Power Quality Blog

Experiment and Analysis of High Power Line-Start PM Motor

Published by Qinfen LU, Xiaoyan HUANG, Yunyue YE, Youtong FANG, Zhejiang University

Abstract. This paper investigates the performance of a high power line-start permanent-magnet motor (LSPM) by experiment, which is developed for industrial fans, pumps and compressors to reduce the energy consumption. The no-load back-EMF is measured and compared with predicted result of FEM. In order to assess the line starting ability, the rotor-locked test is carried out and then the starting torque ratio is deduced which is lower than that of induction motor of the same power. By adjusting the load, the efficiency and power factor during all operation condition are obtained. It is found this proposed LSPM has not only higher power factor and efficiency, but also high overload ability. After its starting ability of reduced voltage is analyzed, several useful methods are pointed out for designing high power LSPM which should start with limited current.

Streszczenie. Zbadano właściwości silnika wysokiej mocy LSPM w zastosowaniu przemysłowym do pomp, wentylatorów i kompresorów pod kątem redukcji zużycia energii. Zbadano silnik przy zablokowanym wirniku i na tej podstawie przewidywano moment startowy. Przy zmianie obciążenia określono współczynnik mocy i sprawność. (Eksperyment i analiza silnika dużej mocy o rozruchu bezpośrednim typu LSPM)

Keywords: High power, line-start, Permanent-magnet motor, experiment, start ability, reduced voltage
Słowa kluczowe: silnik z magnesami trwałymi, silnik LSPM.

Introduction

The high power motors are widely used to drive fans, pumps and compressors in industry, so their efficiency is improved as possible for saving the energy. Compared with induction motor, line-start permanent-magnet motor (LSPM) has higher efficiency and power factor. Moreover, it can direct replace the existing induction motor without adding any equipment. Therefore, it is an attractive choice [1-3].

From topology, the stator of LSPM is the same as that of a normal induction motor, and permanent magnets are inserted in the squirrel cage rotor. In ideal condition, its starting torque is produced by electromagnetic induction phenomenon at the rotor conductor bars, and the synchronously operating torque is generated by permanent magnets. In fact, the inserted permanent magnet not only decides LSPM’s performance at synchronous speed, but also worsens its starting ability because it produces braking torque and affects the magnetic field circuit. Since the start ability of LSPM depends on both squirrel cage rotor bars and the inserted permanent magnets including their shape, material, size and position [4-6], the suitable configuration of rotors are continually proposed to improve the performance [7].

Normally, the low power LSPM is designed to line start which can makes the starting torque maximize. But it should be indicated high power LSPM (>100kW) is often not allowed to line start in normal industrial application. Although there are many papers on the research on the low power LSPM [1-9], the high power LSPM still need be developed in theory and application due to rigorous starting condition [10-12].

In this paper, the performance of a 4-pole 250kW LSPM which keeps the configuration of induction motor as much as possible is measured including no-load test, rotor-locked test and load test. By analysis these test data, it is found that this LSPM has not only high efficiency at synchronous speed, 1500r/min, but also a sufficient line starting ability with voltage, 380V. Since this LSPM is often asked to start at low voltage in industry, the starting ability of low voltage is analyzed. The results show this design method of only inserting permanent magnets to rotor is not suitable to high power LSPM with requirement of reduced voltage starting. At last, several useful designing methods are introduced to improve starting ability.

Motor configuration

As many low power LSPMs, this 250kW LSPM also keeps the configuration of induction motor as much as possible. Table I lists the main specifications.

Table 1. Specifications of proposed LSPM

Items	Quantity
Rated power (kW)	250
Rated speed (rpm)	1500
Rated voltage (V)	380
Rated current(A)	410
Rated efficiency	0.97
Rated power factor	0.96
Winding connection	Δ
Number of pole pairs	2
Stator outer diameter(mm)	590
Stator inner diameter(mm)	400
Number of turns of stator slot	10
Number of stator slots	72
Air gap length(mm)	1.6
Number of rotor slots	62
Rotor outer diameter(mm)	396.8
Rotor inner diameter(mm)	130
The material of rotor bar	Aluminium
Coercive force of magnet (kA/m)	987
Remanence of NdFeB magnets (T)	1.3

Fig.1. Cross section of half of proposed LSPM.

Fig.1 shows the cross sections and Fig.2 shows photo of its rotor. Its stator is almost same to that of induction motor with same power. The only difference is that the stator slots are skewed by one rotor slot pitch in order to reduce the cogging torque. To rotor, squirrel cage and axis are same and the interior permanent magnets are inserted in rotor yoke without any vents. In addition, its air gap is larger than that of induction motor. There are three pieces of permanent magnets of one pole, one is large and radial magnetized, and other two are small and circumferential magnetized. Two air holes between permanent magnets have functions of the flux barrier and vents.

Motor experiments

The test platform is shown in Fig.3 including test LSPM, transducer, DC motor, temperature tester, resistance tester and digital testing system. The test LSPM is connected with a DC motor by a torque-speed transducer. The DC motor acts as motor to drive the LSPM at no-load, while acts as generator at load. By this test platform, the steady performance and transient starting performance can be obtained by adjusting operation condition.

A. No-load back-EMF

When DC motor drives the LSPM to rated speed, 1500r/min, the no-load back-EMF is measured. Fig.4 shows its fundamental wave component of measurement and predicted results by FEM. As it can be seen, the measurement is equal to rated line voltage, 380V, and is a little bigger than that of FEM, 365V. The error is mainly caused by two reasons, one is performance of permanent magnet is better than calculation value and the other is actual air-gap length exists certain error. That is to say, the prototype is a little overexcitation. Although it improves the stability performance and pull-in torque, it also worsens the start ability. If the line voltage improves to 400V, the start ability becomes better in line start condition.

Fig.4. Fundamental component of Back-EMF.

B. Starting torque

Due to the line-start current is much bigger than that of power limitation, it can’t be direct measured. Therefore, this paper adopted rotor-locked test to measure starting torques at serial low voltages. Based on these data, the short-circuit impedance is calculated, and then the line-start current and torque are calculated. Fig.5 shows the measurements. The line-start current is 2650A and the line-start torque is 2683.1 N.m. Compared with rated value, the starting current ratio is 6.46 and the starting torque ratio is 1.69. They are lower than that of induction motor due to reducing magnetic field circuit. Apparently, it can start smoothly at full line voltage with pump load.

Fig.5. The rotor-locked measurements of LSPM.

C. Load Performance

Due to the limited of power supply, this LSPM can’t realize line-start function in this platform. In this experiment, the DC motor is adopted to help the start of this LSPM. There are three steps in this experiment. First, this LSPM without power supply is driven close to synchronous speed. Secondly, this LSPM is connected with power supply when the back-EMF and line voltage have same phase angle measured by rotating-lamp method. Finally, this LSPM can be measured at different load by adjusting excitation current of DC motor. At line voltage 380V, the measured rating power factor and efficiency are 0.964, 0.966 respectively, which accord with the design requirement.

Since the back-EMF is equal 380V, the line voltage class can be increased to 400V in order to improving the start ability. The steady performance of different load is shown in fig.6. At rating output power, the power factor and efficiency are 0.932, 0.969 respectively. At output power, 315kW, the power factor and efficiency are 0.93, 0.968 respectively. As it can be seen, the efficiency keeps almost constant and power factor is lowered along with voltage improving, which is still higher than that of induction motor. Provided that line start is allowed, the voltage class of this LSPM prefers 400V to 380V.

D. Temperature

Compared with induction motor, the LSPM have lower steady-state current and high efficiency, therefore, the temperature is certainly lower than that of induction motor without changing the stator. When this LSPM operates in steady temperature condition, the measured temperature rise of winding is only 43.7K. In addition, the measured temperatures of stator iron, bearing and shell are 55.7℃, 47.7℃ and 37.7℃. Apparently, the steady temperature is much lower than that of insulation class. Therefore, the output power can be improved to 315kW without any problem.

By experimental investigation, this LSPM meets the design requirement including high steady performance at rating power and sufficient line-start ability. Moreover, it can improve its power class to 315kW due to low temperature rise.

Fig.6. Measured results of LSPM at voltage, 400V.

Fig.7. The transient starting speed and current of LSPM at no load with current limitation, 1000A.

By transient model of FEM, the starting ability of different voltage is investigated. The results are shown in Fig.7 and Fig.8. Apparently, Fig.7 shows this LSPM can’t start at no load with current limitation, 1000A. In order to start this LSPM at no load, the minimum voltage is 257V. The corresponding starting current is approximate 1792A and starting torque is about 1227N.m. The braking torque is so big that the start process becomes difficult. On this point, the permanent magnet is overused in order to guarantee high rated power factor. Therefore, the design value of rating power factor should be lowered for improving the start ability of reduced voltage.

Fig.8. Transient starting speed of different voltage.

Method of improving starting ability

When the LSPM starts, the starting torque includes asynchronous driving torque produced by rotor bars and synchronous braking torque produced by permanent magnets. The former one is mainly decided by voltage and rotor resistance, while the latter one depends on slip, back-EMF, stator resistance and synchronous reactance. At line start, the former one arrives to maximum value so it is much bigger than the latter one. It can start without question with pump load, only the starting time is longer than that of induction motor. Moreover, the speed of LSPM increases not so smoothly as that of induction motor, especially at lower speed.

To low power LSPM, the starting is no problem since the line-start is allowed. Except this, its power factor and efficiency can be improved much since that of corresponding induction motor are not so high. That is to say, this design of low power LSPM is relatively easy. Sometimes, the amending method is only inserting the permanent magnet to available rotor.

Unlike low power LSPM, the high power LSPM is often asked to start of reduced voltage due to the limitation of power system. Its starting ability worsens rapidly because the former one decreases along with the square of voltage and the latter one almost keeps constant. Therefore, the improving starting ability of reduced voltage should be carried out on two hands. One is improving asynchronous driving torque as possible, and the other is decreasing the synchronous braking torque properly. Of course, the design should make sure the steady performance of LSPM is better than that of induction motor at first. Since the high power of induction motor has high power factor and efficiency, the rated power factor of LSPM can’t be asked improving so much as that of low power LSPM. To the high power LSPM of reduced voltage starting, the amending method of only inserting permanent magnets to rotor as that lower power LSPM can’t be adopted any more in order to improving the starting ability and high rated performance. In general, the main amending methods are follows:

(1) The rated power factor of designed LSPM should adopt suitable value. Then the volume of permanent magnets can be controlled to let LSPM operate in underexcitation condition.

(2) Both rotor and stator of iron core are optimized in order to enlarge the rotor room as possible.

(3) Rotor slots are shortened and shaped for large starting ability. The starting torque ratio prefers to three times more.

(4) Due to line start capability of the high power LSPM is limited by large staring current, so high voltage is better choice to obtain good performance.

Conclusions

This paper investigates the performance of a high power LSPM which keeps the configuration as much as that of induction motor. Its no-load back-EMF, starting torque and steady-state performances at different loads are measured by a test platform. Compared with design requirement, this LSPM not only has higher efficiency and power factor, moreover keeps sufficient line-start ability at pump load. But it can’t start considering current limitation, 1000A. As a result, the amending method of only inserting permanent magnets into the rotor isn’t suitable to high power LSPM with reduced voltage starting. Finally, corresponding useful methods are introduced. In the future, the new LSPM with starting ability of reduced voltage will be developed.

The authors acknowledge the financial support of the National Natural Science Foundation of China (NSFC 51077115 ) and and Zhejiang Provincial Natural Science Foundation of China (R1110033).

REFERENCES

[1] R.Y. Tang, Modern Permanent Magnet machines- theory and design, Beijing: Machine Industry press, 1997(In Chinese).
[2] K. Kurihara and M. A. Rahman, “High-efficiency line-start interior permanent-magnet synchronous motors,” IEEE Trans. Ind. Appl.,vol.40, no.3, pp.789-796, 2004.
[3] G.H. Kang, J. Hur, H. Nam, J.P. Hong and G.T. Kim, “Analysis of irreversible magnet demagnetization in line-start motors based on the finite-element method,” IEEE Trans. Magn.,vol.39, no.3, pp.1488-1491, 2003.
[4] C.K. Lee, B.I. Kwon, B.T. Kim, K.I. Woo and M.G. Han, “Analysis of magnetization of magnet in the rotor of line start permanent magnet motor,” IEEE Trans. Magn.,vol.39, no.3, pp.1499-1502, 2003
[5] F. Libert, J. Soulard, and J. Engstrom, “Design of a 4-pole line start permanent magnet synchronous motor,” In Proc. ICEM 2002, Brugge, Belgium, Aug. 25–28, 2002
[6] D. Rodger, H.C. Lai, R.J. Hill-cottingham, P.C. Coles and F. Robinson, “A new high efficiency line start motor with high starting torque, In Proc. IET 2006, Mar.,2006, pp.551-555
[7] W. Fei, P. C. K. Luk, J. Ma, J. X. Shen and G. Yang, “A High-performance line-Start permanent magnet synchronous motor amended from a small industrial three-phase induction motor”, IEEE Trans. Magn.,vol.45, no.10, pp.4724-4727, 2009.
[8] A.M. Knight and C. Mcclay, “The design of high-efficiency linestart motors,” IEEE Trans. Ind. Appl., vol.36, no.6, pp.1555-1562, 2004.
[9] D. Stoia, M. Antonozie, D. Ilea and M. Cernat, “Design of linestart PM motors with high power factor,” In Proc. Powereng 2007, Portugal, Apr. 2007, pp.342-346.
[10] M. A. Rahman and A. M. Osheiba, “Performance of a large line-start permanent magnet synchronous motor,” IEEE Trans. Energy Convers., vol. 5, Mar. 1990,pp. 211–217.
[11] Q. Zhao, X. Wang, S. Yu, D. Zhang, Z. An and R. Tang, “Study and design for large line-start permanent magnet synchronous motor,” In Proc. ICEMS 2003, vol.1, Beijing, 2003, pp.132-133.
[12] Qinfen Lu and Yunyue Ye, “Design and analysis of high power line-start Permanent-Magnet motor”, IEEE Trans. Magn.,vol.44, no.11, pp.4417-4420, 2008.
[13] C. K. Lee and B.I. Kwon, “Design of post-assembly magnetization system of line start permanent-magnet motors using FEM,” IEEE Trans. Magn.,vol.41, no.5, 2005, pp.1928- 1928

Authors: Associate professor Qinfen Lu works in college of Electrical Engineering, Zhejiang Unversity, P.R.China, 310027 Dr. Xiaoyan Huang works in college of Electrical Engineering, Zhejiang Unversity, P.R.China, 310027, Email:eezxh@zju.edu.cn.

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 88 NR 2/20

Harmonic Evaluation at an Industrial Facility

Published by Electrotek Concepts, Inc., PQSoft Case Study: Harmonic Evaluation at an Industrial Facility, Document ID: PQS0502, Date: March 31, 2005.

Abstract: A harmonic evaluation was performed at the plastic film manufacturer’s facility. The goals of the evaluation were to develop a solution to mitigate the harmonic voltage distortion caused by the ac and dc adjustable speed drives; the solution must allow the utility to install power factor correction equipment on the 13.8 kV distribution system that supplies the facility. The customer is also interested in improving power factor at the manufacturing facility.

INTRODUCTION

Plastic Film Maker is a manufacturer of polypropylene film that is extruded into plastic sheets for use in many different industries. Local Utility supplies power to the Plastic Film Maker facility through six 13.8kV/480/277V padmount service transformers. The transformers are either 2,500 kVA or 3,000 kVA and are connected delta/wye. The six facility transformers are supplied from a 69/13.8kV substation transformer that is about 1,000 feet from the plant.

The Plastic Film Maker process load is made up of resistive heating, adjustable speed drives, and miscellaneous facility load. The process utilizes both ac and dc adjustable speed drives.

Passive harmonic filters are installed at the 480 volt buses of each of the six facility transformers. Five of the filters are rated at 300 kVAR and one is a 600 kVAR bank. All of the filters are tuned to about 249 Hz (4.1 to 4.2 harmonic).

The harmonic evaluation includes measurements at Plastic Film Maker, modeling of the Plastic Film Maker power system, and harmonic simulations.

The harmonic evaluation meets the following objectives:

1. Perform a site survey and power quality audit of the Plastic Film Maker facility.
2. Evaluate the effect of power quality on reliable operation of equipment.
3. Evaluate transformer overheating, derating and impact of harmonic distortion on transformer life.
4. Evaluate harmonic distortion with respect to IEEE Std. 519-1992.
5. Provide recommendations on how to add 10 MW of process load to the Plastic Film Maker facility.

Figure 1 – Electrical Power System One-line

Field Measurements

Field measurements were taken at each main bus.

