Electrical and Electronics Engineering An Internat ional Journal ELELIJ Vol  No  August   A
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Electrical and Electronics Engineering An Internat ional Journal ELELIJ Vol No August A

J Ghanizadeh S H Hosseinian G B Gharehpetian Electrical Engineering Department Amirkabir Univer sity of Technology Tehran Iran ghanizadehhosseiniangrptianautacir BSTRACT This paper presents methods to compensate and monit or the disturbance generate

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Electrical and Electronics Engineering An Internat ional Journal ELELIJ Vol No August A




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Electrical and Electronics Engineering: An Internat ional Journal (ELELIJ) Vol 2, No 3, August 2013 1 A. J. Ghanizadeh, S. H. Hosseinian, G. B. Gharehpetian Electrical Engineering Department, Amirkabir Univer sity of Technology, Tehran, Iran (ghanizadeh/hosseinian/grptian)@aut.ac.ir BSTRACT This paper presents methods to compensate and monit or the disturbance generated by electric traction units, considering their position in different time s, in a railway system. For this purpose, first of all, experimental data of Italy traction system is used and its components are

modeled. Then, using propose d algorithm a suitable location for a passive filter is determined. Subsequently, considering Speed of t raction units, the location of each traction unit is predic ted and with proposed THD index, created disturbanc e in each time is determined. Finally, in the span of 1 minute, proposed index is monitored. It is worth mentioning that the Matlab / Simulink software is u sed to simulate proposed model. EYWORDS Total Harmonic Distortion, Power quality, Electric traction system, Monitoring, Harmonic filtering 1. NTRODUCTION With increasing the number of non-linear

loads, the main requirement of any power system is to supply electricity with a determined power quality and reliability to minimize possible cost. As well known, traction systems can cause distortion a nd harmonic in shape of voltage and current waves and these harmonics can lead to unacceptable effects like energy loss, communication interference and the like. As a result, attention h as to be paid to improve their operations. In literature, there are attentions in this serious pr oblem. In [1-3], effect of electric traction system s is analyzed on power quality. In references [4, 5],

interaction between AC and DC electric railway systems, which cause turbulence and reduce the quality of the network, has been studied. In addition, reference [4] investigates the use of AC/DC converters in electric railway system that causes voltage and current distortions. In [6a], a DC electric traction system has been modelled and Static Var Compensator (SVC) and a filter was a dded to the distribution network to improve the power quality problems. The interconnection bet ween the new European railway lines (25 kV/50 Hz) and the existing DC 3kV Italian railway l ines has been presented in

[7a]. Analysis of the filters has been done in order to mitigate the effects between the two systems. A harmonic study for a simplified model of line in a traction system without considering earth effect is done in [8]. Subsequently, reference [9] proposed a bett er model for transmission line considering earth return path with time domain modeling. So far, no s tudy on DC traction system is done that be able to analyze Total Harmonic Distortion (THD) ind ex with considering speed and position of traction units and all components (filters, feed li nes and motors) are modeled completely. In

this paper firstly, using Matlab/Simulink softwa re, all components of traction system are modeled and then using proposed algorithm a suitabl e location for a passive filter is determined. Subsequently, considering speed of traction units, the location of each traction unit is predicted and THD index is monitored in each bus of traction system. It is worth mentioning that THD
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Electrical and Electronics Engineering: An Internat ional Journal (ELELIJ) Vol 2, No 3, August 2013 2 index is monitored over the time of 1 minute in dif ferent states. The First state is when there is

no filter in traction system. The second state is when passive filter, determined by proposed algorithm, is located on proper location. Finally, the third state is when all traction units have their suitable filter. This paper is organized as follows: in the next sec tion, different components of Italy traction system are modeled using Matlab/Simulink software a nd proposed algorithm to determine suitable location of passive filter is defined. Fin ally, in section 3, simulation result and analysis is shown. 2. ESCRIPTION OF THE RACTION YSTEM The electrical power system in study is a part of e

lectric traction system in Italy [4]. This system is shown in Fig. 1. This system is fed by a 380 kV, 1000 MVA bus. Also, this system consist of a AC traction unit, 25 kV, 50 Hz, and four DC tracti on units, 3 kV and with 6 pulse AC/DC converters 132 kV, 5.4 MW. Moreover, total active p ower absorbed by AC traction station and each DC traction stations are equal to 54 MW and 4. 1 MW respectively. Figure 1. Three-phase transmission system along wit h AC and DC electric railway systems Subsystem of AC and DC traction units are shown in Fig. 2. Moreover data of lines, transformers and linear

