu sterowania SAPF zastosowano teorię logiki rozmytej. Pierwsza dotyczy techniki modulacji, w której pasmo histerezy jest generowane przez rozmyty system wnioskowania. W drugiej części logika rozmyta została zintegrowana z zewnętrzną pętlą sterowania SAPF, aby utrzymać napięcie stałe na jego wartości odniesienia. (Algorytm ekstrakcji harmonicznych ADALINE zastosowany do bocznikowego aktywnego filtru mocy w oparciu o sterowanie prądem adaptacyjnej rozmytej histerezy)

Keywords: Shunt active power filter, ADALINE estimation, fuzzy band hysteresis, DC fuzzy logic control.
Słowa kluczowe: równoległy aktywny filtr mocy, estymacja ADALINE, histereza pasma rozmytego, sterowanie logiką rozmytą DC.

Introduction

The proliferation of power electronics devices and the intensive use of nonlinear loads, as well as the widespread use of static converters in industrial systems and appliances, have a harmful effect on the energy quality of the power grid [1,2]. This degradation of the electrical energy quality is mainly due to the absorption of non-sinusoidal currents and the reactive power consumption by these non-linear loads.[2,3].

Active filtering of electric power using a shunt active power filter (SAPF) has now become a mature technology and a superior solution to passive filters for harmonic mitigation and reactive power compensation[3]. Since their basic compensation principles were introduced by Gyugyi and Strycula in 1976, many researches have been done on active filters and their practical applications[5,6]. Connected to the three-phase line system, the SAPF works as voltage source inverter. Its basic function is the injection of harmonic load currents in opposite-phase into the system so that to ensure a sinusoidal line current[6]–[8].

The control system of an SAPF is usually divided into two parts. The first, which is of a great importance, is the generation of reference harmonic signals. The second is the generation of control signals of the inverter switches. These two parts are crucial in the performance of the SAPF. The reduction of the THD of the line current and the improvement of the power factor, are related to the performance of the generation of the harmonic current references, but also depend on the control strategy adopted.

The present paper proposes improvements to the SAPF control system using the theory of artificial neural networks and that of fuzzy sets. Harmonic currents are identified by the famous instantaneous power method based on the use of an ADALINE for the extraction of harmonic components (ANN-RIIP). The proposed method can estimate total harmonic currents and harmonic components by independently performing selective compensation. This method consists in replacing the two low-pass filters of the RIIP method by two ADALINE networks [9]. Secondly the generation of switching times is done by the hysteresis current control technique where the hysteresis band will be generated by a fuzzy inference system. In this case, the fuzzy logic concept is introduced to reduce the deviations between the reference currents and the currents generated by the active filter[8]. Concerning the control strategy on the DC side, the fuzzy logic will still play an important role to maintain the measured value of the DC voltage at its reference value.

Fig.1. Principle diagram of the SAPF connected to the power grid

Shunt active power filter (SAPF)

The principle diagram of the SAPF with its control circuit is shown in Figure 1. The power part has a bridge of six power transistors with anti-parallel diodes, which is used for the bidirectional power exchange.

In order to reduce the ripple due to the active filter’s switching operation, it is essential to connect the active filter to the network though a passive filter usually of the first order (Lf, Rf). On the DC side, a capacity C is connected in parallel to store energy. The capacity serves as a voltage source and allows the operation of the static converter as a rectifier or inverter.

The generation of reference signals is ensured by the p-q method. The switching times of the inverter are generated by the hysteresis control method where two techniques will be considered: a hysteresis current control with fixed band and another with fuzzy band. In order to ensure effective DC voltage control, a fuzzy logic controller is used in place of a PI regulator

PQ theory based on ADALINE algorithm extraction

Generally, the extraction of harmonic powers is carried out in this technique by two low-pass filters. In order to be able to achieve good power separation and thus provide an exact set point for the SAPF modulation technique, the two low-pass filters will be replaced by two ADALINE-type neural networks (Fig.2.).

The first step of the harmonic extraction process using ADALINE is to generate the input vector xi of the ADALINE; this vector is constituted of a combination of Sine and Cosine waves at the frequency of the fundamental and the most dominant harmonics. Then, sensing the waveform of the signal to process and feeding it as a target result. Later, random widths vector wi is initiated, and the ADALINE is lunched. During every iteration the ADALINE force its output to converge toward the target signal by constantly updating the widths vector using the LMS algorithm (Fig.3.).[10].

Fig.2. PQ theory based on two ADALINEs algorithm extraction

In order to estimate the real and imaginary instantaneous powers, it is possible to decompose the currents Isabc and voltages Vsabc of an electric network into a Fourier series as follows[11]:

.

Where: ω – fundamental frequency of the electrical network, In1 and In2 – amplitudes of the sinus and cosine components of the network current, a – phase angle between current and voltage, Vn1 and Vn2 – amplitudes of the sine and cosine components of the main voltages.

Using a frequency analysis, the expressions (3) of the instantaneous powers is developed as follows:

.
.

p1cosα and –q1sinα represent the continuous parts of p and q respectively. The rest of terms is the alternative parts. To extract estimate active and reactive powers, two ADALINE are developed, where the inputs are sinusoidal functions that correspond to each harmonic order in the mathematical developments shown in equations (4).The Fourier analysis can express the instantaneous real and imaginary powers in the general case as follows:

.

Where: A0 – continuous part, An1, An2 and Bn1, Bn2 – amplitudes of the sinus and cosines terms respectively. The vector representation of equation (5) is given by:

where: WT – weight vector of the network, X(t) – input vector of the network.

.

The equation (6) can then be implemented by the ADALINE configuration illustrated by Fig.3. where WT is the weight vector of the network and X(t) its input. Figure 4, shows this instantaneous power topology for p reel power (which is the same topology for q imaginary power) to be compensated by two ADALINE as illustrated in the figure below.

Fig.3. The general network topology of an ADALINE
Hysteresis current control with fixed and fuzzy band

Switching times of the SAPF are generated using two modulation techniques: the hysteresis current control with fixed band (Fig.4) and fuzzy band (Fig.5).

Fig.4. Principle diagram of the hysteresis current control with fixed band

The hysteresis fixed band constitutes a major disadvantage for this control structure. The switching frequency depends essentially on the derivative of the set point current. The amplitude of the derivative is not mastered and the switching frequency is not fixed[8], [12].

This point can be particularly penalizing in the case of high power systems where the switching frequency is limited to values of the order of KHz because of the characteristics of the electronic power components. New techniques based on the same concept have been developed to improve performance of the hysteresis current control strategy: The most popular are the auto-adaptive band hysteresis, and the fuzzy auto-adaptive band hysteresis (figure 5)[12].

The current control with adaptive band hysteresis overcomes the problem of switching frequency variation, but this technique is sensitive to parametric variations in the SAPF. This is because this strategy control is based on the calculation of the hysteresis band so that the switching frequency remains constant[8]. Taking into account the parameters of the active filter (Lf, Vdc) as well as the reference current, the width of the band is regularly updated by the calculation algorithm making it possible to adapt it to the desired frequency.

.

Fuzzy logic has been introduced to solve problems of conventional techniques of hysteresis current control. Current control with fuzzy hysteresis band is based on a dynamic tuning of the hysteresis band. This setting allows a constant switching frequency. The main advantage is the insensitivity of this control structure of the parametric variations of the SAPF.

The fuzzy hysteresis technique improves the performance of the network compared to the fixed hysteresis strategy and has a good filtering quality with more sinusoidal network currents[13].

Fig.5. Hysteresis control with fuzzy auto adaptive band
Fig.6. Membership functions of the input and output variables of the fuzzy inference system

As input to the fuzzy controller, the main voltage and the current reference slop can be selected. The hysteresis band magnitude is used as output. To determinate the set of the linguistic values associated with each variable the following step is used. Each input variable is transformed into a linguistic size with five fuzzy subsets: PL is positive large, PM is positive medium, PS is positive small, EZ is zero, NL is negative large, NM is negative medium, and NS is negative small; for the output variable, HB, PVS is positive very small, PS is positive small, PM is medium positive, PL is positive large, and PVL is positive very large. The member ship functions of the input and output variables are shown in Fig. 8 and the resulting inference rules are listed in Table1[8].

Table 1. Matrix of inferences

.
Fuzzy DC voltage control

A fuzzy controller has been developed for controlling DC link voltage and improves filtering performance of the SAPF. To do this, we have introduced the concept of fuzzy logic as shown in Figure 9[14]. A fuzzy logic controller is based on a collection of control rules governed by the compositional rule of inference applied to maintain the constant voltage across the capacitor by minimizing the error between the capacitor voltage and it’s reference voltage[15].

Fig.7. Structure of the DC voltage fuzzy control

The control law of the system is a function of the error and its variation:

.

The most general form of this control law is defined as follows:

.

The error and its variation are defined as follows:

.

Where: X(t) – input, k – Iteration number, ∆u – command signal.

Table 2. Inference table of the fuzzy DC voltage controller

.
Results and discussion

Simulation results were obtained under the Matlab \ Simulink environment and also using the Fuzzy toolbox. In order to show the advantages of Adaline Neural Network and fuzzy set theory to the SAPF control system, three comparative studies were carried out in this section: On the one hand, between the PI regulator of the SAPF DC voltage and a fuzzy logic controller, and on the other hand between the fixed band hysteresis and the fuzzy band modulation technique .the third study is the replacing of the two lowpass filters of RIIP method by two ADALINE networks for generation of reference currents of the SAPF, This is the Neural-RIIP (Real and Imaginary Instantaneous Powers) method. In order to further verify the effectiveness of the proposed control techniques, a load variation occurs from t=0.1 second (Fig.8). Figs.9, 10 shows the frequency spectrum of the load current before and after the load variation respectively. The THD of the line current is equal to 12.64%.We can see that the load variation has a negative effect on the value of the THD, since it goes from 9.02% to 12.64%. These spectral representations allow us to consider the 5th and the 7th harmonics as being the most dominant.

Table 3. Parameters of the studied system

.
Fig.8. Waveform of the load current
Fig.9.Frequency spectrum of load current before the load variation
Fig.10. Frequency spectrum of load current after the load variation
Fig.11. Waveform of the source current after filtering used low-pass filters
Fig.12. Injected current by the fixed band and fuzzy band hysteresis technique used low-pass filters
Fig.13. Frequency spectrum of source current for fixed band hysteresis and PI DC voltage used low-pass filters
Fig.14. Frequency spectrum of source current for fixed band hysteresis and fuzzy DC voltage used low-pass filters
Fig.15. Frequency spectrum of source current for fuzzy band hysteresis and PI DC voltage used low-pass filters
Fig.16. Frequency spectrum of source current for fuzzy band hysteresis and fuzzy DC voltage used low-pass filters
Fig.17. DC bus voltage responses with a PI regulator and a fuzzy logic controller used low-pass filters

Figure 11 shows that the deformation of the line current has been corrected following the intervention of the SAPF. From the zoom performed on the spectral representations of the line current, the fixed band hysteresis current control technique generates additional harmonics of small amplitudes, unlike the fuzzy band hysteresis current control. which generates no additional harmonic.

The waveform of the current injected by the SAPF is illustrated in Fig. 12, where it is possible to observe the adaptation capacity of the SAPF during a disturbance in the load. The zooms performed on these figures show that the combination of fuzzy logic theory with the hysteresis current control strategy has eliminated the ripples of the line current. Effectively, the fuzzy band hysteresis improves the filtering performance of the SAPF by reducing the error between the reference current generated by the identification method and the current that the SAPF is injected on the grid.

Figures 13 and 15 shows that the application of the fuzzy band hysteresis current control technique has further improved the harmonic content of the line current by decreasing the THD from 1.34% to 1.23%

Fig.18. Waveform of the source current used ADALINE filters and fuzzy band hysteresis
Fig.19. Frequency spectrum of source current for fuzzy band hysteresis and fuzzy DC voltage used ADALINE filter
Fig.20. Active power separation with ADALINE filters and low-pass filter
Fig.21. Reactive power separation with ADALINE filters and lowpass filter
Fig.22. DC bus voltage responses with a PI regulator and a fuzzy logic controller used ADALINE filters

The results obtained correspond to a control of the DC voltage by a PI regulator. The use of a fuzzy logic controller allowed, according to Figs. 14, 16 and 17, to reduce the THD of the line current from 1.08% to 0.80%. The efficiency of the fuzzy logic controller can be clearly seen in Fig. 17 where the response of the DC voltage controlled by a fuzzy regulator is better compared to that of a PI regulator in terms of stability and rapidity.

For Adaline Neural Network can be seen that with this method it is possible to estimate the harmonics individually and all harmonic currents considered in the inputs of the two ADALINE. The results obtained by the proposed ANN-RIIP extraction method have showed a great efficiency in harmonic identification. The waveforms show the measured load current before compensation, Fig. 10 with THD =12.64%. After the filtering used the ADALINE filter for harmonic extraction and the fuzzy hysteresis band technique for inverter modulation control and DC fuzzy controller to ensure DC voltage stability. We have given a very high development term of THD =0.7 fig.19 with a very efficient compensation of the reactive energy.

It is simple to calculate and allows a good dynamic response time, particularly when implementing the Neural- RIIP theory, which uses two ADALINE filters in place of a lowpass filter. The THD decreased from 12.64% to 0.7% meaning that in the case used ADALINE filters in place of low pass filters the THD decreased from 0.8%, to 0.7% figs.16, 19. The weak points of RIIP theory classic are the delay created by the low pass filter and the fact that it is limited to provide good filtering performance in the case of a balanced sinusoidal voltage system.

The separation of the active and reactive power which is made by the ADALINE technique shows a very clear improvement between the low-pass filter and the other ADALINE filter used, in the active power separated by the ADALINE filter gives a fast response time and less amplitude disturbances on the other hand the low-pass filter shows a large amplitude disturbance and slow response time compared to the ADALINE filter fig.20. For the reactive power, the ADALINE filter used gives a better compensation than the low-pass filter fig.21

Fuzzy control of the DC voltage has resulted in good disturbance rejection compared to a PI controller (Fig.22), especially when using the ADALINE filter for harmonic extraction.

Table 4. THD values of the source current for the different techniques used

.
Conclusion

In this paper, several control techniques have been discussed. These are the identification of harmonics by the classical RIIP and neural-RIIP theory, the fixed band and fuzzy band hysteresis control technique for current control and the use of a fuzzy logic controller for DC voltage control. In order to show the effectiveness of the proposed strategies, simulation tests were carried out under the conditions of a non-linear load variation. The results obtained show an improvement in the performance of the shunt active power filter in terms of current control. The fixed-band hysteresis current control provides a fast response but generates excessive current ripple due to the variable modulation frequency. This problem was solved using a fuzzy hysteresis band current control technique, which allowed the system to achieve good active filtering and minimize ripple and harmonic distortion of the line current. Fuzzy control of the DC voltage has resulted in good disturbance rejection compared to a PI controller, especially when using the ADALINE filter for harmonic extraction, and a satisfactory improvement in harmonic distortion of the current. ADALINE networks are linear estimators capable of learning signals on-line as a function of time. The learning is fast and robust while being compatible with a real-time constraint; moreover, the simplicity of its architecture gives it additional advantages: the interpretation of its weights and the lower harmonic reduction of 5% as required by the standards.

Acknowledgement This project was financially supported by the Directorate General for Scientific Research and Technological Development – Algerian Ministry of Higher Education and Scientific Research of Algeria.

