SCs III F 2. MOV/airgap F 1

Transcription

1 Protection and Fault Locating ethod of Serie Compenated Line by Wavelet Baed Energy raveling Wave Yu Liu, Student ember, IEEE; Saki eliopoulo, Fellow, IEEE; engling ai, ember, IEEE; Liangyi Sun, Student ember, IEEE and Boqi Xie, Student ember, IEEE Abtract: Serie capacitor (SC) in tranmiion line increae the complexity of tranmiion line protection. In thi paper, a wavelet baed energy traveling wave protection and fault locating method for erie compenated tranmiion line i propoed. he method require GPS ynchronized meaurement at both end of the line. he paper firt preent the propagation propertie of tranient current with different frequency, and then a proper frequency band condition i generated to minimize the tranient attenuation. he method ue energy traveling wave in certain frequency band extracted by wavelet tranform, and the wavefront time difference of two meaurement unit at each end of tranmiion line i introduced for the purpoe of executing tripping logic and computing fault location. umerical imulation verify that the method provide a robut protection criterion and an accurate fault locating method, independently of type, fault impedance and location along the line. he algorithm alo work for different SC location, and it i not influenced by OV/air gap operation. Key word: Serie Capacitor (SC), tranmiion line protection, etal Oxide Varitor (OV), wavelet tranform, energy traveling wave. S I IROUCIO ERIES Capacitor (SC) can improve tability of power ytem, increae tranmiion capability, reduce loe and damp ub-ynchronou ocillation. he preence of SC change the continuity of the line inductive impedance and create protection problem uch a voltage/current inverion [-]. oreover, the operation of the etal Oxide Varitor (OV) and the air gap may change the compenation ratio of the line and generate additional tranient, cauing additional protection problem [-]. In the tranmiion ytem of Fig., SC are located at ide of tranmiion line. Overcurrent protection, ditance protection and directional element will all confront ome iue. Fault F may caue mi-operation of overcurrent protection and ditance protection at relay I, becaue SC reduce the impedance between F and relay I; to prevent relay I from overreaching, the protection zone hould be hortened. Additionally, with the fault at F, directional element at relay II may fail to operate, while directional element at relay III and IV may mi-operate, due to capacitive impedance between F and relay II. Enabled by communication between two end, pilot Yu Liu, Saki. eliopoulo, Liangyi Sun and Boqi Xie are with the School of Electrical and Computer Engineering, Georgia Intitute of echnology, Atlanta, GA USA ( yliu@gatech.edu, aki.m@gatech.edu, lun@gatech.edu, airxbq@gatech.edu). engling ai i with Shanghai Jiao ong Univerity, Shanghai, China ( nltai@jtu.edu.cn). protection of tranmiion line i uually more reliable than ingle-ended protection. However, phae/direction comparion protection, pilot ditance protection and line differential protection till have their own limitation in erie compenated tranmiion line. Firt, phae/direction comparion protection may fail during fault F, ince directional element at relay II may ee a current in revere direction. Second, pilot ditance protection may fail to trip fault F, ince the hortened protection zone of relay I will not ee fault F, and relay II may wrongly conider it a an external fault. oreover, the widely adopted line differential protection alo ha it own problem due to ditributed capacitance, current inverion and limited enitivity during high impedance fault []. F III IV II SC OV/airgap F Fig.. ranmiion ytem with SC any attempt have been made to addre thee iue of erie compenated line protection. Girgi et al [6] propoed a Kalman and adaptive Kalman filtering approach. hi method i baed on the aumption that SC will be bypaed during fault, which i not trictly correct ince ome internal fault with lower fault current may not trigger OV or air gap operation. Fault ection method [7-8], which identify