Figure 2 – Example Measurement Snapshot at Main Bus 1

Simulations

A power system model for the Plastic Film Maker facility and the supplying Local Utility power system was developed. The model was used to simulate harmonic voltage distortion and to evaluate power system impedance with respect to power system configurations and equipment.

Harmonic Simulations

The harmonic simulations performed with SuperHarm were verified with the measurements that were taken at the Plastic Film Maker facility. Measurements are used to create the base case for the harmonic simulations. The measurements that represent the worst case harmonic current injected into the power system are used to develop the base case model. The base case represents “normal” conditions at Plastic Film Maker.

The base case simulations are compared with the measurements to verify the accuracy of the model. Table 1 – Simulation Base Case Comparison to Measurements shows the comparison between the measurement THDV and the simulated THDV at the 480 volt main buses.

Table 1 – Simulation Base Case Comparison to Measurements

Measurements were not performed at the 13.8 kV bus on November 16^thor 17^th. Simulations show the harmonic voltage and current distortion that can be expected at the PCC for different conditions. The base case THDV at the PCC is 1.50% and the base case TDD is 9.75%. The demand current used to calculate the TDD is 250 amps.

IEEE Std. 519-1992 Evaluation

The point of common coupling (PCC) is the point on the electrical power system that is common between the utility, the customer performing the evaluation, and all other customers served from the same supply. At Plastic Film Maker’s Morristown facility, the PCC is the 13.8 kV Local Utility supply to the 6 facility substation transformers. The 13.8 kV supply to Plastic Film Maker is the point that is common to Local Utility, Plastic Film Maker, and other customers served from the 13.8 kV supply.

The total demand distortion (TDD) is the ratio of the harmonic current injected into the utility power system by a facility to the maximum average monthly demand current. TDD is a better indicator of harmonic current than THD_I. THD_Iis a measure of how distorted the current is and it does not provide any indication of whether or not the current distortion should be a concern or not. TDD has an inherent quality that THDI does not have because it evaluates harmonic current relative to demand current.

The IEEE Std. 519 recommended TDD limit at Plastic Film Maker’s 13.8 kV bus is 8.0%. The maximum simulated TDD at the PCC with Option 1 exercised is 4.24%.

The recommended THDV limit at Plastic Film Maker’s 13.8 kV bus is 5.0%. The maximum simulated THDV at the PCC with the recommended harmonic filters on-line is 1.60%.

Frequency Scans

Figure 3 shows the results of the base case frequency scan. The series resonance is at the 4.2 harmonic. The series resonance results from the installed filters at the 480 volt main buses. The frequency scan for the recommended option will look the same except the series resonance (notch) will be at the 4.7^th harmonic.

Figure 3 – Electrical Power System Impedance

There are filters installed at Plastic Film Maker. The filters are installed at the 480 volt main buses and are tuned to about the 4.2 harmonic. The reactors installed in series with the capacitor banks appear to be an after thought because the capacitors are rated at 480 volts. Capacitor banks configured as filters at the 480 volt level should use capacitors that are rated greater than 480 volts due to the voltage rise at the capacitors. 600 volt capacitors work well in these applications since the voltage does not exceed the rating of the capacitors.

Power Factor Correction

This section summarizes the power factor improvement that results from the installation of passive filters at Plastic Film Maker.

Summary of Reactive Power Requirements

Table 2 summarizes the power factor improvement that results from adding compensation at the main 480 volt buses 4, 5, and 6. A compensation of about 320 kVAR results from adding 500 kVAR of 600 volt capacitors for this application on the 480 volt system.

Table 2 – Results of adding Compensation to Buses 4, 5, and 6

Table 3 summarizes the power factor improvement that results from adding compensation at the main 480 volt buses 1, 2, and 3. A compensation of about 960 kVAR results from adding 1,500 kVAR of 600 volt capacitors for this application on the 480 volt system.

Table 3 – Results of adding Compensation to Buses 1, 2, and 3

The power factor correction should be configured as a harmonic filter tuned to the 4.7^thharmonic (282 Hz) to prevent excessive distortion and problems with magnification of capacitor switching transients at the 480 volt level.

Recommendations

Install Harmonic Filters at All Main Buses Tuned to 4.7h

The existing filters that are tuned near the 4.1 harmonic should be removed before the installation of passive harmonic filter banks tuned to 282 Hz (4.7 harmonic). The results of the study indicate the installation of 1,500 kVAR filters at main buses 1, 2, and 3 and the installation of 500 kVAR filters at main buses 4, 5, and 6. Appendix A includes the filter design spreadsheets for both the 1,500 kVAR and the 500 kVAR filter.

Recommended filter sizes and buses:

1. 1,500 kVAR at Main Bus 1
2. 1,500 kVAR at Main Bus 2
3. 1,500 kVAR at Main Bus 3
4. 500 kVAR expandable to 1,000 kVAR, or more, at Main Bus 4
5. 500 kVAR expandable to 1,000 kVAR, or more, at Main Bus 5
6. 500 kVAR expandable to 1,000 kVAR, or more, at Main Bus 6

The new filters could be installed as fixed banks. The voltage rise associated with the 1,500 kVAR filters is 3.3%. The calculated voltage rise at the 480 volt buses with no load, or a small amount of load, is 16 volts. Controls should be implemented to remove the filters from service during light load conditions. The new filters at buses 4, 5, and 6 can be installed to allow for the installation of additional compensation in the future.

Billing data shows that the power factor of the facility is lowest during the summer months. The power factor may be low during the summer because of air conditioner operation. The billing data shows that 1,000 kVAR banks may be required to prevent the power factor from decreasing during the summer. Calculations show that the reactive demand charge during the summer will be about $1,200 with 500 kVAR banks at buses 4, 5, and 6. The reactive demand charge would be reduced to $498 if at least 1,000 kVAR filters were installed at these buses.

1,000 kVAR filters at buses 4, 5, and 6 would help improve the overall power factor of the facility. A leading power factor at these buses is not a problem as long as the voltage does not exceed an unacceptably high level.

Calculations show that plant power factor will range from about 0.87 to 0.95 with the following conditions:

− Existing filters removed from all buses.
− New 1,500 kVAR tuned banks installed at buses 1, 2, and 3.
− New 500 kVAR tuned banks installed at buses 4, 5, and 6.

Calculations show that plant power factor will range from about 0.91 to 0.95 with the following conditions:

− Existing filters removed from all buses.
− New 1,500 kVAR tuned banks installed at buses 1, 2, and 3.
− New 1,000 kVAR tuned banks installed at buses 4, 5, and 6.

Additional compensation must be installed for Plastic Film Maker’s plant power factor to be maintained greater than 0.95 when process load is increased. The recommended filters will reduce the average monthly reactive demand charge from $1,808 to $498.

This option requires the purchase of at least 6,000 kVAR of compensation as harmonic filters. This option does not allow Plastic Film Maker to continue to utilize any of the existing filters. Filters tuned to the 4.7 harmonic perform a better job of reducing the harmonic current injected into the utility power system than filters tuned to the 4.2 harmonic. The new filters will be more robust and more reliable than the existing filters.

Harmonic cancellation

The results of the study do not indicate a need for the installation of 13.8kV/480V delta/delta transformers at Plastic Film Maker. Applying a mix of delta/wye and delta/delta transformers had been considered because this practice can provide additional cancellation of harmonic current, especially the 5th and 7th harmonics that are usually dominant in industrial facilities.

Simulations show that some harmonic cancellation exists at the 480 volt level and the 13.8 kV level. The significant amount of dc drives at Plastic Film Maker makes the application of delta/delta transformers less attractive than if ac drives were a larger part of the total load. The operating conditions of dc drives can vary greatly. If the drive is running near it’s rating the displacement power factor is high. When the drive operates at relatively low power levels, the displacement power factor will be low. The variation in load levels and dc drive displacement power factor enhances the cancellation of harmonics.

Facility electrical personnel need to be aware of the 30 degree phase differential when delta/delta and delta/wye transformers do supply a facility. The 480 volt system would not be able to be completely paralleled without the use of additional phase shifting transformers. Paralleling the secondary, or low voltage, windings of the facility transformers may or may not be a concern at Plastic Film Maker.

The results of the study do not indicate that the application of delta/delta transformers at Plastic Film Maker would improve the cancellation of harmonic current at the PCC significantly.

Transformer derating

The 13.8kV/480V facility transformers at Plastic Film Maker do not need to be derated after the recommended filters are installed and they are in operation. Calculations show that transformers without new filters installed should be derated to 0.92 p.u. This amount of derating is typical. Transformer derating is more of a concern when a transformer is supplying one adjustable speed drive. When a transformer is dedicated to serving only one drive there is no harmonic cancellation and transformer derating factors can range from 0.90 to 0.80 p.u.

Addition of process load at Plastic Film Maker

The results of the study do indicate that the Plastic Film Maker use the recommendations of this harmonic evaluation when new facility transformers and process load is added. The recommended filters that will be installed at buses 1, 2, and 3 allow Plastic Film Maker to add process load to those buses up to the rating of the transformers.

A harmonic filter should be installed at the transformer secondary, the 480 volt bus, when additional facility transformers are added to supply new process load. If the load supplied by the new transformer is comparable to the load supplied by facility transformers 1, 2, or 3, then a 1,500 kVAR filter should be applied. If the load supplied by the transformer is comparable to the load supplied by facility transformers 4, 5, or 6, then a 500 kVAR filter should be applied. A check should be performed to verify the proper filter size before additional process lines are in operation at Plastic Film Maker.

Plastic Film Maker can add load to all of the existing facility transformers. The 1,500 kVAR filters are based on 3,000 kVA of load with harmonic load current of 900 amps (25% of the fundamental current for 3,000 kVA). The 500 kVAR filters are based on 1,500 kVA of load with harmonic load current of 270 amps (15% of the fundamental current for 1,500 kVA).

Enhancing of a DC Air-Conditioning System Based on Solar Power Generation

Published by Marwa Ben SLIMENE²,³, Mohamed Arbi KHLIFI¹,³,
Faculty Engineering, Islamic University of Madinah KSA (1), College of Computer Science and Engineering, University of Haʼil, Haʼil, (2), SIME Laboratory, ENSIT, University of Tunis, (3)

Abstract. Photovoltaics powered DC air conditioners have a lot of potential for energy-efficient cooling while also being very cost-effective. They have the potential to significantly cut energy consumption in the construction sector, which is critical in meeting the larger goal of lowering greenhouse gas emissions. In this paper, the performance of a split-unit DC air conditioner is evaluated. The DC air conditioner, which operates directly on 48 VDC and includes a variable-speed compressor, has lately become accessible on the international market. This study discusses a number of topics, including energy use, investigation of the coefficient of performance (COP) and power quality concerns. Solar power is the primary energy source, as it is a renewable resource that is both readily available and beneficial to future generations. The output of the DC air conditioner can be alternatively changed according to the size of the room by altering the speed of the Brushless DC motor in this work.

Streszczenie. Klimatyzatory DC zasilane fotowoltaiką mają duży potencjał w zakresie energooszczędnego chłodzenia, a jednocześnie są bardzo opłacalne. Mają potencjał, aby znacząco obniżyć zużycie energii w sektorze budowlanym, co ma kluczowe znaczenie dla osiągnięcia większego celu, jakim jest obniżenie emisji gazów cieplarnianych. W tym artykule oceniana jest wydajność klimatyzatora DC typu split. Klimatyzator DC, który działa bezpośrednio na 48 VDC i zawiera sprężarkę o zmiennej prędkości, stał się ostatnio dostępny na rynku międzynarodowym. W niniejszym opracowaniu omówiono szereg tematów, w tym zużycie energii, badanie współczynnika wydajności (COP) i problemy z jakością energii. Energia słoneczna jest podstawowym źródłem energii, ponieważ jest zasobem odnawialnym, który jest zarówno łatwo dostępny, jak i korzystny dla przyszłych pokoleń. Moc klimatyzatora DC można alternatywnie zmienić w zależności od wielkości pomieszczenia, zmieniając prędkość bezszczotkowego silnika prądu stałego w tej pracy. (Wzmocnienie systemu klimatyzacji DC opartego na wykorzystaniu energii słonecznej)

Keywords: DC Compressor, Performance, Solar Energy, COP, Solar air-conditioner,
Słowa kluczowe: kompresor DC, klimatyzacja, energia słoneczna

Introduction

The United Nations Framework Convention on Climate Change decided to keep global average temperature increases well below 2 degrees Celsius over pre-industrial levels in order to limit climate change risks and impacts. Aside from the need to reduce emissions, the growing number of HVAC systems leads to a rise in grid electricity costs due to high peak demands [1-5].

Direct current (DC) compressors have the potential to be used in energy-efficient refrigeration systems because these compressors do not require additional components such as a power inverter that an alternative current compressor would require. By utilizing this compressor, any problem related to the interaction of the refrigerant cycle components and the rapidly-changing operating conditions of the air conditioners is solved [6-8].

Solar-powered air conditioning has made significant development in recent years, owing to the fact that air conditioning is nearly a requirement in every structure in Saudi Arabia if the summer temperature exceeds 45 degrees Celsius [9-11].

The building energy consumption accounts for about 75% of the total energy consumption, and air conditioning energy consumption accounts for more than half of the building energy consumption in KSA. So energy saving of the air conditioning system is necessary [12-14].

Air conditioners are important especially in countries like Kingdom of Saudi Arabia (KSA) which has a hot weather most of the year. Air conditioner consider as one of the devices which needs a lot of power to work properly and that may incur high cost so we want to use some technology to reduce this amount of power consumed. Photovoltaic solar energy is a suitable choice for usage in buildings because of its high reliability, availability, low maintenance requirements, and potential to reduce greenhouse gas emissions.

In fact, the number of solar cooling and heating systems on the market is steadily expanding, as are the technologies accessible [15-18].

DC grid has gained a special attention by many researchers, especially in the last decade. The two main factors that emphasize the DC grid area of study include the DC nature of the majority of distributed generation sources, as well as the emerging of new DC loads that need several power conversion stages when connected into the current AC network. Therefore, it is needed to study the possibility of converting, either partially or completely, the current AC network to a corresponding DC network [19-23].

Our paper which is enhancing technologies for solar powered DC air conditioners is aim to reduce the power consumed by the air conditioners by controlling the speed of the rotor of the brushless DC motor. In this paper we will going to explain this technology in details and try to understand all its advantages and disadvantages. Also, we will be going to explain the design of a solar-powered air conditioning system in depth in this paper, and its performance over the course of a cooling season will be explored using PV panels to generate the required electricity for a small-scale air conditioning system.

In comparison with other systems which also use renewable energy for air conditioning, this one presents significant advantages. It is comparatively simple, reliable, has low maintenance needs and its renewable energy production is entirely self-consumed.

Analysis of the DC Air Conditioner with Rotary Compressor

In order to calculate overall efficiency of air conditioner we must find electrical and thermal power and divide them to find ratio, but our focus here is only for efficiency. The next figure shows the refrigerant cycle inside air conditioner. In order to calculate thermal efficiency, we must measure temp before and after the desired component so in our case we need to do that for condenser, compressor, evaporator and expansion valve. so, we need to measure temperature on point 1,2,3 and 4 as shown in figure 1.

Hence, we find efficiency of each part by doing rest of calculation and by the mean of using density and refrigerant flow rate.
For compressor: T4-T1;
For evaporator: T3-T4;

After measure temperature we can know calculate heat energy from this formula:

Q_vaporator = m_eC_p [T₃ -T₄]

Where:

Q: heat energy
m_e: mass flow rate
C_p: specific heat Air Flow Thermal Efficiency

We can apply same concept but this time for air instead of refrigerant for evaporator we measure temperature of warm air before passing evaporator and then measure its temperature after passing it and same thing done for condenser. so, by calculating air efficiency and refrigerant efficiency we can now find the overall thermal efficiency.

Before calculating heat energy, we need first to find mass flow rate, which can be find by multiplying flow speed, cross sectional area and gas constant of air.

m_e= (ρ) (A) (V)
Q_air = m_eC_p [T_warm – T_cold]

Another way to express specific heat and temperature is Enthalpy, it can be expressed as:

Δh = C_p [T_warm – T_cold]

Hence

Q_air = m_eΔh

As we can see here there are four cases each case is set to percentage of compressor consumption so we can see the difference between measurement in each case. But we must mention that this case is in steady state which make calculation and measurement way easier. where the room temperature is lower than reference value and hence compressor will not be working. The solution for this is to use heater in order to increase temperature in the room and hence compressor start working. In each case we must set different temperature. After calculating output heat energy, we must compute input electric energy to compressor in order to find efficiency percentage. It can be expressed by the following formula:

𝜂 = W_th / W_elc

After finding the efficiency, we can compare it to regular air conditioners to find if our project is sufficient to save energy or not.