REFERENCES

[1] A CHAOUI,J-P. GAUBERT,A BOUAFIA,” Experimental validation of new direct power control switching table for shunt active power filter power”, conference on Electronics and Applications (EPE),2013
[2] R. BELAIDI, M.HATTI,A HADDOUCHE, M. M. LARAFI,” Shunt active power filter connected to a photovoltaic array for compensating harmonics and reactive power simultaneously”, 4th international conference on power engineering, energy and electrical drives, may 2013
[3] B. SINGH, K. AL-HADDAD, A CHANDRA, “A review of active filters for power quality improvement”, IEEE transactions on industrial electronics, vol. 46,no. 5,October 1999
[4] G. W. CHANG, C. M. YEH, “Optimisation-based strategy for shunt active power filter control under non-ideal supply voltages “,lEE proceedings – electric power applications, vol.152,no. 2,pp. 182,2005
[5] H. AKAGI,E. HIROKAZU WATANABE,M AREDES,” Instantaneous power theory and application to
power conditioning”, USA: IEEE Press 200
[6] N.MESBAHI, AOUARI, D. OULD ABDESLAM, T.DJAMAH, AOMEIRI, “Direct power control of shunt active filter using high selectivity filter(HSF) under distorted or unbalanced conditions”, electric power systems research 108 (2014) 113-123
[7] GHADBANE Ismail BENCHOUIA Mohamed Toufik BARKAT Said “Real time implementation of feedback linearization control based three phase shunt active power filter”, European Journal of Electrical Engineering – n° 4/2018, 1-5
[8] B. MAZARI, F. MEKRI, “Fuzzy hysteresis control and parameter optimization of a shunt active power filter”, journal of information science and engineering 21,1139-1156 (2005)
[9] Larbi Hamiche1, Salah Saad*1, Leila Merabet1 & Fares Zaamouche2 “Adaline Neural Network and Real-Imaginary Instantaneous Powers Method for Harmonic Identification La méthode réseau de neurone Adaline et puissances instantanés réels imaginaires pour l’identification des harmoniques”, Rev. Sci. Technol., Synthèse 36: 129-140 (2018)
[10] Kadem, M., Semmah, A., Wira, P., & Slimane, A. (2020). Artificial Neural Network Active Power Filter with Immunity in Distributed Generation. Periodica Polytechnica Mechanical Engineering. doi:10.3311/ppme.12775
[11] Abdeslam, D. O., Wira, P., Merckle, J., Flieller, D., & Chapuis, Y.-A. (2007). A Unified Artificial Neural Network Architecture for Active Power Filters. IEEE Transactions on Industrial Electronics, 54(1), 61–76. doi:10.1109/tie.2006.888758
[12] F. Merki ‘Commande robuste des conditionneurs Actifs de puissances,’ thèse de doctorat, USTO,2007
[13] Loutfi, B. (2019). Comparative analysis hysteresis and fuzzy logic hysteresis controller of shunt active filter. Advances in Modelling and Analysis B, Vol. 62, No. 2-4, pp. 37-42. https://doi.org/10.18280/ama_b.622-401
[14] Georgios A. Tsengenes and al. « Performance Evaluation of PI and Fuzzy Controlled Power Electronic Inverters for Power Quality Improvement ». Chapter from the book Fuzzy Controllers – Recent Advances in Theory and Applications
[15] Rathika, P., Devaraj, D. (2010). Fuzzy logic based approach for adaptive hysteresis band and dc voltage control in shunt active filter. International Journal of Computer and Electrical Engineering, 2(3): 1793-8163

Authors: Khenfar noureddine, ICEPS Laboratory, phd student Sciences Faculty, Electrical Engineering Department, Djillali Liabes University of Sidi Bel Abbes 22000, Algeria..E-mail : khenfar.noredine@gmail.com.

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 97 NR 5/2021. doi:10.15199/48.2021.05.21

Start-up of PM Synchronous Motors

Published by Stanisław GAWRON, Jakub BERNATT, Artur POLAK,
Sieć Badawcza Łukasiewicz – Instytut Napędów i Maszyn Elektrycznych KOMEL

Abstract. Three variants of starting synchronous motors are presented. In simplest solution, cage winding is placed in rotor, asynchronous start-up is obtained. This method generates large surge currents adversely affecting power grid and motor (impact forces/impact torque are generated). The second solution is to place three-phase ring winding in rotor – asynchronous start-up is obtained, same as in slip-ring induction motors. Start-up is smooth. Asynchronous phase of start-up is terminated by synchronization. The third method is frequency start-up. Drive system must contain additional frequency inverter. Start-up is smooth. This is recommended primarily for set of several motors installed in the plant.

Streszczenie. W artykule przedstawiono trzy wariantowe sposoby rozruchu silników synchronicznych. Najprostszym rozwiązaniem jest umieszczenie w wirniku uzwojenia klatkowego i rozruch asynchroniczny. Ten sposób rozruchu wymusza duże prądy udarowe niekorzystnie oddziałujące na sieć elektroenergetyczną i na silnik, gdyż generują siły udarowe i moment udarowy. Drugim rozwiązaniem jest umieszczenie w wirniku uzwojenia trójfazowego pierścieniowego i rozruch asynchroniczny, identycznie jak w silnikach indukcyjnych pierścieniowych. Rozruch przebiega łagodnie. Rozruch asynchroniczny kończy się synchronizacją. Trzecim sposobem rozruch jest rozruch częstotliwościowy. Układ napędowy musi być wyposażony w dodatkowy falownik z regulacją częstotliwości. Rozruch jest łagodny. Taki sposób rozruchu poleca się przede wszystkim dla grupy kilku silników zainstalowanych w firmie. (Rozruch silników synchronicznych wzbudzanych magnesami trwałymi).

Słowa kluczowe: silniki synchroniczne, rozruch asynchroniczny, rozruch częstotliwościowy.
Keywords: synchronous motors, asynchronous starting, frequency starting.

Introduction

High power machinery operating in mines, steel plants, chemical works and other industrial plants is often driven by synchronous motors with electromagnetic excitation. When synchronous motors are compared to induction motors, we find that their power efficiency is higher and they operate at capacitative power factor cosφ, so that reactive power in the plant may be compensated. Lately, some attempts have been made to apply synchronous motors with permanent magnet excitation to these drives. Such motors do not require exciters and their efficiency is higher. However, the problem of start-up must be resolved.

Fig.1. The end windings of the excitation winding and start-up cage winding of asynchronous motor, rated at: 7400 kW, 6 kV- Y. 814 A, rotor – 180 V DC, 335 A, 1500 rpm

Asynchronous start-up utilizing cage winding

The asynchronous start-up of synchronous motors is most commonly used. Apart from excitation winding present in rotor of synchronous motor, another start-up winding is mounted; usually this is a cage winding. When stator winding is connected to the power network, current flowing in cage winding interacts with stator current and asynchronous torque emerges; this causes the rotor to rotate and accelerate up to near-synchronous speed. At this point, excitation current is switched on and rotor self-synchronizes. The end windings of rotor in synchronous motor with cage winding are shown in Fig.1 (the wrappings have been taken out).

Oscillogram of start-up current for motor rated at 1250 kW, 6 kV is shown in Fig.2. This is motor with electromagnetic excitation and cage start-up winding, the so-called SAS motor. This particular motor is installed in copper ore ball mill.

Fig.2. Oscillogram of start-up current for SMH-1732S motor rated at: 1250 kW, 6 kV, 140 A, 187.5 rpm

The recorded value of surge current is Iu = 5500 A or 40I_N; this is a very high value. The start-up lasted for 2.5 seconds, so we are able to classify this as a short start-up. The surge current generates axial impact forces and impact torque. The impact forces lead to high stresses and radial vibrations, which negatively affect the stator’s winding insulation, magnetic circuit, motor’s structural elements, bearings and foundations. The impact torque affects the coupling and gear box, and this may lead to teeth shearing.

The cage start-up winding has also been used in synchronous motor with permanent magnet excitation [7]. In this design, rotor contains permanent magnets as well as cage winding. The permanent magnets are placed in slots within rotor yoke, and cage winding consists of copper bars placed in slots along rotor’s outer circumference. These bars are short-circuited with end rings. The start-up takes place at full excitation provided by the PM-generated magnetic flux. Rotor of prototype motor dedicated to a fan drive in one of the coal mines is shown in Fig.3.

Fig.3. Rotor of synchronous motor (LSPMSM) with permanent magnets and cage start-up winding; motor rated at 1100 kW, 6 kV, 500 rpm [8]

Calculated curves for starting torque of this motor are shown in Fig.4. The rated torque is TN = 21 kNm. On the basis of presented curves, it may be concluded that total start-up torque over entire speed range is greater than rated torque.

Fig.4. Start-up torques of LSPMSM motor rated at 1100 kW, 6 kV, 500 rpm [8]

Synchronous motor excited by permanent magnets, type SMH-1732T, rated at: 630 kW, 6 kV, 63 A, 187.5 rpm, 32.1 kN·m drives the copper ore ball mill. Attempt was made to record speed and vibration waveforms of this motor during start-up, but it failed. Current and vibration surges exceeded measurement ranges of the transducers and the measurement devices froze. The maintenance staff did not allow a retry. We may assume that current waveform during start-up would be similar as in the case of SMH-1732S motor (Fig. 2), but surge current will be higher.

Asynchronous start-up utilizing ring winding

Machinery with high moment of inertia is characterized by long start-up times. The starting time becomes longer, if start-up takes place with loaded motor. This sort of start-up may occur in service and the drive motor should be able to withstand such conditions. The synchronous machines proposed for such drives are equipped with start-up ring windings. These are synchronized asynchronous motors (popularly termed SAS). Rotor winding in such motor is usually three-phase and it fulfils the role of start-up winding as well as excitation winding. The start-up is rheostatic and identical to that of typical induction slip-ring machine. When near-synchronous speed is reached by the motor, excitation current is switched on and self-synchronization takes place. Identical start-up winding has been applied to motors with permanent magnet excitation, these are so-called SASPM motors [2]. There are several possible design variants. Rotor with permanent magnets nested inside rotor yoke is shown in Fig.5. Winding is placed in slots along the rotor circumference and its ends are led out to the slip rings.

Fig.5. Rotor of model permanent magnet synchronous motor SASPM [1]

Fig.6. Torque-speed curves for model motor with shorted rings [1]

Torque-speed curves of model motor SASPM rated at 1.5 kW, 400 V, 1500 rpm (slip rings shorted) are shown in Fig. 6. They relate to: Ta – asynchronous torque generated by rotor winding, Tpm – torque due to permanent magnets, Tr – total torque.

Synchronous characteristics of model motor are shown in Fig.7, these are torque Tel, current Iph, power factor cosφ and efficiency η curves. The start-up proceeds in identical manner as in slip-ring induction motor. During the start-up, stator/rotor currents are much lower than in cage winding. The start-up is smoother. At near-synchronous speed the slip rings are opened, excitation current is turned on, synchronizing torque pulls the rotor and it accelerates up to synchronous speed – self synchronization takes place. Oscillograms of stator and rotor current for a SAS motor driving a mill in a cement plant are presented in Fig.8.

Fig.7. Synchronous curves of model motor: torque Tel, current Iph, power factor cosφ and efficiency η [1]

Fig.8. The waveforms of start-up currents for SAS motor rated at: 800 kW, 6000 V, 105 A, rotor 1360 VAC, 24 VDC, with three-phase controlled rheostat; a) stator windings, b) rotor windings.

The envelope of rotor current is proportional to motor’s asynchronous torque. When motor supply is switched on, surge current appears and it reaches 4.3 IN. When the rheostat is switched and its resistance changes, the current (RMS-value) does not exceed 1.2IN. Rotor’s surge current is equal to 700 A. The impact torque is calculated on the basis of rotor current waveform in the following way:

.

The start-up is smooth.

Frequency start-up

If several electric motors are present in large industrial works, then it is a good idea to use a smooth (soft) frequency start-up. The frequency start-up of synchronous machines has been known for a long time and used for start-ups of synchronous compensators [4] and high-power synchronous motors. It is also perfectly suited to the startup of synchronous motors excited with permanent magnets. A single AC/DC/AC inverter may be used for a group of motors together with synchronizer and switches (see Fig.9). The synchronizer may be built into inverter. A single inverter operating with several motors means that investment costs are less, since high power motors are rated at 6 kV or 10 kV and inverter’s rated voltage must be the same.

Fig.9. Electrical circuit – connecting synchronous motors to startup inverter

Synchronous motors M (2) excited with permanent magnets are connected to the power system (U1) via switches W3 and to inverter AC/DC/AC (1) via switches W4. All elements of the circuit are three-phase ones. One AC/DC/AC inverter (1) serves four motors M (2). The frequency control range of this inverter should extend from minimum c. 3 Hz to 50 Hz, with rotational emf to frequency ratio. AC/DC/AC inverter (1) executes the start-up of each motor M (2) separately. Number of motors may vary. AC/DC/AC inverter (1) is supplied from the same power network (U1) as the motors.

The start-up of each motor M (2) progresses in a following way:

• AC/DC/AC inverter (1) is connected to the power network (U1) by switch W1,
• inverter (1) is connected to bus U2 by switch W2; minimum frequency value is set at the inverter (1),
• selected motor M (2) is connected to bus U2 by switch W4; inverter’s frequency is increased up to subsynchronous
value, e.g. 49.5 Hz,
• synchronizer (3) is connected to network U1 and bus U2 via switches W5 and W6,
• motor is synchronized with power network U1 by adjusting frequency of inverter (1),
• when frequency is adjusted and the phase sequence is correct, switch W3 is tripped and switch W4 is switched off; this constitutes end of start-up.

The system inverter-synchronizer is ready for subsequent start-up (another motor M). If this start-up is not required, then inverter 1 should be disconnected from the network U1 via switch W1 and from bus U2 via switch W2. Synchronizer 3 should also be disconnected from network U1 and bus U2 (breakers W5 and W6 are switched off).

If the circuit is to be constructed economically, then inverter and synchronizer should be connected directly to bus U2, breakers W2 and W6 may be absent.

Fig.10. Rotor with permanent magnets 4 mounted on the yoke surface 1 with overlaying copper sleeve 5: 2 – yoke tooth, 3- shaft, 6 – sleeve flange

The presented start-up system guarantees a smooth, surgeless start-up of PM synchronous motors. This start-up method offers one more advantage, permanent magnets 4 may be glued into the channels outside the rotor yoke 1. The terminal laminations are uncut and therefore they provide additional protection to the permanent magnets (against axial shift). The magnetic flux in the air-gap is maximum, since permanent magnets are located at the rotor yoke surface and they are not shunted by the yoke. The flux determines the maximum synchronous torque of the motor. The motor equipped with such rotor exhibits higher torque overload capacity than motor with permanent magnets affixed inside yoke slots. Rotor should be also fitted with winding attenuating hunting due to variable component of load torque. This role may be fulfilled by a copper sleeve 5 located on the permanent magnets (see Fig.10). Ends of the sleeve are turned back, constituting flange 6. This protects the sleeve against axial displacement.

In the magnetic circuit, the copper sleeve 5 is placed in the air-gap. This rotor design is recommended for medium and high power motors. In these machines the air-gap is usually greater than 2 mm and placing a 1 mm thick sleeve in this slot does not pose technological problems. The relative magnetic permeability of copper is the same as of air. Sleeve 5 does not decrease excitation’s magnetic flux, while it ensures attenuation of the rotor hunting.

Conclusion

High power synchronous motor with permanent magnet excitation must be designed for start-up conditions. The simplest solution is to place a cage winding in the rotor. When cage winding is used, start-up is achieved by connecting motor to the supply network; when synchronous speed is attained, motor self-synchronizes. This type of start-up is accompanied by high surge current which has negative impact on the power network as well as on the motor itself, since it generates impact forces and torque.

The second design is based upon placing a three-phase ring winding in the rotor. The start-up is executed by connecting a rheostat to the rotor winding circuit. The startup is asynchronous and its progress is identical as in slipring induction motors. When near-synchronous speed is attained, motor self-synchronizes. The start-up is smooth, but the rotor construction is much more expensive.

The third start-up method is frequency start-up. The drive system is equipped with additional inverter operating on frequency control principle. During start-up, motor is accelerated up to synchronous speed and synchronized with network voltage. After synchronization the inverter is disconnected. During starting process, synchronous torque is used and start-up is smooth. In this design, additional cost is incurred (inverter). This start-up procedure is mostly recommended for a group of several motors installed on the company premises.

REFERENCES

[1] J. Bernatt J., T.Glinka, “Asynchronous Slip-Ring Motor Synchronized with Permanent Magnet”, Archives of Electrical Engineering. ISSN 1427-4221. Nr 1/2017, pp. 199-206.
[2] J. Bernatt., S. Gawron, T.Glinka, E.Pacholski, K. Staszewski,: Wirnik silnika elektrycznego z magnesami trwałymi. Patent PL 226639 ogłoszono: 31.08.2017. Instytut Napędów i Maszyn
Elektrycznych KOMEL.
[3] W. Paszek, Stany nieustalone maszyn elektrycznych prądu przemiennego. WNT, ISBN 83-204-0707-9, 1986.
[4] R.Rossa, Silnik reluktancyjny z dodatkowym wzbudzeniem magnesami trwałymi. Praca doktorska. Biblioteka Politechniki Śląskiej. Listopad 2006 r.
[5] T.Zawilak, Utilizing the deep bar effect in direct on start of permanent magnet machines, Przegląd Elektrotechniczny. ISSN 0033-2007. Nr 2/2013. s. 177 – 179.
[6] T. Zawilak, J. Zawilak, Silnik synchroniczny wzbudzany magnesami trwałymi w napędzie młyna kulowego, Maszyny Elektryczne – Zeszyty Problemowe, ISSN 0239-3646. Nr 3/2016 r. s. 169 – 173.
[7] T. Zawilak, J. Zawilak, Wirnik silnika elektrycznego z magnesami trwałymi. Patent PL nr 218489, ogłoszono. 31.12.2014. Politechnika Wrocławska.
[8] T. Zawilak, J. Zawilak: “Energooszczędne silniki synchroniczne dużej mocy wzbudzane magnesami trwałymi”, Przegląd Elektrotechniczny, ISSN 0033-2097, R. 91 NR 10/2015, str.117-120.

