Power Quality Blog

Voltage withstand Tests and PD Measurements on Cable Accessories with Assembly Mistakes

Published by Maciej OWSIŃSKI¹, Paweł KLUGE¹, Andrzej ŁASICA², Przemysław SUL², Tomasz SALAK², Bartosz ZAJĄC², Institute of Power Engineering (1), Warsaw University of Technology (2)

Abstract. The paper presents the results of voltage withstand tests and partial discharges measurements made on MV cable accessories made with assembly errors. The tested equipment was subjected to tests developed according to its own program on samples from different manufacturers. The paper presents the results of the discussed tests compared to the prepared reference equipment.

Streszczenie. W pracy przedstawiono wyniki testów wytrzymałości napięciowej i pomiarów wyładowań niezupełnych wykonanych na osprzęcie kablowym SN z błędami montażowymi. Testowany osprzęt poddano testom opracowanym zgodnie z własnym programem, na próbkach od różnych producentów. W pracy przedstawiono wyniki omawianych testów w porównaniu do przygotowanego sprzętu referencyjnego. (Próby wytrzymałości napięciowej i WNZ na mufach kablowych z błędami montażowymi).

Keywords: cable joints, electric field distribution, assembly fault, cable accessories.
Słowa kluczowe: mufy kablowe, rozkład pola elektrycznego, błędy montażowe, osprzęt kablowy.

Introduction

The main problem with cable accessories is that its assembly process is made by a human. It is not important if someone made a good product if it is not assembled in a way that guarantees its work without failures. Proper knowledge and skills of the personnel are extremely important when assembling the cable accessories. Quality of the cable system is very important because of the possibility of causing human life threat, power system failures, and huge financial problems.

Laboratory tests of cable accessories are based on standard requirements [4, 5]. It does not allow for their in-depth analysis and drawing of larger conclusions. Evaluation of the research very often depends only on whether the result will be positive or negative based on the standardized criteria.

However, it should be remembered that the cable accessories themselves are a specific test object, because they are installed by the electrician in the place of use and therefore susceptible to errors. Therefore, this article attempts to describe possible problems that may go unnoticed in the process of normative tests.

The purpose of the research was to check the impact of the process of preparing test specimens and the testing methodology on obtained results. That is why the number of tested samples was limited and some of them were prepared with the same error in the assembly process.

The tested samples had the same design solutions but were produced by different manufacturers. This was to check the similarities of the obtained results for theoretically identical solutions available on the market.

The basic assumption of the work was to perform a series of voltage tests with normalized alternating voltage. Then, on samples with a defect, AC tests were carried out with a value far exceeding the normative requirements in order to check whether, despite the errors, they would be able to withstand such a voltage level.

Two methods were used to check the insulation quality of the tested samples: partial discharges measurements and determination of the dielectric loss – tanδ. Standard requirements do not specify how and when to perform partial discharges measurements after assembly. That is why it has been checked how the measurement results differ from each other in different time periods, without modification of the test objects.

Theoretical basis

Partial discharges are defined as electric discharges occurring in a limited area of insulation, and more precisely in the inhomogeneity of the structure and leading to the initiation of the degradation process, the effect of which will be the penetration of the insulation. In other way, it can be said that defects in insulation systems are the source of partial discharges in the tested objects.

The isolation degradation process itself usually occurs in the area of defects created in the technological process or during the standard usage [1].

One should mention, that partial discharge source may be improper layers assembly for paper insulation or gas inclusions, shown on the simplified diagram in Figure 1.

Fig.1. A simplified substitute diagram of the dielectric system,

where: C_o – the capacity of the tested object, C_g – a volume of gas inclusion, C_o‘, C_o” – the volume of newly formed parts of the permanent discharge dielectric

It should be remembered that the use of increasingly high values of an electric field in insulation systems promotes the occurrence of partial discharges. This means that the current trend aimed at minimizing production costs by reducing the number of necessary materials poses a great threat to the proper operation.

In the case of gaseous inclusions in the insulation system being the source of partial discharges, the relationship tanδ = f(U), has a course characterized by an increase in tanδ with exceeding the initial voltage of partial discharges. This means that for test specimens with assembly errors showing a high level of partial discharges should also have a higher level of tanδ then test specimens without errors. Exceeding the ionization voltage leads to an increase in dielectric losses. At a voltage lower than the ionization voltage, the loss power in the dielectric (active and reactive) increases in proportion to the voltage, which means a constant value of the dielectric loss factor tanδ. After exceeding the ionization voltage, when the PD discharges appear, the active losses and tanδ increase significantly. An increase of dielectric loss factor is a signal of overloading the insulation [2].

Description of the Tested Objects

There were 8 test specimens prepared for the tests. These test specimens consisted of 4 different types of cable joints, from 4 different manufacturers. Each of cable accessories types was assembled in the version according to the manufacturer’s instructions and without the electric field stress control mastic. Samples made correctly were marked with the letter “a” while the samples without the electric field stress control, with the letter “b”. Samples marked 1a, 1b, 2a, 2b, 3a, 3b and 4a, 4b were prepared.