Simulation of Air Conditioner

In this Part we are going to make simulation for two things: Refrigeration Cycle, Compressor and Refrigeration Cycle Simulation

And the results be as following:

Inside compressor there is crankshaft that connected to piston that used to compress refrigerant, then we can imagine that compression curve is not continuous as rotation curve of the motor. Same thing that appears in figure 10.

The cooling capacity increased with decreasing the outdoor temperature and increasing the indoor temperature. Also, it increased with increasing the compressor operation ratio. The temperature of the condenser was more sensitive for the variation of the outdoor temperature and the temperature of the evaporator was more sensitive for the variation of the indoor temperature.

If the air conditioning system has reached steady state and normal operation, the temperature of air blowing out of the outside compressor/condenser unit will feel warmer than the ambient outdoor air temperature. Not too much to say here but as we can see compartment (room temperature) is almost constant and does not have sudden change as inlet temperature.

Fig.12 shows mass flow of refrigerant inside cooling cycle. mass flow is arbitrary high now were piston pressures refrigerant. Again, shape must be as pulses.

As it absorbs as much heat as possible while it’s a liquid the temperature Remains the same, roughly around 40 degrees but will vary according to conditions ( room temperature, outside temperature, charge- over or undercharged) then it will begin to increase in temperature, what is called superheat ( the temperature of a substance above its boiling point at a given pressure) superheat on most ac is 8–12 ( so given that approximate 40 degrees it would be 48–52 degree) degrees depending on type of system and if it’s operating properly.

Conclusion

The purpose of this research is to develop, simulate, and analyze the performance of a solar-powered air conditioning system that is also a photovoltaic (PV) system. Solar air conditioners can be a cost-effective alternative to traditional air conditioners. Electrical equivalent, characteristic curve, and factors affecting PV cell output are only a few of the parameters that must be considered whether on a PV system or an air conditioning system.

Acknowledgements

The authors extend their appreciation to the Deputyship for Research & Innovation, Ministry of Education in Saudi Arabia for finding this research work through the project number (20/11)

REFERENCES

[1] Al Qdah, K.S. Performance of Solar-Powered Air Conditioning System under AlMadinah AlMunawwarah Climatic Conditions. Smart Grid and Renewable Energy, 6, 209-219.2015.
[2] Aguilar, F.J.; Ruiz, J.; Lucas, M.; Vicente, P.G. Performance Analysis and Optimisation of a Solar On-Grid Air Conditioner. Energies, 14, 8054. 2021.
[3] IEA. The Future of Cooling: Opportunities for Energy-Efficient Air Conditioning; Annual report; The Organisation for Economic Co-operation and Development: Paris, France, 2018.
[4] Mohamed Arbi Khlifi, Marwa Ben Slimene “Efficient Off Grid Solar Powered DC Air Conditioning System” PRZEGLĄD ELEKTROTECHNICZNY, 10.15199/48.2021.06.2. 2021.
[5] Alrashed, F.; Asif, M. Saudi building industry’s views on sustainability in buildings: Questionnaire survey. Energy Procedia 2014, 62, 382–390.
[6] Matar, W. A look at the response of households to time-of-use electricity pricing in Saudi Arabia and its impact on the wider economy. Energy Strateg. Rev. 2017, 16, 13–23.
[7] S. Bharath Subramaniam, Air Conditioner Using Exhaust Gas of Automobiles, International Journal of Mechanical Engineering and Technology, 8(5), 2017, pp. 11191126.
[8] Ghanim Kadhim Abdul Sada, Dhamyaa Saad Khudhour and Moumin Mahdi Issa, Utilization of Solar Energy for Enhancement Efficiency of Steam Power Plant.International Journal of Mechanical Engineering and Technology, 7(5), 2016, pp. 336–343.
[9] Wang, X.; Xia, L.; Bales, C.; Zhang, X.; Copertaro, B.; Pan, S.; Wu, J. A systematic review of recent air source heat pump (ASHP) systems assisted by solar thermal, photovoltaic and photovoltaic/thermal sources. Renew. Energy 2020, 146, 2472–2487.
[10] Fernández Bandera, C.; Pachano, J.; Salom, J.; Peppas, A.; Ramos Ruiz, G. Photovoltaic Plant Optimization to Leverage Electric Self Consumption by Harnessing Building Thermal Mass. Sustainability 2020, 12, 553.
[11] Aguilar, F.; Aledo, S.; Quiles, P. Experimental analysis of an air conditioner powered by photovoltaic energy and supported by the grid. Appl. Therm. Eng. 2017, 123, 486–497.
[12] Aguilar, F.; Crespí-Llorens, D.; Quiles, P. Techno-economic analysis of an air conditioning heat pump powered by photovoltaic panels and the grid. Sol. Energy 2019, 180, 169– 179
[13] Opoku, R.; Mensah-Darkwa, K.; Samed Muntaka, A. Technoeconomic analysis of a hybrid solar PV-grid powered airconditionerfor daytime office use in hot humid climates—A case study in Kumasi city, Ghana. Sol. Energy 2018, 165, 65–74.
[14] Hui Ren, Wenhao Cai: Research on Grid-Connected Photovoltaic System Based on Improved Algorithm. PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 98 NR 7/2019
[15] Li, Y.; Zhao, B.; Zhao, Z.; Taylor, R.; Wang, R. Performance study of a grid-connected photovoltaic powered central air conditioner in the South China climate. Renew. Energy 2018, 126, 1113–1125.
[16] M. J. Abdul-Kareem, F. M. Mohammed, and M. A. Jabbar, “Investigation of high performance split air conditioning system by using Hybrid PID controller,” Applied Thermal Engineering, 129, 1240-1251, 2018.
[17] Y. Lia, G. Zhanga, G.Z. Lva, A.N. Zhangb, R.Z. Wang. “Performance study of a solar photovoltaic air conditioner in the hot summer and cold winter zone,” Solar Energy 117,167-179, 2015.
[18] B. J. Huanga, T. Houa, P. C. Hsua, T. H. Lina, Y. T. Chena, C. W. Chena, K. Lia, K.Y. Lee, “Design of direct solar PV driven air conditioner,” Renewable Energy, 88, 95-101, 2016.
[19] L. Farkad, M. A. Atiya, and A. A. Al-Hemiri, “Test of solar adsorption air-conditioning powered by evacuated tube collectors under the climatic conditions of Iraq,” Renewable Energy, 142, 20-29, 2019.
[20] Li, Y., Zhao, B., Zhao, Z., Taylor, R., Wang, R. Performance study of a grid-connected photovoltaic powered central air conditioner in the South China climate. Renew. Energy 126, 1113–1125.2019.
[21] Mugnier, D., Neyer, D., White, S.D. (Eds.). The Solar Cooling Design Guide Case Studies of Successful Solar Air Conditioning Design. Wiley. 2017.
[22] Opoku, R., Mensah-Darkwa, K., Samed Muntaka, A. Technoeconomic analysis of a hybrid solar PV-grid powered airconditioner for daytime office use in hot humid climates? A case study in Kumasi city, Ghana. Sol. Energy 165, 65–74. 2018.
[23] Xu, Y., Li, M., Luo, X., Ma, X., Wang, Y., Li, G., Hassanien, R.H.E. Experimental investigation of solar photovoltaic operated ice thermal storage air-conditioning system. Int. J. Refrig. 86, 258 –272, 2018.

Authors: Dr. Marwa Ben Slimene, College of Computer Science and Engineering, University of Haʼil, Haʼil, KSA, PO Box 2440. Ha’il – 81451, E-mail: benslimene.marwa@gmail.com; Prof. Mohamed Arbi KHLIFI, Faculty Engineering, Islamic University of Madinah, AlMadinah Monawarah, KSA, Abo Bakr Al Siddiq, Al Jamiah, Medina 42351, E-mail: medarbi.khlifi@gmail.com;

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 98 NR 8/2022. doi:10.15199/48.2022.08.04

Use of the Renewable and Waste Energy Sources in Heat Storage Systems Combined with ORC Power Plants

Published by Piotr KOLASIŃSKI, Politechnika Wrocławska, Instytut Techniki Cieplnej i Mechaniki Płynów, Zakład Termodynamik

Abstract. ORC systems are mainly powered from waste and renewable energy sources. In many cases this type of energy sources are specified by the dynamic capacity and thermal characteristics. Such situation has negative influence on ORC power plant working conditions. In this paper the conception of heat storage systems (HSS) combined with the ORC power plants was presented. Use of (HSS) in ORC power plant can improve working conditions and can have influence for raise of the energy generation efficiency.

Streszczenie. Najczęściej układy ORC zasilane są przez odpadowe lub odnawialne źródła energii o zmiennych w czasie charakterystykach termicznych wydajnościowych. Mają one negatywny wpływ na warunki pracy układów ORC. W artykule przedstawiono koncepcję wykorzystania systemów akumulacji ciepła skojarzonych z układami ORC. Takie rozwiązanie może poprawić warunki pracy siłowni oraz mieć wpływ na zwiększenie efektywności procesów konwersji energii (Wykorzystanie odnawialnych i odpadowych źródeł energii w akumulatorach ciepła skojarzonych z układami ORC)

Słowa kluczowe: ORC, akumulator ciepła, HSS, analiza termodynamiczna
Keywords: ORC system, heat accumulator, HSS, thermodynamic analysis.

Introduction

Characteristic feature of the ORC systems is their often mating with the heat sources characterized by changeable, dynamic characteristics. Such heat source characteristic in many cases has negative influence for ORC system work conditions, including continuous system operation. Changeable sources can be found mainly in the group of alternative energy sources. It is possible to consider the changeable characteristic of:

– waste energy sources,
– renewable energy sources

The first group refers to the heat carriers practically appearing in each industrial energy conversion process, and being the waste of main technological chain. Such refers to the heat collected in the following products: flue gases, cooling mediums, solid waste (slags, coke, etc.) and technical gases with higher thermodynamic parameters than those occurring in the surroundings. In most cases energy from these mediums is not recovered and it is being dissipated to the surroundings. Comprehensively problems connected with industrial waste energy and techniques of its recovery were described in [1], [2], [3] and [4].

The second group is formed by the natural sources with higher thermodynamic parameters than those in surroundings, but occurring periodically. A good example of such source can be the geyser, or solar collector working in changeable insolation conditions and different time of day and a year.

For the economical and energy profitable assessment of this specific energy sources the energetic analyses can be used. Problems connected with this analysis were comprehensively described in [1].

According to the described above problems it is interesting to consider potential of the HSS application in ORC systems. Such solution can enable possibility of changeable heat source characteristic modulation and in the result improve ORC system work conditions.

Heat Accumulators and Heat Storage Systems

Heat accumulators are the devices useful for the effective and long term heat storage and its recovery for further use. Such devices were comprehensively described in [5]. Ideal heat accumulator should be characterized by the following features:

– large heat capacity – obtained by use of the proper construction material and a proper material structure (for ex. honeycomb); the material should have large ability of heat absorption,
– compact dimensions,
– simple construction,
– easiness in assembly and transport,
– large reliability,
– full automation.

Ideal heat accumulator should enable realization of the heat accumulation process without the necessity of phase change in heat accumulating medium – according to isochoric process described by v=idem. equation. In fig.1 the isochoric heat accumulation process on T-s diagram is presented. In fig.2 the comparison with the other thermodynamic processes is presented.

Fig.1. Isochoric heat accumulation process 2’- 1’ – cooling of the heat source, 1 – 2 – isochoric heat accumulation process

The heat amount transferred from the heat source to the accumulating medium can be calculated for each of process with help of relation:

As it can be observed from fig.2 the highest value of accumulated heat is obtained for the isochoric process.

The heat accumulators can be useful for heat storage and its transport for further distances. In this case the heat storage system (HSS) design and construction is needed. The example of HSS can be use of the industrial glycerine, which large amounts are produced in chemical industry. Often the glycerine is secondary product of the main production process and it is treated as the waste medium. The idea of glycerine use in HSS for the waste heat accumulation and district heating is presented in fig.3.

Nowadays the possibility of phase changing materials (PCM), such as the hydrated salts, for heat accumulation is being analysed in many scientific units worldwide. The list of possible to use in HSS PCM materials were presented in [6]. Author has presented initial results of his own research in this matter in [7]. Interesting application of HSS based on PCM for the central heating in Court Centre in Düsseldorf was presented in [8].

Fig.2. Comparison of other possible heat accumulation processes with isochoric process

Fig.3. Idea of glycerin use in HSS for the waste heat accumulation and district heating

Fig.4. Scheme of the ORC power plant combined with the HSS 1 – vapour generator; 2 – heat accumulator/HSS; 3 – expander; 4 – generator; 5 – condenser; 6 – feeding pump

Fig. 5. Different possibilities of the HSS use in the ORC systems a) stabilization of the heat source characteristic; b) ensure of the additional vapour inlet to the expander; c) preheating of working substance; d) assist in CHP 1 – vapour generator; 2 – heat accumulator/HSS; 3 – expander; 4 – generator; 5 – condenser; 6 – feeding pump; 7 – working medium reservoir

The Analysis of Possibility of Heat Accumulators and HSS Use in the ORC Power Plant Powered by the Heat Source with Changeable Characteristic

Use of the heat accumulator or HSS in ORC power plant powered by the heat source with changeable characteristic can have following purposes:

– modulation of the energy source characteristic in order to its stabilization and improvement of the ORC system work conditions,
– initial heating of the working medium,
– provision of the reserve energy source in case of momentary decay of the main energy source,
– assist in the CHP realization, – raise of the system efficiency,
– ensure of the additional vapour inlet to the expander. In fig.4 the ORC power plant combined with the HSS is presented, in Fig. 5 the different possibilities of the HSS use in the ORC systems are presented.

Modulation of the heat source characteristic

In fig.6 the changeable capacity characteristic of vapour obtained with use of dynamic energy source is presented. As it can be observed the vapour generator working with this source has dynamic changeable and momentary nearly decayed characteristic. In fig.7 the same characteristic but combined with capacity characteristic of vapour obtained from HSS is presented. HSS is modulating the changeable vapour generator capacity in such a way that total vapour amount characteristic is nearly stable.

Fig.6. Changeable capacity characteristic of vapour obtained with use of dynamic energy source

Fig.7. Modulation of changeable vapour generator capacity characteristic with use of HSS

The modulation of changeable vapour generator capacity characteristic can be realized with use of the system presented In fig.5a. The efficiency of this system can be calculated from the following equation:

where: W_ORC– work done in the expander, Q_ORC – heat transferred to the working medium in the evaporator, Q_HSS – heat transferred to the working medium in the HSS.

Ensure of additional vapour inlet to the expander

Such solution would be helpful for use of the energy collected in additional flux of vapour, transferred directly to the expander inlet. Additional flux of working medium can be supplied from other modules if the module system formed by different subassemblies with different technical tasks is being considered.

Such solution can be realized with use of system presented In fig.5b. The efficiency of this system can be calculated from the following equation:

where: W_ORC – work done in the first stage of the expander, W’_ORC – work done in the second stage of the expander, Q_ORC – heat transferred to the working medium in the evaporator, Q_HSS – heat transferred to the working medium in the HSS.

Additional flux of working medium (liquid or vapour) is transferred to the HSS where its thermodynamic parameters are raised. Then this medium is transferred to the expander where it is being expanded and additional work is done. Such solution can be helpful also in case of the main energy source decay – the system would be able to continue the operation for some time period. As it results from authors estimations [4] application of the additional vapour inlet to the expander can contribute to raise the efficiency of ORC system by 1-2%.

Initial heating of working medium

The heat collected in the HSS can be used for initial heating of working medium. Use of such solution can be helpful in:

– lowering energy load of main energy source,
– possibility of many energy sources with different temperatures use in system,
– raising of ORC system efficiency. In fig.5c the construction scheme of ORC power plant with initial heating of working medium provided by HSS is presented. The efficiency of this system can be calculated from the following equation:

where: W_ORC– work done in the expander, Q_ORC– heat transferred to the working medium in the evaporator, Q_HSS – heat transferred to the working medium in the HSS. The initial heating of working medium can contribute to raise of the ORC system efficiency by approx. 1% [4].

Assist in CHP realization

The HSS can be also helpful as assist in CHP realization. It can be assumed that the condenser cooling medium is water, which is then used for heating up of the water in central heating system. The heat transferred in the condenser by the ORC system working medium, for the sake of the low range of operation temperatures, can be insufficient for ensure of needed raise of heated medium temperature. In this purpose the HSS can be used in order to heat up the water to the needed temperature. In fig. 5d the construction scheme of ORC power plant with HSS used for heating up the central heating water is presented. The efficiency of this system can be calculated from the following equation:

where: W_ORC – work done in the expander, Q_CHP – generated heat, Q_ORC – heat transferred to the working medium in the evaporator, Q_HSS – heat transferred to the working medium in the HSS.

The application of HSS for warming up of the central heating water can contribute to raise of the ORC system efficiency by 3 – 4% [4].