Authors: dr inż. Stanisław Gawron, e-mail: stanislaw.gawron@komel.lukasiewicz.gov.pl; dr hab. inż. Jakub Bernatt, prof. Ł-KOMEL e-mail: jakub.bernatt@komel.lukasiewicz.gov.pl; dr inż. Artur Polak, e-mail: artur.polak@komel.lukasiewicz.gov.pl; Sieć Badawcza Łukasiewicz – Instytut Napędów i Maszyn Elektrycznych KOMEL, Al. Roździeńskiego 188, 40-203 Katowice.

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 97 NR 5/2021. doi:10.15199/48.2021.05.01

METSyS Panel Capacity Analyzer (PCA)

Published by POWERetc Corporation, Corporate Headquarters,3350 Scott Blvd, Bldg. 55-03, Santa Clara, CA 95054. Phone: (408) 540-3199 Email: info@poweretc.com, Website: poweretc.com

The Right Tool for Conducting a Connected Load Study to Confirm Panel Capacity 

METSyS NEC 220 Current logger

The METSyS Panel Capacity Analyzer (PCA) is a specially-designed instrument for measuring and recording 3- or 4-phase current to confirm the distribution panel’s capacity in compliance with NFPA’s National Electrical Code (NEC) 2014 Article 220.87 and meeting the requirements for uniform load calculations in accordance with the requirements of the California Electrical Code (CEC).

The METSyS PCA packaged with POWERetc’s proprietary macro-based Excel spreadsheet provides users with the capability of conducting connected load studies of various lengths to meet specific regulatory requirements. This provides a definitive and documented result enabling electrical contractors and facilities engineers to quickly obtain electrical inspection approval when adding new loads to a panel. 

The process requires both the calculation of the average current over an extended period in order to confirm that – with planned load additions – will remain less than 80% of the breaker rating(s). In addition, the standard requires that MIN and MAX currents are also determined over the sampling period.

The METSyS logger samples every cycle using an 8-cycle “window” and calculates the average value of the 8-cycles. These readings are accumulated for the user-selected averaging period–10s, 30s, 1m, 5m, 10m, 15m, 30m, 60m–and the average of the averages is saved as the average value for the period and the minimum and maximum sample are saved as the MIN/MAX values. The PCA’s MIN/MAX values are really a composite of 8-cycles which will result in understating the peak inrush but is probably more reflective of levels that might cause breaker tripping problems.

METSyS 3-Phase Panel Capacity Analyzer including: 3-Phase 4000A MicroFlex bundle – 6″ diameter loop (also available with 2″ and 15″ diameter loops)

METSyS NEC 220 Current logger_Package

POWERetc METSyS Current Probe Kit Facilitates Safe 480V Panel Connected Load Studies. The CCPK-6 Cabinet Current Probe Kit enables routine panel capacity studies to be performed in 480V panels – without the need to open or power down the panel.

METSyS NEC 220 Current logger_Cabinet Current Probe Kit [CCPK-6]
Features

• True RMS current measurement (50 Hz and 60 Hz) – 3 phase + Neutral
• Calibrated Rogowski coils to ease interchangeability
• 2GB internal memory for non-volatile data storage
• A USB flash drive to be used for transferring the data from the logger to the PC
• A charge port for battery charging through the micro USB port
• A two-line LCD display and a three-button keypad to ease setup and data transfer
• Logging of measurements to internal memory
• Records Min, Max, Average and Peak currents
• Current display on an LCD screen
• 3 button simplified User Interface
• 72 Hour internal battery (for operation without connection to a power supply)
• Connectivity – Bluetooth (BLE) and USB Generates CSV log files for easy transfer to a PC
• iOS and Android apps
– Live reading display
– Log setup
– Start, Stop & Resume logging remotely
– Email logged data

Specifications

Electrical Characteristics

Measuring Range : 4000A AC RMS
Overload Capability : 10000 A
Accuracy ( 45-65Hz) : ± 1 % of reading ± 1 A
Position Sensitivity : ± 2.5%
Resolution : ± 1 A
Temperature Coefficient : ± 0.05% of reading / °C

Power Supply : Internal Rechargeable Lithium-Ion battery
Battery Life : 100 hours, typical. (Recharge fully depleted battery, 4-5 Hr)
Battery FULL/Charging/Not Charging Indication
Changing Voltage : Via USB micro-B charging socket (5V, 1 00mA)
Working Voltage (see Safety Standards section) : 600 V ACRMs or DC

Enclosure
Material : ABS
Dimensions : 160 (I) x 80 (w) x 45 (d) mm

Probe
Probe Conductor Diameter: 6mm (0.24″)
Probe Diameter : 50mm (2″), 150mm (6″), 375mm (15″), double insulated
Degree of Protection : IP67 (not certified by UL)
Phase Indication (Probe Color) : Black (A), Red (B), Blue (C), Gray (Neutral)

General Characteristics
Display : Back lit 2 line alpha numeric display
Log Intervals : 10s, 30s, 1 m, 2m, 5m, 10m, 15m, 30m, 60m.
Log Duration : 1, 3, 8, 24, 48, 72, Unlimited (Max 1 year@ 1 Os)
Data Transfer : Via USB memory stick (FAT 32)
File Format : Comma separated values file (.CSV)
Operating Temperature Range : -20 to +65 °c (-4° F to +149° F)
Storage Temperature Range : -40 to +85 °c (-40° F to + 167° F)

Safety Standards
EN 61010-1
EN 61010-2-032
600 VRMs, Category IV, Pollution Degree 2
EMC Standards
EN 61326-1

About POWERetc Corporation: POWERetc Corporation was founded by Bruce Lonie in March of 2019. With thirty plus years of experience as president and co-founder of PowerCET Corporation, Bruce has extensive experience in the investigation and diagnosis of complex electrical environment problems. The firm specializes in the application of electrical and electromagnetic monitoring equipment to identify and resolve complex productivity and equipment reliability issues. Services include the sale and rental of selected power and energy instruments, operational training, data analysis and report generation.

President: Bruce B. Lonie, Phone: (408) 666-6500, Email: BruceL@poweretc.com

Source URL: https://poweretc.com/products/prosys/metsys-energy-monitor

Detection of Fault Events in Medium Voltage Grid Based on Analysis of Data from Fault Recorders

Published by Dariusz SAJEWICZ1, Augustyn WÓJCIK2, Piotr ZEGADLO3,
Bialystok University of Technology (1), Warsaw University of Technology (2), Kozminski University (3)
ORCID: 1.0000-0002-3488-5674; 2.0000-0003-0597-1634; 3.0000-0002-0219-297X

Abstract. The aim of this paper is to demonstrate the effectiveness of newly developed fault detection methods based on a simple statistical approach encompassing linear discriminant analysis and signal processing. Fault prediction relates to the detection of: the type of operation of the medium voltage network, leakage (damaged insulator in the line string) and a measure of the distance of ground fault in an unbranched line, in a branched line and on its branches. The conducted research confirms the high efficiency of detection faults in all areas concerned.

Streszczenie. Celem pracy jest wykazanie skuteczności nowo opracowanych metod detekcji uszkodzeń opartych na prostym podejściu statystycznym obejmującym liniową analizę dyskryminacyjną i przetwarzanie sygnałów. Przeprowadzone badania potwierdzają wysoką skuteczność wykrywania uszkodzeń we wszystkich rozpatrywanych obszarach. (Wykrywanie zdarzeń awaryjnych w sieciach SN na podstawie analizy danych z rejestratorów zakłóceń.

Keywords: fault detection; linear discriminant analysis; high resistance fault; medium voltage network.
Słowa kluczowe: wykrywanie uszkodzeń; liniowa analiza dyskryminacyjna; uszkodzenie wysokorezystancyjne; sieć średniego napięcia.

Introduction

Today’s power systems are becoming increasingly unmanned and, at the same time, saturated with control and monitoring systems, with the consequent aim of increasing reliability, availability, lifespan and meeting other power quality indicators. This is a key power system design concept linked to risk management. Currently, the goal of distribution companies is to minimize contingencies and outages in power grids and at the same time improve power continuity indices such as the System Average Interruption Duration Index (SAIDI) or the System Average Interruption Frequency Index (SAIFI).

Some failures are predictable before they occur, so responding at this stage makes it possible to reduce power outages. To this end, power equipment should be equipped with an intelligent metering tool that will play an important role in making decisions about grid operation and maintenance.

The country’s power industry, both industrial and commercial, requires the introduction of modern High Voltage / Medium Voltage (HV/MV) substations and the modernization of existing ones, since most of the equipment currently operating in the networks should be immediately withdrawn from the power system due to outdated systems and the lack of advanced measurement tools. Currently, the HV/MV substations are equipped with protections that operate on the basis of current and voltage measurements.

The protections are currently installed in HV/MV substations and they work with current measurements of currents and voltages and on this basis they generate the signal to switch off (open), but only in case of emergency. Some currently available devices enable recording of only this type of events, which is often insufficient for the analysis of the situation that occurred before the protections were triggered. Both the operation of protections and the analysis of causes are currently performed after the occurrence of the event.

The research work presented within the paper is aimed at increasing the range of recorded data, their current analysis and prediction of failure events in medium voltage networks. Fault prediction relates to the detection of: the type of operation of the medium voltage network, leakage (damaged insulator in the line) and a measure of the distance of ground fault in an unbranched line, in a branched line and on its branches. This will increase the reliability of substation operation, shorten the no-voltage interruptions, and in the case of a fault occurrence will allow a quick and precise analysis of the causes and location of the fault occurrence.

Literature review

Fault diagnosis in medium voltage grids is difficult due to their extensive nature, inefficiently earthed neutral point and numerous branches. In the literature, there are various approaches to this kind of subject, starting from taking into account the type of network – isolated, compensated and earthed [1], detect arc faults [2,3] and high-resistance faults [4,5]. Data for modeling are often extracted from mathematical models of networks using PSCAD/EMTDC [3] or MATLAB [1] software. A variety of statistical methods can be effectively used for fault detection – including relatively simple approaches such as logistic regression or linear discriminant analysis [6] to more complex methods based on modeling the phasor angles across the buses as a Markov random field (MRF) [7]. Then the effectiveness of the developed method is simulated or laboratory tests are performed for further validation.

This paper aims to demonstrate the high effectiveness of newly developed fault detection methods based on a simple statistical approach encompassing linear discriminant analysis and appropriate signal processing. The methods are applied to the waveforms obtained from fault recorders and a laboratory model of a medium voltage grid including an overhead line and two cables and a cable branch in the overhead line. In this study, three algorithms were developed: network type detection, high-resistance fault detection and ground fault distance detection from HV/MV stations.

Medium voltage line model

Disturbances in the operation of the protected object occur quite rarely, therefore it is difficult to obtain examples characterizing the operation of the object under fault conditions. Preparation of appropriate training data using simulation systems or laboratory models may be helpful then.

The protected object (Fig.1), a 15kV MV line, was represented by an electrical model in the form of four segments with focused parameters: reactance and line capacitance.

The calculation data were obtained from the line construction data. The values of individual parameters of the line model were determined taking into account: type, cross-section of working conductors, type of slopes (distance between conductors and between conductors and ground) and type of ground. The parameters were determined and a model of MV line was built containing four overhead sections with lengths of 1.5, 2.5, 1.75 and 1.5km. The preload of active power at the end of the simulated line was three 250W bulbs associated in a star. The test stand was equipped with a field controller with a disturbance recorder with a sampling frequency of 1.6kHz (Fig.2).

Fig.1. One-line diagram of a medium voltage overhead line with a branch circuit in the form of a cable line with described values of reactance and resistance of individual components, where: Osz – disconnector, WA – breaker, Uz – grounding switch, PP – current transformers.

Fig. 2. Front panel view of the laboratory station with implemented model of MV line (designation A), where: TG – HV/MV power transformer, TU – grounding transformer, B and C – auxiliary cable lines, PN – voltage transformers, PP – current transformers.

The construction of a laboratory model of MV line allowed to obtain the waveforms from the disturbance recorder reproducing the operation of a medium-voltage line in an isolated network, compensated and grounded by a resistor with a better resolution of registration. The test stand has generated about 300 high-resistive registrations of ground faults eliminated by means of the ground fault and admittance protection.

Fig.3. View of the model of a cable section (branch) of a medium voltage overhead line. Focused elements of the model: line inductance (1), line capacitance (2), line active power load (3).

The next stage of work was further extension of the line model by adding a branch (cable section) in order to recognize its influence on the possibility of fault detection (Fig.3). The branch line was incorporated into the MV line model at a distance of 4km from the HV/MV power stations. Approximately 6km of cable line was modelled with symmetrically loaded resistive load in the form of three 560Ω resistors connected in a star at the end. The branch line was divided into two sections with lengths of 3.7km and 2.1km. The next step was to generate another ca. 300 registrations of ground faults in the branched network, eliminated by means of earth fault protection, where the line faults of resistive character were simulated.

Signal Processing Method

The purpose of the signal processing method is to determine the properties of recorded currents and voltages for further use in fault detection. Metrics used for fault identification should meet two criteria. Firstly, they have to be as similar as possible for many observations of the same type of faults. Secondly, it is expected that such metrics will have different values for different types of faults. As a result of using the signal processing method, a signature is obtained. Signature is a vector of characteristic quantities (numbers) describing the properties of signals important for recognizing the type of damage. The measurement data processing algorithm (Fig. 4) consists of four steps. Firstly, recorded signals are divided into time windows. This step is necessary to precisely separate parts of the signal occurring before and during the failure. Then, auxiliary measurement quantities are calculated: admittance and phase shift. The last step is calculation of metrics characterizing the fault. The result of the processing method is the fault’s signature. Details about each step of signal processing method are discussed in the following sections.

Fig.4. Block diagram of signal processing method

Time Windows

The fault recording is triggered by activation of the ground fault circuit protection (P_I0>1). There are three segments visible in obtained waveforms: before the fault, during the fault and after the protection is triggered. In order to accurately characterize the fault, signal metrics should be determined within the aforementioned signal segments. Therefore, for further processing, signals are portioned into 2 time windows:

• before damage (BF), lasting around 200ms,
• during damage (IN), lasting around 250ms.

The boundary between the windows BF and IN is determined by the moment in which the digital signal P_I0> 1 achieves the value of 1. The end of window IN is determined by the moments when the triggering of the ground fault protection (Z_I0>1) achieves the value of 1. Time windows are shifted relative to the mentioned digital signals to omit transients at the start and the end of the damage. Fig. 5 shows recorded waveforms with marked time windows.

Fig.5. Current and voltage waveforms with marked time windows
Admittance

In order to calculate this quantity, the RMS of current and voltage values are determined. Admittance is calculated as the ratio of current to voltage for each considered time moment.

Phase shift

The phase shift of current and voltage signals is determined in several steps. Firstly, Fourier Transform F{•} of the current and voltage signals for each time moment n is determined according to (1) and (2):

(1) I(n) = F {i( n…n + N50)}
(2) U(n) = F {u( n…n + N50)}

Spectrum is calculated in N50 samples long window, where N50 is one period of fundamental harmonic (50Hz). In the next step, differences between voltage phase spectrum and current phase spectrum are calculated according to (3):

(3) Δφ(n) = arg{U(n)} – arg{I(n)}

Metrics were calculated using phase shift for fundamental component of 50 Hz.

Metrics calculation

Metrics are calculated using the auxiliary measurement quantities in one time window. The following five parameters are determined:

• Y0_RMS_AVG_IN – the average admittance during the damage occurrence (IN),
• FI0_50HZ_AVG_BF – the average phase shift of the current relative to the voltage for zero sequence component in the time window before damage (BF),
• FI_50HZ_AVG_MAX_IN – the average phase shift of the current relative to the voltage for the phase (L1, L2 or L3) for which the highest average admittance was obtained, during the damage occurrence (IN),
• FI_50HZ_AVG_SUM_IN – the average sum of phase shifts for all phases (L1, L2 and L3) during the damage occurrence (IN),
• FI0_50HZ_MEDIAN_IN – the median phase shift of the current relative to the voltage for zero sequence component during the damage occurrence (IN).

Fault Detection Procedure Leakage

The first step in the proposed fault detection procedure entails the detection of leakage in the grid, which is not severe enough to trigger safety measures. In the presence of such a fault, the values of certain other analyzed metrics may be noisier and more difficult to interpret. Moreover, the possibility of detecting leakage is valuable in itself for the sake of the line’s reliability.

Regardless of the grid type and length, in case of leakage, significantly higher values of the FI0_50HZ_AVG_BF are observed in the sample (Fig. 6.). This allows for flawless detection of this type of fault, as shown in Table I.

Table 1. Detecting leakage with the FI0_50HZ_AVG_BF

.
Fig.6. Box plot for FI0_50HZ_AVG_BF metric value (rad) conditional on leakage

Network type

Next, identification of the network type is performed. In applications when the type is known, this step may be redundant. However, it may be necessary for fully automated examination of data stemming from a variety of different sources. Metric Y0_RMS_AVG_IN uniquely identifies the network type for a given line length, as shown in Table II, although some of the largest metric values for unbranched isolated network are close to the smallest values for branched grounded network (Fig. 7.). Moreover, in case of branched lines, the presence of leakage pushes the metric values up slightly.