Main test objects were cable joints. For this reason, before the assembly of cable joints, specimens with an outdoor termination on both sides were prepared and the level of partial discharges was measured on them. In any case, the level of partial discharges with mounted outdoor terminations did not exceed the background level equal to 2 pC. After that, the specimens were cut in the middle and reconnected with the tested cable joints. This allowed stating that the measured level of discharges comes mainly from the joints and not from the rest of the test samples.

The tested joints were a MV equipment for the voltage level of 12/20 kV. All samples were assembled on the same cable with the producer marking as follows XRUHAKXS 1×120 12/20 kV.

Fig.2. Preparation of the test specimens: cable before an assembly of the tested joints and after PD measurements

Figure 3 is showing the assembly process of electric field control tape. In samples without this solution, the mastic for controlling the electric field was not installed. The remaining samples were made identically to the ones shown.

Fig.3. Preparation of the test specimens: a) connector before and b) after assembly of stress control mastic for test specimen No. 1

Prepared tests program

The prepared research program included tests as follow:

• PD measurement before installation of joints for all test specimens;
• PD measurement after installation of the joints for all test specimens;
• tanδ dielectric loss measurements for all test specimens;
• AC voltage withstand tests: 54 kV / 5 min according to the requirements of the standard [4] for all tested specimens; AC voltage withstand tests 90 kV / 5 min for all specimens without mastic;
• PD measurements after AC voltage withstand tests.
• Re-make of PD measurements for test specimens 1a, 2a, 3a and 4a after 30 days.

Before installing the cable joints, the level of partial discharges of all samples was examined. None exceeded the permissible level of 2 pC. The tests parameter was as follow:

A. Partial Discharge measurements

•The voltage applied: 2U₀ for 1 min;
• The voltage has been applied to the conductor, the metallic screen has been grounded.

B. Dielectric loss measurement

• The dielectric tangent stat coefficients were measured for two different values of the applied voltage: U₀ and 2U₀;
• The voltage was gradually increased at a rate of 1 kV/s;
• The voltage has been applied to the conductor, the metallic screen has been grounded.

C. AC voltage tests

• The dielectric tangent stat coefficients were measured for two different values of the applied voltage: 4.5U₀ for 5 minutes and 7.5U₀ for 5 min;
• The voltage was gradually increased at a rate of 1 kV/s;
• The voltage has been applied to the conductor, the metallic screen has been grounded.

All PD and tanδ measurements performed to compare the results were performed at the same voltage level of 2U₀.

The test stands had appropriate calibrations and the staff performing the measurements consisted of experts, which minimized the measurement errors during the tests.

Before the measurements, each of the test samples been properly cleaned.

Fig.4. A view of the stand for measuring the level of PD

Test measuring stands

All tests were carried out at the Institute of Power Engineering in Warsaw and at the Warsaw University of Technology.

A. Partial discharge

The test and measurement system consisted of Haefely Hipotronics devices: a separation transformer 400/400 V, a voltage regulator, a low-pass filter, a test transformer up to 150 kV, a capacitive voltage divider, a coupling capacitor, a measurement impedance LDM-5/U – Doble Lemke, and digital measuring system for measuring the level of partial discharge PD Smart – Doble Lemke. The electric diagram of the measurement system is shown in Figure 5, and the view of the measurement stand is shown in Figure 4.

Fig.5. Diagram of a PD test and measurement system;

where: T_r – TP150 kV test transformer, Z – supply impedance, U – voltage measurement on the control and measurement unit, C_k – coupling capacitor, Z_a – impedance, D – PD SMART analyzer, OK – PC computer with software for visualization of test results, C_x – a test object [3]

B. Dielectric loss measurement and AC voltage tests

The test and measurement system consisted of: a voltage regulator, a test transformer up to 300 kV, a capacitive voltage divider Phoenix, a standard capacitor and digital measuring system for measuring the tangent delta Omicron TANDO 700. The electric diagram of the measurement system is shown in Figure 6.

Fig.6. Diagram of a tan delta and AC voltage test and measurement system;

where: V_R – voltage regulator, T₁ – 300 kV test transformer, R_l – limiting resistor, D – voltage divider, kV – voltmeter, C_Ref– standard capacitor, T_O – tested object, TANDO 700 – tan delta measurement system, PC – computer with software for visualization of test results

The research results

All tests were performed according to the prepared research program. Following results have been obtained:

A. Partial discharge results

Table 1. PD results before and after dielectric loss tests and AC voltage tests

As can be seen from the results shown in Table 1, all samples without the electric field stress control mastic have a significantly elevated level of partial discharges. What may be surprising, also two correctly assembled samples were characterized by a fairly high level of partial discharges.

B. Dielectric loss measurement

Table 2. AC voltage tests results for U₀ and 2U₀ voltage applied

As can be seen from the results in Table 2, most (but not all) of the results of the delta tangent are increased for samples with assembly error. However, they are not clear and it would be difficult to detect a defect in acceptance tests.

C. AC voltage tests results for 4.5U₀ and 7.5U₀ voltage applied

Table 3. AC voltage tests results for 4.5U₀ and 7.5U₀ voltage applied

Sample No. 4b failed during the first AC voltage withstand test at the 40 kV voltage level. All other samples with assembly errors have been tested with AC voltage at 90 kV, and the results for samples 1b, 2b and 3b were positive. As can also be seen, the voltage test does not allow for the detection of a serious assembly error in most cases.