Summary and Conclusions

Presented in paper proposals of HSS use in ORC power systems can contribute to:

– raise in renewable and waste energy sources use,
– raise of efficiency of different energy forms generation in ORC systems,
– decentralization of energy supply system,
– raise of energy safety,
– development of regional energetic systems and Autonomous Energy Regions described in [9], [10] and [11],
– use of local energy sources with low potentials.

At present author is working on design of test set-up of hybrid ORC-HSS system. The system will be powered by the low thermal potential heat source. R1234ze is considered as a working fluid. The HSS will be specially constructed with use of honeycomb shape cooper plates. Specially shaped working fluid flow channels will enable the possibility of carrying out a wide range of experiments. In particular the following research analyses will be carried out:

– influence of the heat transfer processes in HSS for the changeable heat source characteristic modulation,
– influence of the additional vapour inlet to the expander on the ORC system efficiency,
– influence of the heat transfer processes in HSS on the hybrid ORC-CHP system efficiency.

Initially, during the tests, the HSS will be loaded with help of the electric heaters. During the research analysis it will be loaded from the real waste heat source. The design and construction of the HSS prototype is the subject of currently prepared patent application.

REFERENCES

[1] Praca zbiorowa, Przemysłowa energia odpadowa: zasady wykorzystania; urządzenia, WNT Warszawa (1993).
[2] Gnutek Z., Kolasiński P., Lamperski J., Odzysk ciepła z odpadowych źródeł energii, Materiały XIII Sympozjum Wymiany Ciepła i Masy, Tom 1, pod red. H. Chauna, Wydawnictwa Uczelniane Politechniki Koszalińskiej, (2007).
[3] Ochęduszko S., Teoria maszyn cieplnych cz. III, PWT, (1955).
[4] Kolasiński P., Termodynamika układów konwersji energii o zmiennej ilości czynnika roboczego, Praca doktorska, Politechnika Wrocławska, Wrocław (2010).
[5] Domański R., Magazynowanie energii cieplnej, PWN, (1990).
[6] Agyenim F., Hewitt N., Eames P., Smyth M., A review of materials, heat transfer and phase change problem formulation for latent heat thermal energy storage systems (LHTESS), Renewable and Sustainable Energy Reviews vol. 10, (2010).
[7] Kolasiński P., Zawadzka E., Wstępna analiza możliwości wykorzystania roztworów przesyconych do pozyskiwania ciepła ze źródeł alternatywnych o niskich potencjałach, Materiały XIV Sympozjum Wymiany Ciepła i Masy, Wydawnictwo Politechniki Szczecińskiej, Szczecin (2010).
[8] Kuczia P., Wielkogabarytowy gruntowy wymiennik ciepła w korelacji z centralnym zasobnikiem ciepła z materiałów zmiennofazowych PCM w Centrum Sądowym w Düsseldorfie – studium przypadku, Instal nr.3 rocznik 2012, Warszawa (2012).
[9] Gnutek Z., Kolasiński P., Struktura energetyczna Dolnego Śląska – zagadnienia wybrane, Cieplne Maszyny Przepływowe – Turbomachinery nr 132, Wyd. Politechniki Łódzkiej, (2007).
[10] Gnutek Z., Analiza w obszarze potencjału rozwojowego regionu: Cz.5. Analiza potencjału rozwojowego regionu w dziedzinie energii odnawialnych i alternatywnych, Raport I-20, Wrocław (2007).
[11] Gnutek Z., Autonomiczne regiony energetyczne sposobem na racjonalizację wykorzystania odpadowych i odnawialnych źródeł energii, Przyszłość energii odnawialnej – polityka energetyczna, trendy, Materiały I Dolnośląskiego Forum Energii Odnawialnej, Wrocław (2007).

Autorzy: dr inż. Piotr Kolasiński, Politechnika Wrocławska, Instytut Techniki Cieplnej i Mechaniki Płynów, Zakład Termodynamiki, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, E-mail: piotr.kolasinski@pwr.wroc.pl;

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 89 NR 7/2013

Harmonic Resonance Evaluation for Feeder and Substation Capacitor Banks

Published by Electrotek Concepts, Inc., PQSoft Case Study: Harmonic Resonance Evaluation for Feeder and Substation Capacitor Banks, Document ID: PQS0706, Date: July 27, 2007.

Abstract: A utility operates feeder and substation capacitor banks on a 25.56kV distribution feeder. The utility uses frequency scan simulations to determine the effect of distribution feeder and substation capacitor banks on harmonic resonance and frequency response characteristics. It is assumed that the simulations will show that the frequency response characteristics of the feeder are very dependent on the status of the feeder and substation capacitor banks.

This case study evaluates the effect of substation and feeder capacitor banks on the frequency response characteristic of a 25.56kV distribution feeder.

INTRODUCTION AND MODEL DEVELOPMENT

The effect of distribution feeder and substation capacitor banks on harmonic resonance and frequency response characteristics was studied for the system shown in Figure 1. The accuracy of the system model was verified using three-phase and single-line-to-ground fault currents and other steady-state quantities, such as capacitor bank rated current and voltage rise.

Figure 1 – Oneline Diagram for the Feeder Resonance Case Study

SIMULATION RESULTS

Frequency scan analysis was used to determine the impedance vs. frequency characteristic for the circuit for various operating conditions. The frequency range for these cases was 60 Hz to 5,000 Hz (1 Hz increment). The load on the feeder for the full load condition was approximately 10.4 MVA at 98% power factor. The following frequency scan cases were completed:

Case Number	Scan Location	Load Condition	Substation Capacitor Bank	Feeder Capacitor Bank
Case 1a	1	Full Load	Off	All Off
Case 1b	1	Full Load	Off	All On
Case 1c	1	Full Load	On	All Off
Case 1d	1	Full Load	On	All On
Case 2a	2	Full Load	Off	All Off
Case 2b	2	Full Load	Off	All On
Case 2c	2	Full Load	On	All Off
Case 2d	2	Full Load	On	All On
Case 3a	3	Full Load	Off	All Off
Case 3b	3	Full Load	Off	All On
Case 3c	3	Full Load	On	All Off
Case 3d	3	Full Load	On	All On

Figure 2 shows the impedance vs. frequency simulation results for scan location number 1 for the four operating conditions.

Figure 2 – Frequency Response at Scan Location Number 1

Figure 3 shows the impedance vs. frequency simulation results for scan location number 2 for the four operating conditions.

Figure 3 – Frequency Response at Scan Location Number 2

Figure 4 shows the impedance vs. frequency simulation results for scan location number 3 for the four operating conditions.

Figure 4 – Frequency Response at Scan Location Number 3

SUMMARY

The simulations show that the frequency response characteristics of the feeder are very dependent on the status of the feeder and substation capacitor banks. Additional observations include:

1. For scan locations number 1 and number 2 (end of feeder segments), the simulated frequency response is generally more severe for the condition of having the smaller distributed feeder capacitor banks in service as compared to having the larger substation capacitor bank in service.

2. For scan location number 3 (substation bus), the simulated frequency response is generally more severe for the condition of having the larger substation capacitor bank in service as compared to having the smaller distributed feeder capacitor banks in service.

3. It is often difficult to generalize the affect on voltage distortion levels when the location and characteristics of the harmonic producing loads are not known. The resulting voltage distortion for the different operating conditions will depend on the locations, ratings, and characteristics of the various nonlinear loads on the circuit. For example, if the nonlinear loads are near the ends of two feeder segments (scan locations 1 and 2), it is likely that the feeder voltage distortion will be somewhat higher for the condition of having the feeder capacitors in services. However, if the nonlinear loads are near the substation (scan location 3), it is likely that the feeder voltage distortion will be somewhat higher for the condition of having the larger substation capacitor bank in service. Actual current and voltage distortion levels may be determined by field measurement and/or more detailed computer simulations that include the harmonic current source characteristics.

REFERENCES

Power System Harmonics, IEEE Tutorial Course, 84 EH0221-2-PWR, 1984.

RELATED STANDARDS
IEEE Std. 519-1992 IEEE Std. 1036-1992

GLOSSARY AND ACRONYMS
ASD: Adjustable-Speed Drive
CF: Crest Factor
DPF: Displacement Power Factor
PF: Power Factor
PWM: Pulse Width Modulation
THDG: Total Harmonic Distortion
TPF: True Power Factor

Study on a New Method for Overvoltage Measurement using CVT

Published by Si WENRONG, Jin HENG, Huang HUA, Fu CHENZHAO,
East China Electric Power Test & Research Institute Company Limited, Shanghai, China

Abstract. This paper introduces a new method for overvoltage measurements in 500kV power system using capacitor voltage transformer (CVT). It is realized with a voltage sensor installed within CVT as the low-voltage capacitor C₃connection in series with the high-voltage (HV) capacitor C₁ and the median-voltage capacitor C₂. Simulations studies and laboratory tests in manufactory (NISSIN ELECTRIC WUXI Co., Ltd.) have confirmed the validity and practicability of the technique.

Streszczenie. Opisano nowa metodę pomiaru przepięć w sieci 500 KV przy użyciu dzielnika kondensatorowego. Urządzenie sprawdzono w laboratorium. (Analiza nowej metody pomiaru przepięć z wykorzystaniem kondensatorów)

Keywords: capacitor voltage transformer (CVT); overvoltage measurement; low-voltage capacitor C₃.
Słowa kluczowe: przepięcia, pomiar napięcia.

Introduction

The measurement of voltages in a.c. networks is a necessity which does not create undue difficulties in low- or medium-voltage systems. As the system voltage rises, however, the cost of any additional apparatus connected to it rapidly increases on account of the large amount of insulating material required. For this reason, the CVT is the main instrument transformer in the extra high voltage (EHV) systems due to their reduced size and cost compared to wound voltage transformers. Reference [1] described the design of a CVT with the analyze of the performance of a CVT with compensating reactor and intermediate voltage transformer.

But, as we all know, the conventional CVTs do not have a uniform (flat) frequency response, which makes them unsuitable for use in harmonic or overvoltage (transient disturbances) measurements. Other devices between EHV power systems and instrumentation, such as capacitor or resistance dividers are expensive options in terms of cost and space in substations, as they cannot be used for supplying relays and require regular calibration [2]. A method that has been mentioned in literature is the use of CVT transfer function to compensate for the CVT response at harmonic frequencies [3]. Reference [4] showed a test method that is used to determine CVT transfer function. And overvoltage measurement was suggested in literature [5] resorting the secondary protection terminals of CVT.

In this article, a new method is proposed that makes it possible to use the conventional CVTs in overvoltage measurements of EHV systems. The technique has the advantages of minimal cost and time involved in retrofitting to installed CVTs and implementing it in new units without changing CVT design parameters or procedure. According to the present stage of the project, this contribution deals mainly with two aspects: a) Laboratory experiments regarding the transmission of lightning and switching impulse voltages through a CVT within a low-voltage capacitor C₃ (voltage sensor) installed; b) The development of a online measuring device based on CVTs in substation for the monitoring of HV transient overvoltages. As the part one, only aspect a) will be shown in this paper.

Description of overvoltage measurement using CVT

The basic diagram of a 500kV rated voltage CVT is given in Figure 1. It consists mainly in a capacitive voltage divider C₁-C₂ and a medium-to-low transformer T. An auxiliary terminal may be used for telecommunication between substations (shown in Figure 1(c)), with a high-frequency carrier in the range of tens of kHz, having as support one conductor of HV transmission line. In this case, the switch K is open and the earthing reactor L₁ assures the 50 Hz grounding of capacitive voltage divider. Regarding to the secondary terminals 1a and 2a, the 50 Hz rated secondary voltage can be output. Besides those electrical components introduced, the P is protective gap, L is the medium voltage choke, and BL is a surge arrester.

Actually, some researchers once tried to use the secondary terminals 1a or 2a to record transient disturbances as mentioned above, the test result with lightning impulse voltage will be also shown in the section “Overvoltage tests in laboratory” in this paper.

Fig.1. (a) Picture of a CVT with 500kV level widely used in East China Grid; (b) Circuit diagram for a conventional CVT; (c) Circuit diagram for a CVT with high-frequency carrier; (d) Using C₃ instead of L₁

To characterize, in a statistical approach, the share of HV events at the electromagnetic environment of an open-air substation, a long-term record of transient overvoltages may be useful. The main difficulty, to fulfil a suitable recording system, regarding the costs and locations, in a substation is that of HV impulse divider. The proposed solution is based on a modification of existing CVTs consisting in (shown in Figure 1(d)): a) the removal of the earthing reactor L₁; b) the addition to CVT of a measuring capacitor C₃ as the low-voltage arm of a capacitive voltage divider. This relatively cheap and simple solution doesn’t need an additional place in substation and doesn’t disturb the basic functions of CVT regarding the measuring and the protection. Design and installation of the capacitor C₃ will be shown in following sections.

For the circuit diagram given in Figure 1(d) with C3 instead of L₁, simulation tests with switching and lightning impulse voltages are shown in the Figure 2, which supports the modification in theoretically. In the simulation circuit, the rated capacitance value of CVT is 5.1 nF, while C₃ is 20 µF.

Fig.2. (a) Simulation result of a switching impulse voltage; (b) Simulation result of a lightning impulse voltage

Here, it should be pointed that the method with C₃ instead of L₁ was once used to harmonic voltage measurements in NISSIN ELECTRIC WUXI Co., Ltd. The C₃ is shown in Figure 3 with a value of 20 µF. And it does not influence the output error of the secondary terminals.

Fig.3. The C₃ used to harmonic voltage measurements

Fig.4. Lightning impulses tests on the C₃ shown in Figure 3

Depending on this C₃, the lightning impulse tests were done in our high voltage laboratory (harmonic voltage measurements are ignored in this paper). It shows a poor result that the peak values of overvoltages form the C₃ are unstable including the waveshapes, which is shown in Figure 4. The reason to explain the results is that the C₃ is a shunt power capacitor of self-healing type and its value is unstable under high frequency impulse voltage. Apparently, a non-inductive capacitor should be made as the C₃ to measured impulse voltages with high frequency components.

Design and temperature coefficient of the C₃

Figure 5 gives the geometry parameters of an element capacitance of the designed C₃ and its inside configuration. The coaxial distribution of those capacitance elements make the C₃ more non-inductive relatively.

Fig.5. (a) Geometry parameters of an element capacitance of C₃; (b) the C₃ developed and its inside configuration

Fig.6. Temperature coefficient

The temperature coefficient shown in Figure 6 is the capacitance change of the C₃ per ℃ over a specified temperature range. The performance is extremely good during the variation of -25 ℃ to 50 ℃, which fits well the environment temperature of an open-air substation.

Overvoltage tests in laboratory

Figure 7 shows the impulse voltage tests arrangement. In Figure 7(b), F is the standard HV impulse divider and S is the impulse voltage generator. Impulse waveshapes from the F, the capacitance C₃ and the secondary terminal 1a are recorded synchronously by the oscilloscope of DPO7104 type (its analog bandwidth is 1 GHz, the maximum sample rate is 20 GSample/s). The impulse waveshape from F obtained at the same time as the signal source is used to verify the signals detected from the C₃ and the secondary terminal 1a connected to a resistor equivalent to the rated load. In Figure 7(b), the voltage signal from F is set to be the trigger source.

Fig.7. (a) Picture of impulse voltage test arrangement for CVT in laboratory; (b) Circuit diagram of impulse voltage test for CVT

The transmission of lightning impulse (fast front) transient overvoltages was investigated for applied impulse voltages with various rise times between 5 µs to 100 µs, peak values between 400 kV to 1600 kV, and the time to half-values between 50 µs to 250 µs. While the transmission of switching impulse (slow front) transient overvoltages was investigated for applied impulse voltages with various rise times between 250 µs to 1000 µs, peak values between 300 kV to 900 kV, and the time to half-values between 2500 µs to 5000 µs. Figure 8 and Figure 9 shows the typical test results of the applied and the measured voltage waveshapes under lightning impulse 5.5/65 µs and switching impulse 375/2800 µs, with sample rate of 100 MSample/s and 5 MSample/s respectively. The one with high amplitude is from the F and the one with low amplitude is from the C₃ (see the Figure 7). In case of the lightning impulse, average deviations of the measured voltage against the applied voltage for 30 tests were:

– for the front time -6.29%
– for the half-value time -1.25%

In case of the switching impulse, average deviations of the measured voltage against the applied voltage for 30 tests were:

– for the front time -1.05%
– for the half-value time -2.38%

Fig.8. (a) One of test results under lightning impulse voltage of 1500 kV (negative polarity); (b) One of test results under lightning impulse voltage of 1500 kV (positive polarity)

Fig.9. (a) One of test results under switching impulse voltage of 900 kV (negative polarity); (b) One of test results under switching impulse voltage of 900 kV (positive polarity)

The measuring device preserves the crest value ratio of 3600 with a small deviations under different test voltages shown in Figure 10. The result of switching impulse is better than the ones of lightning impulse for the transmission of slower front transient overvoltages.