Table 2. Detecting network type with the use of the Y0_RMS_AVG_IN METRIC

.
Fig.7. Box plot for Y0_RMS_AVG_IN metric value (S) conditional on network type

Ground fault location

Having checked for leakage and with the network type known, we are able to identify incident location in case of a ground fault when using our main 5 metrics. To this end, multi-class linear discriminant analysis (LDA) is applied.

Table III. presents the confusion matrix for the LDA classification output aimed at locating ground faults in the unbranched line. The performance is virtually flawless, with accuracy standing at 98.6%. The errors appear only for neighboring locations.

Table 3. Confusion matrix for the LDA model of fault location (Unbranch line)

.

Locating ground faults in the branched line proves to be a more difficult task (Table IV.). Faults located on the main line near the fork (2/4 of the main line) are occasionally confused with faults located in the branch. The branch also makes it harder to detect faults behind the fork in the line – hence the relatively large number of mistakes for the faults located in locations 3/4 and 4/4. Still, the classifier achieves a satisfactory accuracy of 85.6%, with errors again generally appearing for neighboring locations.

Table 4. Confusion matrix for the LDA model of fault locations (Branch line)

.
Conclusion

The research was conducted on data from a disturbance recorder on a laboratory test stand. Our results indicate that detection of high-resistance faults and location of ground faults in MV lines can be performed with high accuracy using a relatively simple set of statistical tools. Appropriate signal processing prior to statistical modelling is the key to this methodology. This is especially true for real-life applications outside a laboratory, where the data is noisier and the lines themselves exhibit diverse structural characteristics.

Acknowledgments The paper is the result of research work carried out by Elektrometal Energetyka S.A. as part of the project “Construction of integrated systems supporting and optimizing the work and safety of MV switchgear” PROJECT CO-FINANCED BY THE EUROPEAN UNION FROM THE MEANS OF THE EUROPEAN REGIONAL DEVELOPMENT FUND UNDER THE PRIORITY Axis I “The use of research and development activities in the economy” OF THE REGIONAL OPERATIONAL PROGRAMME OF THE MAZOWIECKIE VOIVODSHIP 2014-2020″.

REFERENCES

1. Eduardo F. Ferreiraa, J. Dionísio Barrosb, ”Faults Monitoring System in the Electric Power Grid of Medium Voltage”, Procedia Computer Science, vol. 130, pp. 696-703, 2018.
2. S. Hamid Mortazavi, Zahra Moravej, S. Mohammad Shahrtash, “A Searching Based Method for Locating High Impedance Arcing Fault in Distribution Networks”, Power Delivery IEEE Transactions on, vol. 34, no. 2, pp. 438-447, 2019.
3. Wenhai Zhang, Yindi Jing, Xianyong Xiao, ”Model-Based General Arcing Fault Detection in Medium-Voltage Distribution Lines” IEEE Transactions on Power Delivery vol. 31, no. 3, pp. 2231 – 2241, 2016.
4. Mingjie Wei, Weisheng Liu, Hengxu Zhang, Fang Shi, Weijiang Chen, “Distortion-Based Detection of High Impedance Fault in Distribution Systems”, Power Delivery IEEE Transactions on, vol. 36, no. 3, pp. 1603-1618, 2021.
5. Masa, A. V.; Werben, S.; Maun, J.C. Incorporation of Data- Mining in Protection Technology for High Impedance Fault Detection. // IEEE Power and Energy Society General Meeting, San Diego, California, July 22-26, 2012.
6. Y. Cai and M. Chow, “Exploratory analysis of massive data for distribution fault diagnosis in smart grids,” 2009 IEEE Power & Energy Society General Meeting, 2009, pp. 1-6, doi: 10.1109/PES.2009.5275689.
7. Miao He, Junshan Zhang, ”A Dependency Graph Approach for Fault Detection and Localization Towards Secure Smart Grid” IEEE Transactions on Smart Grid, vol. 2, no. 2, pp. 342 – 351, 2011.

Authors: dr inż. Dariusz Sajewicz, Bialystok University of Technology, Faculty of Electrical Engineering, Białystok, Poland, Email: d.sajewicz@pb.edu.pl; mgr inż. Augustyn Wójcik, Institute of Radioelectronics and Multimedia Technologies, Warsaw University of Technology Warsaw, Poland, E-mail: a.wojcik@ire.pw.edu.pl; dr Piotr Zegadło, Kozminski University, Warsaw, Poland, E-mail: pzegadlo@kozminski.edu.pl

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 98 NR 3/2022. doi:10.15199/48.2022.03.30

Applications of Supercapacitor Systems in Photovoltaic Installations

Published by Szymon ROGOWSKI1, Maciej SIBIŃSKI2, Karol GARLIKOWSKI3,
Katedra Przyrządów Półprzewodnikowych i Optoelektronicznych, Politechnika Łódzka,
ORCID. 1. 0000‐0002‐1279‐3592, 2. 0000‐0002‐9752‐3400

Abstract. The following article presents results of measurements and parameter comparison of energy bank based on supercapacitor batteries and a typical lead-acid solution designed for PV microinstallation. For the purposes of the research, basic measurements of the charging and discharging characteristics of the energy storage consisting of 10 supercapacitors were carried out. Then this set was adopted as an energy storage system in a typical off-grid photovoltaic installation, which was launched and tested with the use of various types of loads in a static and dynamic conditions.

Streszczenie. Poniższy artykuł przedstawia wyniki pomiarów oraz porównania baterii superkondensatorów oraz typowego rozwiązania kwasowoołowiowego dla magazynowania energii w instalacji PV. Na potrzeby badań przeprowadzone zostały pomiary podstawowych charakterystyk ładowania i rozładowywania magazynu energii składającego się z 10 superkondensatorów. Następnie tak przygotowany zestaw został zastosowany jako układ magazynujący energię w typowej instalacji fotowoltaicznej typu off-grid, która została uruchomiona i przebadana z wykorzystaniem różnego rodzaju obciążeń w warunkach statycznych i dynamicznych. (Zastosowanie superkondensatorów w instalacjach fotowoltaicznych)

Słowa kluczowe: instalacja PV, superkondensatory, akumulatory, instalacja off-grid, żywotność
Keywords: PV installation, supercapacitors, batteries, off-grid installation, service life.

Introduction

One of the most important elements influencing the off-grid or hybrid photovoltaic installations lifetime is the energy storage system, which is considered to be the element with the shortest lifetime. In order to increase the operating time of the entire installation, and at the same time to improve its efficiency, it is necessary to extend the work time of the storage elements. Currently, the most commonly used elements for storing energy produced by a photovoltaic installation are lead-acid batteries or the increasingly popular lithium-ion cells. The advantage of lead-acid batteries is a relatively low price per unit of power, however, this solution has a very big disadvantage, which is a small number of charging and discharging cycles and high sensitivity to external parameters, including ambient temperature. Additionally, installations based on gel or AGM batteries do not allow for high currents charging and discharging cycles. The elimination of these obvious conventional energy storages limitations can increase the efficiency and profitability of the entire installation, and additionally extend the failure-free operation time without the need to replace the energy supply.

One of the ways to eliminate problems with the limitations of the charging and discharging currents is to use elements that are not current-sensitive up to level of several dozens of amps. Such solution may be supercapacitors, which are characterized by the long-term stability with operation currents exceeding 100 A and excellent dynamics. In addition, their use can also extend the working time of the entire storage system, owing to much greater number of charging and discharging cycles, which according to the manufacturer’s data, may exceed one million [1-3].

This article will present the results of research on the use of supercapacitors as energy storage elements in a typical PV off-grid installation and, additionally, their comparison with conventional AGM batteries.

Supercapacitors and typical energy storage operation.

Energy storage is a process whose purpose is to preserve electric energy and allow it to be used at another point in time. In the case of photovoltaic installations two most important applications may be indicated. Firstly off-grid installations, where there is no connection to the power grid, and secondly hybrid solution where it is important to increase the household consumption of energy produced by the installation. In this case also temporary stabilization of local grid is an important issue to be addressed. Currently, the most commonly used energy storage systems in PV installations are constructed with:

• Gel batteries,
• AGM (Absorbed Glass Mat) batteries.

The biggest advantage of the first type of batteries is that they may successfully withstand cyclic operation, making them suitable for off-grid installations, and they are practically maintenance-free. Unfortunately, despite the above advantages, the use of electrolyte in the form of a gel has some disadvantages, the greatest of which is the low power value during high current discharge and the significant influence of the ambient temperature on their capacity. Despite these disadvantages, structures of this type are the most frequently chosen solutions used as energy storage for photovoltaics, which is mainly due to the wide range of available products and the low price. AGM technology batteries are characterized by higher values of current and power in the short discharge event which results from the low internal resistance. In addition, they also have a high level of energy concentration and more effectively remove the heat generated during the current flow comparing to the gel solutions. Unfortunately, apart from the above advantages, AGM batteries are characterized by the shortest operating time, amongst all batteries made in lead-acid technology which results in the lowest number of charging and discharging cycles. A very big limitation in the operation of this type batteries is their high sensitivity to deep discharge, which demands the usage of specialized charge regulators. [4-6].

Comparison of described batteries basic parameters is presented in Table 1.

Regardless of the type, each conventional energy bank is characterized by a relatively small number of charging cycles which significantly reduces operation time. A way to extend life of the energy bank is to use elements that are characterized by much better cyclic parameters and resistance to very high currents. Supercapacitors can be components meeting the above criteria.

Supercapacitors can be placed between batteries and dielectric capacitors. They can store up to 200 times more energy than standard batteries and release it with much more power, while maintaining the current density typical for capacitors [8]. They owe their properties to special structure of electrodes which are made of activated carbon in the form of nanotubes, obtaining huge active surface of over 3000 m2/g and high electrical conductivity. The energy is stored in the micropores of the electrode material and in the space between them and the electrolyte. The process of recovering energy delivered during charging is very effective reaching the efficiency of 96-98% [9-12,17].

Table 1. Basic parameters of exemplary PV system batteries[7,8]

.

We can divide supercapacitors in several ways. The first is the division according to the principle of operation and charge accumulation. We can distinguish:

• Double layer electrochemical capacitors,
• Pseudocapacitance capacitors (redox capacitors).

Regardless of the type of supercapacitors, they have many properties that don’t have typical batteries. One of the greatest advantages of supercapacitors is a very large capacity of up to 3000 F, which, combined with a very short charging and discharging time, allows for very high power densities. Typical values for this parameter range from 1 kW/kg to 10 kW/kg [1,10,13]. Very short charging and discharging time of supercapacitors results from a very low internal resistance, the value of which, is about 0,3 mΩ, which is 10 times smaller than typical value for a lead-acid battery However their greatest advantage over typical solutions is a very large number of charging and discharging cycles, which according to the experiments can even exceed a million.

Apart from the advantages supercapacitors also have some pretty significant drawbacks that limit their capabilities for direct use as energy storages. One of the greatest is the low energy density stored in comparison to conventional solutions, which is only 20 Wh/kg. The average value for a gel batteries is about 3,5 times greater. Typically it is about 70 Wh/kg [7,8,10,11]. Very significant problem when using supercapacitors as alternatives to conventional batteries creates the shape of the voltage during discharging process. When drawing energy from a standard battery, the voltage remains practically constant until the total discharge, when it drops sharply. In case of capacitors, from the beginning the voltage drop takes an exponential shape, which forces the use of much better control systems.

Fig.1. Diagram of discharge battery and supercapacitor[14]

The last parameter limiting the operation of supercapacitors in energy storage systems is the relatively low permissible voltage, which is typically 2,7 V for a single element. Exceeding this value may cause the phenomenon of electrolysis when large amounts of gases are generated that can lead to an explosion of the capacitor. One way to increase the operating voltage of a group of superacapacitors is to connect elements in series. Such a procedure allows to achieve voltages at any level, unfortunately it is associated with a reduction of the resultant capacity of the entire system.

Thanks to their properties, including resistance to environmental conditions, very long service life and low service requirements, supercapacitors may be very interesting solution for storing energy produced from photovoltaic installations.

Purpose of research

The article presents a solution that allows to extend the working time of PV installation energy storage systems by using supercapacitors in their construction. The main purpose of the research is to construct and test an energy storage built on the basis of supercapacitors. Thanks to the use of their greatest advantages, such a solution can significantly extend the working time of the energy storage. An additional purpose is to confirm the the possibility of using such energy bank with the standard off-grid inverter.

One of the basic assumptions of the research is to check whether the battery built on the basis of supercapacitors is suitable for direct use as an energy storage for a commercial PV inverter. In order to verify the efficiency and profitability of this system a special analysis will be carried out to estimate the amount of charge collected and consumed during the typical operation of the entire system. As an additional element of the research temperature measurements were made to check how the charging and discharging processes affect this parameter, and consequently, the safety of the proposed solution.

Methods and experiments

The research carried out for the purposes of this article was divided into two stages. The first stage was aimed at determining the operation parameters of the supercapacitors and batteries and was performed using DC voltages. In the second stage the complete PV system equipped with mixed energy storage bank was constructed and investigated by DC and AC analysis.

Measurements of supercapacitors and batteries

To build energy storage series connection of 10 supercapacitors BCAP3000P by Maxwell Technologies was used [16]. The need to use as many as 10 elements resulted from the minimum voltage suitable for inverter input which was equal to 24 V DC.

The parameters of used supercapacitors are presented in Table 2.

Table 2. Basic parameters of supercapacitors BCAP3000P [1]

.

Firstly the basic parameters of supercapacitors were measured including charging and discharging characteristics. Such measurements allowed to predict how ready battery set would work, when consisting of several supercapacitors connected in series and what would be the differences compared to typical batteries. Additionally, owing to these measurements, it is be possible to calculate the actual capacity of the prepared bank, as well as to check how relatively large values of incoming and outgoing currents will affect the supercapacitors.

To determine the characteristics of the supercapacitor and AGM battery, the measuring system, which scheme is shown in Figure 2 was constructed.

Fig.2. Scheme of constructed battery and supercapacitor measurement system

Initially the determination of the charging and discharging characteristics of supercapacitors was performed. It was carried out to check how these elements cooperate when connected in series. For proper operation of this setup a special safety box was designed and a set of balancers was attached for parameters equalization. The results of the research are presented in the figure 3.

Fig.3. Characteristics of charging and discharging of 10 supercapacitors connected in series with their specific values.

The shapes of the charging and discharging curves are very similar to what we can find in the literature [9]. The charging process was carried out for a relatively low starting current of 20 A, so as to observe the voltage distribution on individual supercapacitors. As we could see during both of these processes, the voltage on individual elements changed in a very similar way, which means that they were charged and discharged evenly.

At the time of both characteristics measurements, the surface temperature of supercapacitors was monitored, using a Fluke VT04 Visual IR Thermometer. The temperature in the room where the measurements were taken was kept at a constant level of 22,5°C.

As we can see in figure 4, during the charging of supercapacitors, there was a slight increase of their surface temperature resulting from the processes taking place inside them [9]. The observed difference is relatively small, which during standard use will not significantly affect their work. The same measurement was done during the discharge process, but in this case the difference was 0,1°C, which can be considered a measurement error. Similar studies were performed for much higher currents. Their results were analogous, namely, there was small temperature increases during the charging process.

Fig.4. Temperature of 10 supercapacitors set during charging

In order to compare supercapacitors with typical AGM batteries basic charging and discharging characteristics for them were also verified. The results are shown in Figure 5. As in the case of supercapacitors, it was necessary to adjust the voltages of the energy storage to the inverter level, therefore the characteristics and further tests were performed for 2 AGM28 12/65 batteries connected in series.

Fig.5. Characteristics of AGM batteries a) constant charging b) dynamic discharging

As we can see, the shapes of the curves are completely different than in the case of supercapacitor batteries. During the process of discharging the voltage at the terminals remained practically at the same level. The difference between the initial and final voltage during the charging process in the case of an AGM battery was only 3%, while in the case of supercapacitors the difference is almost 100% which corresponds to the information that can be found in the literature [4].

During discharge measurements, the load was changed in order to observe the voltage shape, which was marked on the diagram. As can be seen, with a lower value of the current drawn from the battery, there was a slight increase in the voltage at the terminals, which does not occur in the case of supercapacitors which is visible, for example, in the picture 7. A sudden voltage drop should be noticed only at the time of a very deep discharge, which is a disadvantageous phenomenon for this type of energy storage, therefore it has not been presented in the above characteristics. During the charging process, is visible a constant voltage value at the terminals, while the current decreases with time. This phenomenon is a typical solution when charging chemical cells [3,4].

Comparing the characteristics of batteries and supercapacitors, we can see a big difference between them, which unfortunately may have a negative impact on the possibility of using the second ones with typical inverters, because we will only use a small part of the stored energy.

As for the supercapacitor batteries, was also measured the temperature of the AGM battery during charging and discharging. The results are presented below in figure 6.