loads are listed in table 1, 2 and 3.
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Electrical and Electronics Engineering: An Internat ional Journal (ELELIJ) Vol 2, No 3, August 2013 3 Figure 2. (a) DC traction system subsystem, (b) AC traction system subsystem L km c nf/km x /km r /km n kV ) Line Type Lines 3.85 220 0.122 0.0291 132 Cable 1-2 24 8.5 0.424 0.172 132 Overhead 1-3 700 0.046 0.04 20 Cable 1-7 17 8.5 0.424 0.172 132 Overhead 3-4 18 8.5 0.424 0.172 132 Overhead 4-5 8.16 220 0.122 0.0291 132 Cable AT-2 Table 1. Lines data x (%) r (%) /V (kV/kV) (MVA) Trans. 13 0.2 380/132 250 AT 14 0.8 132/20 25 T1 14 0.8

132/20 25 T2 14 0.8 132/20 25 T3 Table 2. Transformer data Qn (MVar) Pn (MW) Vn (kV) Bus 6 8 20 6 21.8 20 20 7 Table 3. Linear loads data 2.1. DC line model Considering the movement of train between two stati ons, amount of electric parameters of DC line are changing perpetually. As a result, for acc urate analysis of power quality index in traction system, it is needed to model these changes complet ely. According Fig. 3, train in each time, is located in special position with special speed.
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Electrical and Electronics Engineering: An Internat ional Journal (ELELIJ) Vol 2, No

3, August 2013 4 Figure 3. Spatial status between the two train stat ions To model position and speed of railway in power qua lity calculation, first of all, parameters per length of DC line should be determined. Table 4 lis ted these parameters. 1.37 H/m l= /L 0.5 /m r = R/L 20 pF/m c = C/L Table 4. Electrical parameters of line Now with these parameters and speed characteristic of train that shown in shown in Fig. 4, model of DC line can be obtained. As Fig. 4, shown, it is assumed that railway start moving from first station and with accelerating movement arrive to ma ximum speed after t1

seconds. Then, continue with the same speed until t2 that railway reduces its speed to stop at the second station at tmax. To model the position of train and the effect of DC line in simulation, every moment, the train speed and distance traveled by it computes. After t hat, considering amount of length that is determined by speed of train and Table 4, electric parameters of DC line are determined. Since the distance between stations, about 1.5 km is assu med, the appropriate model for the DC line, pi model is considered. Figure 4. Speed characteristics of the train sets w ith time variations

2.2. Motor model There are different kinds of DC electric motors tha t feed by DC current. Series motors have high initial torque, hence suitable for electric railway s. In addition, in equal load, series motors consume fewer current in comparing with other elect ric motors. In traction systems, both series and independent excitation motors are used. In [4], railway motors are modeled by resistor. It is clear that this model is so simple and it is not reliable. In this paper, a perfect model is used. A s mentioned, a series motor is used to model
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Electrical and Electronics

Engineering: An Internat ional Journal (ELELIJ) Vol 2, No 3, August 2013 5 railway motor. In addition, considering speed chara cteristic of railway, speed of motor in each time is given as input to the model of motor. 2.3. Harmonic filtering Using power electronic converter in electric transp ortation systems such as electric trains causes a lot of harmonic levels inject to distribution netwo rks. Harmonic filters are used to limit the harmonic currents flowing into the upstream network . The filter could be located on the loco itself or at the substation. Because of different t ype of trains

running simultaneously on the same traction section move in a section, the best place can be offered to install them, are traction posts [10]. Passive, active and their mixture (hybrid) are thre e kinds of filters. Passive filters as classic methods for power quality improvement of distributi on systems consist of series LC tuned for removing a specific harmonic or blocking a bandwidt h of severe harmonics of nonlinear loads current. These filters have low impedances for the tuned frequencies such as 5th and 7th. Low cost is a great benefit of these filters. To reduce the overall amount of

distortion, after calculatin g the amount of THD index at every bus of system, the proposed algorithm, choose two higher harmonic to set parameters of filter. With considering the location of filter, three stat es are discussed in this paper. Firstly, using proposed algorithm, the proper location for filter in one station is determined and THD index is monitored in each bus. In Second state, without any filter in system, THD index in all buses are monitored. Finally, with locating filter in each ra ilway, THD index in third state is monitor in each bus. 2.4. Description of the Matlab model The