Apparently, these registered deviations, regarding the time’s parameters are in acceptable tolerances for transient overvoltage measurements [6].

The transmission of fast front overvoltage form the secondary terminal 1a connected to a resistor equivalent to the rated load is illustrated in Figure 11 with main frequency component analyzed. The transmitted overvoltage has an entirely different waveshape from the applied voltage, characterized by a strong oscillation, with a main ground frequency about 0.8 MHz, followed by a very long tail in range of hundred of µs, but with meaningless small values.

The shape of transmitted voltage suggests a capacitive coupling of the high-frequencies during the whole applied overvoltage and the secondary terminals cannot be used to measure transient disturbances for the medium-to-low transformer T existing.

Fig.10. (a) The crest value ratio under lightning impulse tests; (b) The crest value ratio under switching impulse tests

Fig.11. (a) One of test results from the secondary terminal 1a under lightning impulse tests; (b) Main frequency components analysis for two voltage waveshape in (a)

Conclusions

A new method is proposed that makes it possible to use the conventional CVTs in overvoltage measurement of EHV systems. It is realized with a voltage sensor installed within CVT as the low-voltage capacitor C₃ connection in series with the high-voltage capacitor C₁ and the median-voltage capacitor C₂. Laboratory tests have confirmed the validity and practicability of this technique. All deviations of the impulse waveshape detected from the C₃ including the time’s parameters compared with standard impulse divider are in acceptable tolerances for transient disturbances measurements.

Based on these works, the planned future works are: a) Completion of transient overvoltageas monitoring system based on existing CVTs within the designed C₃ with an adequate acquisition system; b) Implementation the transient overvoltage monitoring system in a representative substation and starting a monitoring program.

REFERENCES

[1] Billig E., The design of a capacitor votlage transformer, The Proceedings of the Intuition of Electrical Engineers, 96 (1949), No. 54, 793-802
[2] Ghassemi F., Gale P., Cumming T., Coutts C., Harmonic voltage measurements using CVTs, IEEE Transactions on Power Delivery, 20 (2005), No. 1, 443-449
[3] Iravani M., Wang X., Polishchuk J., Sarshar A., A new method for the ccvt performance analysis using field measurements, signal processing and EMTP modeling, IEEE Transactions on Power Delivery, 9 (1994), No. 4, 1904-1917
[4] Ghassemi F., Gale P., Clegg B., Cumming T., Coutts C., Method to measure cvt transfer function, IEEE Transactions on Power Delivery, 17 (2002), No. 4, 915-920
[5] Guo Q., Chen P., Huang H., Study on the transfer overvoltage test of capacitor voltage transformer, Power Capacitor & Reactive Power Compensation, 30 (2009), No. 4, 25-28
[6] IEC Standard 60-2: High-voltage test techniques. Part 2: measuring sytems. 2^nd edition, 1994.

Authors: Dr. Si Wenrong, East China Electric Power Test & Research Institude Company Limited, Shanghai, China, 200437, Email: siwenrong@gmail.com; Jin Heng, East China Electric Power Test & Research Institude Company Limited, Shanghai, China, 200437, E-mail: dsy_jinh@ec.sgcc.com.cn; Huang Hua, East China Electric Power Test & Research Institude Company Limited, Shanghai, China, 200437, E-mail: dsy_huangh@ec.sgcc.com.cn; Dr. Fu Chenzhao, East China Electric Power Test & Research Institude Company Limited, Shanghai, China, 200437, E-mail: dsy_fucz@ec.sgcc.com.cn.

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 87 NR 9a/2011

Effect of Distribution Feeder Loading on Harmonic Resonance

Published by Electrotek Concepts, Inc., PQSoft Case Study: Effect of Distribution Feeder Loading on Harmonic Resonance, Document ID: PQS0703, Date: July 26, 2007.

Abstract: A utility operates 1200 kVAr and 600 kVAr capacitor banks on a 25.56kV distribution feeder. The utility uses frequency scan simulations to determine the effect of the capacitor banks and seasonal load levels on the impedance vs. frequency response characteristics for the feeder. It is assumed that the results will be more severe for the low load condition because there are lower levels of damping.

This case study evaluates the effect of seasonal load variation on the frequency response characteristic of a 25.56kV distribution feeder.

INTRODUCTION AND MODEL DEVELOPMENT

The effect of seasonal load variation on the frequency response characteristic of a 25.56kV distribution feeder was studied for the system shown in Figure 1. The accuracy of the system model was verified using three-phase and single-line-to-ground fault currents and other steady-state quantities, such as capacitor bank rated current and voltage rise. Frequency scan analysis was used to determine the impedance vs. frequency characteristic for the feeder for various operating conditions.

SIMULATION RESULTS

The following frequency scan cases were completed for the case study:

Case Number	Scan Location	Load Condition	Capacitor Bank Status
Case 1a	1	Full Load	All Off
Case 1b	1	Full Load	All On
Case 1c	2	Full Load	All Off
Case 1d	2	Full Load	All On
Case 1e	3	Full Load	All Off
Case 1f	3	Full Load	All On
Case 1g	1	30% Load	All Off
Case 1h	1	30% Load	All On
Case 1i	2	30% Load	All Off
Case 1j	2	30% Load	All On
Case 1k	3	30% Load	All Off
Case 1l	3	30% Load	All On

The frequency range for these cases was 60 Hz to 5,000 Hz (1 Hz increment). The load on the feeder for the “full load” condition was approximately 10.4 MVA at 98% power factor.

Figure 2 shows the impedance vs. frequency simulation results for scan location number 1 (600kVAr, full load) without and with the feeder capacitor banks in service.

Figure 2 – Frequency Response at Scan Location Number 1 with Full Load

Figure 3 shows the impedance vs. frequency simulation results for scan location number 2 (1,200kVAr, full load) without and with the feeder capacitor banks in service.

Figure 3 – Frequency Response at Scan Location Number 2 with Full Load

Figure 4 shows the impedance vs. frequency simulation results for scan location number 3 (substation bus, full load) without and with the feeder capacitor banks in service.

Figure 4 – Frequency Response at Scan Location Number 3 with Full Load

Figure 5 shows the impedance vs. frequency simulation results for scan location number 1 (600kVAr, 30% load) without and with the feeder capacitor banks in service.

Figure 5 – Frequency Response at Scan Location Number 1 with 30% Load

Figure 6 shows the impedance vs. frequency simulation results for scan location number 2 (1,200kVAr, 30% load) without and with the feeder capacitor banks in service.

Figure 6 – Frequency Response at Scan Location Number 2 with 30% Load

Figure 7 shows the impedance vs. frequency simulation results for scan location number 3 (substation bus, 30% load) without and with the feeder capacitor banks in service.

Figure 7 – Frequency Response at Scan Location Number 3 with 30% Load

Figure 8 shows the amplification factors for scan location number 1 (600kVAr) for the full load and 30% load conditions. Amplification factor is defined as the ratio of impedance with capacitor banks to the impedance without capacitor banks (e.g., Case 1b divided by Case 1a).

Figure 8 – Amplification Factors for Scan Location Number 1

Figure 9 shows the amplification factors for scan location number 2 (1,200kVAr).

Figure 9 – Amplification Factors for Scan Location Number 2

Figure 10 shows the amplification factors for scan location number 3 (substation bus).

Figure 10 – Amplification Factors for Scan Location Number 3

SUMMARY

The simulation results show that the impedance vs. frequency response characteristics for the feeder are more severe for the low load condition due to the fact that there are lower levels of damping (resistive elements).

Additional observations include:

1. For scan location number 1, the simulated parallel (high impedance) resonant frequencies were approximately 360 Hz, 700 Hz, and 1420 Hz. The series (lower impedance) resonant frequencies were approximately 540 Hz, and 1,200 Hz. The amplification factor range was between 0 and 3.4.

2. For scan location number 2, the parallel resonant frequencies were approximately 360 Hz and 700 Hz. The series resonant frequency was approximately 500 Hz. The amplification factor range was between 0 and 4.2.

3. For scan location number 3, the parallel resonant frequencies were approximately 360 Hz, 660 Hz, and 1380 Hz. The series resonant frequencies were approximately 460 Hz, 700 Hz, and 1440 Hz. The amplification factor range was between 0 and 1.83.

REFERENCES

Power System Harmonics, IEEE Tutorial Course, 84 EH0221-2-PWR, 1984.

RELATED STANDARDS
IEEE Std. 519-1992, IEEE Std. 1036-1992

GLOSSARY AND ACRONYMS
ASD: Adjustable-Speed Drive
CF: Crest Factor
DPF: Displacement Power Factor
PF: Power Factor
PWM: Pulse Width Modulation
THD: Total Harmonic Distortion
TPF: True Power Factor

Power Network Parameters Standards with Implements IEEE-1459 Power Definitions

Published by Andrzej OLENCKI¹, Daniel BELICA², Jarosław MARKIEWICZ³, Piotr MRÓZ⁴ ,
Calmet Spółka z o.o. Zielona Góra (1,2,3), Uniwersytet Zielonogórski (4)

Abstract. The development of Polish portable standards of power network parameters and their concepts are presented, taking into account the requirements of the IEEE-1459 standard in the scope of the separation of the fundamental frequency power components P₁ and Q₁ from apparent power S for the purpose of calibrating electricity meters. The issues of calibration uncertainty of working active power P₁ meters were discussed and two concepts of their calibration were presented: with the use of active power P standards and wit the use of working active power P₁ standards.

Streszczenie. Przedstawiono rozwój krajowych przenośnych wzorców parametrów sieci energetycznej i ich koncepcje z uwzględnieniem wymagań standardu IEEE-1459 w zakresie wydzielenia komponentów mocy P₁ i Q₁ o częstotliwości podstawowej z mocy pozornej S dla potrzeb wzorcowania liczników energii. Omówiono zagadnienia niepewności wzorcowania liczników roboczej mocy czynnej P₁ oraz przedstawiono dwie koncepcje ich wzorcowania: z zastosowaniem wzorców mocy czynnej P i z zastosowaniem wzorców roboczej mocy czynnej P₁. (Wzorce parametrów sieci energetycznej z implementacją definicji mocy wg IEEE-1459).

Keywords: electricity meter, reference meter, power calibrator, automatic test system.
Słowa kluczowe: licznik energii elektrycznej, licznik wzorcowy, kalibrator mocy, automatyczny system testujący.

Introduction

The state of the three-phase power network is presented by means of a vector graph and a set of values of such network parameters as: voltages and currents, phase shift angles (or power factors), angles between voltages, frequency and also active, reactive and apparent powers and energies. To calculate the values of these parameters, parameter definitions and their analytical models in the form of equations are needed, which are implemented in the algorithms of measurement (for meters) and reproduction (for sources) of the power network parameter standards.

In 2010, after 30 years of discussing new power definitions, when the mechanism of electricity flow under non-sinusoidal conditions was well known, IEEE 1459 [1] was developed, which provides consistent and unambiguous power definitions better suited for electricity billing purposes under sinusoidal and non-sinusoidal conditions. The primary innovation of the IEEE 1459 standard is the separation of the fundamental frequency power components P₁ and Q₁ from the apparent power S. The active, reactive and apparent powers with basic frequency are the quintessence of the power flow in electric networks. They define what is generated, transmitted, distributed and sold by the electric utilities and bought by the end users. This standard is based on the belief that a fair distribution of financial burdens between the electricity supplier and recipient is a prerequisite for maintaining a high quality of electricity supply. In addition, it is stated that the current level of microprocessor technology allows manufacturers of electrical instruments to construct new, accurate and versatile metering equipment that are able to measure electricity defined by means of advanced mathematical models.

Technical specifications and subject standards for active energy meters currently used in North America (ANSI C12 series) and Europe (IEC 62052 series) and international recommendations OIML R46 [2] are not yet adapted to the rational settlement of energy in non-sinusoidal conditions. Currently, the need to measure the first harmonics of power for energy billing purposes only applies to reactive energy measurement [3].

Works [4, 5] describe the design of electricity meter construction with implemented the new power definitions of the IEEE 1459 standard for the needs of comparative measurements of power P and P₁, Q and Q₁ as well as S and S₁ of energy flow in connections of real users. A Radian 4150 Meter Test Set [6] was used to calibrate and test these electricity meters. The 4150 includes a Radian RD-30 Reference Standard for determining the accuracy of the meter under test. Unfortunately the Radian RD-30 measures only P and Q powers and it is not possible to measure the fundamental frequency power components P₁ and Q₁ in non-sinusoidal conditions.

The errors evaluation of a wattmeter for the measurement of IEEE 1459 standard power quantities in non-sinusoidal conditions was described in [7]. A Multifunction Calibrator Fluke 5720A [8] and a precision current shunt were used as a power network parameters standard.

Induction meters are replaced for electronic meters in the last 20 years on a massive scale. During this time, many papers [9-12] were published on the errors of active energy electronic meters in relation to the requirements of current standards for meters. Unfortunately, these standards are based on the definition of power developed in the 1940s, this definition does not take into account the changes that have occurred in the last 50 years, in particular the flow of energy caused by harmonic voltages and currents [1, 13].

The development of polish standards for sinusoidal and non-sinusoidal, stable and variable power networks parameters, by 2009, is described in [14]. At that time, papers were published on the subject of energy flow directions as well as working and reflected active power [15] as well as the correctness of electricity meter readings. An important area of using network parameter standards is checking revenue electricity meters in two situations: meters connected to the network and meters disconnected from the network. The next part of the work describes the development of polish standards of network parameters in the last decade, with particular emphasis on the possibility of checking electricity meters P, P₁, Q and Q₁ under non-sinusoidal voltages and currents.

Standards for testing of electricity meters connected to the network

The indications of revenue electricity meters are the basis for financial settlements between the energy supplier and its recipient, and therefore checking the accuracy of meter indications is given big attention. This is manifested, inter alia, in checking the accuracy of the meters connected to the network on site of their installation. The recommended form of verifying the correctness of connecting the meter to the network and checking the error of the meter is the non-invasive connection of the meter tester (reference meter) into the circuit of the measuring and billing system, without the need to disconnect the current and voltage circuits of the meter, as shown in Figure 1.

Fig.1. The scheme of connecting the meter tester in the measuring and billing circuit

Meter testers, in accordance with the draft standard IEC 62057-2 [16], are named as the Portable Working Standard [17] or the Portable Reference Meter [18] and according to the definition [16] are working standards used for measurement of current, voltage, power, energy and error of electricity meters and also, if needed, for measurement of the burden for voltage and current transformers, determination of the ratio error and phase displacement for current transformers. The most advanced testers have implemented the power quality analyzer functionality, such as MTE PWS 3.3 [17] or the polish Calmet TE30 [19], which according to the terminology used in the standard [16] is named as a Portable Three Phase Standard Meter and Energy Quality Analyzer.

The TE30 tester introduced in 2014 meets the requirements of the IEC 62057 standard and has the functionality of an power quality analyzer and also is distinguished by the innovation possibility of measuring power and energy according to various versions of the power cuboid [20], in particular according to the IEEE 1459 [1] with separate components power P₁ and Q₁. The implemented functions of measuring the power spectrum, reflected active power, harmonic power and distortion power allow evaluation of energy flows. The reference meter function of the fundamental active power enables the measurement of percentage error in the calculation of electricity due to uncontrolled energy flows through the installed measuring and billing system. The energy cuboid measurement function with separated components of the first harmonics enables the measurement of all energy components for the calculation of non-technical losses of electricity caused to the harmonic energy flow [21].

Standards for testing of electricity meters disconnected from the network

The advantage of using standards to reproduce network parameters is that they allow checking electricity meters at all required load points of the meter, but this requires disconnecting the voltage and current circuits of the meter from the power grid, as shown in Figure 2. Two concepts are used to construction of standards to reproduce power network parameters:

• as a set of measuring power supply and reference meter necessary to ensure the required accuracy of voltage, current and power reproducing,
• as a three-phase power and energy calibrator (Fig. 2).

In Poland, in Zielona Góra, from many years [14], the building concept of standards for testing of electricity meters disconnected from the network is been developing, based on the power and energy calibrators. In 2014, the three-phase power and energy calibrator Calmet C300B [22] was introduced with the function of an automatic electricity meter tester, which allows checking the meter error in two measurement configurations:

• with reference to the accuracy of the internal calibrator standard (Fig. 2). This makes it possible to check the electricity meter error of powers P and P₁, Q and Q₁ with uncertainty up to 0.02%,

• with reference to the accuracy of the external reference meter (Fig. 3). The measurement system is then implemented according to the first concept of standard construction, in which the calibrator performs the function of a precise three-phase measuring power supply and the function of standard is taken over by an external reference meter.

