TRANSIENT CURRENT BASED EARTH FAULT LOCATION FOR DISTRIBUTION AUTOMATION IN NON-EFFECTIVELY EARTHED NETWORKS

Transcription

1 C I R E D 2 t Internatonal Conference on Electrcty Dstrbuton Prague, 8- June 29 Paper 464 TRANIENT CURRENT BAED EARTH FAULT LOCATION FOR DITRIBUTION AUTOMATION IN NON-EFFECTIVELY EARTHED NETWORK XU Bngyn MA cong XUE Yongduan Plp GALE andong Unv. of Tecnology andong Unv. Keu Power Automaton Ltd. Keu (UK) Ltd. xuby@cna.com mascong22@63.com xueyd@keu.cn PlpFGale@aol.com ABTRACT A sngle pase eart fault locaton metod for dstrbuton automaton of non-effectvely earted networks s presented. It s based on comparng te smlartes of zero mode transent currents of faulty feeder, wc s measured by te correlaton coeffcent. Te correlaton coeffcent between te transent currents at te bot end of a feeder secton s close to for te ealty secton and - for te faulty secton. Te feasblty of te metod was proved by smulaton and feld test results. INTRODUCTION One of te most mportant dstrbuton automaton functons s fault locaton and solaton based on measurements n feeder termnal unts (FTUs) or fault passage ndcators (FPIs) []. Wle te locaton of a sortcrcut fault can be easly determned by comparng te overcurrent detecton results of FTUs, te dentfcaton of te secton wt a sngle pase eart fault n a noneffectvely earted system (ereafter abbrevated as eart fault) as not been satsfactorly solved as te steady state fault current s very small and very often te fault arc s ntermttent [2]. Actve metods ncludng te temporary resstve groundng metod and te sgnal njecton metod [3] can be used to dentfy te faulty secton but te passve metod, wc makes use of te fault generated sgnals only, s always preferred as t s smple, cost effectve and as no adverse effect on prmary system operaton. It as been realzed for a long tme tat fault detecton metods usng transent sgnals ave better relablty and senstvty. Te conventonal transent faulty feeder dentfcaton, or fault drecton ndcaton metod, s to compare te ntal polartes of zero mode (known as zero sequence for steady state fault analyss) voltage v and current [4]. Ts metod s prone to wrong ndcatons as te tme nterval durng wc te polartes between v and are correct vares wt fault ncepton angle and system parameters. A new transent metod wc compares te polartes of dv /dt and was developed recently []. Te new metod as muc better relablty as te polarty relatonsp between dv /dt and s always correct rrespectve of fault angle and system confguratons. However bot tese two transent metods requre te measurement of zero mode voltage, wc s usually not provded n te standard sectonalzng swtc. Anoter transent metod dentfes te faulty secton smply by detectng and comparng te magntude of zero mode transent current (ereafter abbrevated as ZMTC) lke te overcurrent prncple used for sort-crcut fault locaton. Te relablty of ts metod s poor as te magntude of downstream (after fault) ZMTC may be very close to te upstream ZMTC (before te fault) wen a large sub-network, e.g. a swtcng staton, s connected to te remote end of faulty feeder. A new fault locaton metod based on comparng te smlarty of ZMTCs captured by te FTU n te faulty feeder s presented n ts paper. It can be easly ncorporated nto a dstrbuton automaton system (DA) as no voltage measurement s needed. TRANIENT CURRENT ANALYI OF EARTH FAULT Te equvalent zero mode network of an eart fault n a non-effectvely earted network s as sown n Fg.(a), n wc e f s a supermposed or fcttous voltage source beng equal to te zero mode voltage at te fault pont. Ts equvalent network s vald for te frequency components below a crtcal frequency? wc s usually larger tan 2Hz n practcal networks and contans te domnant transent components [6]. Assume te faulty feeder s sectonalzed by two swtces and 2. Te caracterstcs of ZMTCs of te faulty feeder are analyzed as follows. To smplfy te analyss te nfluence of te Peterson col s neglected. Fault n te frst secton For a fault at pont F n te frst outgong secton, as sown n Fg.(b), te ZMTC troug crcut breaker CB of te faulty feeder s = () c were c s te current n te dstrbuted capactance of te wole network excludng te faulty feeder. Wle te ZMTCs of swtc and 2 are = c + (2) 2 co3 = (3) 2 co3 were c2 s te ZMTC n te dstrbuted capactance of te second secton, and c3 ZMTC of te trd secton. CIRED29 esson 3 Paper No 464