power system block set of Matlab/Simulink is de sign tools that can be build the simulation models for electrical power system. Part of Simulin k model of whole system which consists of DC and AC electric substation (ESS) is proposed in Fig. 5. The model that has been used in the train simulation that consists of inverter and DC l ine and DC machine is shown in Fig. 6. 3. IMULATION ESULTS Harmonic has undesirable effects in the network, su ch as reduction in transformers efficiency and more losses in motors; therefore, identification of the disturbance and determination amount of them and

finally its reduction in the electric trai n system is important. In this section several simulations on the system i n figure .1, has been done. Let the maximum speed of train be 100 km/h and the radius of the wh eels of train is 0.406m. t1, t2 and t3 respectively 5, 55 and 60 seconds have been conside red. Sampling time is 5*10-5. In the first simulation, motor of train and DC line is modeled w ith resistance and assumed that no filter is installed.
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Electrical and Electronics Engineering: An Internat ional Journal (ELELIJ) Vol 2, No 3, August 2013 6 Figure 5. Part of

traction system simulink model The value of THD on each bus has been calculated. I n order to perform the harmonic analysis of voltage and current signals present in the traction system, the proposed algorithm, shows graphically the harmonic spectrum of the analyzed s ignal. For example, the voltage of bus no. 5 (phase A), and the amount of THD and harmonic spect rum is given in Fig. 7. As shown in this figure, the value of 5th and 7th harmonics are10.69 6% and 8.297% respectively. The value of THD% in other buses of system is given in Table 5. Figure 6. The whole simulink model of DC-ESS


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Electrical and Electronics Engineering: An Internat ional Journal (ELELIJ) Vol 2, No 3, August 2013 7 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 -1 -0.5 0.5 V5 (phase A) time (s) 100 200 300 400 500 600 700 10 Fundamental (60 Hz)= 0.961803 THD= 13.6133 Mag (% of 60 Hz component) Frequency (Hz) Figure 7. Voltage of bus 5 and its harmonic spectru m bus7 bus6 bus5 bus4 bus3 bus2 bus1 phase 10.491 10.479 13.613 13.084 12.044 9.924 10.024 A 8.871 8.863 16.323 15.665 14.365 11.543 11.685 B 12.174 12.163 17.406 16.850 15.731 13.258 13.388 C Table 5. The amount of THD% for other

Buses In the next step, to reduce the amount of THD index , the proposed algorithm chooses two higher harmonic to set parameters of filter and then place d it at different buses. Results are shown in Table 6. It is noted that the installation of filter reduces the amount of THD. If the average amount of total harmonic distortion at all buses, for each test as a criterion for measuring the different scenario to be considered, best achieved when the filter is int ended to be installed in the bus no. 3. That improves the value of THD from 12.759% to 3.65%. In the next simulations, a perfect model

is used to simulate the DC line and motor of train. To see their effect and monitor the value of THD% at any m oment in time, Assumed that train will move toward from one station to another station. For exa mple, the amount of THD for bus no.1 (phase B), at different moments of train moving, is shown in Fig. 8. Position of passive filte bus phase Without filter bus1 bus2 bus3 bus4 bus5 b us6 bus7 1 A 10.0235 1.64037 1.62761 2.45633 3.92694 4.57236 9 .41162 9.59333 B 11.685 3.01672 3.03987 3.49987 3.81001 4.15739 9. 68616 9.92667 C 13.3882 4.10133 4.07718 4.59243 5.88083 5.73307 1 1.3269

11.6200 2 A 9.9236 1.61876 1.60169 2.44448 3.94148 4.56619 9. 3311 9.51086 B 11.5434 2.96903 3.00251 3.51618 3.8289 4.14885 9. 57276 9.80969 C 13.2575 4.0327 4.04721 4.59865 5.91932 5.72974 11 .2279 11.5177 3 A 12.0438 3.76292 3.95992 2.6075 3.39185 4.42345 11 .7456 11.8828 B 14.3654 5.10691 5.30555 3.34679 3.55694 4.08937 1 2.6588 12.8921 C 15.7311 5.61073 5.69912 4.67579 5.24526 5.64176 1 3.9325 14.2012
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Electrical and Electronics Engineering: An Internat ional Journal (ELELIJ) Vol 2, No 3, August 2013 8 4 A 13.0836 5.18738 5.41696 3.06023 3.30901 4.18818 1 2.9098 13.0258 B