Fig.2. The scheme of the measuring system for checking the electricity meter error with the accuracy related to the calibrator

In the system with an external reference meter, shown in Figure 3, the calibrator has two impulse inputs for counting impulses from the meter under test and the reference meter. In this system it is possible to check electricity meters of such powers, which are measured by reference meters and with such uncertainties as guaranteed by reference meters. Well-known reference meters measure electricity of P and Q powers, e.g. the Radian RD33 meter [23], while the authors are not known of other, than TE30 [19], reference meters of P₁ and Q₁ powers.

Comparing the systems presented in Figures 2 and 3, it can be seen that the use of an external reference meter (Fig. 3) results in an almost double increase in the number of connections required. The revenue meter is a highly nonlinear load and connected as a meter under test to the calibrator output can cause additional distortion of the calibrator output signals. In a situation where additional and uncontrolled distortion of the calibrator output voltages and currents affects the accuracy of the meter error determination, it is recommended to use a system with an external reference meter.

Fig.3. The scheme of the measuring system for checking the electricity meter error with the accuracy related to the external reference meter

Automatic Test Systems

In recent years, a new kind of standards for checking electricity meters has appeared, which are named as the Three-phase Fully Automatic Test System with Reference Standard and Integrated Current and Voltage Source. Examples of such systems are Zera MT781 / MT786 [24], MTE PTS 3.3C [25] and the first Polish Calmet TS33 system [26]. These systems allow the checking of meters completely connected to the network (Fig. 1) or completely disconnected from the network (Fig. 2) and additionally checking the meters in the “mixed” connection system shown in Figure 4.

Fig.4. The scheme of the measuring system for checking the electricity meters in current injection mode

Checking the electricity meter error in a mixed system has two advantages simultaneously:

• non-invasive test – no need to disconnect the meter voltage and current circuits,
• the possibility to perform an automatic test at predefined load points.

In the discussed connection system, the TS33 test system is used as a system with a reference meter and an integrated current source – the power calibrator of this system works in the mode of a three-phase synchronized current source (frequency and phase shift angles) with input voltage.

The TS33 system introduced in 2019 meets the requirements of the IEC 62057-2 standard [16] for the function of a reference meter, has the functionality of the power quality analyzer and is distinguished by the innovation possibility to measure and reproduce power and energy according to the IEEE 1459 [1] with separate components P₁ and Q₁ power for checking the error of electricity meters P, P₁, Q and Q₁ powers with uncertainty up to 0.05%.

Calibration uncertainty of electricity meters at fundamental frequency

Active power in non-sinusoidal conditions is given by the formula:

where: P₁ – fundamental active power, P_n – harmonic active power of order n, P_H – harmonic active power, V_n – RMS value of harmonic voltage of order n, I_n – RMS value of harmonic current of order n, φ_n – phase angle between the V_n and I_n.

Equation (1) shows, that two concepts of P₁ electricity meter calibration are possible. The first, using the standard of fundamental harmonic active power, according to the following calibration equation:

where: P_1MUT – reading from meter under test, P_1S – fundamental active power measured or reproduced with used power network parameters standard, u(P_1S) – uncertainty of fundamental active power of standard.

In the second concept, the active power standard can be used according to the following calibration equation:

where: P_S – active power measured or reproduced with used power network parameters standard, u(P_S) – uncertainty of active power of standard, P_H – harmonic active power, u(P_H) – uncertainty of harmonic active power of standard.

Equation (3) shows that calibration of the P₁ electricity meter using the P power standard under non-sinusoidal conditions is possible – the P₁ working power value is obtained by subtracting the calculated value of the harmonic power P_H from the active power value P_S . However, the uncertainty balance should take into account the uncertainty of harmonic active power expressed by the formula:

where: u(V_n)/V_n and u(I_n)/I_n are the uncertainties of voltage and current harmonics and u(cosφ_n) is the uncertainty of the harmonic power factor given by the formula:

where: u(φ_n) is the uncertainty of the harmonic phase shift angle.

Analysis of equations (4) and (5) shows that when calibrating the P₁ active power meter using the P active power reference meter in the measuring systems shown in Figures 1 and 3, or using a calibrator (Fig. 2), knowledge is required on the values of amplitudes and harmonic phases of test voltages and currents of distorted signals and on the uncertainty of their reproduction.

The TE30 [19] reference meter, the C300B [22] calibrator and the TS33 [26] test system with the error check function of the P and P₁, Q and Q₁ power meters in non-sinusoidal conditions allow to check electricity meters according to the IEEE 1459 without the need for laborious procedures associated with taking into account the uncertainty of harmonics reproduction according to the formula (4).

Conclusions

The discussion about the need to measure the electricity of the fundamental active power for accounting purposes has been going on for many years and was crowned with the development of the IEEE 1459 standard. Over the past ten years, a new generation of portable power network parameters standards has been developed and introduced for production: TE30 reference meter with power quality analyzer function, C300B three-phase power / energy calibrator with automatic meter tester function and the first Polish Automatic Test System with a reference meter and integrated current and voltage source model TS33. All of the above standards have the functions of automated checking of active and reactive power electricity meters as well as the first harmonics of these powers implemented, which is an innovation in the area of power network parameters standards for the purposes of checking electricity meters. Calibration of P₁ electricity meters using the P₁ reference meter improves the calibration process because there is no need to include harmonics uncertainty (uncertainty of amplitudes and phases) in the uncertainty balance, what is required when using the P reference meter.

REFERENCES

[1] IEEE Std 1459-2010, IEEE Standard Definitions for the Measurement of Electric Power Quantities Under Sinusoidal, Nonsinusoidal, Balanced, or Unbalanced Conditions, The Institute of Electrical and Electronics Engineers, USA, 2010
[2] OIML R 46-1/-2 Edition 2012, Active electrical energy meters. Part 1: Metrological and technical requirements. Part 2: Metrological controls and performance tests, France, 2012
[3] IEC 62053-24:2014, Electricity metering equipment (a.c.) – Particular requirements – Part 24: Static meters for reactive energy at fundamental frequency (classes 0,5 S, 1 S and 1)
[4] Berrisford A.J.: Smart Meters Should be Smarter, IEEE PES Conference, San Diego, California, USA, 2012
[5] Berrisford A.J.: A Smarter Meter: IEEE-1459 power definitions in an Off-the-Shelf Smart Meter, IEEE I2MTC Conference, Pisa, Italy, 2015, 830-835
[6] Automated Test Platform Model 4150, Radian Research, USA, http://www.radianresearch.com/pdf/Model_4150_Brochure_INTER.pdf
[7] Cataliotti A., Cosentino V., Cara D., Lipari A., Nuccio S.: A DAQ-based sampling wattmeter for IEEE Std. 1459-2010 powers measurements. Uncertainty evaluation in non-sinusoidal conditions, Measurement, Volume 61, 2015, 27-38
[8] The 5700A/5720A Series II High Performance Multifunction Calibrators. Extended Specifications, Fluke, USA
[9] Rui Wang, Jing Yuan: Study on electrical energy meter for energy measuring under harmonics condition, AEST Conference, China, 2016
[10] Volokhin V., Diahovchenko I., Kurochkina V., Kanalik M.: The influence of non-sinusoidal supply voltage on the amount of power consumption and electricity meter readings, Energetika,
T .63 (2017), Nr. 1, 1-7
[11] Bilik P., Prauzek M., Josefova T.: Precision check of energy meters under nonsinusoidal conditions, CIRED Conference, Stockholm, 2013, 1-4
[12] Novotny J., Drapela J., Topolanek D.: Fraquency responce of revenue meters in measured active energy, ICHQP Conference, Brazil, 2016, 524-529
[13] Cetina Quijano, Roscoe A., Wright P.: Challenges for Smart Electricity Meters due to Dynamic Power Quality Conditions of the Grid: A Review, AMPS Conference, Liverpool, UK, 2017
[14] Olencki A.: Rozwój wzorców parametrów sieci energetycznej, Pomiary, Automatyka, Kontrola, nr 12, 2009, 409-411
[15] Czarnecki L., Toups T., Working and Reflected Active Powers of Three Phase Loads, Przegląd Elektrotechniczny, 91 (2015), nr.11, 149-153
[16] IEC 62057-2 /Ed.1, Portable Test Equipment and Test Procedure for Electricity Meter and Electricity Meter Installation, 2009
[17] PWS 3.3 Three-phase Portable Working Standard and Power Quality Analyzer, MTE, Switzerland, 2016, https://www.mte.ch/data/files/PWS%203.3%20English_R02%20(07.2016).pdf
[18] MT320 Three Phase Reference Meter, ZERA, Germany, https://www.zera.de/fileadmin/pdf_and_more/Products/Meters/Portable/MT320_CAT_EXT_GB_V105.pdf
[19] Three Phase Network Analyzer and Tester of Electricity Meters and Instrument Transformers TE30. Calmet, TE30 Data sheet EN 2018-03 https://www.calmet.com.pl/images/pdf/TE30-Three-Phase-Working-Standard-Data-Sheet-EN.pdf
[20] Olencki A.: Sprawdzanie poprawności pomiaru energii elektrycznej z zastosowaniem wzorca prostopadłościanu mocy i energii, Zeszyty Naukowe Wydziału Elektrotechniki i Automatyki Politechniki Gdańskiej, Nr 66, 2019, 67-70
[21] Olencki A.: Pomiar strat nietechnicznych energii elektrycznej z wykorzystaniem nowoczesnych technik diagnostycznych, Pomiary i Diagnostyka w Sieciach Elektroenergetycznych, Kołobrzeg, 2018, 35-44
[22] Three Phase Power Calibrator and Tester of Power Engineering Devices C300B. Calmet, C300B Data sheet EN 2019-06 https://www.calmet.com.pl/images/pdf/C300B-ThreePhase-Power-Calibrator-Data-Sheet-EN.pdf
[23] RD33 Portable Three-phase Electricity Standard, Operations Manual, Radian Research, USA,
http://www.radianresearch.com/manuals/RD-33.pdf
[24] Moving Test – MT781/MT786 Three-phase Fully Automatic Test System with Integrated Current and Voltage Source, Zera,Germany, 2016, https://www.zera.de/fileadmin/pdf_and_more/Products/Meters/Portable/MT78x_Pros_EXT_GB_V404.pdf
[25] PTS 3.3C Three-phase fully automatic test system with class 0.05 reference standard and integrated three-phase current and voltage source, MTE Meter Test Equipment, Switzerland, 2015, https://www.mte.ch/data/files/PTS%203.3%20C%20English_R04%20(08.2015).pdf
[26] Three-phase Fully Automatic Test System with Reference Standard and Integrated Current and Voltage Source TS33. Calmet, TS33 Data sheet EN 2019-06 https://www.calmet.com.pl/images/pdf/TS33-Three-PhaseFully-Automatic-Test-System-Data-Sheet-EN.

Authors: dr hab. inż. Andrzej Olencki, Calmet Spółka z o.o., ul. Kukułcza 18, 65-472 Zielona Góra, E-mail: A.Olencki@calmet.eu; mgr inż. Daniel Belica, Calmet Spółka z o.o., ul. Kukułcza 18, 65- 472 Zielona Góra, E-mail: D.Belica@calmet.eu; mgr inż. Jarosław Markiewicz, Calmet spółka z o.o., ul. Kukułcza 18, 65-472 Zielona Góra, E-mail: J.Markiewicz@calmet.eu; dr inż. Piotr Mróz, Uniwersytet Zielonogórski, Instytut Metrologii, Elektroniki i Informatyki, ul. Prof. Z. Szafrana 2, 65-516 Zielona Góra, E-mail: P.Mroz@imei.uz.zgora.pl

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 96 NR 3/2020. doi:10.15199/48.2020.03.01

Selected Methods for Improving Power Reliability

Published by Krzysztof PRZYSTUPA¹, Lublin University of Technology (1)

Abstract. The article discusses the problem of the widespread use of devices that require increased quality electric power supply. An example of a practical division of electricity receipts into several categories is shown. Methods of increasing the reliability of power supply are described and the most commonly used technical solutions for this purpose are discussed.

Streszczenie. W artykule omówiono problem powszechnego występowania urządzeń, które wymagają zasilania o podwyższonej jakości dostaw energii elektrycznej. Pokazano przykład praktycznego podziału odbiorów energii elektrycznej na kilka kategorii. Opisano metody zwiększenia niezawodności zasilania oraz omówiono najczęściej stosowane w tym celu rozwiązania techniczne. Wybrane metody poprawy niezawodności zasilania

Keywords: power negativity, power quality, Uninterruptible Power Supply (UPS)
Słowa kluczowe: niezawodność zasilania, jakość zasilania, zasilacz bezprzerwowy (UPS)

Introduction

There are many types of electricity receivers that require continuous and almost ideal power supply. Despite the fact that the degree of power supply reliability in the power system is very high, IT equipment, data processing and transmission equipment, precise control units and control of long-term industrial processes are sensitive to various types of interference that may occur in the power grid. The scale of the problem is also shown by the fact that the requirements for the power quality are important for different receivers: on the one hand, it can be medical equipment, and on the other, ordinary LED lighting [1].

Phenomena disrupting energy supply not only cause deterioration of power quality in the sense defined by ISO 9000 series standards but also affect the durability of devices, their lifetime and reliability. Poor power quality also has an adverse effect on the quality of products manufactured with sensitive devices. An example may be the quality of the produced light, errors in data transmission or the quality of the surface worked in the milling process. For correct operation of the described devices, it is necessary to use guaranteed electric power supply systems, both AC and DC [2-4].

Different requirements as to the reliability of the power supply resulted in the development of recipients’ classification. The main division concerns two groups: industrial recipients and municipal recipients. It has been assumed that there are three categories of recipients in the group of industrial recipients:

• Category I – with the highest requirements (highest reliability of power supply). These are devices whose failure may cause a threat to human life or very serious material losses.

• Category II – with increased requirements regarding the quality and reliability of power supply. These are devices whose failure causes losses in production.

• Category III – with no special requirements. These are other devices not classified in categories I or II.

When designing the power system for devices of category I, it is necessary to take into account the detailed requirements of individual devices and, without using a relatively adequate back-up power supply system, which must be independent of the basic power supply. In the case of the third category, sometimes the back-up systems are also used, but only when it is economically justified. The described division results from project findings and it is not directly related to the applicable law. It should be noted that the categorization of devices is very often related to the structure of the external power grid and distribution network inside the plant.

In practice, the technical capabilities of the local electricity supplier (distribution company) are very important and decisive.

Municipal recipients, i.e. recipients supplied from public distribution networks usually with a voltage of up to 1kV, are non-industrial recipients with public facilities (residential buildings, banks and hospital buildings with some exceptions, offices, railway facilities, aviation objects, commercial facilities, etc.). This group is sometimes also divided into three or four categories.

In category I with the highest priority power supply, the recipients require uninterruptible power supply or have devices in the case of which the power supply must be reliable. The applied solutions consist in using uninterruptible power supply from a back-up source, e.g. power generator adapted for long-lasting work. This solution is used for hospital operating rooms, banking computer systems, etc.

In category II with a high priority supply power, breaks should not exceed 1 second. For this purpose, for example, two independent power lines from the energy system are used. Entities belonging to this group are: hospitals, radio stations, railway stations and equipment, airports, etc.

In category III with a medium power supply priority, breaks should not exceed several seconds. The solutions applied mainly concern emergency lighting as well as numerically controlled elements and devices. The problem is solved by power generators. The energy consumers in this group are, for example, large residential buildings, large office buildings, and sometimes road infrastructure elements.

In the last IV category there are no additional requirements as to the reliability of power supply. Relatively long power interruptions lasting even many minutes are allowed. Typical objects in this category are single-family houses in rural areas, houses in sparse urban buildings, blocks of flats etc. Most often, these objects are powered by a single radial line.

The presented division, similarly as in the case of industrial recipients, is not legally defined, but it rather results from design practice and distribution companies [5].

Increased reliability of power supply

Increasing the reliability of power supply can be obtained through various financial investments, with the increase in reliability being determined by the exponential function.

This makes it necessary to choose a reasonable investment, which should be determined by considering the required parameters, which include:

The power of the source and the maximum time to deliver energy.

• Switchover time, i.e. the time from the moment of voltage decay on the basic source until the load is supplied from the back-up source. Yet, this time is often extended by the time of decreasing the power quality and the time of returning to the appropriate minimum level of power quality.
• Efficiency of the applied solution.
• Maintenance cost both during work and stand-by.

An ideal alternative source of back-up power should meet the following requirements:

• Unlimited source of energy, i.e. high power.
• Unlimited working time.
• Zero changeover time.
• Low operating costs during operation.
• Zero operating costs while waiting.