Summary

Described researches have allowed obtaining a new approach to the testing of cable accessories. In accordance with the adopted assumptions, it has been shown that in the discussed case the influence of the preparation of test specimens and research methodology have a huge impact on the obtained test results.

Figure 7 shows the relationship between PD measurements and tanδ results from tests.

As can be seen, the results obtained during PD and tanδ measurements are not convergent. The high value of partial discharges is not always identical with the increased dielectric loss factor.

During the tests, it was confirmed that PD measurements should not be made immediately after the assembly of the test specimens, because due to the construction of the samples, the measurement results are not reliable. Diagrams 8 and 9 are showing confirmations for this conclusion.

Fig.7. Correlation between partial discharge and dielectric loss measurements; blue – PD, red – tanδ

Fig.8. Comparison of all measurements of partial discharges carried out in the interval of time; blue – before all tests, red – after all tests, green – about 30 days after all tests

Fig.9. Comparison of all measurements of partial discharges made in the interval of time on an example; blue – 1^st measurements, red – 2^nd measurements, green – 3^rd measurements

Fig.10. Comparison of results AC voltage test; blue – positive, red – negative

The obtained results show that AC voltage withstands tests do not have to break down test samples after its assembly despite installation errors. That conclusion is confirmed based on test results showing that only 1 of 4 tested samples without the electric field stress control mastic did not pass the test (Figure 10).

Conclusion

In the given case, it can be seen that without proper care during measurements, obtained results can lead to wrong conclusions. The following conclusions were drawn from the studies of test results:

• Despite the presented theoretical foundations, in this case, the obtained results did not show the relationship between the level of partial discharges and the tanδ dielectric loss for cable accessories tests;

• Standardization does not give any information about when to do PD measurements after test specimens assembly. The results obtained show that they can change over time and this has an impact on the test result;

• The voltage test in very few cases allows detection of assembly errors at an early stage. It should be taken under consideration during the tests results evaluation.

REFERENCES

[1] Duda D., Gacek Z.: Propozycja kwalifikowania i ustalania kolejności badań diagnostycznych linii kablowych, Przegląd Elektrotechniczny, No. 11b, 2012, 166-169
[2] Florkowska B., Florkowski M., Włodek R., Zydroń P.: Mechanizmy, pomiary i analiza wyładowań niezupełnych w diagnostyce układów izolacyjnych wysokiego napięcia. Wydawnictwo IPPT PAN, Warszawa 2001.
[3] Sul P., Owsiński M., Stepnowska D., Sobolewski K., Samsel S.: Laboratoryjne stanowiska badawcze do pomiaru intensywności wyładowań niezupełnych jako podstawa współczesnej oceny jakości izolacji urządzeń elektroenergetycznych. Biuletyn Techniczny Oddziału Krakowskiego SEP, No. 2 (65), 2016
[4] HD 629.1 S2: 2006 Test requirements on accessories for use on power cables of rated voltage from 3,6/6(7,2) kV up to 20,8/36(42) kV Part 1: Cables with extruded insulation.
[5] IEC 60270: 2003 High-voltage test techniques. Partial discharge measurement.

Authors: Maciej Owsiński, Paweł Kluge, Institute of Power Engineering High Current Laboratory ul. Mory 8, 01-330 Warszawa, E-mail: maciej.owsinski@ien.com.pl; pawel.kluge@ien.com.pl; Andrzej Łasica, Przemysław Sul, Tomasz Salak, Bartosz Zając Warsaw University of Technology, Institute of Theory of Electrical Engineering, Measurement and Information Systems, ul. Koszykowa 75, 00-661 Warszawa; alasica@ee.pw.edu.pl, przemyslaw.sul@ee.pw.edu.pl.

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 96 NR 1/2020. doi:10.15199/48.2020.01.05

Anomalous Leakage Currents on Silicone Rubber Hollow Insulators

Published by Krystian Leonard CHRZAN¹, Maciej ZIPP²,
Wrocław University of Science and Technology (1), Gates Corporation (2)

Abstract. Leakage currents on silicone and porcelain housings were measured at a 110 kV substation (site pollution severity class heavy) for 7 months. Both types of housing had a similar geometry. The current on porcelain housings is usually up to 4,7 times higher than on silicone housings. However, significantly smaller currents (up to 2,6 times) were recorded on the porcelain insulators over a period of 8 days. Similar rare behavior was earlier seen at Glogow pollution test station and at Koeberg pollution test station on porcelain and silicone insulators with the same profiles. A better washability of porcelain during stronger rains plays a very important role in this phenomenon. It was shown that small leakage currents, usually in the range 4 -10 mA, cause surface erosion of silicone rubber housings.

