Analysis on the Effect of the Nonlinear Resistance on the Locomotive Operating Overvoltages

Transcription

1 Energy and Power Engineering, 3, 5, doi:.436/epe.3.54b36 Published Online July 3 ( Analysis on the Effect of the Nonlinear Resistance on the Locootive Operating Overvoltages Zhengqing Han, Donglin Zhang, Yuning Wu, Shibin Gao School of Electrical Engineering, Southwest Jiaotong University, Chengdu, China Received February, 3 ABSRAC With the application of the articulated phase insulator, and the speed of electric locootive rising, it is inevitable for the electric locootive to adopt the technology autoatic passing through the electric phase separation. However, when the locootive passes the electric phase separation, a variety of overvoltages will be generated, such as the cut-off overvoltage and the closing overvoltage. In this paper, the causes of the two overvoltages above are analyzed theoretically and siulated in Siulink. hen this paper discusses the suppression effects on the cut-off overvoltage and the closing overvoltage by paralleling the nonlinear resistance and the ain breaker, or parallelling the nonlinear resistance and the locootive transforer. he siulation results show that parallelling the nonlinear resistance and the locootive transforer has suppressive effects on the two overvoltages entioned above. Keywords: Articulated Phase Insulator; Switching Overvoltage; Nonlinear Resistance; SIMULINK. Introduction he application of the articulated phase insulator can eliinate the echanical hard point proble caused by the device phase separation, and increase the reliability of the electric locootive. With the speed rising, the tie interval of passing through the phase separation is reduced. When the electric locootive passes through the electric phase separation, the traditional approach relies on the driver s operation, deoting and closing auxiliary otor, and disconnecting ain breakers in order. After the locootive passes, it is then operated in the reverse order, so the pantograph can pass through phase separation in the non-current way, ensuring the service life of the catenary and pantograph []. he ethod is not adopted in the odern railway syste because of its frequent operation and low safety factor, so it becoes a necessity to use the technology of autoatic passing through the electric phase separation (including the vehicle auto-passing phase separation, colun auto-passing phase separation, ground switching auto-passing phase separation []). When the locootive passes autoatically through the phase separation, the operation of ain breaker will cause the cut-off overvoltage and the closing overvoltage, which are analyzed in literature [3]. As the generated overvoltage threatens the running safety of locootive, it is iportant to find the corresponding suppressive easures to ensure the safe operation of the electric locootive. his paper analyzes the causes of the cut-off overvoltage and the closing overvoltage when passing through the phase separation with adopting the cobination of the ground installations and the colun switch. Literature [6] researched the RC coponents suppressor. Literature [], [6] entioned the suppression of nonlinear resistances, but both were with no siulations. his paper discusses the suppressive effects of the operating overvoltage by using Matlab.. Electric Process Analysis.. he Cut-off Overvoltage he Figure that can found in [7] shows that the locootive passes through the phase separation with the cobination of the ground installations and the colun switch. When the electric locootive passes point A, the ain breaker is autoatically disconnected, with the huge current being cut off which generates arcs. If the interrupters are not strong enough, the electric locootive will rush through the phase separation charged, leading Figure. he scheatic diagra of electric locootive passing the articulated phase insulator. Copyright 3 SciRes.

2 44 Z. Q. HAN E AL. to the daage of the pantograph and catenary. In severe cases, it will result in the traction substation tripped accident. Otherwise, it will generate high cut-off overvoltage... he Closing Overvoltage After the locootive passes through the phase separation to point B, the breaker is required to be closing to resue power. his operation of the breaker ay generate the closing overvoltage whose peak is related to the catenary voltage. And locootive auxiliary winding and asynchronous auxiliary cluster are still in the working state. Soe otors act as the electrootor, while others act as the generator, so the auxiliary systes can be seen as a power. he voltage of auxiliary, which is called the residual voltage, can be coupled to the priary side of the locootive transforer, whose peak is related to the nuber of auxiliary otors. Due to the presence of residual voltage, the coplete response of the closing circuit is the superposition of the zero-state response and the zero-input response, which ay increase the peak of overvoltage, and even lead to the tripped accident of the traction substation. 3. he Equivalent Circuit of the Overvoltage 3.. he Equivalent Circuit of Cut-off Overvoltage According to the characteristics of the traction network that the line reactance is uch bigger than the resistance, the intercepting overvoltage equivalent circuit is set up as shown in Figure. L is the su of the equivalent reactance of the traction substation and the contact line. C is the circuit equivalent capacitance of the circuit ground. L is the locootive s ain circuit, while C is its equivalent capacitance to earth. As seen in Figure that can found in [], an equation can be drawn as follows. du C udt dt L Naely, du dt u () LC Figure. he equivalent circuit of the intercepti ng overvoltage. Assuing that the two initial values are u and u ', the Equation () can be siplified by using Laplace transfor. U s ' su u s L C Using the inverse transforation of Laplace to si- the Equation (), plify jwt jwt ' jwt jwt u jwue e ue e jw ' u cos w t u sin w t / w (3) u ( u / w ) sin w t ' where w / L C and arctg uw ' u Whe n the current is cut off, it is known that u E cos and i I sin. hen the conclusion can be drawn as both the inductive current and the ca- could not utate. pacitance voltage u E cos ' u I sin / C I E / fl f N / LC () K is the ratio of intercepting overvoltage to the trac- tion voltage. K u Because of ' N ( u / w ) f cos sin E f f N (4) (5) f, K can be approxiately seen as K f N sin (6) f Fro Equation (6), it could be obtained that the inter- overvoltage is proportional to the circuit reso- cepting nance frequency and the contact line when the current is cut down. 3.. he Equivalent Circuit of Closing Overvoltage After the locootive passes through the phase separation, the circuit can be equivalent as shown in Figure 3 for the oent the switch is on. he paraeters in Figure 3 [8] are basically the sae with the ones in the Figure. In Figure 3, L L and C C. herefore, the influence of L, C can be ignored, the differential equation can be listed as follows: du R RC u () dt L udt e t (7) Copyright 3 SciRes.