Fig.6. Temperature at AGM battery during charging a) before charging; b) at the end of charging

As we can see, there is a much higher temperature rise during charging a battery than with supercapacitors. The difference between the initial and final temperature in this case is as high as 4,4°C, whereas for capacitors this difference was only 0,4°C. This temperature change is the result of chemical reactions taking place inside the electrolyte and on the surface of the electrodes during the charging process, which produces heat as a side effect [4].

A similar measurement was made during the discharge process, however, in this process, there were no noted temperature changes as in the case of supercapacitors.

As we can see when measuring the temperature for both types of energy storages, its increase is noticeable, but it is not large enough to affect the safety of any of the magazines. In this aspect, supercapacitors operate much better because in their case the difference before and after charging was 10 times smaller than that of a lead-acid battery.

The next step in preparing supercapacitors to work in a typical installation was to calculate the amount of energy that they are able to store in such a configuration. For this purpose we can count the charge accumulated in the supercapacitor battery in a following way:

Q = C・U

Where: Q – accumulated charge, C – capacity of supercapacitors, U – voltage across capacitors.

Q = 8100 C

Using the dependence that 1 Ah = 3600 C, we can calculate that 2,25 Ah is stored in the entire supercapacitor package. This means that this value is several times smaller than the capacity of typical lead-acid batteries. For comparison, the two batteries connected in series used for earlier measurements had a capacity of 65 Ah.

Measurements of a working PV installation

After proper preparation and protection, the supercapacitor store was connected to the inverter, which was then loaded with various types of receivers in order to observe the behavior of the energy bank during frequent and sudden load changes and to check the actual amount of energy that we are able to extract from it.

The performed measurements were made using a PV installation, which the block diagram is presented in Figure 7.

Fig.7. Block diagram of the PV installation used for the measurements

The installation consists of 7 polycrystalline photovoltaic modules SH-250P6-20, which parameters are presented in Table 3.

Table 3. Basic parameters of modules SH-250P6-20 [18]

.

In addition, the entire system includes an inverter Axpert VM II 3KVA, which basic parameters are presented in Table 4.

Table 4. Basic parameters of inverter Axpert VM II 3KVA [19]

.

The first load measurements were made in the evening hours, when there was no generation from the connected PV installation. During these measurements, various loads were connected to the AC output of the inverter. Additionally in the inverter setup the battery cut-off value was set to 21 V. The example shape of the voltage at the supercapacitor terminals and the outgoing current are presented in the Figure 8.

Fig.8. Energy consumption from supercapacitor set when there is no production from PV installation

The discharge process was performed with the use of a variable load, started twice. The first start-up took place around 70 seconds, which is visible in the diagram by an increase in the current drawn from supercapacitors. The increase in the consumed current during the first switching on results from the type of operation of used load. The device was turned off for about 140 seconds, which is visible as a decrease the current consumption to about 1,5 A. A similar process was performed in approximately 240 second and completed after 80 seconds. The remaining time during which the current is consumed at the level of about 1,5 A is the state in which the receivers were completely disconnected and the consumed energy only supplied the inverter. After about 10 minutes, the system was turned off because the voltage at the battery terminals dropped to about 21 V, which is the safety limit implemented in the inverter. As a result of such operation of the system, we are not able to use all the energy stored in the supercapacitors, but only a small part of it. The value of energy, consumed by the load is only Q = 1843 C, which when converted to Ah gives only 0,51 Ah. This means that, we can only use about 23% of the energy stored in supercapacitors. Such a small value significantly affects the economic aspect of this solution. To increase the efficiency, it may be necessary to design a dedicated inverter for such a solution that would allow for a much greater DC voltage drop, which is not a failure in the case of supercapacitors.

Another type of measurements is a typical off-grid operation with a connected photovoltaic installation. This research was made on a sunny day, which allowed to generate a large input power from the PV installation. Exemplary results of the performed measurements are shown in Figure 9.

Fig.9. Energy consumption from supercapacitor batteries when there is production from PV installations

The waveform of the current in the diagram above takes both positive and negative values, which shows the current flow to and from the supercapacitors. A positive current value means that in the given period of time the current charges the energy bank, while a negative value means that the current flows discharging the supercapacitors. When the current value is practically close to 0 , it means that the amount of energy generated by the installation is sufficient to power the load, and the supercapacitors are fully charged. Figure 8 shows two characteristic points for which the power consumption is very high in a very short period of time. In the first case it was caused by an increase of the system load for a few seconds, which took place around 1650 second and was marked on the graph as “temporary heavy load”. The next characteristic point is the case when the inductive load was started, which is characterized by a current peak during start-up, and then the value of this load slightly decreases. In addition, there is a third case in which the load was heavy and lasted about a minute. During its duration, the current drawn from supercapacitors was at the level of 20A. After each load jump, there was a period when the energy storage was charged, which is visible as a positive value of the current flowing in the system.

As the last one the characteristic of all the operating parameters of the photovoltaic installation was measured. Results are based on the data recorded by the inverter. In this case, apart from the parameters of the supercapacitors battery, the input parameters from the installation are visible as well as power and current consumed by the receivers. The results monitored by the inverter are recorded at 30 s intervals, which allowed for the precise detection of characteristics presented in Figure 10.

Fig.10. Characteristics of: a) input and output power; b) currents flowing in the installation

The above characteristics show the input and output parameters of the installation, such as power and current. In the case of first waveform one can see significant temporary energy consumption peaks, the value of which exceeds 1000 W. During these moments, some of the energy is supplied directly from the PV installation, but due to the fact that it is not enough, the missing amount must be taken from the storage bank. It may observed in curve b), because for these moments the value of the current drawn from the supercapacitors is very high at the level of 20A. When the amount of energy drawn from the inverter is lower than that produced, the storage is recharged, which is visible as positive current value of supercapacitors. The current characteristics also show the time intervals in which the supercapacitor current is practically zero, which means that the amount of energy produced by the PV installation is sufficient to meet the demand on the AC side.

As we can see from all the above mentioned experiments of typical operation of an off-grid installation, the energy storage in the form of supercapacitor bank connected by standard PV inverter is very good at dealing with both long-term heavy loads as well as in the case of temporary current consumption at the level of several dozen amperes. The only problem that arises in their case is the small capacity resulting from the quite high cut-off voltage declared in the inverter, which does not allow for their effective use.

Conclusion

Using the obtained results, it can be concluded that supercapacitors are elements that can effectively store energy in PV off grid and on-grid installations. Their dynamic parameters and the ability to work at much higher currents than in the case of typical batteries allow for much faster and more effective energy transfer compared to typical lead-acid batteries.

In addition, the possibility of charging them with currents several times greater than in conventional solutions can be very convenient in hybrid installations, where the converter, after charging the batteries, transfers the energy produced from the installation to the power grid, thus increasing the profitability of the entire installation from the prosumer side. The greatest undoubted advantage that speaks in favor of their use as an energy storage in PV installations is the practically unlimited number of charging and discharging cycles. During the tests, the phenomenon of full discharge of supercapacitors occurred several times, which did not affect the amount of energy accumulated by the battery. Unfortunately, the supercapacitor battery also had an unquestionable disadvantage, which is a much lower capacity value compared to lead acid batteries. The limited capacity is unfortunately the result of low voltage protection at the magazine terminals in order to increase its service life. One of the ways to increase the amount of energy drawn from the supercapacitor battery is to design a dedicated inverter that will allow to work with a much lower voltage. This investigation will be continued in the near future.

At a further stage of the research, it is planned to perform measurements of parallel connection of a typical AGM battery with supercapacitors. The aim of this stage of the research will be to check the behavior of such hybrid energy storage for large and short-term currents drawn from it. In addition, it will be checked whether such a connection will increase the lifetime of the energy bank by reducing the value of the battery currents.

REFERENCES

[1] Datasheet K2 SERIES 650 F – 3,000 F
[2] Szymański B., Instalacje fotowoltaiczne, Wydawnictwo Globenergia, (2019)
[3] Sarniak M., Budowa i eksploatacja systemów fotowoltaicznych., Wydawnictwo Grupa MEDIUM, Seria: ZESZYTY DLA ELEKTRYKÓW NR 13., (2015)
[4] Czerwiński A., Akumulatory, baterie, ogniwa. Wydawnictwo Komunikacji i Łączności, (2016)
[5] https://www.solarreviews.com/blog/lead-acid-batteries-forsolar- storage
[6] Jastrzębska G., Odnawialne źródła energii i pojazdy proekologiczne, WNT Wydawnictwa Naukowo- Techniczne (2011)
[7] datasheet.GEL FM-12-60
[8] datasheet_AKU_AP12-60_PL.pdf
[9] Frąckowiak E., Beguin F., Supercapacitors: Materials, Systems, and Applications, Wiley online library, Chapter 2
[10] Wang T., Chen H.C., Yu F., Zhao, X.S., Wang H., Boosting the cycling stability of transition metal compounds-based supercapacitors., Energy Storage Mater. (2019)
[11] Waseem R. ,Faizan A. ,Nadeem R.,Yiwei L., Ki-Hyun K., Jianhua Y., Sandeep K., Andleeb M., Eilhann E. K., Recent advancements in supercapacitor technology, Nano Energy, Volume 52, (2018,)
[12] Kouchachvili L., Yaïci W., Entchev E., Hybrid battery/supercapacitor energy storage system for the electric vehicles, Journal of Power Sources, (2018)
[13]Akumulatory i nie tylko…”,,Elektronika Praktyczna, (2015)
[14] https://www.elektro.info.pl/artykul/instalacjeelektroenergetyczne/58186,inicjatywa-zastosowaniasuperkondensatorow-w-ukladzie-zasilania-napedowrozlacznikow-sredniego-napiecia
[15] Zhang Q., Li G., Experimental Study on a Semi-Active Battery-Supercapacitor Hybrid Energy Storage System for Electric Vehicle Application, IEEE Transactions on Power Electronics, (2020),
[16] USER MANUAL Maxwell Technologies® Integration Kit
[17] http://www.maxwell.com
[18] http://www.photon-solar.de/uploads/SH-250P6-20%201650x992x40%20%206X10.pdf
[19] https://voltronicpower.com/en-US/Product/Detail/Axpert-VM-II-3KVA-5KVA

Authors: dr hab. inż. Maciej Sibiński, Politechnika Łódzka, Katedra Przyrządów Półprzewodnikowych i Optoelektronicznych, ul. ul. Wólczańska 211/215 90-924 Łódź, Budynek B9 E-mail: maciej.sibinski@p.lodz.pl; mgr inż. Szymon Rogowski Katedra Przyrządów Półprzewodnikowych i Optoelektronicznych, ul. ul. Wólczańska 211/215 90-924 Łódź, Budynek B9 Email: szymon.rogowski@dokt.p.lodz.pl; Karol Garlikowski Katedra Przyrządów Półprzewodnikowych i Optoelektronicznych, ul. ul. Wólczańska 211/215 90-924 Łódź, Budynek B9 E- mail: 194718@edu.p.lodz.pl

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 97 NR 12/2021. doi:10.15199/48.2021.12.36

Energy Sector of Pakistan – A Review

Published by Rana Muneeb Hassan, Andrzej Bie´n, Szymon Barczentewicz, Mohammad Abu Sarha, AGH University of Science and Technology

Abstract. Any country’s socio-economic growth is interlinked with number of factors, some of more significance with devastating impact whereas the others with very less impact. Amongst all such factors, energy is one of the major player in economic growth of a country, now a days as the energy sector drives the engine of progress, growth, and development in industrial, agricultural, and defense sectors, adding the impact to domestic consumers. The purpose of the study is to discuss the Pakistan’s current energy crisis which is getting worse and worse by everyday passing. Mainly the official data, along with the research work of scholars, international data and some raw data, all are collectively used to understand and convey a clear picture. This study would lay a basis for future studies which will uncover the solution to take the energy sector of Pakistan out of energy crisis.

Streszczenie. Na rozwój socjoekonomiczny kraju wpływa, w ró˙znym stopinu, wiele czynników. Po´sród nich jednym z najwa˙zniejszych jest energia. Dost˛epno´s´c energii wpływa na przemysł, rolnictwo, sektor obronny oraz ˙zycie codzienne mieszka´nców kraju. W niniejszym artykule opisano kryzys energetyczny w Pakistanie. Na podstawie danych oficjalnych i przegla˛du literaturowego oceniono stan energetyki w Pakistanie. W pracy zaproponowano tez˙ moz˙liwe droge˛ rozwoju sektora energetycznego Pakistanu.(Przegla˛d Systemu Energetycznego w Pakistanie)

Keywords: Pakistan, Energy, Development
Słowa kluczowe: Pakistan, Energetyka, Rozwój

1. Introduction

1.1. Overview

Recent technological developments and increasing concern over the sustainability and environmental influence of traditional fuel usage, the long term benefits of producing green and clean, sustainable energy in extensive amount from renewable energy sources arouses interest around the world.

In this study the energy sector operating in all parts of the country are discussed in detail. To make this study more versatile, convenient and understandable, not only the governmental but also private sector, the controlling authorities, the transmission and distribution companies along with production houses are also included. This paper will start from the government of Pakistan and then further going down to the consumer level.

While having discussed country’s domestic energy resources, this paper will lay a solid foundation of the available energy mix and also highlight the trend of supply and demand over a certain period of time. This study focuses on the diversity of energy resources projects—both national and international— that mostly remained short of realization. A statistical comparison of energy generation and energy consumption, and yearly basis comparison. Because of the limited nature of the subject, only a few published topics are accessible. Most of the data considered for this study comes from official government documents, official seminars, and scholarly journals and articles.

2. Energy sector in Pakistan

2.1. History

In the earlier decades, a significant increase in energy demand witnessed in Pakistan’s energy sector. On the contrary, energy production has followed a declined trajectory, which caused increase in the demand and supply gap exponentially. The contemporary energy resources and local potential will be discussed further in this paper.

Pakistan’s energy mix is not spread over many sources, also the major dependence is on imported fuel which leaves no other option in addressing the energy deficit. The current energy mix consists of the below sources [1]:

• Thermal 62.1
• Hydro energy 25.8
• Nuclear 8.2
• Renewable 3.9

2.2. Infrastructure

To get a better understanding of the current energy situation in Pakistan, this paper will present the inherited, & implemented infrastructure, needs of stake holders, and expectations of shareholders and layout of energy sector. The three main sectors of energy sector generation, transmission and distribution system of Pakistan’s energy sector is a bit more complex. The generation companies, transmission sector[9] and distribution companies[10] are working all together with the Government of Pakistan.

2.2.1. Inherited Infrastructure

From 1947 the independence time, energy shortage was also one of the challenges amongst the others Pakistan has been facing which till today is still unresolved. In early 1960s, Pakistan military took the responsibility and played their role in delivering huge infrastructure and accumulate thousands of watts in national energy sector, with the help of local and foreign funding[2]. At that time, energy mix mainly comprised of hydro-power and thermal power stations. In the 1970s, the first nuclear power station was established and commissioned in Karachi. In the 1980s, the utilization of nuclear sources further improved and the authorities continued with the development of nuclear power infrastructure.

In early 1990s, the government launched energy conservation program by introducing Independent Power Producers (IPPs) to produce 13000 megawatts of energy [3]. In 1990s, the total installed capacity was 11000 megawatts, out of which more than 50% of energy was producing from the hydro power sources whereas nuclear and thermal sources were contributing around 40% of the total generation [3].

2.2.2. Contemporary Infrastructure

In 2007, the shortage was 6000 MW responsible for prolonged and consistent blackouts [6]around the country. After 2010, energy crisis, frequent power shortages and failure hit the ceiling and became worst [7].

According to the 2017-18 national economic survey, by February 2018 the country’s installed capacity to generate electricity increased over 29000 MW whereas previously in June 2013 was around 23000 MW, which shows significant growth of around 30% during 5 years but still is not satisfactory to meet the needs [5].

2.3. Governing Bodies

Fig. 1. Energy Sector in Pakistan

A number of governmental, semi-governmental, autonomous, and private departments, authorities, companies and organizations are involved in the whole process of generating energy through different means, then transmission of energy nationwide and finally pass on the energy to the consumer level. The energy generation is based on more than one source i.e, hydro, thermal, nuclear, renewable, and others and more than 42 Independent Power Producers (IPPs) are involved in the generation. All generated energy are then entered into the national grid managed by another independent body responsible for transmission lines and infrastructure. Then 11 distribution companies came into play for distribution within their specified areas. (Fig. 1), presents the hierarchical structure of energy sector in Pakistan:

2.3.1. MINISTRY OF WATER AND POWER

The Ministry of Water and Power was a federal ministry in Pakistan. The ministry was dissolved in August 2017. The water and power divisions shifted to Ministry of Water Resources and Ministry of Energy respectively.

2.3.2. WAPDA

Pakistan Water and Power Development Authority (WAPDA) was came into being in 1958. Federal government took the administrative control of this autonomous authority. Structural changes were made in past to make sure that WAPDA could solely focus on the development of water reservoirs and hydro-power resources in more effective and efficient manner.