Streszczenie. Przez 7 miesięcy mierzono prąd upływu na osłonach silikonowych I porcelanowych na rozdzielni 110 kV znajdującej się w III strefie zabrudzeniowej). Osłony miały podobny kształt. Prąd na osłonie porcelanowej był zazwyczaj większy niż na osłonie silikonowej (do 4,7 razy). Jednakże w ciągu 8 dni prąd na osłonie porcelanowej był mniejszy (do 2, 6 razy). Podobne takie rzadkie przypadki zauważono wcześniej na stacjach zabrudzeniowych w Koeberg i w Hucie Głogów na izolatorach o identycznym kształcie. Bardzo ważną rolę w tym zjawisku odgrywa lepsze oczyszczanie porcelany przez silniejsze deszcze. Wykazano, że niewielkie prądy upływu rzędu 4 –10 mA powodują erozję powierzchniową osłon silikonowych. (Nietypowe prądy upływu na osłonach silikonowych).

Keywords: Flashover, Surface contamination, surface discharges.
Słowa kluczowe: Przeskok, zanieczyszczenie powierzchni, wyładowania powierzchniowe.

Introduction

The flashover voltage of silicone rubber insulators is higher than the flashover voltage of porcelain insulators under the same contamination conditions. And similarly, the leakage current on contaminated and hydrophobic silicone insulators is smaller than the leakage current on hydrophilic porcelain insulators. A lot of research in laboratories and in the field confirms the excellent properties of silicone insulators [1]. The best comparison could be demonstrated after rapid wetting of both insulators. When both insulators are uniformly sprayed, and after switching the voltage, the current on a porcelain insulator is many times higher (e.g. 100 times) than on a silicone insulator [2]. However, under natural conditions and under continuous operating voltage, the currents on porcelain insulators are only up to a few times higher than the currents on silicone insulators [3]. Wallce Vosloo [4, 5] and Krystian L. Chrzan [2] showed that the currents on porcelain insulators are sometimes 10% – 20% higher than on porcelain insulators with identical profiles. In this paper we show that the ratio of currents on porcelain insulators to the currents on silicone insulators changes in the range of 0,38 – 4,7 over the course of one day.

The direct impulse to measure the leakage current on silicone housing was surface erosion found two years after the installation of combined voltage/current transformers at a 110 kV substation located in a heavily contaminated industrial environment with daily dust precipitation of 2 g/m² (Figure 1). The aim of the leakage current measurements was to determine the level of current causing silicone rubber erosion.

Fig.1. Surface erosion on shank (a) and on sheds (b) of silicone rubber

Current measurements and test objects The current measurements were carried out with a 4 channel digital recorder manufactured by KORIN Company. The sampling rate was 5 kHz, the sampling resolution was 10 bits and the measuring range was 1 – 400 mA (with 250 Ω current shunt). The data was stored in 2 GB memory. Thanks to a special algorithm, the memory enabled a very long collecting data period of 8 years. The current peak was only storied in the memory when its value was higher than the previous value. The installation of the measuring system at the substation is shown in Figure 2.

Fig.2. A Schematic representation of the current measuring system.

1 – Insulator, 2 – Current collection ring, 3 – Housing, 4 – Surge arrester, 5 – Current shunt (resistance), 6 – Data acquisition system

Table 1. Dimensions of research objects

The currents were measured on a 110 kV porcelain housing of EDF SV 2-1 switchgear and on two silicone housings of SVAS 123/OG combined voltage/current transformers (Figure 3). The leakage distance of the porcelain housing amounted to 328 cm, and that of the silicone housing to 288 cm. Moreover, the other dimensions of both housings are similar (Table 1).

Fig.3. Porcelain housing (1) and silicone housing (2)

Results

The currents measured in November on the porcelain housing were considerably higher for 22 days than those on the silicone housing (Figure 4). The currents on both silicone housings were sometimes equal, but sometimes small differences were observed. The maximum amplitude of 17,4 mA was noted on the porcelain housing on November, 29. On the same day, the current on the silicone housing reached the value of 4 mA (Table 2). The maximum ratio of 4,7 of current on the porcelain to the current on the silicone rubber was noted on March, 24.

Fig. 4. Daily maximum leakage currents in November

Table 2. Maximum ratio of currents on the porcelain housing to currents on the silicone rubber housing

In January and in the following months a strange phenomenon was detected. The currents on the porcelain insulators on some days were considerably smaller than the currents on the silicone insulators. The eight cases from the period January – May are listed in Table 3. The observed anomalous differences between the current peaks on the porcelain and silicone rubber were larger this time than when previously published [2, 5]. On May, 28 and on May, 30, the current on the silicone housing was higher than on the porcelain housing (Figure 5).

Table 3. Anomalous relation of currents on the porcelain insulators to currents on the silicone rubbers insulators

Fig.5. Daily maximum leakage currents in May

Correction due to different insulator profiles

The silicone housings and porcelain housing have not identical profiles. Their form factors are 3,2 and 4,5 respectively (table 1). Assuming a uniform hydrophilic pollution layer and the same surface conductivity on silicone an porcelain housings, we get the following leakage current ratio:

Under such (unrealistic) conditions the current on porcelain housing would be smaller than the current flowing on the silicone housing.

If the porcelain housing were in the shape of the silicone housing, then its leakage current would be greater 4,5/3,2=1,41 times. These corrected current values on the porcelain housing and corrected current ratios from table 3 are compiled in the table 4.