Unfortunately, practical solutions do not have such parameters. Table 1 presents the most common practical solutions for back-up power supply and their feature

Table 1. Backup power supply devices and their parameters

Type of supply	Source power	Changeover time	Installation costs
Additional power line from the grid	Unlimited	From milliseconds to seconds	Very high
Power generator	Nearly unlimited	From a few seconds to a few minutes (rarely less than a second)	From medium to high
Batteries	Usually low, Rarely medium, Occasionally high.	From a few seconds to nearly seamless	Low or medium
Uninterruptible power supply (UPS)	From low to high. Rarely low.	From less than a second to nearly seamless	From medium to high

According to Table 1, recipients with increased requirements for energy quality and reliability of its supply should be supplied from at least two power lines. Such a power supply requires the use of ATS automatics – automatic switching on of the reserve. This solution is the most expensive, but at the same time provides unlimited power supplies. An alternative to using power from the second power line is the use of a power generator. In this case, the investment costs are much lower than those related to the construction of the power line but the delivered power drops significantly. The time required to start the unit can also be extended. This solution also requires ATS automation and complex automation to control the operation of the unit. The use of the generator may be the third route of energy supply in the case of particularly demanding customers (two power lines and generator), such a solution greatly increases the reliability of energy supplies but increases the possibility of extending the total time of reserve power supply [6].

Fig.1. The power supply system of a customer with increased requirements for reliability

In case of recipients using important IT systems, local computer networks, microprocessor devices controlling complex technological processes, UPS uninterruptible power supplies are used. They provide an almost reliable power supply, with low power, in a relatively long time with a very short switching time of the power source. UPS devices in the internal structure have ASS automatics. Fig.1 shows an example of a customer supply system with increased requirements for power reliability [7-9].

Two-sided power supply

The two-sided power supply from the power grid is implemented from two independent main power points, so-called MSP (main supply point). It can be implemented using high voltage (HV) networks, medium voltage (MV) networks and sometimes even low voltage (LV) networks.

Generators

There are four groups of power generators:

• In the first group there are generators that are switched on manually after power supply decay. The power of these generators is from several dozen KW to several MW. The time of readiness for loading depends on the power and ranges from 5-15 seconds for small devices up to 3-4 minutes for the largest devices.

• In the second group there are devices with powers similar to those of the first group, but these are devices equipped with electronics enabling automatic start. This solution significantly shortens the time of preparing the device for load.

• In the third group there are devices equipped with a flywheel (constantly rotating mass). The second characteristic feature of these devices is equipping them with the most frequently controlled electronic clutch. Aggregates of this group work according to the following algorithm: an electric motor powered from the basic power line continuously drives the flywheel on the common shaft with an electric generator. However, the generator does not work because it is disconnected by the clutch. In the event of a failure, the clutch is switched and the generator starts producing energy. During the nominal operation of the generator, the drive is carried out by combustion engines. In the group of these devices there are those in which the generator operates in the idle state and after the supply voltage decays, the generator goes into the rated operating state. The spinning mass provides the necessary energy for a period of time from the power supply failure until the generator’s generator drive is fully started.

• In the fourth group there are devices of similar construction to those from the third group, with the generator working in them continuously supplying selected important devices. At the moment of the power supply decay, the generator load is increased by attaching additional receivers.

Batteries

In industrial practice, two types of systems are used in which the batteries work [10]:

• In the normal operating condition of the supply network, the batteries are constantly recharged. In the event of a failure of the basic power supply, the battery is switched on. This system is used to power the so-called own needs, e.g. telephone switchboard, power supply for DC receivers, as well as receivers that can be powered by both direct and alternating current, e.g. emergency lighting.

• In the second system there is a much larger rectifier that simultaneously recharges the batteries and supplies the load. It is only in the event of an emergency that the energy consumption from the batteries is started. The system of such work has features characteristic for uninterruptible power supplies.

Uninterruptible Power Supply (UPS)

Uninterruptible Power Supply UPS units are intended for supplying loads with the highest quality requirements, and especially for power supply continuity [11-14]. In industrial practice there are three basic types of UPS:

• Passive readiness (VFD class sometimes referred to as off-line).
• Double conversion (VFI class sometimes referred to as on-line).
• Interactive line (class VI sometimes referred to as hybrid).

Off-line systems charge the battery during normal operation of the basic power supply. At the moment of the failure of the basic power supply, the inverter is started, which draws energy from the batteries providing the necessary power supply to the receivers (Fig. 2). In off-line power supplies, the primary power source is the power grid. The backup power source is batteries, or less often their sets. In simplified terms, it can be said that the off-line power supply “does nothing” until a power failure occurs. This failure does not have to involve a power failure. It may also be a change in amplitude or frequency. The operation of the switch (6 fig. 2) depends on the electronic logic used.

Fig.2. Block diagram of UPS, off-line type (standby)

(1 – surge suppressor, 2 – filter, 3 – battery charging system, 4 – battery, 5 – DC/AC converter, 6 – switch)

The relatively long time of switching paths from primary to standby is a fundamental disadvantage of VFD (off-line) power supplies.

On-line systems are based on a complete idea from separating the receiver from the power grid (Fig. 3). The energy taken from the network is used only for charging the battery. The power supply is supplied from the energy accumulated in the battery through the inverter.

Fig.3. Block diagram of UPS, on-line type without bypass

(1 – battery charging system, 2 – battery, 3 – DC/AC converter)

On-line UPS can be implemented using two paths similar to off-line devices (Figure 4)

(1 – surge suppressor, 2 – filter, 3 – battery charging system, 4 – battery, 5 – DC/AC converter, 6 – switch)

Theoretically, a completely smooth and imperceptible transition of the receiver from the basic power supply to the standby power supply is the key advantage of the VFI (online) power supplies. The second advantageous feature of this type of power supplies is the possibility of the receiver working with the frequency of the supply voltage other than the frequency of charging the battery system.

Linear interactive UPSs work in such a way that during normal operation of the basic power part of the energy is consumed permanently recharging the battery. At the same time, some of the battery energy continuously goes to the receiver. In this solution, there is a constant power backup for the primary energy backup (Fig.5 and Fig. 6).

Fig.5. Block diagram of UPS, hybrid type

(1 – surge suppressor, 2 – filter, 3 – battery charging system, 4 – battery, 5 – DC/DC converter, 6 – transformer, 7 – DC/AC converter)

The main part of the solution shown in Fig.5. is a transformer with three windings (6). Two of them constitute a classical network transformer and the third winding placed on the primary side has a control and intervention role. In its circuit there is a battery and DC/AC converter or an electronic system that works in one direction as an inverter and in the opposite direction as a rectifier. This winding is used to introduce corrective energy in the moments of loss of basic power supply or energy reception when there is too much of it. In the event of a power failure, the auxiliary winding takes over the whole task of supplying energy.

In the situation of power supply of devices that do not allow disturbances in the shape and frequency of power supply, systems similar to the solution proposed in Fig. 6 are used.

Fig.6. Block diagram of UPS, hybrid type

(1 – surge suppressor, 2 – filter, 3 – battery charging system, 4 – battery, 5 – DC/DC converter, 6 – semiconductor driver, 7 – DC/AC converter)

The inverter (5 -Fig.6) in the state of waiting for power failures does not work. It is launched when it is detected. The battery charging system (3 -Fig.6.) is small because it works only for the needs of the battery. This type of power supply does not show or has a very low switching time. The last group of devices used to improve the reliability of power supply are non-conventional devices. We include devices using super capacitors, flywheels and superconducting magnetic energy storage (SMES) [15].

REFERENCES

[1] Arrillaga J., Neville R., Watson S., and Chen S., Power system quality assessment. Chichester, England: John Wiley & Sons, 2000.
[2] Bollen M. H. & Bollen M. H., Understanding power quality problems: voltage sags and interruptions. Vol. 445. New York: IEEE press, 2000.
[3] Arrilaga J., Watson N. R., Chen S., Power system quality assessment. John Wiley & Sons, Chichester, New York, Weinheim, Brisbane, Singapore, Toronto, 2000.
[4] Barlik R., Nowak M., Jakość energii elektrycznej-stan obecny i perspektywy. Przegląd Elektrotechniczny, 2005, 81: 1-12.
[5] Klajn A., Markiewicz H., Jakość energii i nie zawodność zasilania w instalacjach elektrycznych. Dodatek do miesięcznika INPE, Zeszyt 14, marzec 2017.
[6] Siwy, E., Witek B., Wybrane zagadnienia technicznej realizacji koncepcji Smart Grid w kontekście jakości zasilania z sieci z generacją rozproszoną. Przegląd Elektrotechniczny 88.8 (2012): 116-119.
[7] Dołęga W., Układy zasilania zakładów przemysłowych w aspekcie niezawodności i pewności dostawy energii elektrycznej. Mechanizacja i automatyzacja górnictwa 49 (2011): 23-26.
[8] Sutkowski T., Rezerwowe i bezprzerwowe zasilanie w energię elektryczną-urządzenia i układy. Stowarzyszenie Elektryków Polskich. Centralny Ośrodek Szkolenia i Wydawnictw, 2007.
[9] Martyniak T., Nawrocki J., Antończyk B., Optymalizacja doboru agregatów prądotwórczych oraz wytyczne ich zabudowy w pojazdach specjalnych, Szybkobieżne Pojazdy Gąsienicowe 1 (2005).
[10] Wiatr J., Miegoń M., Zasilacze UPS oraz baterie akumulatorów w układach zasilania gwarantowanego. Dom Wydawniczy MEDIUM, 2008.
[11] PN-EN 62040, Systemy bezprzerwowego zasilania (UPS).
[12] Lasseter R. H., Eto J. H., Schenkman B., Stevens J., Vollkommer H., Klapp D., Linton E., Hurtado H., Roy J., CERTS microgrid laboratory test Bed, IEEE Transactions on Power Delivery, 26 (1), art. no. 5673682, pp. 325-332. 2011.
[13] Lasseter R.H., Smart distribution: Coupled microgrids, Proceedings of the IEEE, 99 (6), art. no. 5768104, pp. 1074-1082, 2011.
[14] Aamir M., Mekhilef S., An Online Transformerless Uninterruptible Power Supply (UPS) System with a Smaller Battery Bank for Low-Power Applications, IEEE Transactions on Power Electronics, 32 (1), art. no. 7428955, pp. 233-247, 2017.
[15] Cieśla A., Skowron M., Pole magnetyczne jako źródło energii w nadprzewodnikowych zasobnikach energii. Przegląd Elektrotechniczny 94 (2018).

Authors: Krzysztof Przystupa, PhD, Eng. Politechnika Lubelska, Wydział Mechaniczny, Katedra Automatyzacji, ul. Nadbystrzycka 36, 20-618 Lublin, E-mail: k.przystupa@pollub.pl

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 94 NR 12/2018. doi:10.15199/48.2018.12.62

Temperature, Overcharge and Short-Circuit Studies of Batteries used in Electric Vehicles

Published by Andrzej ŁEBKOWSKI, Gdynia Maritime University, Department of Ship Automation

Abstract. The paper presents the results of temperature and short-circuit research of battery types most commonly used in electric vehicles. Basing on performed tests, the plots of changing internal resistance of lead-acid and lithium batteries are shown. On the basis of conducted short-circuit experiments of selected lithium based batteries of types used in electric vehicles, the risk of fire occurrence is made. (Badania termiczne, przeładowania oraz zwarciowe akumulatorów stosowanych w pojazdach elektrycznych).

Streszczenie. W pracy przedstawiono wyniki badań temperaturowych oraz zwarciowych dla najczęściej stosowanych typów akumulatorów w pojazdach elektrycznych. W oparciu o przeprowadzone badania, przedstawiono przebiegi zmian rezystancji wewnętrznej akumulatorów kwasowych oraz litowych w zależności od temperatury. Na podstawie przeprowadzonych badań zwarciowych wybranych typów akumulatorów litowych stosowanych w pojazdach z napędem elektrycznym, dokonano oceny możliwości pojawienia się pożaru.

Słowa kluczowe: pojazdy elektryczne, akumulatory litowe, właściwości termiczne i zwarciowe, rezystancja wewnętrzna.
Keywords: electric vehicles (EV), lithium batteries (Li-Ion, LiFePO4, LTO), thermal & short-circuit behavior, internal resistance.

Introduction

The problem of properties of batteries powering the electric powertrains in vehicles is a topic of many academic papers. The vehicles manufacturers are offering their products with many battery types, beginning from the cheapest Lead-Acid (Pb-A), through nickel based batteries (Ni-Fe, Ni-Zn, Ni-Cd, Ni-MH), lithium based (Li-Ion, LiTiO, LiCoO, Li-MnO₂ LiMn₂O₄, LiFePO₄, LiSO₂, Li-SOCl₂, LTO), up to the newest, state of the art graphene polymer batteries.

The engineers are trying to optimize the performance of traction batteries in order to maximize the vehicle’s functionality (largest possible usable volume inside the vehicle, high range) while minimizing the manufacture costs and maximizing the battery lifetime.

The newly incoming battery types are characterized by having few times more energy density (ca. 1000 Wh/kg [1]) than batteries used by now, and promise to revolutionize the automotive market. The wave of electric vehicle battery technology progress [2,3] is as of now passing through the biggest research centers in the world. This progress is causing some governments to consider future halting of the possibility of registration of new, internal combustion powered cars. Projects of such bans effective from 2025 are discussed in the Netherlands [4], and from 2030 in the Germany [5]. These changes make one wonder, whether the chemical batteries are a safe energy storage medium?

The contemporary traction battery types can supply the energy at the rate of 30-fold time their rated capacity (30C), with a charging rate of 5C, where C is the capacity of the battery in [Ah]. The newly designed battery types offer even higher performance levels, with discharge on the order of 100C [6,7]. The available battery types caused the available car types to divide into segments, such as: small electric cars with a range of 150 to 200 km, middle class cars with range between 200 and 400 km, luxury cars with range in excess of 400 km, utility vans (100-200 km), cargo trucks (1200-1900 km) and urban area busses (100 to 500 km). The introduction of new generation of graphene-polymer batteries can blur the existing boundaries, due to the great reduction of mass to energy capacity ratio.

The article presents the results of research on currently used energy storage device types, which are deployed in electric vehicles. The testing included following batteries: prismatic type LiFePO₄ with 160 Ah capacity (energy density of 95 Wh/kg, Fig. 1-1), : prismatic type LiFePO₄ with 60Ah capacity (energy density of 85 Wh/kg, Fig. 1-1), caseless LiFePO₄with 20 Ah capacity (125 Wh/kg, Fig. 1-2), LiFePO₄ with 8 Ah capacity (energy density of 100 Wh/kg, Fig.1-3), Li-PO with 1000 mAh capacity (110 Wh/kg, Fig. 1-4), Li-Ion with 2200 mAh capacity (energy density of 160 Wh/kg, Fig. 1-5) and a lithium-thionyl chloride (Li-SOCl₂) primary cell with 13 Ah capacity (470 Wh/kg, Fig. 1-6). For comparison, the tests also included a Lead- Acid battery with 150 Ah capacity and energy density of 50 Wh/kg (Fig. 1-7).

LiFePO₄ 160Ah and 60Ah (1), LiFePO₄ 20Ah (2), LiFePO₄ 8Ah (3), Li-PO 1000mAh (4), Li-Ion 2200 mAh (5), Li-SOCl₂ 13 Ah (6),

Due to the environmental conditions in which the batteries are normally used and their operation mode (charge – discharge), four tests were performed: chilled battery, heated battery, overcharged battery and short-circuit.

Table 1 contains the basic parameters of the batteries used in electric vehicles.

Table 1. EV traction battery parameters [6,7]

Type	Energy density [Wh/kg]	No of cycles [SOH 80%]	Charge / Discharge current [C]	Working Temp. [°C]	Nominal Voltage [V]
Lead-Acid	35÷50	600	0,1 / 2	-20÷40	2,1
Ni-Cd	50÷80	500	1 / 15	-20÷50	1,2
Ni-MH	50÷100	800	1 / 5	-20÷50	1,2
Na-NiCl₂	90÷110	1 500	1 / 2	245÷350	2,6
LiFePO₄	90÷120	3 000	5 / 30	-20÷60	3,2
Li-PO	130÷220	500	2 / 25	-20÷60	3,7
Li-ION	160÷200	1 000	5 / 30	-20÷50	3,6
LTO	70÷80	20 000	5 / 20	-25÷55	2,4
Graphene polymer	1000	8000	100 / 100	-20÷60	2,3

The battery working temperature refers mostly to the operational mode in which the energy is taken from the battery. Most of the batteries including Li-Ion cannot be charged when their temperature is lower than 0°C (32°F). The stated number of cycles coincides with battery State of Health (SOH) reaching the level of 80%. Most battery manufacturers recommend replacing the battery when SOH drops below that value, it does not mean, however, that the battery will cease to work afterwards. Everything depends on conditions in which the particular vehicle were operated. For instance, if a newly manufactured vehicle could achieve a range of 150km on one charge, that vehicle will have a range of 120km at SOH of 80% (≥3000 charge-discharge cycles), 105km at SOH of 70% (≥5000 charge-discharge cycles), 90km at SOH of 60% (≥7000 cycles). Assuming 250 working days per one year, the SOH level of 80% corresponds to 12 years of battery operation, SOH 70% – 20 years, SOH 60% – 28 years, SOH 50% – 36 years. The situation is different in case of Li – Ion batteries, when SOH of 80% is reached after 4 years of operation, SOH 70% – 6 years, SOH 60% – 8 years, SOH 50% – 10 years. During the research, the batteries were tested when exposed to low temperatures and short-circuit conditions. No tests of battery heating and overcharge were performed.