WAPDA is focused on the construction of five, multidimensional short and long-term water reservoirs in coming years to serve purposes like water storage, energy generation and flood control. The goal is to ensure the continuous supply of economical, green and clean energy to the consumers. The construction of water reservoirs like dams will be vital for hydro-power projects and to meet the water requirements.

2.3.3. AEDB

In May 2003, the Federal Government established the Alternative Energy Development Board (AEDB) and set milestone for year 2030, of generating over 5% of total power capacity through renewable energy technologies. The government of Pakistan authorize AEDB to perform following tasks:

• Evolve private sector to implement policies, programs and projects within the scope of ARE
• Ensuring the sustainable economic growth through development & generation of ARE
• Proactively transferring of technology & developing local manufacturing units for ARE
• Promotion and commercialization of ARE resources based energy generation

2.3.4. PEPCO

Another company working as a division of Ministry of Water and Power is Pakistan Electric Power Company (PEPCO). Following companies are operating under PEPCO:

• National Transmission & Despatch Company (NTDC)
• Generation companies (GENCOs)
• Distribution companies (DISCOs)

2.3.4.1. GENCOs

Generation Company (GENCO) is a company responsible for power generation in Pakistan. The Water and Power Development Authority is the owner of all these companies but still they are operating separately [8]. There are currently four GENCOs which are working with WAPDA.

2.3.4.2. DISCOs

Distribution companies (DISCOs) are operating under Pakistan Electric Power Company (PEPCO) and are responsible for the distribution of electricity in the respective specified allocated areas by purchasing electricity from generation companies and sell it to consumer. The Government of Pakistan owned all the distribution companies except the KElectric which was privatized.

2.3.4.3. NTDC

National Transmission & Despatch Company (NTDC) is a governmental company solely engaged in power transmission across the country.[11][12] The NTDC owned network of 5970 kilometers of 500 KV transmission lines and 11322 kilometers of 220 KV also sixteen 500 KV and forty-five 220 KV grid stations all across the country.[12]National Transmission and Despatch Company (NTDC) administers the interconnected transmission networks by linking power generation units with load centers which are spread all over the country.

2.3.5. PAEC

The Pakistan Atomic Energy Commission (PAEC) is an autonomous governmental authority & a scientific research institute, focused on promotion of nuclear science, and nuclear technology [13–14].

PAEC was established in 1956, and the active nuclear power plants are shown in (Fig. 2). PAEC has successfully delivered 5 commercial nuclear power plants. As of 2012, approximately 3.6% of overall power produced in the country is generated by commercial nuclear power plants, as compared to 62% from traditional energy resources, 33% from hydro power and approximately 0.3% from coal power plants. Pakistan plans on constructing 32 nuclear power plants by 2050.

Fig. 2. Nuclear Power Plants

In 1972, PAEC somehow managed to develop one nuclear reactor of only 85 MW with foreign help and it remained the only reactor for 3 decades. From 2000 on-wards, PAEC successfully launched 4 more nuclear power reactors and added 1320 MW collectively till 2017. The overall generation capacity of all nuclear power plants are presented in Table 1.

Table 1. Nuclear Power Plants Capacity

.
2.3.6. PRIVATE SECTOR

2.3.6.1. KESC

The electric supply company operating only in Karachi is K-electric. K-Electric (KE) is absolutely a joined investor owned company responsible for all three stages – generation, transmission and distribution. In short responsible of producing and delivering energy to consumers.

2.3.7. IPPs

An independent power producer (IPP) is an entity, not a public company but owns facilities to generate electricity power for sale to utilities and end users. In 1994, Pakistan Government announced an investor oriented strategy to develop IPPs based on oil, coal and gas, which was vital in formation of 16 IPPS. Later on, in 1995, a hydro power policy was also pronounced which rose in development of country’s first Hydro IPP.

In 2002, new government came up with new policy, through which more 12 IPPs added into the main stream. In 2015, again policy changed which further caused the addition of another 13 IPPs, mostly by Chinese companies. As of 2018, currently more than 40 IPPs are working in Pakistan.

3. Energy Mix

3.1. Electricity Generation

The hydropower generation share in overall total electricity generation has increased in FY2020 as compared to its share in FY2019. Recently, thermal has the largest share in the electricity generation. Gas and Re-gasified Liquefied Natural Gas (RLNG) are other cheaper sources. Decent growth of RLNG usage in energy mix has already taken part in improving supply to various power plants like Bhikki, Haveli Bahadur Shah, Balloki, Halmore, Orient, Rousch, KAPCO, Saif and Sapphir. Furthermore RLNG is also being supplied to massive fertilizer plants, industrial and transport sectors. The comparison of share of different sources of electricity generation is given below:

Table 2. Share in Electricity Generation

.

In recent years the country is shifting the energy mix towards more sustainable resources and in just an year it can be seen, that the share in electricity generation through hydro-power, and nuclear increased by 5 % each whereas dependency on thermal has been decreased till here, the numbers are depicting a good picture, except that the decrease in renewable sources increased by remained almost the same between the same period of time in 2019 and 2020.

Fig. 3. Comparison Installed Capacity (FY 2019-2020)

Till April, FY2020, installed capacity of electricity was reached to 35,972 MW which in April 2019, was 33,452 MW, grew by 7.5 percent.

3.2. Electricity Consumption

As far as consumption is concerned, no major change witnessed in the pattern of electricity consumption. Whereas, during July-April FY2020, because of the better and prolonged rainy season, the consumption of electricity in agriculture sector declined.

Table 3. Sector wise Electricity consumption share

.

As far as consumption is concerned, no major change witnessed in the pattern of electricity consumption. Whereas, during July-April FY2020, because of the better and prolonged rainy season, the consumption of electricity in agriculture sector declined. As the increase in population and more tendency of digitization has caused the increased household electricity consumption. The comparison between consumption patterns of electricity during March 2019-20 is shown above.

Also the change in percentage consumption during the Mar-2019 and 2020 is depicted in Fig.4.

Fig. 4. Sector wise consumption comparison

4. Transmission Lines

The country is divided into two sectors, based on the geographical grounds, Northern part of the country where the major hydro-power plants are in installed and southern part of the country where thermal generation plants are responsible of generating electricity. One major challenge in this sector is the generation installations are remote and far from the load centers. The flow of power through transmission lines are as:

• Power transmission from north to center of the country in summer
• Power transmission from south to center of the country and north in winter

Table 4. Transmission Sector

.

In summer, due to increased flow of water, the hydropower plants in north supply the electricity to center and coup with the increased demand of electricity whereas in winters the hydro-power plants could not generate at the fullest capacity because of harsh cold weather and the demand in the center also decreased so the electricity is transmitted from south to north.

5. Renewable Energy

The renewable energy sources are not given enough space and importance in energy policy as well as current energy mix whereas the focus was only on traditional nonrenewable sources, which had a lasting impact on country’s energy sector. Pakistan’s first wind power project introduced and came live in 2012 which was the time when the whole world already have producing thousands of megawatts through such renewable projects.[4]

5.1. Wind Energy

Pakistan possess about 346 GW potential for wind energy generation. In 2006’s Energy Security Action plan, the government of Pakistan tasked the Alternative Energy Development Board to increase the wind energy share by 5 % in power generation capacity by year 2030. AEDB has developed commercial opportunities and numerous high paced projects to promote wind power generation. AEDB is running 40 wind power projects generating total of approximately 2010.2 MW.

• Twenty-Four (24) wind power projects generating total of 1235.20 MW
• Twelve (12) under construction wind power projects of potential 610 MW
• Four (04) wind power projects of potential 165 MW capacity are at different stages of completion

5.2. Solar Energy

Geographically, Pakistan is situated in a region offering over 2,900 GW of solar energy potential with over 300 sunshine days, having annual average temperature of 26-28 degree Celsius and 1900-2200 kWh/m3 annual global irradiance as shown in Fig.5. Pakistan started the solar journey with 440KW installed capacity of 18 photo-voltaic systems in 1980. Nonetheless, the life of the system was relatively short because of poor maintenance, carelessness and lack of knowledge. Later on, the authorities introduced a concept of solar villages’ for the remote areas where power transmission was neither possible nor feasible.

Fig.5. Pakistan’s Annual Global Irradiance KWh/m3

Installation of up to 500W/unit photo-voltaic systems of for electricity generation and water heating increased the import of solar water heaters which was 260 in 2007 and increased to 16175 in 2013. So far, Pakistan has been increasing share of solar energy but remarkable and giant steps are still required for this sector to decrease the load shedding duration.

AEDB is pursuing 22 solar PV power projects of cumulative capacity of approximately 890.80 MW.

• The operational projects are six (06) solar power projects contributing total of 430 MW
• IPPs have four (04) projects sharing total of 41.80 MW
• Furthermore twelve (12) projects accumulating capacity of 419 MW are under construction.

5.3. Small Hydro

The massive hydro power potential of Pakistan is non match-able. The geographic layout of the country, the natural water flow systems and irrigation system in the country manifest hydro power potential that can be harnessed to meet the increasing energy needs of the country. Other than the large hydro, there are certain prospects of development of small mini- micro hydro power which are considered as the worthwhile options for power generation. Currently, the generation is 128 MW whereas 877 MW is under construction and 1500 MW is under development.

Table 5. Transmission Sector

.
6. Conclusion

This research discovered and shed light over the energy situation and also provides a brief overview and understanding of energy sector operating in Pakistan also pertain the policies and planning implemented during different regimes from the independence. The whole study concluded that during the early years the governments proactively focused on water resources management which somehow also contributed in energy generation. Furthermore in 1960s, the priority shifted towards energy generation, which resulted in the development of infrastructure like hydro-power plants and implementation of energy policies. This review provides a detailed analysis of energy sector of Pakistan, the energy policies and departments involved from generation to consumer level. The dependence of the energy generation majorly is upon imported conventional resources and even during the worst energy shortage period during last decade, Pakistan could not generate clean, green and sustainable energy also because of the involvement of international oil, the tariff is always fluctuating which is troublesome at consumer end. The involvement of large number of public and private departments have put the whole energy sector in a more vulnerable situation and also make it more difficult to come up with effective and efficient solution.

This research paper is a part of an ongoing doctorate studies. In coming days, a more detailed research based solution will be presented. The solution will involve demand side management through designing, modeling and analysis of energy mix. More strategic energy planning framework will be developed to coup the continuous increase of energy demand.

REFERENCES

[1] Yearly Survey Book “Pakistan Economic Survey 2018-19” Retrieved from: [web page] http://www.finance.gov.pk/survey_1819.html/. Energy, Ministry of Finance, Government of Pakistan,,pp. 234–241, 2019.
[2] Inter-Services Public Relations (ISPR) Retrieved from: [web page] https://www.pakistanarmy.gov.pk/journeyscratch-nuclear-power.php.
[3] Aziz, Sartaj. “Who is responsible?” Retrieved from: [web page] https://archive.pakistantoday.com.pk/2013/04/23/who-is-responsible-4/.
[4] “50 MW wind power project connected to national
grid” Retrieved from: [web page] https://nation.com.pk/09-Nov-2012/50mw-wind-project-connected-to-national-grid.
[5] “Country’s installed electricity capacity increases by 30pc to 29,573MW” Retrieved from: [web page] https://www.thenews.com.pk/print/309535-country-s-installed-electricity-capacity-increases-by-30pc-to-29-573mw.
[6] “Pakistan’s Ongoing Electricity Shortage” Retrieved from: [web page] http://www.energytribune.com/articles.cfm?aid=864/articles.cfm?aid=864/.
[7] “More Crises in Pakistan: Electricity, Flour, Sugar, Water, Sui Gas Crises – What is the way out? : ALL THINGS PAKISTAN” Retrieved from: [web page] http://pakistaniat.com/2008/01/03/more-crises-in-pakistan-electricity-floursugar-water-sui-gas-crises-what-is-the-way-out/.
[8] NEPRA Retrieved from: [web page] http://www.nepra.org.pk/lic_gencos.html/.
[9] National Transmission & Despatch Company Limited Retrieved from: [web page] https://ntdc.com.pk/vision-mission/.
[10] National Electric Power Regulatory Authority (NEPRA) Retrieved from: [web page] https://nepra.org.pk/.
[11] “NTDC to pay Rs5m fine for violating performance standards The Express Tribune” Retrieved from [web page] https://tribune.com.pk/story/1570268/2-ntdc-pay-rs5m-fine-violating-performance-standards/.
[12] National Transmission & Despatch Company Limited Retrieved from: [web page] https://ntdc.com.pk/.
[13] “IAEA presentation on nuclear power by PAEC” Retrieved from: [web page] http://www.iaea.org/NuclearPower/Downloadable/Meetings/2013/2013-10-01-10-04-TM-NPE/2.3.pakistan.pdf/.
[14] “Nuclear Power in Pakistan” Retrieved from: [web page] http://www.world-nuclear.org/info/Country-Profiles/Countries-O-S/Pakistan/.
[15] “Biomedical engineering at PAEC” Retrieved from: [web page] http://www.paec.gov.pk/Medical/.
[16] “Agriculture and Biotechnology” Retrieved from: [web page] http://www.paec.gov.pk/Agriculture/.
[17] ”PAEC & Summer College on Physics”. International Nathiagali Summer College. Pakistan Atomic Energy Commission Retrieved from: [web page] http://www.paec.gov.pk/INSC/.
[18] “CERN and Pakistan: a personal perspective” Retrieved from: [web page] http://cerncourier.com/cws/article/cern/28934/.
[19] “Pakistan and CERN”. Express Tribune Retrieved from: [web page] http://tribune.com.pk/story/769312/pakistan-and-cern-2/.
[20] “National Command Authority”. Director-General of the Inter-Services Public Relations Retrieved from: [web page] https://www.ispr.gov.pk/front/main.asp?o=t-nca_press_release_archive/.
[21] “Prime Minister inaugurates 340 MW Chashma Nuclear Power Plant Unit-2: Government to provide full support to PAEC for Nuclear Power Projects Urges International Community to make nuclear technology accessible to Pakistan for power generation” Retrieved from: [web page] http://www.paec.gov.pk/p-mj11-news1b.htm/.
[22] Zia H. Siddiqui, I. H. Qureshi Nuclear Power in Pakistan The Nucleus,A Quarterly International Scientific Journal, pp. 31—33.
[23] “Nuclear Power Generation Programme” Retrieved from: [web page] https://en.wikipedia.org/wiki/Pakistan_Atomic_Energy_Commission/.

Authors: Ph.D. Rana Muneeb Hassan, dr hab. in˙z. Andrzej Bie´ n, dr in˙z. Szymon Barczentewicz, Ph.D. Mohammad Abu Sarhan, Department of Power Electronics and Energy Control System, Faculty of Electrical Engineering, Automatics, Computer Science and Biomedical Engineering, AGH University of Science and Technology, aleja Adama Mickiewicza 30, 30-059 Kraków, Poland, email: hassan@agh.edu.pl

Source & Publisher Item Identifier: PRZEGLA˛D ELEKTROTECHNICZNY, ISSN 0033-2097, R. 97 NR 10/2021. doi:10.15199/48.2021.10.07

Improving the Charging Technology for Electric Vehicles

Published by Peter Lutter, EE Power – Technical Articles: Improving the Charging Technology for Electric Vehicles, September 26, 2018.

This article discusses the concept of universal inductive energy transmission and its possible applications and implications.

With the development of a universal inductive charging system, Finepower GmbH near Munich underpins its leading position in power electronics and battery charging. After numerous developments of off- and onboard chargers in the fields of industry and electric mobility, Finepower is now focusing on improving the charging technology of tomorrow.

EPCOS AG, a manufacturer of transceiver and receiver coils for inductive charging systems, is involved as a partner. Special attention is paid to the electromagnetic compatibility (EMC) of universal systems. In addition, the Technical University of Munich (TUM), Department of Energy Conversion Technology, and the Kempten University of Applied Sciences, as well as the Technology Network Allgäu (TNA), are providing fundamental research support.

Research Objectives for Universal Inductive Charging Systems

Inductive charging systems for electric vehicles presently form the focus of intensive research, development, and standardization. A typical application example is the possibility of contactless recharging of industrial trucks and autonomous electric vehicles. A wide variety of vehicle system properties such as ground clearance, battery voltages, coil geometries, current-carrying capacity, etc. are currently prompting manufacturers to strive for an inductive loading unit developed individually for a particular vehicle fleet.

One of the main objectives in the development of a universal inductive charging system is to allow the highest possible tolerance in the vehicle position. If different vehicle types are to be charged wirelessly, different positioning of the coils on the station side and on the vehicle side cannot be avoided due to the vehicle dimensions alone, but above all also due to the different receiver coil geometries and configurations.

Another reason for the highest possible positioning tolerance is the fact that it is often not possible—especially due to parking and waiting restrictions at public charging points—to position the vehicle exactly right in order to enable optimum energy transmission, either by means of an electronic parking positioning system or manual maneuvering. 