3 Z. Q. HAN E AL. 45 nary = 7.5 kv, L =.749 H, C =.85e-9F, C =.973e-F, L =.H. Figure 3. he equivalent circuit of the closing overvoltage. Naely du du R ' () RC u e t (8) dt dt L Due to the effect of residual voltages, the forula above can be seen as a constant coefficient second order linear inhoogeneous differential equation, whose solution includes the zero-input response and zero-state response. he zero-input response he zero-input responses of the forula (8) is RC du dt And the eigenvalues are P, du R u dt L RC RC L C he initial value can be defined as u E f sin aand u E f sin a. (9) () E f denotes the residual peak, the equation (9) can be siplified by using Laplace tr ansfor as follows: U() s RCSu u RCS S R / L he zero-state response of circuit is ux pu pu e e p p p p pt pt () () he zero-state response Defining et E sin wt, the ipulse response can be got with the zero-state response. he ipulse response is got as follows: / RC pt pt ht () e e (3) p p he zero-state response is: t d uf f h t (4) he coplete response of the syste is the su of both the zero-input response and the zero-state response. 4. Siulation 4.. Siulation of the Cut-off Overvoltage Based on the theoretical analysis, a large nuber of si- out by using the odel in Siulink. ulations are carried he siulation paraeters are as below: voltage of cate- Figure 4(a) shows high voltages will not be generated when disconnecting the ain breaker while the voltage of catenary reaches. Figure 4(c) shows it will produce an overvoltage with the peak value reaching 9.9 kv when disconnecting the ain breaker while the voltage of catenary reaches its peak value. he value 9.9 kv is 3.34 ties of the noral peak value, and far beyond the regulated voltage level of the safe operation of the electric locootive. 4.. Siulation of the Closing Overvoltage he closing operation needs to be done after the locoo- tive passed through the phase separation. Different peak values of the closing overvoltage will be generated when the catenary voltage is in different phases. he siulation results Figure 5 (a) show that higher overvoltage will not be caused when the phase of the catenary voltage is around or 8. While the phase of the catenary voltage is around 9 or 8, the Figure 5 (b), (c) show the peak value of the overvoltage reaches 74 kv, which is far beyond the regulated voltage level of the safe operation of the electric locootive. 5 x (a) he phase of the catenary voltage being x (b) he phase of the catenary voltage being 45 x (c) he phase of the catenary voltage being 9 Figure 4. he cut-off overvoltage caused by differen t phases of the catenary voltage. Copyright 3 SciRes.

4 46 Z. Q. HAN E AL. /V Ua 4 x (a) he phase of the catenary voltage being x (b) he phase of the catenary voltage being 45 Fcn (User-defined function: I*(u/V) ^alap), V eter (volteter), and a first-order transfer function []. Figure 6(b) shows the characteristics of the siulation circuit. Figures 6(c), (d) and (e) respectively show the voltage wavefor, the current wavefor and the volt-apere characteristics. Figure 6(e) presents the properties of nonlinear resistance when its terinal voltage changes. When the terinal voltage is sall, its resistance value is infinity, and when its terinal voltage is up to a certain extent, its resistance value reduces to zero quickly. hese properties are called as the claping voltage effect which can be used to suppress the cut-off overvoltage and the closing overvoltage..5 x (c) he phase of the catenary voltage being 9 Figure 5. he closing overvoltage caused by different phases of the catenary voltage. 5. Suppression Measures 5.. Model of the Nonlinear Resistance he overvoltage has a serious influence on the safe operation of the electric locootive. he traditional deoting operation ais to decrease the levels of the overvoltages, but it is no longer suitable for the high-speed train, so better suppression easures involving hardwares need to be found. Usually, in power systes, transient voltages caused by direct lightning strikes are prevented by installing arrester (MOA) [9]. he arrester itself is a kind of nonlinear resistance (MOV), coposed of ZnO (the ain ingredient) and a few other etal oxygen content additives that are used to constitute grain boundaries phase and iprove soe properties of the arrester []. If the device is specially processed to lower its voltage level, the arrester can be installed in electric locootive to suppress the operating overvoltage. he following is the analysis of the arrester s characteristics and the suppression effects on the two overvoltages entioned above. According to the characteristics of the nonlinear resistance, its odel is built by using Matlab/Siulink platfor, and its features are verified through siulation. Figure 6(a) shows the structure of the nonlinear resistance odel, including CCS (Controlled current source), U/V I/A (a) he structure of the nonlinear resistance odel (b) he siulation circuit of the nonlinear resistance 5 x U/V - (c) he wavefor of the voltage x 4 (d) he wavefor of the current - - I/A (e) he volt-apere characteristics Figure 6. Model and perforances of the MOV. Copyright 3 SciRes.