whether SC exit in the fault loop, are propoed to calculate fault location by conidering the impedance of SC. hee approache do not conider the uncertainty of the SC block (SC, OV, air gap) reactance due to nonlinear V-I characteritic of OV a well a the air gap. Pattern claification and feature extraction ha been alo propoed to determine the fault location via neural network-baed procedure [9-]. hee method are enitive to ytem change, and require large training et and long training time. ranient traveling wave contain plenty of information and can be ued in analyzing and locating the fault [-]. everthele, recent method rarely conider the attenuation of the traveling wave. In fact, ince the traveling wave i a broad-band ignal, it attenuation propertie a tranmitting /reflecting at each dicontinuity of the line (fault, erie capacitor, bue, etc.) are different for different frequency component. Conequently, in order to increae the accuracy of wavefront detection, the paper extract the tranient ignal in a proper frequency band. Wavelet tranform ha been widely ued in power ytem to analyze tranient ignal, extract characteritic on different frequency band, and capture I V VI

2 feature of propagating wave on tranmiion line due to it multi-reolution capability. he modulu maxima of wavelet tranform can detect harp variation of ignal [-] which i very ueful to preciely locating the wavefront. In thi paper, wavelet tranform i ued to extract traveling wave in certain frequency band. he time difference between the arrival of the firt wavefront at both end of the tranmiion line i introduced to determine fault location and enable trip deciion. umerical imulation reult are provided to demontrate the effectivene of thi algorithm. II PROPAGAIO PROPERIES OF RAVELIG WAVES When a fault occur, high frequency broad-band traveling wave are generated and propagate along the tranmiion line. At each dicontinuity, the traveling wave partially reflect and partially tranmit generating more traveling wave. he fault location can be calculated by detecting the firt wavefront arrival time of traveling wave (uually current traveling wave) at both end of the tranmiion line. he accuracy of thi fault locating method largely depend on the accuracy of the wavefront detection. Bu capacitance and the tranmiion line erie capacitance influence the attenuation of traveling wave and make the detection of the wavefront challenging. he accuracy of traditional traveling wave algorithm may be compromied. In thi ection, we will analyze the effect of SC and bu capacitance on different frequency component of current traveling wave, from which we can find a proper frequency band that enable higher accuracy detection of the wavefront via wavelet tranform. Fig. how a typical ytem with SC. It include bue P,, and Q with bu capacitance C. here are tranmiion line P, and Q with urge impedance Z, Z and Z, repectively. Bu and alo have branche with equivalent urge impedance Z and Z, repectively. SC with capacitance C are intalled in tranmiion line. Here erie reitance and hunt conductance are neglectable compared to erie reactance and hunt uceptance of the tranmiion line. Alo, ditributed capacitance C Line and inductance L Line are approximately contant, which reult in a contant urge impedance LLine C Line. ext, we will analyze the criterion of a proper frequency band to minimize current traveling wave attenuation along the line. Here four poible fault location F ~F are conidered. he current traveling wave are meaured at the location of relay I and II. P C F F F Z Σ Z II Z Z I Z Σ Z Fig. ranmiion line ytem with SC A. Reflection and Refraction of Fault Current ranient Reflection and refraction propertie of fault current tranient F Q with frequency f are aeed below. ) At SC, the input urge impedance i Z, and the output urge impedance i Z j. Current wave refraction coefficient i, Z j Z Z ( Z j ) j Z Current wave reflection coefficient i, Z ( Z j ) Z ( Z j ) j Z he current ratio between output and input current at SC i, j Z j Z () ) At bu with bu capacitance C, for the current wave