15.6649 6.59954 6.83678 3.97497 3.76406 3.91534 1 4.1113 14.3364 C 16.8504 6.79105 6.9038 5.1680 5.42461 5.64513 15. 1844 15.4394 5 A 13.6133 5.93366 6.17495 3.53583 3.44305 4.20007 1 3.4974 13.6021 B 16.3225 7.40997 7.66147 4.5263 3.90406 4.01243 14 .8521 15.0709 C 17.4057 7.45839 7.57841 5.58978 5.56641 5.91137 1 5.8098 16.0565 6 A 10.4787 3.2043 3.1544 3.48213 4.47295 4.79036 2.5 4488 2.6123 B 8.86261 1.29654 1.32918 1.91481 2.52157 3.39341 3 .75009 3.40301 C 12.1628 4.21491 4.19796 4.12115 4.59194 4.66916 4 .98671 4.6568 7 A 10.4907 3.21498 3.16414 3.4965 4.48288 4.79907 2. 55052 2.43059 B

8.87125 1.2986 1.33186 1.91879 2.52799 3.40076 3. 75392 3.56571 C 12.1741 4.22785 4.21067 4.13379 4.60088 4.67655 4 .99271 4.81052 Avg 12.75915 4.22365 4.301011 3.65049 4.195759 4.603048 9.896999 9.998304 Table 6.The value of THD% at different buses of sys tem, for different scenario of passive filter posit ion 10 20 30 40 50 60 10 15 20 25 30 35 40 Instantaneous Voltage THD(%) for Bus1 THD% Time(s) Figure 8. THD index at different moments of moving train in the span of 1 minute (no filter) Considering that the number of simulated cases is h igh, only some of the state is expressed. Fig. 9

represents the results for the prior case with the difference that the filter is installed in system. The results for other buses in system for the recen t case are shown in Fig. 10. Variable and nonlinear characteristics of the electric railway s ystem always cause harmonic distortion, especially in the beginning to move and stop. 10 20 30 40 50 60 Instantaneous Voltage THD(%) for Bus1 Time(s) THD(%) Figure 9. THD index at different moments of moving train in the span of 1 minute (with filter)
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Electrical and Electronics Engineering: An Internat ional Journal (ELELIJ) Vol 2,

No 3, August 2013 9 Figure 10. Instantaneous THD at different Buses in the span of 1 minute (with filter) Hence one basic and inexpensive way to improve the power quality is using passive filter. If the parameter of this filter is selected as optimal, th en this approach has required efficiency. Electric railway system is complex, as it includes electronic converter along with systems like track, electrical motor, control and mechanical par ts. Future work will be devoted to a more detailed modeling of the train, simultaneous moveme nt of two trains in a section and using of active filter for

improving power quality. 4. ONCLUSION Harmonic has undesirable effects in the network, su ch as reduction in transformers efficiency and more losses in motors; therefore, identification of the disturbance and determination amount of them and finally its reduction in the electric trai n system is important. For evaluation of system performance considering the power quality, it is ne cessary to select appropriate indicators. In this paper, the THD harmonic distortion index, which is famous for the power quality studies, was used. Due to changes in train speed and location at different moments,

the value of the index is change. In this paper, considering speed of tractio n units, the location of each traction unit is
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Electrical and Electronics Engineering: An Internat ional Journal (ELELIJ) Vol 2, No 3, August 2013 10 predicted and THD index is monitored in each bus of traction system at each moment of time. Subsequently, proposed algorithm trying to improve the THD using the appropriate filter set and suitable location of passive filter is defined. EFERENCES [1] A. Capasso: The Power Quality Concern in Railwa y Electrification Studies., Proceedings of 8th IEEE PES

International Conference on Harmonics and Quality of Power, Athens (Greece), Vol. 2, 1998, pp. 647-652. [2] R.E. Morrison: Power Quality Issues on AC Tract ion systems., Proceedings of 9th IEEE PES International conference on Harmonics and Quality o f Power, Orlando (USA), Vol. 2, Oct. 2000, pp. 709-714. [3] M. Brenna, F. Foiadelli, and D. Zaninelli: E lectromagnetic model of high speed railway lines fo r power quality studies., IEEE Transactions on Power System, Vol. 25, No. 3, 2010, pp. 1301–1308. [4] L. Battistelli, P. Caramia, G. Carpinelli, D Pr oto: Power Quality Disturbance Due to