5 Z. Q. HAN E AL Suppression Siulation of the Overvoltage Parallelling the nonlinear resistance and the ain breaker, the suppressive effects on the two overvoltages are shown in Figure 7 (disconnecting or closing ain breaker when the catenary voltage reaches its peak value). When parallelling the nonlinear resistance and the ain transforer of the locootive, the suppressive effects on the two overvoltages are shown in Figure Conclusions hrough theoretical analysis and siulations, the conclusions can be drawn as follows: 5 x (a) he suppressive effects on the cut-off overvoltage x (b) he suppressive effects on the closing overvoltage Figure 7. Parallelling the nonlinear resistance and the ain breaker. 5 x (a) he suppressive effects on the cut-off overvoltage 5 x (b) he suppressive effects on the closing overvoltage Figure 8. Parallelling the nonlinear resistance and th e ain transforer of the locootive. ) If the ain circuit breaker is off when the phase of the catenary voltage is close to its peak phase, the cut-off overvoltage will be very high. Otherwise, if the ain circuit breaker is on when the phase of the catenary voltage is close to its peak phase, the closing overvoltage will be very high. ) he suppressive effects on the cut-off overvoltage and the switching overvoltage by placing the nonlinear resistances in different positions are obtained. When parallelling the nonlinear resistance and the ain circuit breaker, the cut-off overvoltage can be inhibited efficiently, while the closing overvoltage cannot be inhibited; when parallelling the nonlinear resistance and the ain transforer of the locootive, both the cut-off overvoltage and the closing overvoltage can be inhibited efficiently. 7. Acknowledgeents he authors acknowledge the supports of the National Natural Science Foundation of China (Grant No and U345), the Sichuan Province Key echnology Research and Developent Progra of China (Grant No. GZ79) and the Fundaental Research Funds for the Central Universities (Grant No. SWJUCX8) REFERENCES [] C. Z. Chen, he Analysis on the Course of Electric Motive Passing though Phase Separation, 7, pp. 7-. [] Y. S. Yan, he Discussion on Electric Locootive Auto-passing the Phase Separation, Electric Drive for Locootive, Vol. 6, 999, pp. -3. [3] W. Ran, X. Li, B. Liu and Q. L. Zheng, Research on ransient Process of Ground s Auto-passing Neutral Section at Switching ie, ransactions of China Electro echnical Society, Vol. 6, No.,, pp [4] X. J. Wei, H.. Wang and Y. S. Wu, Study on the Ground Autoatic Passing the Articulated Phase Insulator with Parallel Resistance, Electric Railway, Vol.,, pp [5] Y. N. Gu, Y. Wang and H. Wang, he Analysis on Overvoltage of Electric Locootive Autoatic Passing Phase Separation, Electric Railway, Vol. 3, 9, pp. -3. [6] P. F. Yin and W. C. Du, Generation and Control of Cut-off over Voltage of a Vacuu Circuit Breaker, Electrical Switching, Vol., 5, pp [7] Y. S. Gong, Research of Over-voltages of Electric Locootive Passing the Articulated Phase Insulator, Journal of the China Railway Society, Vol. 3, No. 4, 8, pp [8] W. G. Pan, he Analyze on the ransient Process of Switch-Ground s Autoatic Passing Phase-Separation Device for raction Network of Electrified Railway, Copyright 3 SciRes.

6 48 Z. Q. HAN E AL. 8. [9] Y. L. Wang, D. Y. Zhao and S. H. Hu, Developent rends of Line Arresters, Electrical Porcelain Lightning Arrester, Vol.,, pp [] Y. J. Liang, Application of Metal Oxide Varistors in Power Syste, Beijing, Vol. 5, 997, pp [] J. Wang and G. Q. Weng, MALAB/SIMULINK Siulation and Application of Electric Power Syste, Xi an, 8, pp Copyright 3 SciRes.