A system for parking positioning causes additional costs when purchasing an electrically powered vehicle. In addition, such a positioning system can fail, which could lead to a considerable waste of time for the driver or completely prevent an inductive charging process.

Short-term Intermediate Charges are Possible 

By implementing the above-mentioned objectives, it is conceivable to use such a charging station at conventional filling stations, public places such as multistory car parks in shopping centers, airports, railway stations, but also for short-term intermediate charging, for example at red traffic lights or motorway service stations. In such cases, due to the short duration of the energy transfer, full charging of the battery storage is not possible, but nevertheless, this increases the range of the vehicles without any additional expenditure of time for the driver, since all these downtimes occur independently of the charging requirement of the vehicle.

Since complete charging is not possible due to the limited length of stay, it is particularly important to start the charging process as quickly and straightforwardly as possible, even if this could represent a loss of performance in inductive transmission.

Motorway Service Stations will Gain Importance for Mobility in the Future

The following rough calculation is intended to illustrate the power transmission that can be expected with short downtimes and poor positioning: A vehicle stands on a highway service area. The parking time should amount to 10 minutes. For example, if a charging station with a nominal capacity of 22 kW is provided and the vehicle stops offset from the transmitting coil, it should be assumed that a charging capacity of 10 kW is still possible. This results in an energy input of approx. 1.7 kWh into the vehicle for the assumed downtime. Taking a total capacity of a typical vehicle battery of 30 kWh into account, this corresponds to about 5.7 % recharging; assuming a total range of 150 km, this would amount to about 8.5 km. However, if the vehicle comes to an optimum stop, recharging of 11.4 % or 17 km would be possible.

Figure 1. The operating situations and challenges of inductive charging as well as the approaches and objectives of the joint project.

From a technical point of view, there is no reason not to install even higher charging capacities. The downtime in other cases, such as when shopping or doing similar things, is even considerably longer and ranges from 30 minutes to several hours, so that, according to the above example, recharging quantities of 17.1% (30 minutes) to 68.4% (2 hours) respectively 25 km (30 minutes) to 100 km would be achieved in a bad parking position. The basic idea is that the driver does not have to carry out any additional tasks other than finding a suitable parking space, and that one and the same charging station can be used for a variety of different vehicle types.

In order to compensate for or to avoid the variance of the positioning elaborate methods have been used up to now in order to always keep the coil positions relative to each other as optimal and constant as possible. Just to mention the keywords “loading above number plate” or “positioning system”. Even if certain position tolerances were permitted in these cases, the result was a considerable loss of performance.

The following objectives, approaches, and characteristics of this research project represent a significant difference and progress compared to the previous approaches:

• No need for time-consuming and cost-intensive positioning
• Intelligent / adaptive compensation
• Inductive charging of a wide range of vehicle types
• Minimization of the communication effort
• An increase of the offset range

In summary, it can be concluded that with adaptive compensation the electromagnetic interference emission can be kept low, thus enabling power transmission without precise positioning measures or significantly increasing power transmission while complying with the EMC limits, even if, for example, a vehicle is not parked optimally.

On the one hand, these features enable a high utilization and thus also an economically sensible operation of the planned system; on the other hand, the costs for communication, positioning and shielding measures can be kept low by the planned electronic compensation and control strategies.

Measurement Results of the Inductive Charging System Prototype

Up to now, Finepower has constructed the prototype of an inductive charging system and carried out first comparative measurements with and without adaptive compensation. As shown in Figure 3, the measured degree of efficiency is plotted for different power outputs depending on the positional offset. The measurements examined in this project can increase the efficiency at full charge by approximately 1%, or considerably more as the charge decreases. In the case of extreme offset, these measurements alone allow an appreciable operation.

Figure 2. Increase of the transmittable active power
Figure 3. Increase of efficiency in the offset range

Finepower has already confirmed the basic functionality and the technical improvement goals with the help of first measurement results. In the further course of the project, the adaptive compensation and the primary coil design will be revised so that, on the one hand, energy can be transmitted at all even in the event of extreme positional offset and, on the other hand, a further increase in efficiency can be achieved in rated operation.

Applying Universal Inductive Energy Transmission Can Extend to Industrial Areas

The concept of universal inductive energy transmission is not limited to the field of automotive or electric mobility, but can also be used for industrial purposes, especially in the production process, for example for contactless charging of commercial vehicles such as forklifts or small transport units.

In the context of industrial areas, it is crucially important to achieve the most efficient, rapid, and straightforward charging of the energy storage devices since electricity consumption essentially determines the operating costs, possibly leading to an increase in manufacturing and sales prices of the respective company’s products.

Author: Peter Lutter is a Graduate Engineer in Physics and Semiconductor Electronics at Chemnitz University of Technology. He currently works as the General Manager at Finepower GmbH since January 2002.

Source URL: https://eepower.com/technical-articles/improving-the-charging-technology-for-electric-vehicles/

Review on Techniques of Optimal Placement and Sizing of DG in Distribution Systems

Published by Veeraraghavulu vemula1, R. Vanitha, sathyabama2, institute of science and technology , India. ORCID: 1. 0000-0001-5872-8537 2. 0000-0003-2195-7242

Abstract: Distributed generation (DG)is a term describing the generation of the electricity use on other side rather than transmitting energy over the electric grid. By using this (Distribution generation) DG in power system plays a major role in improving voltage profile, reduce the power losses and improves stability of the substation. Distribution generations (DG) are located near to load centres, so care should be taken while allocating DG in the power system to increases the benefits. By placing the distributed generators in the distribution system (primary distribution system) the real, reactive power and improving the voltage profile can be managed in optimal way will be explained in this paper. Optimal Allocation of the DG is identified by using the using the VSI, ratings are computed by using the different optimal techniques. The power loss reduction and better voltage regulation can be attained by using the optimal techniques. A clear and complete analysis of performance should be carried throughout the work to demonstrate the efficiency of the system.

Streszczenie. Generacja rozproszona (DG) to termin opisujący wytwarzanie energii elektrycznej po drugiej stronie, a nie przesyłanie energii przez sieć elektryczną. Dzięki zastosowaniu tego (Generacja dystrybucyjna) DG w systemie elektroenergetycznym odgrywa główną rolę w poprawie profilu napięcia, zmniejszeniu strat mocy i poprawie stabilności podstacji. Generacje dystrybucyjne (DG) znajdują się w pobliżu centrów obciążenia, dlatego należy zachować ostrożność podczas przydzielania DG w systemie elektroenergetycznym, aby zwiększyć korzyści. Poprzez umieszczenie rozproszonych generatorów w systemie dystrybucyjnym (pierwotny system dystrybucyjny) w niniejszym artykule zostanie wyjaśniona rzeczywista moc bierna i poprawa profilu napięcia. Optymalna alokacja DG jest identyfikowana przy użyciu VSI, oceny są obliczane przy użyciu różnych optymalnych technik. Zmniejszenie strat mocy i lepszą regulację napięcia można osiągnąć przy użyciu optymalnych technik. W trakcie prac należy przeprowadzić jasną i kompletną analizę wydajności, aby wykazać skuteczność systemu. (Przegląd technik optymalnego rozmieszczenia i wielkości DG w systemie dystrybucji)

Key words: Distribution systems, Optimal placement of DG, Sizing of DG
Słowa kluczowe: rozproszone systemy dystrybucji energii, optyma;lizacja

Introduction

Nowadays, the demand for electrical power has been increasing rapidly. Due to the limited resources the generation stations and transmission systems expansion is less. For last 20 years a lot of research going on the DG. Dugan and MC. Dermott, T.E[1] defined the dispersed generators systems as below: dispersed generators are the generators that are interconnected with the distribution system and power distribution is less than 10Mega Watt. Basically, the larger units are connected to the transmission lines directly. Dispersed generators are installed in system where the power distribution is not more than 1 or 2Mege Watt and most of them are installed by utility. This type of power generation is called as “Dispersed Generation”.

By the load flow analysis, the system operation conditions like phasor voltages, real and reactive power flow will obtain. To solve the power flow problem, many algorithms are developed for transmission network. These algorithms for low voltage distribution network are not suitable, since they are inefficient to these networks. Forward and Backward Sweep (FBS) methods are proposed by Augusto Cesar dos Santos and Marcelo for easy implementation and robustness in power flow analysis, to get load flow solutions without solving the equations, they consider radial distribution network [2].

The problems arise as the load demand on the distribution system increases and many changes occur when the load increases from low to high. M. Chakravorty and D. Das [3] proposed VSI technique is used in RDS. The sensitive node of the system will be identified by a numerical method approach, which was represented by voltage source index(VSI). This method will protect the distribution system from the faults by initiating automatic remedial actions and the distance between two points (working and the constant point) can be find by the voltage source index (VSI). Voltage faults will occur at the node (sensitive node) of the distribution system and later all other nodes (sensitive nodes)of the system will effect.

Kyu-Ho-Kim and Yu-Jeong-Lee [4] presented a logic approach for placing distributed generation (DG) in radial distribution system. The main aim of the technique is to decreases the cost of the power loss of the radial distribution system. By implementing this logic, constrains can be transformed into the unconstrained multi-objective function. To reduce the losses, Caisheng Wang[5] proposed a method for calculating the optimal size of the Dispersed Generators and for identifying optimum location. This technique is tested with different sizes and complexities, the obtained results are compared with exhaustive power flow techniques.

A. Lakshmi Devi [6] proposed the Optimal Dispersed Generation unit by using the Frizzy logic. By using this method, we can find the optimal size of Dispersed Generation and the node is identified by using reasoning technique. Dispersed Generation installed at the node with high suitable index and power. The power losses of the radial distribution system nodes are designed by using the frizzy logic.

As the load demand increases the power distribution network is facing many problems to meet the demand, this increasing load reduced voltage and increases of the power loss[7].If the voltage at the nodes reduces as the nodes are far away from the substations. The voltage varies by the requirement of the reactive power in the system. In industrial sector this is the main reason to collapse the voltage. For improving the voltage profile and to avoid voltage collage in the power system reactive compensation is required [8-9].The ratio of reactance to resistance for the distribution system is low compared to that of the transmission system. This causes large amount of power losses and voltage magnitude drops along the RDS (radial distribution system) lines [10-11].

Distributed generation

The distributed generation (DG) is divided into two types:

I) Renewable energy sources (RES) distributed generators.
II) Non-renewable resources (NRES) (or) Fossil fuel-based sources distributed generators.

Distributed generators have the low environmental emission and more flexible in installing within short period of time [37]. By using these technologies like renewable powered generators are environmentally friendly in nature. Some of the distributed generations are standard centralized generation technologies in cost and operational aspects. Distribution generators allocation is basically difficult issue in the distribution system, which requires many optimization objectives [34]. For the reduction of reactive power and real power losses, increasing the voltage profile, short circuit capacity and carbon emanation etc is shown in figure 1.

Fig.1. Distributed generation

As the number of distributing generators currently increases uniformly the distribution networks like operation, generation, control and other issues may also effect. In real time by using the power electronic components the smaller quantity of reactive power can be observed or produces [46-47]. So, this will be a great concern for utilities like wind energy generators [48].

Distributed Generation concept has achieved more attention as of its innumerable advantages. So far DG has no uniformity over definition and size across the world. The definition for DG units varies with country and region. For instance, Anglo-American countries habitually use the term ‘embedded generation’, North American countries as ‘dispersed generation’, and Europe and some parts of Asia as ‘decentralized generation’.

Significance of optimal DG allocation and sizing

Optimal DG allotment has accomplished a lot of significance because of its different benefits. Nonetheless, combination of DG into a current framework will be a vital and troublesome undertaking. Since DG mix changes the conduct of organization from uninvolved to dynamic Bidirectional force stream at last ascents framework misfortune and influences unwavering quality and operational strength [11]. In [12], DG limit speculation is treated as an alluring decision in conveyance framework arranging. Financially it is absurd to expect to apportion DG on every single transport which may prompt antagonistic impacts [13].

Generally, power losses of the distribution system are low compare to the transmission system in the power system. These power losses will impact on the efficiency and the financial issues of the distribution system. For improving the overall efficiency, the power losses should be deceased to appropriate level. Many factors are to be considered to reduce the power losses [12-13]. By installing of Distributed Generators in the distributing system will used to reduce the power losses ,Network stability ,improving the voltage profile and the power factor improvement of the system [14-17].

DG integration benefits

Integrated of DG units into a current framework will have specialized (decreased line misfortunes, top shaving, improved voltage profile, solidness, dependability, influence quality, and by and large viability and so forth), monetary (suspension for updates, less establishment cost with diminished activity and support costs and so on) and ecological (decreased outflow of ozone depleting substances) benefits [32,33]. In 1999 a report distributed in the United Kingdom says that 41% of fossil fuel byproduct will be diminished by utilizing CHP based DG units [7,8].

The power delivered in large quantities to the sub stations through transmission lines. The substation is the point at which the transmission lines and distribution lines meet. The power is distributed to the load through feeders. We know that the supply of the distribution system is mainly comprised 3-phase supply, and then tapped off this supply is 1-phase supply [18-19]. The lines used for the distribution system are highly protected from ratio of resistor to impedance than that of the transmission lines [2]. Many problems occur as the load demand increases on the distribution system and the reduced voltage also effects on the various factors like generation, planning, technical and different other issues of the distribution system [20-21].

The power losses became the major issue in the electrical power system. Due to the power losses in the power system, the reactive power compensation has become increasing and it effect on different factors like operation, planning and other issues of the electric power system [22-23].

In [24], different types of dispersion networks arranging model is introduced. The models proposed were arranging with and without reliability consideration. Depending upon the load flow the distributing system is planned. The load flow analysis of DS (distribution system) is different from the TS (transmission system) due to some in born characters.

As the load flow will effect on the operation, planning and control and will result in sensitive node and time quantities of the power system. There are few techniques available at present literature. Ghosh and Das [25] proposed a method for the radial distribution system using the algebraic expression for receiving end voltage. Dharmasetal [26] presented a model of non-repeatable load flow method for improving voltage profile in distributing system by using the tap changing transformer.

DG allocation and sizing 0- Techniques comparison

A. Analytical method
B. Classical method
C. Optimization techniques

with appropriate size to boost techno-financial advantages. It brings about advance like minimum of generally framework power misfortune, activity and support cost, and improvement in voltage profile, influence quality, framework strength, and dependability. Significant specialized methodologies for ODG assignment and measuring are sorted as follows [7-9,34]:

Analytical approach:

Logical strategies are performing great for little and straightforward frameworks, not appropriate for a framework with enormous and complex organizations [46]. Insightful strategies explored in the current paper are as per the following:

Tengetal [27] approaches a method for the load flow analysis of the RDS (radial distribution system) employed with node-injected to branch-current (NIBC) and branch-current and node-voltage (BCNV) of distributing network using the algebraic expression of receiving end voltage [28-29].

Method of Kalman filter:

It is otherwise called Linear Quadratic Estimation. Its precision relies upon the quantity of tests. It is utilized for various DG allotments with a smaller number of tests. Expansion in the quantity of tests raises computational weight. It is utilized to decide DG size and an ideal finder file for DG assignment [38].

Sensitive analysis:

Nowadays there are many research papers on this topic of distributed generation for power loss and improving of voltage profile etc. [35-36] [37-38] [39-40]. Kashem-et-al [41] proposed a sensitive used to detects the change in power losses as respect to the distributed generators current injection. Erlich et al [42] proposed a design a method for balancing the reactive power from a number of DG (distributed generators) in the RDS (radial distributed system). In [43], sensitive analysis is used for finding the optimal allocation of DG (distributed generators) network. In [44], the optimal allocation of (DG) distributed generator by using the voltage source index (VSI). In [45], loss sensitivity factor is used for finding the optimal allocation of DG (distributed generators).

Classical method:

Weak hub node strategy is affectability-based methodology for optimal DG designation which is completed by little world organization hypothesis programming [40]. A misfortune decrease affectability factor technique is utilized for choosing optimal DG area [41-43]. A scientific methodology for taking care of optimal DG assignment issue is utilizing misfortune touchy factor dependent on the same current infusion. In this strategy, absolute force misfortune minimization is accomplished without assessing induction, the backwards of permission or Jacobian lattice.

Gradient Search :

This describe depends on minimization and expansion of a given capacity, inclination plummet for work minimization and angle rising for boost. GS disregards shortcoming level imperatives while incorporating DG unit into coincided network [37,47].

Non-Linear and Mixed Integer Non-Linear Programming:

Non-Linear Programming is utilized for least DG unit portion with improved voltage security in both outspread and coincided networks [48]. In [49], different DG allotment is liked for decreasing generally speaking force misfortune and age cost. Mixed Integer Non-Linear Programming is utilized to settle time-differing load models by changing over discrete probabilistic age load model to deterministic [50].