External Cooling

One of the important properties of any electric vehicle battery is its capacity to supply energy in low temperature conditions. Many thermal models of batteries are available [8-18], but the described behavior does not exactly correspond to real battery parameters, especially for temperatures below 0°C (32°F). These parameters are the cause of most electric vehicles poor performance, especially reduction in range, when the ambient temperature drops below 0°C (32°F). This phenomena is caused by internal battery electrochemical reactions performance being highly dependent on the temperature. The drop in effective battery capacity can span, depending on the battery type, from 8 to 25% each time the temperature drops by 10°C (18°F) in relation to reference temperature of 20°C (68°F). When discharged at too low temperature, the battery can be irreversibly damaged by permanent changes in its internal structure, resulting in large drop of SOH value or even a total failure of a battery.

There are measures available, which can prevent these problems from arising, in the form of battery heating systems. Unfortunately, only a small group of manufacturers is installing these conditioning systems in their products, and then, only for vehicles destined for operation in northern parts of Europe and North America. There are several possible methods to employ in the battery conditioning systems, in order to maintain the temperature in the preset operating area. One of the methods is to power individual battery cells with an alternating current at high frequency [19], which increases the internal cell temperature.

The other solution is a liquid conditioning system which, depending on the ambient temperature, can either cool down or heat up the battery. Another way is to harness the air conditioning system of the vehicle in which the battery is installed. This design uses a part of the air conditioning unit to cool or heat the battery (heating is accomplished by a parking heating system e.g. a Webasto) [20].

Finally, there are battery conditioning systems using specially crafted battery boxes, containing heating mats placed at sides and bottom of the box [21]. The heating system is powered either by energy stored in the battery itself, or from mains supply, when the vehicle is connected for the duration of charging and standby. It can be argued, that using extra energy for raising the battery temperature increases the vehicle operation costs, but keeping in mind, that the maintaining higher (proper) battery temperature increases its life, as well as the vehicle range, these steps seem well justified. An exception from this rule, are the vehicles using the molten salt batteries, which to operate, require a high temperature of 245÷350°C (473÷662°F), at power consumption on the average level of 70÷90W, supplied at all times.

Fig.2. Dependence of internal resistance versus temperature for a LiFePO₄ battery, 160Ah – load of 1C

Fig.3. Dependence of internal resistance versus temperature for a LiFePO₄, 60Ah – load of 1C

Fig.4. Dependence of internal resistance versus temperature for a LiFePO₄, 20Ah (caseless) – load of 1C

Fig.5. Dependence of internal resistance versus temperature for a LiFePO₄, 8Ah – load of 1C

Fig.6. Dependence of internal resistance versus temperature for a Li-PO, 1000mAh – load of 1C

Fig.7. Dependence of internal resistance versus temperature for a Li-Ion, 2200mAh – load of 1C

Fig.8. Dependence of internal resistance versus temperature for a Lead-Acid battery, 150Ah – load of 1C

Fig.9. Dependence of internal resistance versus temperature for a Lead-Acid battery, 4Ah – load of 1C

During testing, the batteries under test were placed in the climate chamber, which could hold a preset temperature in the range of -30°C÷55°C (-22°F÷131°F). Preceding the testing, the batteries were held in the climate chamber for a period of at least 8 hours. The measurement of battery internal resistance were conducted by the Electric Vehicle Battery Tester [22]. Measurements were taken from the minimal temperature of -30°C (-22°F), every 5°C (9°F), up to the maximum temperature of °C (131°F). The results of tests for most popular battery types is presented on Fig. 2 ÷ Fig. 9.

A set of internal resistance versus temperature plots for tested batteries is presented in Fig. 10.

Fig.10. Dependence of internal resistance versus temperature for lithium based batteries (LiFePO₄, Li-PO, Li-Ion), and Lead-Acid battery – load of 1C

External Heating

During operation of electric vehicle, it is possible, it will happen in an extremely high ambient temperature (40°÷50°C (104÷122°F)). Taking into consideration additional heat input from internal heating due to high battery circuit current (from e.g. fast charging, high vehicle acceleration), the battery can overheat and become damaged – its internal structure will be destroyed. Another possible mode of failure is thermal runaway, caused by temperature rise on the level of 10°C/minute or higher (Fig.11). It is caused by an exothermic reaction occurring from high temperature which releases large amount of energy in a very short time. The runaway reaction usually results in total loss of the battery, as well as swelling of the battery enclosure from high internal pressure, or even violent rupture of the enclosure associated with expulsion of boiling electrolyte. To prevent the thermal runaway, cooling systems based on liquid or air cooling (using air conditioning system) are applied [20]. During the testing, the batteries were heated at the rate of 10°C(18°F)/15 minutes [23,24].

Overcharge

The process of charging an electric vehicle’s battery is an essential matter considered during engineering an electric powertrain. Engineers working on the powertrain should choose the correct battery type guaranteeing proper vehicle reliability. Choice of the battery type results in requirement of providing the battery with proper operating conditions, such as: limiting the maximal level of shocks and vibration, ensuring water-tightness by designing proper battery enclosure and proper working temperature range by applying a temperature conditioning system. Apart from proper climatic conditions, the battery requires proper charging and discharging parameters, compatible with its requirements (Table 1). It is the purpose of supervisory systems for charging and discharging usually called BMS (Battery Management System), which operate together with onboard and off-vehicle chargers (regular chargers, fast chargers, contactless (induction) chargers, etc.) BMS systems can be constructed as passive or active, active systems have the capacity for controlling (balancing) the voltage levels on individual battery cells. There exists however, a possibility of malfunction of various system components, of e.g. a charger, or a BMS, or a disruption of data exchange between BMS and charger. Another possible risk exists, which can be overlooked by vehicle designers. When the vehicle is operating with fully charged battery, and the regenerative braking is used, it could result in damage to the battery from overcharging, by supplying a large current to an already fully charged battery.

Overcharging a battery reveals in a rise in battery temperature, its swelling due to vaporizing electrolyte or even loss of containment and release of gases to outside atmosphere (Fig. 12.). If the battery is not fitted with adequate safeguards disconnecting circuit (PTC – Positive Temperature Coefficient (temperature over 90°C (194°F)); CID – Current Interrupt Device (internal pressure over 1MPa (145psi)); mechanical safety vent (pressure over 3MPa (450psi))), which would sever the circuit in such case, there is a possibility of battery fire or even explosion [23, 24] (Fig. 13).

Fig.13. View of Li-PO 1000mAh battery during overcharge test at 2C which ended with explosion and fire

Short Circuit

A very serious matter, from the point of safety of vehicle occupants and other traffic users, is the behavior of the vehicle’s battery when subjected to various possible short circuit scenarios: short circuit in the main traction circuit, short circuit from mechanical damage of the battery (puncture, violent shock, crushing, vibration, etc.) and external battery heating. Short circuits or general overcurrent conditions in the main traction current can cause rapid heating of the battery interior which would lead to permanent damage to internal battery structure or to spontaneous battery combustion. In case of battery being heated, after reaching certain temperature there is a possibility of creating a thermal runaway condition which would lead to even quicker temperature rise and create a fire and explosion risk. In everyday life, there are reports of electronic devices (laptop computers, mobile phones, tablets, electric cars, etc.) catching fire due to stressed battery. In many of these cases, the battery itself was not the direct reason of fire, rather the too thin wires connecting the battery to energy consumers tend to overheat, and ignite flames. In order to mitigate the cases when the batteries become fire hazard from overloading or short circuit, various protective devices are being applied in form of protective thermal fuses, which interrupt flow of current when they detect too high temperature.

Another danger of the safety of vehicle and its passengers is the condition of electrical contacts (wire, battery, inverter, motor, fuse and contactor terminals). Loose or corroded terminals can lead to increased resistance, localized heating and even a fire. There are described cases of authorized vehicle service station recommending replacement of whole battery unit, based on computer diagnostic run which reported a failed battery. Meanwhile a simple terminal cleaning job would suffice to return that battery to operational status [25].

A yet different case exists when battery becomes physically damaged as a result of vehicle collision. Then, any thermal fuse fitted outside the battery would become useless, and in case the battery enclosure is designed from poor materials, the battery fire and/or explosion is likely.

The same type of batteries, as in internal resistance test, were tested. The test was conducted by short circuiting the battery terminals while recording the results of such short circuit. The temperature and current levels were registered, the results are presented on Fig. 14 ÷ Fig. 24.

Fig.15. The plot of current and temperature during short circuit of LiFePO₄ 8Ah battery

The tested lithium iron phosphate batteries were judged as very safe for operators. During the short circuit test the LiFePO₄ 160Ah and 8Ah batteries have neither exploded nor ignited, despite reaching high temperature and high current values. The battery with 160Ah capacity has endured the short circuit for 730 seconds with average current value of 942A. A LiFePO₄ 160Ah battery should supply a current of 3C in 900 seconds, while during the test the recorded value indicated over 6C in almost 800 seconds. After 650 second mark, the battery safety vent activated and released an intense stream of white colored gas cloud from inside the battery (Fig. 14). It has to be stated that vented gasses from a LiFePO₄ battery are vary noxious (they are literally boiling and decomposing electrolyte). Apart from normally expected gasses created during combustion of organic materials, such as CO₂, CO, H₂, CH₄, C₂H₄, C₂H₆, C₃H₆, C₂H₅F₁ and others, other toxic compounds like HF (hydrogen fluoride) and POF₃ (phosphorous oxyfluoride) are present, derived from fluorine used as lithium battery electrolyte [26].

Fig.16. View of LiFePO₄ 8Ah battery, after the short circuit test

The short circuit test of 8Ah battery went similar, with one notable difference, when after 20 second mark a rapid rise of case temperature was recorded, after 60 seconds the enclosure began to swell and after 120 seconds the vent opened (Fig. 15). Whole process of short circuit took about 2 minutes with average current of 80A. During the test, the battery achieved the maximal current value of 10.3C (while manufacturer allows 3C max.). The tested LiFePO₄ batteries demonstrated very good parameters regarding the safety of operation. The neither exploded, nor ignited and thus did not created a danger for human life and health (Fig. 16). The plates of 160Ah LiFePO₄ battery did not ignite even when exposed to open flames (Fig. 17). When operated in proper conditions, this type of battery can be successfully used in electric vehicles for more than 10 years, while retaining their properties (Table 1).

Fig.17. An unsuccessful attempt of ignition of LiFePO₄ battery plate

During test run of Li-PO battery, a rise in temperature with an almost simultaneous swelling of battery case (Fig.19) was observed after about 6s from the beginning of terminal short. After about 14s the case seal was broken, releasing vapors into surrounding atmosphere. Any further activity ceased after 30s mark (Fig. 18). It is worth noticing, that the Li-PO battery has shown a capability to supply an enormous current of 102C (with manufacturer stated max. of 25C) with only 1Ah total capacity. The battery did not ignite or explode during this test.

Fig.18. The plot of current and temperature during short circuit of Li-PO 1000mAh battery

Fig.19. View of Li-PO 1000mAh battery, after the short circuit test

Fig.20. The plot of current and temperature during short circuit of Li-Ion 2200mAh battery

Fig.21. View of Li-Ion 2200mAh battery, after the short circuit test

During test run of Li-Ion battery, which is at the moment the most common chemistry employed in electric vehicles, a rise in temperature was noticed after 10 seconds from the onset of short. After 32s mark the case swelling begun, and 4 seconds after that, a safety valve has opened along with a slight emission of gasses and a squirt of electrolyte. The duration of emission was very short (Fig. 20). During the test, the average current achieved was 21C (4.5C max as stated in the datasheet) for about 50 seconds, with nominal battery capacity of 2.2 Ah. The battery did not ignite or explode during this test (Fig. 21).

To compare the operational properties, a primary battery using Li-SOCl₂ chemistry and 13Ah capacity was also tested. After 30 seconds from shorting of terminals, the battery temperature began to rise. In the next 3 seconds the case begun to swell, and after 52s from the start of the test, the battery exploded and begun to violently emit fire (Fig. 22, Fig. 23).

Fig.22. The plot of current and temperature during short circuit of Li-SOCl₂ 13Ah battery

Fig.23. View of Li-SOCl₂ 13Ah battery, after the short circuit test

Fig.24. Plot of currents and temperatures during the short circuit battery tests

Despite igniting and loosing containment, the battery continued to supply current for next 15 seconds. During the test, the batter was able to source current on the order of 3.9C, while the max. allowable discharge current is stated as 0.14C. This test confirmed, that this battery type is unsuitable for electric vehicles, due to real possibility of explosion and fire emission during extreme stress.

Results

The conducted tests have proven, that:

• with dropping temperature, the battery internal resistance rises, which limits the capacity to supply energy. Because of this fact, the application of thermal conditioning systems (heating and cooling) in electric vehicles is recommended, both when the vehicle is moving and when it is stationary. The battery temperature is crucial parameter, it is important that the battery temperature should be 5°C or higher before beginning of the vehicle operation,
• battery overheating can result in exothermic reaction and possibly destroy the battery completely,
• battery overcharge can destroy its internal structure. Assurance of proper BMS operation (balancing and equalization) is of utmost importance,
• short circuit testing resulted in battery venting and release of hot electrolyte. It has to be emphasized, that all tested rechargeable batteries performed adequately, meaning that none of them have ignited nor exploded. It proves that currently produced batteries are high quality. Unfortunately, a lot of data in the Internet contain reports of traction batteries which exploded or ignited,
• state of charge (SOC) of the battery has impact on the amount of heat emitted during the test. The more fully charged a battery was, the more heat it emitted,
• in order to increase safety level for all battery types, a new type of electrolyte could be designed, which during conditions of overheat, overcharge or short circuit would not emit any toxic compounds,
• correctly designed, batteries for electric vehicles should have capacity to withstand: low and high ambient temperature; overheating; short circuit conditions; high pressure inside the casing; excessive charge and discharge currents; low voltage due to greater than nominal depth of discharge (DOD); over voltage resulting from overcharge; shocks and impacts during collisions,
• following the proper operation procedures (maintaining recommended temperature and voltage ranges) should protect the user from nasty surprises while simultaneously provide long and stress free battery life.

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Author: dr inż. Andrzej Łebkowski, Akademia Morska w Gdyni, Katedra Automatyki Okrętowej, ul. Morska 83, 81-225 Gdynia, E-mail: andrzejl@am.gdynia.pl.

Source & Publisher Item Identifier: PRZEGLĄD ELEKTROTECHNICZNY, ISSN 0033-2097, R. 93 NR 5/2017. doi:10.15199/48.2017.05.13

Introduction

Motor configuration

Motor experiments

Method of improving starting ability

Conclusions

INTRODUCTION

Field Measurements

Simulations

Power Factor Correction

Recommendations

Introduction

Analysis of the DC Air Conditioner with Rotary Compressor

Simulation of Air Conditioner

Conclusion

Introduction

Heat Accumulators and Heat Storage Systems

The Analysis of Possibility of Heat Accumulators and HSS Use in the ORC Power Plant Powered by the Heat Source with Changeable Characteristic

Modulation of the heat source characteristic

Ensure of additional vapour inlet to the expander

Initial heating of working medium

Assist in CHP realization

Summary and Conclusions

INTRODUCTION AND MODEL DEVELOPMENT

SIMULATION RESULTS

SUMMARY

Introduction

Description of overvoltage measurement using CVT

Design and temperature coefficient of the C3

Overvoltage tests in laboratory

Conclusions

INTRODUCTION AND MODEL DEVELOPMENT

SIMULATION RESULTS

SUMMARY

Introduction

Standards for testing of electricity meters connected to the network

Standards for testing of electricity meters disconnected from the network

Automatic Test Systems

Calibration uncertainty of electricity meters at fundamental frequency

Conclusions

Introduction

Increased reliability of power supply

Two-sided power supply

Generators

Batteries

Uninterruptible Power Supply (UPS)

Introduction

External Cooling

External Heating

Overcharge

Short Circuit

Results

Design and temperature coefficient of the C₃