traveling from P to, the input urge impedance i Z, and the output urge impedance i Z ( j ) Z. Current wave refraction coefficient i, Z, Z ( j ) Z Z () ZZ ZZ ZZZ j Z Z Z Z Z Z Z Z Z j Current wave reflection coefficient i, Z Z ( j ) Z, Z Z ( j ) Z Z Z Z j Z Z Z Z Z Z Z Z Z j Z Z Z Z Z Z he current ratio between the output and input current traveling wave at bu i, Z ( j ), ( f), ( f) Z Z ( j ) (6) ZZ Z Z Z Z Z Z Z Z Z j ) At bu with bu capacitance C, for the current wave traveling from Q to, imilarly, the current ratio between the output and input current traveling wave i, ZZ, (7) Z Z Z Z Z Z Z Z Z j B. Proper Frequency Band Condition Conider relay I in Fig. a an example. Four poible fault location F ~F were conidered to invetigate the characteritic of wave with pecific frequency f. ) If fault occur at F, the current traveling wave will not be influenced by neither SC nor bu capacitance. ) If fault occur at F, the current traveling wave will be attenuated by SC. In order to identify a proper energy frequency band to accurately detect the firt wavefront, we hould let, (8) ) If fault occur at F, the current traveling wave will be attenuated by both the bu capacitance at bu and SC. We () () ()

3 hould let, ( f) ( f) (9), ) If fault occur at F, the current traveling wave will be attenuated by the bu capacitance at bu. We hould let,, ( f ) () From equation (), (6), (8), (9) and (), we get the proper frequency band condition, CZ f f () where max ZZ ZZ ZZ ZZ ZZ ZZ fmax min, () ZZ ZC ZZ ZC Similarly, relay II can alo derive the ame concluion a relay I. In ummary, if the condition above i atified, the current traveling wave attenuation along the line will be relatively mall. he detection i deigned to focu on thi frequency band of the traveling wave to obtain the bet enitivity in determining the fault location, which in turn will improve line protection. III WAVELE RASFOR he firt application of wavelet tranform i to effectively extract proper frequency band elected in Section II. he input ignal pae through a high pa filter and a low pa filter repectively, uffer a down ampling, and produce detail coefficient ( i ) a well a approximate coefficient (A i ), correponding to different frequency band. Continue thi proce with A i to generate i+ and A i+ ( i,, ), a illutrated in Fig.. After calculating correponding coefficient, we can recontruct the waveform to obtain tranient wave in pecific frequency band. he econd application of wavelet tranform i to reliably capture harp variation of ignal by the modulu maxima. hi feature i ued to detect the wavefront of the traveling wave. A Signal A Fig. Proce of extracting frequency band by wavelet tranform IV PROPOSE ALGORIH We propoe the ue of an energy traveling wave algorithm which provide very good enitivity. Energy traveling wave i a calculated energy equence of a ignal, where each energy point i obtained within the energy calculation time t energy. Fig. demontrate thi proce with ampling frequency f. Here the current meaurement at both end of the tranmiion line were ued. efine energy calculation time a t energy ; -phae current at both end a i,a, i,b, i,c, i,a, i,b and i,c. hu, the energy calculation data at time t contain 6 current equence, () t () t () t () t () t () t i, i, i, i, i and i, with tenergy f, a, b, c ampling point each., a, b, c Signal Computation Energy traveling wave tenergy f Fig. Calculation of energy traveling wave o calculate the value of the energy traveling wave (energy point) at time t, formulate mode current a follow, i i i i ( j, ) () ( t) ( t) ( t) ( t) j,mode j, a j, b j, c After that, adopt normalization for computed current, i ( n) i ( n) i ( j,) () ( t) ( t) ( t) j,norm j,mode j,mode where n i et to be integer from ~ ( tenergy f ). Here we chooe orthogonal, biorthogonal aubechie wavelet and ue wavelet tranform to calculate detail coefficient () and recontruct high frequency ignal t with band mentioned in equation (). Subequently, we calculate () t correponding energy E. j, tenergy f ( t) ( t) j, j ( ) (,) () i E i j Finally, after formulating energy