Interaction between AC and DC Traction System., Proceedings of the IEE International Conference on Power Electronics, Machine and Drives PEMD, Edinburge, Ap ril, 2004, pp.492-497. [5] L. Battistelli, P. Caramia, G. Carpinelli, D La uria, D. Proto: A Power Quality Compensation Device for Interacting AC-DC Railway Systems., IEEE Power Tech Conference, St. Petersburg, 27-30 J un 2005, pp. 1-6. [6] J. Martinez, G. Ramos: Reactive Power and Har monic Distortion Control in Electric Traction Systems., 2010 IEEE/PES Transmission and Distribution Confere nce and Exposition: Latin America, Sao Paulo,

Brazil, 8-10 Nov. 2010, pp. 190 -195. [7] M. Brenna, F. Foiadelli: Analysis of the Filt ers Installed in the Interconnection Points Between Different Railway Supply Systems., IEEE Transactions on Smart Grid, Vol. 3, No. 1, Mar ch 2012, pp. 551-558. [8] J. Holtz and H.J. Klein: The propagation of har monic currents generated by inverter-fed locomotive s in the distributed overhead supply system., IEEE Transactions on Power Electronics, Vol. 4, No. 2, April 1989, pp. 168-174. [9] P.C. Coles, M. Fracchia, R.J. Hill, P. Pozzobon and G. Sciutto: Modeling and simulation of supply current

interference in traction systems arising fr om multi-level converters in high-power locomotive drives., Proc. of 5th European Conference on Power Electroni cs and Applications, Brighton UK, Vol. 7, 13-16 September 1993, pp. 24-28. [10] P. Kiss and A. Dn: The Application of the Do uble Domain Simulation by Different Harmonic Filtering Methods of 25 kV Electric Traction System s., Proceedings of 13th IEEE International conference on Harmonics and Quality of Power, Vol., 2008, pp. 1-6. Authors’ information Ahmad Javid Ghanizadeh was born in Herat, Afghanistan, in 1981. He receiv ed his

B.Sc. and M.Sc. in electrical engineering from Saha nd University of Technology, Tabriz, Iran and Ferdowsi University of Mashhad, Mashhad, I ran, in 2004 and 2009, respectively. He is currently pursuing the Ph.D. de gree in the electrical engineering department at the Amirkabir University of Technolog y (AUT), Tehran, Iran. His research interests include Power Quality, power system optim ization and operation and transformers transients. Seyed Hossein Hosseinian was born in 1961 in Iran. He received both the B.Sc . and M.Sc. degrees from the Electrical Eng. Dept. of Amirkabir University of

technology, Iran, in 1985, and 1988, respectively, and PhD degree in Ele ctrical Engineering Dept, university of Newcastle England, 1995. At the present, he is the associate Professor of Electrical engineering Department at the Amirkabir University of Technology (AUT). His especial fields of interest include, Power Quality, Restruct uring and Deregulation in power systems.
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Electrical and Electronics Engineering: An Internat ional Journal (ELELIJ) Vol 2, No 3, August 2013 11 Gevork. B. Gharehpetian received his BS, MS and Ph.D. degrees in electrical engineering in 1987, 1989

and 1996 from Tabriz Univ ersity, Tabriz, Iran and Amirkabir University of Technology (AUT), Tehran, Iran and Te hran University, Tehran, Iran, respectively, graduating all with First Class Honor s. As a Ph.D. student, he has received scholarship from DAAD (German Academic Exchange Ser vice) from 1993 to 1996 and he was with High Voltage Institute of RWTH Aachen, Aachen, Germany. He has been holding the Assistant Professor position at AUT fro m 1997 to 2003, the position of Associate Professor from 2004 to 2007 and has been Professor since 2007. The power engineering group o f AUT has been

selected as a Center of Excellence on Power Systems in Iran since 2001. He is a member of this center. He was selected by the ministry of hig her education as the distinguished professor of Ira n and by IAEEE (Iranian Association of Electrical and Ele ctronics Engineers) as the distinguished researcher of Iran and was awarded the National Prize in 2008 and 2010, respectively. Prof. Gharehpetian is a senio r and distinguished member of IEEE and IAEEE, respectivel y, and a member of the central board of IAEEE. Since 2004, he is the Editor-in-Chief of the Journa l of IAEEE. He is the author of

more than 500 journ al and conference papers. His teaching and research in terest include power system and transformers transi ents and power electronics applications in power systems .