Table 4. Anomalous relation of currents on the porcelain insulators to currents on the silicone rubbers insulators after correction

Despite the correction, the leakage currents on the porcelain housing are still smaller than the currents on silicone housing.

Discussion

Hydrophilic contamination on the porcelain surface absorbed water and formed a continuous layer after wetting. Conversely, water droplets on the hydrophobic polluted silicone rubber were separated from each other. Therefore, the surface resistance was high and the current was small. These very different scenarios explain why current on a hydrophilic surface is many times greater than on a hydrophobic surface after a so-called “cold switch on”.

However, under field conditions the insulators had been under the operating voltage for many weeks. There were dry bands on the hydrophilic surface that had a high resistance. Therefore, the ratio of the current on the porcelain to the current on the silicone rubber was not so high. Cleaning of the insulator due to rain also plays a very important role. The contamination from porcelain insulators is easy to remove, but not so easy from the silicone rubber. There was more contamination on the silicone rubber than on the porcelain [6]. The importance of the insulator cleaning by strong rain can be shown in May. On May, 3, 10 and 12, rain with daily precipitations of 28, 9 and 9 mm occurred and the currents on the porcelain insulator were similar to the currents on the silicone insulator. During two periods of rain at the end of May the currents on the porcelain insulator were smaller than on the silicone insulator (Figure 6).

The distribution of contamination is also important. It was very uneven on the porcelain insulators [7], and less uneven on the silicone insulators [8]. The equivalent salt deposit density ESDD on silicone insulators can be 2-3 times greater than on porcelain insulators [2,6], but locally much greater differences were found. The ESDD on the upper side of the top shed of the porcelain post insulator was 15 times greater than on the porcelain post with bare glazes [7].

Fig.6. Current records and daily rain precipitation in May

Conclusions

Anomalous currents on silicone insulators were found at an industrial site with heavy pollution. A similar phenomenon was earlier found under heavy sea salt pollution (Koeberg pollution station) and under light industrial pollution (Glogow test station). Over the course of 7 months, currents on the porcelain housing were for 8 days considerably smaller than currents on the silicone housing. A better washability of the porcelain housing during stronger rains plays a very important role in this phenomenon. 10 mA leakage currents have caused apparent surface erosion of silicone rubber.

The authors gratefully acknowledge S. Maguda, from KORINE Company, and also L. Sieczko and D. Paluch from the Legnica Copper Smelting Plant for their help in organizing the current measurements.

REFERENCES

[1] Amin M., Amin S., Ali S., Monitoring of leakage currents for composite insulators and electrical devices”. Reviews on Advanced Materials Science, vol. 21, (2009) pp. 75-89
[2] Chrzan K.L., Leakage currents on naturally contaminated porcelain and silicone insulators,” IEEE Trans. on Power Delivery, vol. 25, (2009) no. 2, pp. 904–910
[3] Homma H., Kuroyagi T., Ishino R., Takaashi T., Comparison of leakage current properties between polymeric insulators and porcelain insulators under salt contamination conditions,” Int. Symposium on Electrical Insulating Materials, Kitakyushu, Japan, (2005), paper P1-14
[4] Vosloo W.L., A comparison of the performance of high voltage insulator materials in a severely polluted coastal environment”. Ph.D. thesis, University of Stellenbosch, South Africa, 2002
[5] Chrzan, K.L., Vosloo W.L., Holtzhausen J.P., “Leakage currents on porcelain and silicone insulators under sea or light industrial pollution.” IEEE Trans. on Power Delivery, vol. 26, (2011), no. 3, pp. 2051–2052
[6] Zhang H.Ye, Ji Y.M., Sun W.Y., Kondo K., Imakoma T., Contamination accumulation and withstand voltage characteristics of various types of insulators. 7th Int. Conference on Properties and Applications of Dielectric Materials, Nagoya, Japan, (2003), pp.1019-1023
[7] Chrzan K.L., Pollution accumulation on silicone insulators and on porcelain insulators. (in Polish) Przegląd Elektrotechniczny, (2011), vol. 87, no. 12a, pp. 129-132
[8] Gubanski S.M., Wankowicz J.G., Distribution of natural pollution surface layers on silicone rubber insulators and their UV absorption.” IEEE Trans. on Electrical Insulation, vol. 24, (1989), no. 4, pp. 689–697

Authors: dr hab. inż. Krystian Leonard Chrzan, Politechnika Wrocławska, Wydział Elektryczny W5, Katedra K38, ul. Wybrzeże Wyspiańskiego 27, Wrocław, E-mail: krystian.chrzan@pwr.edu.pl; mgr inż. Maciej Zipp, studied at the Wroclaw University of Science and Technology, Faculty of Electrical Engineering, He is now with the Gates Corporation, 59-220 Legnica, Poland, e-mail: m.zipp@10g.pl

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 96 NR 10/2020. doi:10.15199/48.2020.10.15

Investigation of Power Saving Modes in 10/0.4 kV Distribution Networks

Published by Oleksandr MIROSHNYK¹, Andrzej SZAFRANIEC², Kharkiv Petro Vasylenko National Technical University of Agriculture (1), Kazimierz Pulaski University of Technology and Humanities in Radom, Faculty of Transport, Electrical Engineering and Computer Science (2)

Abstract. Operation modes of 0.4/0.23 kV power supply systems are modelled using Monte Carlo method by means of Electronics Workbench software and statistical processing of simulation results and testing of the Pearson distribution law hypothesis using Mathcad are carried out. An analysis of existing power supply systems has been conducted and an alternative, economically feasible version of a power supply system is proposed, where consumers are supplied from low power transformers mounted on supports.