traveling wave at both end, capture the wavefront time and by the modulu maxima of wavelet tranform, and compute time difference. he relay hould operate if, l v (6) where l i the length of the monitored tranmiion line, and v i the peed of traveling wave. he ditance between ide and fault location d f i, f d l v (7) Fig. how time-domain calculation proce of thi algorithm, where t f. t i,a i,b i,c i,a i,b i,c t t kt t t energy t t energy ) t) kt) E, E, E, Capture wavefront time Capture wavefront time by wavelet tranform by wavelet tranform Combining and to get fault location ) t) kt) E, E, E, Fig. Calculation proce in time domain j t

4 Wavelet tranform reult Energy in.khz-.khz frequency band V SIULAIO RESULS A 6 Hz, kv tranmiion ytem, a hown in Fig. 6, ha been ued for numerical imulation. he compenated line under protection i - line, with 8-mile length and.% compenation (.8 mf) intalled at ide. he bu capacitance i. μf. he urge impedance of all line i. ohm. hree phae current are meaured at two end of line -. According to equation () and (), the computed frequency band i,.6 Hz f.76 khz (8) Here we chooe frequency band. khz~. khz, t energy = m, and ampling rate 8 kilo-ample per econd (k/). ranient wave tranmit in two mode, ground mode and line mode, with two different traveling peed [6]. In thi ytem, the ground mode peed i, / 8 v [( L L )( C C )].7 m / (9) g m m he line mode peed i, / 8 v [( L L )( C C )].9 m / () l m m hu, we hould ue the larger peed v l in () for wavefront detection. ext, everal event are tudied to evaluate the performance of our propoed method. P P P P P P G G Fig. 6 umerical imulation ytem A. Event : Bolt Internal Fault A. ohm phae C- internal fault occur at mile from ide. Fig. 7 depict the energy traveling wave and the wavefront detection enabled by the modulu maxima. From Fig. 7 (a), the energy front occur at both end of the tranmiion line after fault. he modulu maxima in Fig. 7 (b) preciely capture the exact wavefront time difference.7.. m. From equation (6), the relay will correctly trip the line. From equation (7), the fault location i d f =.96 mile. hu, the method can rapidly trip internal fault and provide accurate fault location in milli-econd. B. Event : High Impedance Internal Fault A kohm phae C- internal fault occur at mile from ide. Fig. 8 depict the energy traveling wave and the wavefront detection enabled by the modulu maxima. We can oberve the wavefront time difference i.87..m. he relay can rapidly trip thi internal fault and G preciely locate the fault at d f =. mile. 6 x - Reult at ide Reult at ide at ide at ide.... ime after fault (milli-econd) x - Reult at ide Reult at ide odulu aximum at ide - -6 odulu maximum at ide ime after fault (milli-econd) (b) Front detection by the modulu maxima Fig. 7. Simulation Reult - Internal Fault: (C- fault; impedance:.ω; location: - line, ide mile) C. Event : Bolt External Fault A. ohm phae BC- external fault occur inide -P line, at mile from ide. Fig. 9 depict the energy traveling wave and the wavefront detection enabled by the modulu maxima. We can oberve the wavefront time difference i..87.6m. Since it violate equation (6), the relay will not trip.. icuion () OV/air gap operation. he energy traveling wave algorithm can avoid the OV/air gap operation ince they alway operate after fault occur and thi algorithm only detect the time of the firt wavefront. () ifferent location of SC. From the analyi in Section II, the location of SC (at the middle of the line or at terminal of the line) will not impact the proper frequency band of the energy traveling wave and the fault detection procedure. () Limitation of the method. he main limitation of the method i that the fault detecting/locating accuracy highly depend on the ampling rate. Related to thi iue i that, there exit deadzone for internal fault near terminal, to enure ecurity of relay during external fault. hee diadvantage exit in mot of the traveling wave baed protection/locating method. A poible olution i to coordinate with other legacy protection cheme that can detect fault near terminal.