Continuation Power Flow :

Another technique was created dependent on Continuation Power Flow confirm that DG gives a piece of the answer for expanding load request [50]. Optimization techniques

Particle Swarm Optimization (PSO)& Genetic algorithm:

There are number of optimization scheduling methods are present in our technology among them different methods the dynamic programming (deterministic algorithm), mixes integer programming, nonlinear programming and Bender’s decomposing has been used. In [48], a new approach to solve the optimal allocation of distribution system is used. According to recent studies mostly included the heuristic algorithms, it also includes frizzy mathematical programming [50] and genetic algorithm [50]. An artificial immune system and evolutionary programming [25], Partial swarm optimization. Advantage of population based meta-heuristics algorithms are GA & PSO are the set of non-dominated solutions can find because of their multi-point search capacity. Genetic algorithm gives a ‘one size will fit all’ solutions to problem solving search as shown in figure 2 and 3.

Fig.2. Genetic algorithm

Bat Algorithm:

It is a multitude insight-based calculation. It was propelled by echolocation conduct of miniature bats. This is by shifting heartbeat paces of emanation and uproar. It is well appropriate for DG mix into an organization with blended burdens where responsive force misfortune is overlooked IS SHOWN IN Figure[50].

Artificial Bee Colony (ABC):

It is amassing knowledge-based calculation which is roused by rummaging conduct nectar of honey bees. It is well reasonable for complex issues. A tumultuous ABC calculation is utilized for allotment of genuine force DG units on a 38 hub and 69 hub outspread appropriation frameworks (RDSs).

Cuckoo Search (CS):

This calculation was enlivened by commit brood some of cuckoo species’ parasitism. They used to lay their eggs in other host birds’ homes. CS calculation is utilized for genuine force misfortune minimization.

Fig.3. Particle swarm optimization method
Fig.4. Bat algorithm

Bacterial Foraging Optimization (BFO):

It is a nature-enlivened advancement. It is utilized to discover DG size and a misfortune affectability examination for the area.

Ant Colony Optimization (ACO):

It is a populace-based calculation. In this calculation, subterranean insects track down the ideal way from their province to the food source. It is utilized for ideal reclosers along with DG allotment in a dispersion framework. It is a population-based optimization algorithm. Optimization is carried by cooperative search metaphor inspired by natural meme-tics. It is used to improve voltage profile with maximum benefits on a 38 – bus distribution system in modified SFLA is used for multi-DG.

Fig.5. Ant colony optimization

Conclusion

The current paper plainly shows the meaning of ideal circulation age assignment and estimating in an appropriation framework. At the same time the examination explains Distributed Generation coordination benefits like force misfortune minimization, voltage profile improvement, and decreased venture with low activity and upkeep cost and diminished ozone harming substances emanation by incorporating Renewable Energy Resource based Distributed age units. This investigation likewise centres around boundaries which rely upon ideal conveyance age allotment and measuring. Different scientists have effectively recognized ideal conveyance age assignment and measuring benefits like specialized, financial and ecological. Notwithstanding this few insightful, heuristic, meta-heuristic and half and half advancement methods are adjusted for ideal dissemination age assignment and estimating. Logical methodologies are not computationally hard for basic frameworks however not reasonable for a framework with huge and complex organizations. Joining of vulnerabilities related with DG yield, load interest, power valuing and emanation will make framework more intricate. Meta-heuristic and hybrid procedures are well appropriate for broadly enormous frameworks. They measure with high precision and wonderful assembly includes. This strategy gives worldwide ideal answers for basic single or complex multi-target issues. It is discovered that for ideal appropriation age distribution and estimating a few metaheuristic streamlining methods are performing incredibly well.

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Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 97 NR 12/2021. doi:10.15199/48.2021.12.01

Protection Transformer and Transmission Line in Power System Based on MATLAB Simulink

Published by Mohammed A. IBRAHIM1, Bashar M. SALIH2, Mahmoud N. Abd3,
Power Technical Engineering Department, Northern Technical University (1,2)
Ninavah Electricity Distribution, Directorate General Directorate of North Distribution Electricity, Ministry of Electricity, Iraq (3)
ORCID. 1. /0000-0003-3182-2771, 2. 0000-0002-2437-0765, 3. https://orcid.org/0000-0002-8018-0093

Abstract. The main objective of this research work is to build a simulation model of a power system based on MATLAB to detect the faults (symmetric and asymmetric). We also know that the electric power system is made up of important and costly components, so these parts must be protected. The major purpose of this article is to studies and analysis the different faults and declares the impact on power system. Two types of protection are used, differential protection and overcurrent protection. This work is approach to MATLAB/SIMULINK package. In this work, a laboratory board was designed to represent an electrical power system consist of three stages: generation units, transmission lines and distribution systems.

Streszczenie. Głównym celem niniejszej pracy badawczej jest zbudowanie modelu symulacyjnego systemu elektroenergetycznego w oparciu o MATLAB do wykrywania zwarć (symetrycznych i asymetrycznych). Wiemy, że system zasilania elektrycznego składa się z ważnych i kosztownych komponentów, dlatego te części muszą być chronione. Głównym celem tego artykułu jest badanie i analiza różnych usterek oraz deklaracja wpływu na system elektroenergetyczny. Stosowane są dwa rodzaje ochrony: zabezpieczenie różnicowe i zabezpieczenie nadprądowe. Praca ta jest podejściem do pakietu MATLAB/SIMULINK. W pracy zaprojektowano tablicę laboratoryjną do reprezentowania systemu elektroenergetycznego składającego się z trzech etapów: jednostek wytwórczych, linii przesyłowych i systemów dystrybucyjnych (Zabezpieczenie transformatora i linii przesyłowej w systemie elektroenergetycznym w oparciu o MATLAB Simulink)

Keywords: Differential relay, Overcurrent relay, Power system, Power transformer, MATLAB Simulink. Słowa kluczowe: przekaźnik różnicowy, przeciążenie prądowe, transformator, zabezpieczenie

Introduction

Right now, in power system network, fault is a major problem. With an increasing demand for electricity, the distribution system of electricity is growing year on year and for that reason, the protection of power system equipment and maintenance is very important in order to reduce costs and increase the life of the reliable and uninterrupted power system equipment [1]. The power system must be operating in a secure method at all times. Faults will result in a total blackout or a partial system. In order to protect the power system from the disturbances that have happened, a protection system is essential. There are many types of protective relays obtainable to solve this problem [2]. The benefit of protection relay is to reduce a dangerous damage in the electrical equipment at fault occurs, it is designed according to the basis of reliability, selectivity and fast response [3]. In order to protect this equipment from such problems, we need some protective measures. These shall consist of protective relays and circuit breakers. If there is a fault in the system, an automatic protection device is required to insulate the faulty section and maintain a healthy section in operation [4]. Power transformer is the bulk essential applications used in substations and main station. Power transformer is very important toward the effective functioning in the power system. Differential operation is the most popular method of operation of the various power transformer operations [5].

The overcurrent protection plays an essential role in protecting the power system due to unexpected increase in the current that damages the components of the system [6]. As we know, for (T.L) protection the circuit breaker is mounted and it relies on ternary line fault because this type of fault is hyper high compared to the other types of faults. There are two faults on the 3-phase balanced fault power system and the unbalanced faults in the power system are phase to ground, phase-to-phase, phase to phase to ground [7]. This project study the rumor fault types, which classified as symmetrical and unsymmetrical fault. MATLAB environment is used in order to analysis this circuit and obtain on the different simulation parameters of fault types.

Literature review

E. Ali, A. Helal, H. Desouki, K. Shebl, S. Abdelkader, O.P. Malikc, 2018 [8]. These authors work on three-phase power transformer has parameters (25 MVA, 138/13.8 KV, 60 Hz star–star connection. 5 Km (T.L) connected to a 13.8 kV equivalent source). Studied the protection of power transformer based differential relay; also, taking the internal and external fault, the system is simulated based on MATLAB/Simulink software. Satish Karekar, Tripti Barik, 2016 [9]. These authors work on the (T.L) has parameter (440 KV, 300 km length). Studies faults locations on EHV (T.L) parameter are convenient by using MATLAB software, and detection and analysis of faults (symmetrical and unsymmetrical) on long (T.L). The purpose of this paper is to modulate, and simulate the power system based on MATLAB/Simulink. Depending on the results that obtained by modulating and simulating the differential and overcurrent relay, this model will be expand in the future.

The proposed method The aim of this research is to design and implement a laboratory board for an electrical power system, since this design was one of the graduation projects for students of preliminary studies at the College of Engineering, compared with the results of MATLAB Simulink. The main purposes of this project are as follows:

• To study the existing fault classification and to detect faults for the power transformer and (T.L) in the power system.
• Appropriate design of a power system model with specification power system components.
• Power transformer and (T.L) specifications used by Terco Corporation.
• Design MATLAB Simulink model for the suggested methodology using MATLAB 2015a software environment.

Faults and Classifications

When the operation of power system under balanced circumstances, all components are carried. A fault in the circuit can obtained due to the failure that intervenes with the ordinary current flow. When the system insulation fails due to low impedance a path either between phases to ground or phases a short [1]. Circuit fault will occur; can classified this short circuit faults as:

Symmetrical Faults

In this fault’s kinds, the three phases are short circuit to earth or to each other. These faults are considered as a balance case and giving a sense that the system remain symmetrical. The most severe kind of fault is that included large current, for this reason, calculations of the balanced short-circuit case shall be made to determine these large currents.

Asymmetrical Faults

Asymmetrical fault included one phase or two and three phases line fault becomes unbalanced, these kinds of faults happen between lines or line to ground. Faults occur between phases and phase to ground are called asymmetrical fault. While asymmetrical shunt fault considered as an unbalanced in the line impedances. The shunt fault can classified as:

• One phase to ground fault (L-G).
• Two phases fault (L-L).
• Two phases to ground fault (L-L-G).
• Three phases fault (L-L-L).
• Three phases to ground fault (L-L-L-G).

Differential Protection

When the discrepancy between the primary and secondary current equal to zero, this mean that the system is healthy. In the strict transformer, there is no loss of power in the transformer, and eddy current and core losses appeared practically in the transformer in spite of no operation current. Mismatch of the phase shift, (CTs) ratio, ratio of the transformer and tap-changer. Because of this current, it will not be zero. Because of this relay, the sensitivity and the trip signal of the differential relay may decrease due to an increase in uncalled tripping. We use a bias differential relay to avoid this [10].

Figure (1) illustrates single phase of a three-phase differential protection (DP). Figure (1) shows that both of (CTs) enclose the protection zone. Due to its normal tendency, (DP) does not offer backup protection to the rest of the protective devices, for that cause; this form of protection scheme is commonly recognized as a protection scheme of unit. (CTs) current that passes through the conductors, these conductors are name as trial wires. In no condition of fault, the input current of the IP protection unit is same as to the output current of the protection zone at all instants. When considering the (CTs) A. The current that is carrying by a trial wire of (CTs) A and (CTs) are equal to:

(1) IAS = αA IP – IAe

(2) IBS = αB IP – IBe

Where: αA: Ratio of (CT) A; αB: Ratio of (CT) B; IAe, IBe: (CT) A and (CT) B Secondary excitation current.

By considering that the transformation ratios are equally, αA= αB =α, the relay operation current Iop is equal to:

(3) Iop = IAe – IBe

At the time of out-of-zone system faults, the Iop of relay operating current is quite small, but doesn’t to be zero. But when an inside zone fault occurs (internal fault), the input current is no secular worth to the output. Figure (2) represents the differential relay within internal zone [11, 12 and 13].

(4) Iop = α(IF1 + IF2) – IAe – IBe

Fig.1. One line diagram (DR) the fault out of zone.
Fig.2. One line diagram (DR) the fault of internal zone.

In terms of the operational characteristics of the electromechanical relay effect, the inclination of the characteristics increases. The bias differential relay (DR) is used for the (DR) of the high-power transformer. Figure (3) illustrates the operational characteristics of the (DR).

Fig. 3. Characteristics of differential relay.

When the pick-up ratio is set to a higher bias, the pickup ratio is set to a positive (tripping) area, when the pick-up ratio is set to a smaller bias; the pick-up ratio is set to a negative (blocking) area. In this kind of relay, operating coil is putting in parallel with the restraining coils. Conflicting torque is created by restraining coils to the operating torque. When the faults occur out of zone, the restraining torque is bigger than operating torque. Therefore, the relay is no operating. When the fault occurs internal, the relay is operating when the operating torque is greater than the bias torque. The changing in the turn’s number of the restraining coil will effect on the bias torque [10].

Over Current Relay (OCRs)

The function of the OCR is to compare the actual measured value with the preset value. The logical representation of this OCR as shown in Figure (1). As the value of the input current overcome the smallness value, the relay sense this putting-up and send a trip signal to the circuit breaker to disconnect the protected device, and open its contact to disjunction the protected device. Once the relay locates a fault, it is called fault pickup in this case. After the fault has been picked up, the relay can transmit the trip signal instantaneously. (Instantly over current relay) or may be requested for a certain period of time before a trip signal is released (time over current case) [15, 16, 17, 18 and 19].

Fig.4. Logical exemplification of Over-Current Relay

OCRs can be classified according to their operation in to three categories:

• Instantaneous OCRs
• Definite Time OCRs

Inverse Definite Minimum Time (IDMT) OCRs

Protection Part Algorithm

Figure (5) represents the algorithm of case study with two protection types.

Fig.5. Flowchart protection the case study by two methods

Molding and Simulation

Data for this research were taken from the TERCO Company of Sweden. A model is designed for a laboratory electrical power system, where the system consists of three stages the generation system, (T.L) system and distribution system. Two types of protection are used, first one (DR) to protect the power transformer and the second one (OC) protect the (T.L). Table (1) represents the parameter of the power transformer.

Table (2) represents the parameter of the (T.L), the description MV1420 Line Model corresponds to a (T.L) of a length 136 km, 77 KV, 100 A and 13 MW.

Table 1. Terco power transformer (MV1915) specifications

.

Table 2. Parameter of the (T.L)

.
Experimental and Simulation Results

Figure (6) illustrate the diagram of the power system module based on MATLAB/Simulink.

Fig.6. Power system module

Figure (7) illustrate the contents of differential relay subsystem block.

Fig.7. Scheme of differential relay subsystem
Fig.8. Scheme of overcurrent relay subsystem

Figure (8) illustrate the contents of overcurrent relay subsystem block. Figure (9) illustrate the design of the laboratory board for the electrical power system.

Fig.9. Practical power system board

Results and discussion

Case No.1: At no fault (normal operation):

The simulation results of voltages and currents for power system at sending end, receiving end and also T.L are shown in figures (10 – 15).

Fig.10. Primary voltage at sending side of the transformer
Fig.11. Primary current at sending side of the transformer
Fig.12. Voltage of (T.L)
Fig.13. Current of (T.L)
Fig.14. Secondary voltage at receiving transformer
Fig.15. Secondary current at receiving transformer

Case No.2: Fault at sending side of the transformer

The output signal of the differential relay when fault occurred at time 0.1 (sec) is given in figure (16).

Fig.16. Differential relay output signal

Figure (17) illustrate the current signal when the type fault is three phases to ground.

Fig.17. Primary current signal of sending side of the transformer

Figure (18) illustrate the voltage signal when the type fault is three phases to ground.

Fig.18. Primary voltage signal of sending side of the transformer

Case No.3: Fault at (T.L).

Figure (19) illustrate the current signal when the type fault is three phases to ground.

Fig.19. Current signal of (T.L)

Figure (20) illustrate the voltage signal when the type fault is three phases to ground

Fig.20. Voltage signal of (T.L)

Case No.4: Fault at receiving transformer

Figure (21) illustrate the current signal when the type fault is three phases to ground.
Figure (22) illustrate the voltage signal when the type fault is three phases to ground.

Fig.21. Secondary current signal of receiving transformer
Fig.22. Secondary voltage signal of sending side of the transformer
Conclusions

In this paper, the differential relay and overcurrent relay characteristics are advanced using MATLAB/Simulink. The performance characteristics of differential and overcurrent relay were evaluated at a location with three phase faults, and also study the various faults that occur in power system. (MV1915) power transformer and (MV1420) (T.L) Sweden Company (Terco-company). As shown from figure (10-15), when no faults occurred, the current and voltage normal case. As shown from figure (16-18) when internal fault occurred in sending side of the transformer, the differential relay will send signal to the circuit breaker at time (0.1 sec), this signal will be circuit breaker open, because the currents signal of secondary (C.Ts)A are don’t similar to that obtained from secondary (CTs)B, that due to operation of relay. As shown from figure (19-20) the fault occurred in (T.L), the type of fault three phase to ground, when the current increase up to set value the over current relay will be send signal to the circuit breaker, due to operation of the circuit breaker. As shown from figure (21- 22) the fault occurred in internal of receiving transformer.

Acknowledgment: The authors would like to thank Northern Technical University -Technical College of Engineering / Mosul, to provide a simulation package for us to finish our work.

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Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 97 NR 10/2021. doi:10.15199/48.2021.10.04