Streszczenie. Tryby pracy systemów zasilania 0,4/0,23 kV są modelowane stosując metodę Monte Carlo za pomocą programu Electronics Workbench, i przeprowadzane jest statystyczne przetwarzanie wyników symulacji i testowanie hipotezy prawa dystrybucji Pearsona za pomocą programu Mathcad. Przeprowadzono analizę istniejących systemów zasilania i zaproponowano alternatywną, ekonomiczną wersję systemu energetycznego, w którym odbiorcy są zasilani z transformatorów małej mocy zamontowanych na wspornikach. (Badanie trybów energooszczędnych w sieciach dystrybucyjnych 10/0,4 kV).

Keywords: current and voltage asymmetry, energy-saving power supply system, graphs of load, loss of electrical power, network of 0.4/0.23 kV.
Słowa kluczowe: asymetria prądu i napięcia, energooszczędny układ zasilania, diagram obciążenia, strata energii elektrycznej, sieć 0,4/0,23 kV.

Introduction

Improvement of the electric energy quality is a current problem in rural electrical networks with a voltage of 0.4/0.23 kV, inextricably linked with reduction of additional electric power losses which are caused by asymmetric phase load. Analysis of operating modes of rural networks with a voltage of 0.4/0.23 kV [1-3] showed that the current imbalance was due to the household load. This load is for the most part unevenly distributed over the phases of single-phase electric receivers which, as a rule, have random power consumption. Knowledge of current asymmetry in a network makes it possible to clarify levels of energy losses and, if possible, apply measures to reduce them [4, 5]. Modern computer software allows for modelling of unbalanced network modes and calculation of additional power losses, which are the result of asymmetric modes.

The aim of this study is to develop energy-saving modes of distribution networks in order to improve quality of electrical energy and reduce additional losses. Experimental Load changes of single-phase household consumers of electric energy are of a random nature and it is very difficult to accurately determine in advance their value at any time. It is possible only with a certain probability.

Even if single-phase consumers with the same power and equal total daily power consumption are distributed evenly, then due to the probabilistic nature of power consumption for any time in a three-phase supply network, one should always expect asymmetry of phase currents, and, as a consequence, of voltages.

In the asymmetric mode, the technical and economic performance of a network deteriorates sharply: energy losses increase, voltage deviations from nominal values and current flowing in the zero conductor cause appearance of significant potentials across electrical equipment enclosures connected to a zero wire, which leads to the danger of electric shock. Service life of asynchronous electric motors connected to such a network is dramatically reduced. In addition, a number of negative electromagnetic phenomena are observed both in the network and in the load. Thus, losses of active energy resulting from an uneven load of phases in 0.4/0.23 kV lines and consumer 6- 10/0.4 kV transformers increase by more than a third comparing with losses that would occur under a uniform load [4, 5].

Consider a section of a three-phase four-wire overhead 0.4/0.23 kV line with a length of 210 m (six supports). One single-phase consumer is connected to each of the three phases at each support. The network is powered by a transformer whose secondary windings are connected in a “star with neutral wire” scheme. The circuit of the network is modelled in Electronics Workbench [6]. It represents three single-phase voltage sources connected in the “star with neutral wire” scheme, the initial phases of the sinusoid are equal to 0, 120, 240 degrees, respectively, resistance of aluminum wires of the overhead line sections between the points of consumer connection (for air lines it is the distance between supports) is represented by a row of series-connected impedances (R = 0.012 Ω, X = 0.011 Ω for AC35 wire).

The consumers are connected to the phase and zero wires, the consumers’ load resistances have the following values alternating in phases in different sequences on different supports: 20 Ω, 30 Ω, 40 Ω. The consumers are connected to the line in such a way that at the transformer substation 10/0.4 kV, the 0.4/0.23 kV line represents a symmetrical load.

Considering that changes in the load of household consumers are random, subject to the normal distribution law of random variables, we will perform a statistical modelling of the network section scheme using the Monte Carlo method. An example of one test is shown in Figure 1, the current data are given in Table. 1.

Table 1 – Currents on network sections

Basing on 25 tests, we will perform statistical processing of modeling results and verification of hypothesis of the distribution law according to the Pearson criterion. To do this, we use the Mathcad program [7].

Fig.1. Modeling of network modes 0.4/0.23 kV by the Monte-Carlo method using the computer program Electronics Workbench

As a result of the statistical processing of the data, we obtain the following values of the mathematical expectation M and the current dispersion s (Table 2) and the electric power losses (Table 3) for the line sections of the 0.4/0.23 kV.

Fig.2. Calculation of the Pearson criterion using the computer program Mathcad

Thus, the performed studies show that the change in the load currents on the network segments and the electric energy losses in an asymmetrically loaded network of 0.4/0.23 kV are subject to the normal distribution law.