5 Wavelet tranform reult Energy in.khz-.khz frequency band Wavelet tranform reult Energy in.khz-.khz frequency band x -7 Reult at ide Reult at ide at ide at ide ime after fault (milli-econd) 6 x -6 Reult at ide Reult at ide odulu aximum at ide odulu aximum at ide ime after fault (milli-econd) (b) Front detection by the modulu maxima Fig. 8. Simulation Reult High impedance internal Fault: (C-G fault; impedance: kω; location: - line, ide mile) x - Reult at ide Reult at ide at ide at ide ime after fault (milli-econd) x - Reult at ide Reult at ide odulu aximum at ide odulu aximum at ide ime after fault (milli-econd) (b) Front detection of by the modulu maxima Fig. 9. Simulation Reult - External Fault: (BC- fault; impedance:.ω; location: -P line, ide mile) VI COCLUSIO hi paper propoed a wavelet tranform baed energy traveling wave method to accurately determine the location of a fault in erie compenated line and thu to improve protection of thee line. Reflection and refraction propertie of tranient current at bue and erie capacitor are analyzed. By finding a proper frequency band baed on ytem parameter where attenuation of energy traveling wave i relatively maller, the imulation reult how that the algorithm can rapidly detect and locate internal bolt/high impedance fault. he accurate detection of the fault location make the protection of the line dependable and ecure. he algorithm i not influenced by OV/air gap operation, and work for different location of erie capacitor. While there exit deadzone for fault near terminal, it can be coordinated with other legacy protection cheme to enure ecure intantaneou trip for the entire length of the line. REFERECES [] S. K. Salman,. Rajoo, and V. Leitloff, Invetigation of the inertion of erie capacitor in high voltage on the etting of ditance protection, in Proc.Conf. evelop. Power Syt. Protection,, pp [].S.Sidhu,. Khederzadeh, Serie compenated line protection enhancement by modified pilot relaying cheme, IEEE ran. Power el., vol., no., pp. 9-98, July. 6. [] R. J. artilla, Performance of ditance relay HO element on OV protected erie compenated tranmiion line, IEEE ran. Power el., vol. 7, pp , July. 99. [].. Saha, B. Katenny, E. Roolowki, and J. Izykowki, Firt zone algorithm for protection of erie compenated line, IEEE ran. Power el., vol. 6, pp. 7, Apr.. [] S. He, J. Suonan, Z.Q. Bo, Integrated Impedance-Baed Pilot Protection Scheme for the CSC-Compenated EHV/UHV ranmiion Line, IEEE ran. Power el., vol. 8, no., pp. 8-8, Apr.. [6] Girgi, A.A., Sallama, A.A., and Karim El-din, A. An adaptive protection cheme for advanced erie compenated (ASC) tranmiion line, IEEE ran. Power eliv., 998,, pp.-. [7] Reye-Archundia, E., oreno-goytia, E.L. Analyi of the Effect of a High Power Electronic Controller on Electrical Grid during Faulted and Pot-Faulted Condition Uing Wavelet, in th Int. Power Electronic Congr. (CIEP),, pp -. [8] Samantaray, S.R., ah, P.K. Wavelet packet-baed digital relaying for advanced erie compenated line. Gener. ranm. itrib., 7,, [9] B. Bachmann,. ovoel,. Hart, Y. Hu, and.. Saha, Application of artificial neural network for erie compenated line protection, in Proc. Int. Conf. Intelligent Syt. Applicat. Power Syt., 996, pp [] Song, Y.H., John, A.., and Xuan, Q.Y. Artificial neural network baed protection cheme for controllable erie-compenated EHV tranmiion line, IEE Proc. Gener. ranm. itrib., 996, (6), pp.-. []. Kezunovic, Smart fault location for mart grid, IEEE ran. Smart Grid, vol., no., pp., ar.. [] Ying Zhang, engling ai, and Bin Xu. Fault Analyi and raveling- Wave Protection Scheme for Bipolar HVC Line, IEEE ran. Power el., vol. 7, no., pp. 8 9, July.. [] Chui, Charle K. An Introduction to Wavelet. San iego: Academic Pre, 99. [] Wei Chen, O.P. alik, Xianggen Yin, ehu Chen, Zhe Zhang. Study of Wavelet-Baed Ultra High Speed irectional ranmiion Line Protection, IEEE ran. Power eliv., vol. 8, no., pp. -9, Oct.. [] A.H. Oman, O.P. alik, ranmiion Line itance Protection Baed on Wavelet ranform, IEEE ran. Power eliv., vol. 9, no., pp. -, Apr.. [6] A.P. Saki eliopoulo, Power Sytem Grounding and ranient: An Introduction. ew York, arcel ekker, Inc, 988, pp.8-9.