Table 2 – Mathematical expectation and dispersion of current across network segments

With increasing numbers of consumers, the length of the line and the magnitude of the currents flowing along the line increases, which leads to increasing in electric power losses. Therefore, there is a necessary to apply appropriate measures to reduce energy losses. Today, there are many devices for balancing the network, but all of them, because of their high cost and low reliability and inefficiency for long lines feeding the communal – household load, have not been widely used in networks 0.4/0.23 kV. Therefore, with the complete reconstruction of existing transmission lines or during constructing new transmission lines, it is necessary to shift to other power supply systems.

Table 3 – Mathematical expectation and dispersion of electric power losses across network segments

Electricity supply schemes and electrical networks configuration were formed in the middle of the last century, taking into account minimization of capital assets. This has led to their rapid physical deterioration.

Most electrical networks today require a complete replacement, since they have lost reliability, are physically obsolete, and do not meet the requirements of energy saving and safety. Therefore, it becomes necessary to use a system of maximum decentralization in reconstruction of existing or construction of new networks, which will significantly reduce losses and costs of investment.

Using Electronics Workbench [6] software, we will simulate operation of an existing traditional power supply system (Figure 3). Parameters of a three-phase four-wire overhead 0.4/0.23 kV line are the same as for the calculations shown in Figure 1. Its load resistances have the following values: 20 Ω, 30 Ω, 40 Ω. Initial phases of the sinusoid voltage are equal to 0, 120, 240 degrees, respectively. Consumers are connected between a phase conductor and the neutral conductor (3 consumers at the point of attachment, with different sizes in each phase).

Fig.3. Simulation of network modes using Electronics Workbench software

In the above diagram (Figure 3), a full phase segment of a 210 m long line is simulated (six supports, one-phase consumers are connected to each). Table 4 shows the power losses across each segment in the phase and zero wires.

Table 4 – Distribution of losses across wires in segments 0-1 to 5-6

Total losses in the network will be 105 watts.

Now let us consider a network with the same loads, but with a voltage of 10 kV, in which 10/0.4 kV transformers are located directly on the supports [8]. A scheme in Figure 4 also models a full-phase segment of the 210 m long line. Table 5 shows power losses in each section of the network.

Fig.4. Simulation of network modes using Electronics Workbench

Table 5 – Distribution of losses across wires of sections 0-1 to 5-6

Total losses in the network will be 0.15 watts.

Comparison of the losses shows that, in the proposed network, they are 700 times lower (without taking into account losses in the transformers) than in the traditional power supply system. In addition, the number of wires in the proposed power supply system, is reduced by a quarter because three wires are needed instead of four.

Statistical studies show [9] that it is possible to adopt a network with one 10/0.4 kV transformer and an outgoing cable that has a household loading with length of 700 m as the mathematical expectation.

Let’s compare costs of these networks. Table 6 presents the cost of building a transformer substation and the cost of building 1 km of the line. The construction costs for substations and power transmission lines [10] are given in the Table. 6. The basic cost of a line consists of the cost of supports, wires, fittings, territory (the land cost allocated for a support or a substation), and labour. It is also necessary to take into account the cost of landscaping – 3%, design work – 8%, other work – 3.5%, inflation – 2%.

Table 6 – Indicators of the construction costs of substations and transmission lines

Let us consider the cost of building a power supply system for consumers supplied from a 0.4/0.23 kV network (Figure 5).

Let us define the cost of building such a power supply system. For the purposes of calculation, a 10km long 10 kV line and a 700m long 0.4 kV line (for 40 consumers) are taken into consideration.

The total cost of such a power supply system is €263 000. Let us now consider the cost of building a power system for recipients who are supplied from the proposed system shown in Figure 6.

Fig.6. The proposed electricity supply system

Let’s assume a 10.7 km long 10 kV line (for 40 consumers). As a result, the cost of such a power supply system is € 261 000.

Fig.7. Diagram of the 0.4/0.23 kV power supply system

As a concrete example, we consider a real 0.4/0.23 kV power supply system of (Figure 7). To determine the level of current asymmetry, we simulate the operation of this power supply system in Multisim (Figure 8).

Fig.8. Simulated operation of a traditional power supply system in Multisim

Fig.9. Simulated operation of the energy-saving power supply system in Multisim

As a result of the simulation, the following phase currents in the head of the line: І_А = 83.3 А, І_В = 59.5 А, І_С = 80.4 and the current in the zero wire І_N = 22.1 А are produced. The total losses in the network are 783.93 W.

Now we simulate the operation of an energy-saving power supply system with the same loads (Figure 9).

As a result of the simulation, the following phase currents in of the line: І_А = 3.31 А, І_В = 3.67 А, І_С = 3.23 А are generated. The total losses in the wires of the power supply system are 2.03 W.

A comparative analysis of the power supply systems shows that consumers who use the proposed power supply system (from small power transformers installed on supports) have energy quality parameters that fully meet the required standards.

Conclusion

1. Our studies showed that variation of the load currents across the segments and losses of electric energy in an asymmetrically loaded 0.4/0.23 kV network are subject to the normal distribution law. As numbers of consumers rise, the length of the line and the magnitude of the currents along the line increase, which leads to greater power losses. Therefore, there is a need to apply appropriate measures to reduce energy losses.

2. The studies have shown that consumers of traditional power supply systems have an unsatisfactory quality of electrical energy (exceeding the coefficients of non-sinusoidal, zero and reverse sequences several times), high levels of voltage losses (unacceptable voltage deviations in remote consumers).

In addition, the energy losses across the wires of the proposed power supply system are much lower than in the traditional power supply system. Investment in both the projects is equally economical. Therefore, with a complete reconstruction of existing or construction of new transmission lines, it is necessary to shift to the proposed power supply system, which allows to significantly reduce electricity losses in the network, while ensuring higher energy quality indicators.

REFERENCES

[1] Bollen M., Definitions of Voltage Unbalance, IEEE Power Engineering Review, (2002), n.1, 49-50
[2] Faiz J., Ebrahimpour H., Precise Derating of Three-Phase Induction Motors with Unbalanced Voltages, Energy Conversion and Management, 48 (2007), 2579-2586
[3] Komada P., Trunova I., Miroshnyk O., Savchenko O., Shchur T., The incentive scheme for maintaining or improving power supply quality, Przegląd Elektrotechniczny, (2019), nr.5, 79-82
[4] Naumov I., Reducing losses and improvement of the quality of electric energy in rural distribution networks 0,38 kV by means of balancing devices, Dissertation of the Doctor of Technical Sciences, (2002), 05.20.02, Irkutsk, 387
[5] Tavakoli B., Kashefi, A., Three-Phase Unbalance of Distribution Systems: Complementary Analysis and Experimental Case Study, International Journal of Electrical Power & Energy Systems, 33 (2011), 817-826
[6] Miroshnyk O.O., Tymchuk S.O., Uniform distribution of loads in the electric system 0.38/0.22 KV using genetic algorithms, Technical Electrodynamics, Issue 4 (2013), 67-73
[7] Ochkov V., MathCAD 14 for students, engineers and designers, BHV-Petersburg, (2007), 368
[8] Faiz J., Ebrahimpour H., Influence of Unbalanced Voltage Supple on Efficiency of Three Phase Squirrel Cage Induction Motor and Economic Analysis. IEEE Transactions on Energy Conversion, 47 (2006), 289-302
[9] Tymchuk S., Miroshnyk O., Calculation of energy losses in relation to its quality in fuzzy form in rural distribution networks, Eastern-European Journal of Enterprise Technologies, 1(8) (2015), 4-10
[10] Kholiddinov, Ilkombek, Khosiljonovich, Electric Power Quality Analysis 6-10/0.4 kV Distribution Network, Energy and Power Engineering, (2016), Vol.8 n.6, 263-269
[11] Miroshnyk O., Łukasik Z., Szafraniec A., Lezhniuk P., Kovalyshyn S., Shchur T., Reducing the
dissymmetry of load currents in electrical networks 0,4/0,23 kV using artificial neural networks, Przegląd Elektrotechniczny, 95 (2019), nr 11, 245-249
[12] Szafraniec A., Mathematical modelling of transient electromagnetic processes in a power network, IEEE Xplore, (2019), 232-236
[13] Driesen J., Belmans R., Distributed generation in future grids: Will “Energy Islands” become a reality, Electrical Power Quality and Utilisation Magazine, (2005), Vol.1, (1), 11-14
[14] Almasalma H., Claeys S., Deconinck G., Mikhaylov K., Haapola J., Pouttu A., Experimental
Validation of Peer-to-Peer Distributed Voltage Control System, Energies, (2018), (11), 1304-1325
[15] Efkarpidis N, De Rybel T, Driesen J., Technical assessment of centralized and localized voltage control
strategies in low voltage networks, Sustainable Energy, Grids and Networks, (2016), (8), 85-97
[16] Hoornaert F., D’hulst R., Vingerhoets P., Vanthournout K., Driesen J., LV distribution network voltage control mechanism: Analysis of large-scale field-test, Sustainable Energy, Grids and Networks, (2016), (6), 7-13

Authors: prof. dr hab. inż. Oleksandr Miroshnyk, Kharkiv Petro Vasylenko National Technical University of Agriculture, Alchevskyh, 44, Kharkiv, 61002 Ukraine, E-mail: omiroshnyk@ukr.net, dr inż. Andrzej Szafraniec UTH Radom, Faculty of Transport, Electrical Engineering and Computer Science, ul. Malczewskiego 29, 26-600 Radom, E-mail: a.szafraniec@uthrad.pl

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 96 NR 4/2020. doi:10.15199/48.2020.04.36

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. 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 (L_f, 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 I_sabcand voltages V_sabc of an electric network into a Fourier series as follows[11]:

Where: ω – fundamental frequency of the electrical network, I_n1 and I_n2 – amplitudes of the sinus and cosine components of the network current, a – phase angle between current and voltage, V_n1 and V_n2 – 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, A_n1, A_n2 and B_n1, B_n2 – amplitudes of the sinus and cosines terms respectively. The vector representation of equation (5) is given by:

where: W^T– 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 (L_f, V_dc) 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.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

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)

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 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.

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

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.

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

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.

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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