2 C I R E D 2 t Internatonal Conference on Electrcty Dstrbuton Prague, 8- June 29 Paper 464 Fault n te second secton For a fault at pont F2 n te second secton, as sown n Fg.(c), te ZMTCs of CB, and 2 are F C e f c f C C c C C C c C C 2 e f C 2 F 2 C2 f C2 C 3 C 3 e f F 3 C3 C3 Fg.. Te equvalent crcut n te zero mode network for faults n dfferent feeder sectons Fault n te second secton For a fault at pont F2 n te second secton, as sown n Fg.(c), te ZMTCs of CB, and 2 are = (4) c = co () co = (6) 2 co3 were c s te ZMTC n te dstrbuted capactance of te frst secton. Fault n te trd secton For a fault at pont F3 n te second secton, as sown n Fg.(d), te ZMTCs of CB, and 2 are = (7) c f = co (8) co = (9) 2 co co c2 Te caracterstcs of ZMTC of faulty feeder In te equvalent network of Fg., c, c, c2 and c3 are all capactance currents stmulated by te same voltage source, wc means tey ave smlar waveforms. Terefore te caracterstcs of ZMTC of a faulty feeder can be summarzed as:. Te ZMTC of an upstream swtc (before te fault) s te current n all te dstrbuted capactance before te swtc ncludng all ealty feeder capactance, te source capactance and te busbar capactance. It as opposte drecton as te fault current flows from te fault to te busbar. 2. Te ZMTC of a downstream swtc (after te fault) s te current of all dstrbuted capactance after te swtc. It as postve drecton as te current flows from te fault to te remote end. 3. Te ZMTCs of all upstream (or downstream) swtces ave smlar waveforms. 4. Te ZMTCs of swtces at bot sdes of te faulty secton ave smlar waveforms but opposte polartes. Te above summares are obtaned wlst neglectng te transent current of te Peterson col. Tese summares are approxmately true for practcal ZMTCs as te transent current of a Peterson col s very small compared wt capactve currents n te feeders. FAULT LOCATION METHOD To dscrmnate and solate an eart fault, te master staton of te DA needs to know wc secton of wc feeder s faulty. Ts can be aceved by collectng and processng te transent fault sgnals. Wle tere s already a well establsed transent faulty feeder dentfcaton metod, te faulty secton dentfcaton metod usng te ZMTCs of a faulty feeder s descrbed as follows. Recordng of ZMTC After an eart fault occurs, te master staton of te DA collects te ZMTCs recorded by all te FTUs nstalled along te faulty feeder. Te recordng of ZMTC s trggered wen te magntude of ZMTC exceeds a preset tresold. Te ZMTC can be obtaned by a zero mode CT or by summatng te tree pase currents. Te samplng frequency Te samplng frequency sould be ger tan 4 khz as te frequency of te domnant transent components s normally less tan 2 khz. A low pass flter wt 2 khz cutoff frequency s used to remove te g frequency components above wc te feeder cannot be modelled by ts capactance. A samplng frequency of about 6 khz CIRED29 esson 3 Paper No 464

3 C I R E D 2 t Internatonal Conference on Electrcty Dstrbuton Prague, 8- June 29 Paper 464 s can be used n practcal applcatons as a compromse between effectveness of sgnal utlzaton and burden of data processng and transmsson. Te data wndow Te transent of an eart fault usually lasts for 2 or 3 cycles. A data wndow of a quarter cycle s used n practce to reduce te volume of data to be transmtted. Ts data wndow can effectvely guarantee te relable faulty secton dentfcaton as t contans enoug transent sgnals. Calculaton of waveform smlarty Te faulty secton can be dentfed by comparng te smlartes between te ZMTCs of two swtces at opposte ends of te secton (abbrevated as two end ZMTCs). Te smlarty of two ZMTCs a (k) and b (k) can be examned by calculatng ter correlaton functon,.e. ρ ( n) = N a ( k + n) b( k) k = = N 2 a k = = N 2 ( k ) b ( k ) were k s samplng sequence; N s te lengt of data wndow; n s samples sfted between two ZMTCs. It s obvous tat te cross correlaton coeffcent s for two completely smlar waveforms, and - for two smlar waveforms wt opposte polartes. Practcally t s dffcult to syncronze te data recordng of two FTUs. Tere may be a tme sft of a few samples between two recorded ZMTCs. Terefore te actual correlaton ρ n of two smlar ZMTCs may reac ts functon ( ) maxmum value wen n s an nteger around zero. Two ZMTCs wll be dentfed to be smlar f ter? max s larger tan a tresold?, wc can be set as.7 n practcal applcaton, Faulty secton dentfcaton Havng collected all ZMTCs captured by FTUs on te faulty feeder, te master staton can dentfy f a secton s faulty by calculatng te correlaton coeffcent between two end ZMTCs. A secton s dentfed as te faulted one f te? max between ts two end ZMTCs s less tan te tresold?, wc ndcates te two ZMTCs are not smlar. Wle for a ealty secton te? max between ts two end ZMTCs s close to as ter waveforms are smlar. Consderng te fault at pont F2 as sown n Fg.() for example, te frst secton wll be dentfed as a ealty secton as? max between and wll be close to, and te secton two s dentfed as te faulty secton as? max between 2 and 3 wll be a negatve value. Te detecton starts wt te frst secton and contnues untl te faulty secton s found. Very often te downstream crcut of a faulty feeder as lmted lengt and ts transent capactve current s too small to trgger te recordng of ZMTCs. If ts s te case, only upstream = ZMTCs are avalable n te master staton and te secton after te last FTU wc as recorded te ZMTC wll be assumed to be te faulty one. IMULATION REULT Te proposed fault locaton metod as been tested by ATP-EMTP smulaton of a compensated kv overead lne network as sown n Fg.2. Te system s overcompensated wt 8% resonance drft. Te aeral mode mpedance of te lne s Z =.7 + j.38ω / km and te admttance s b = j3.4µ s/ km. Te zero mode mpedance s Z =.23+ j.72 / kmand te zero mode Ω admttance s b = j.884 s / km. Faults were placed on µ feeder 6. Te feeder s set to connect to a swtcng staton at ts remote end to allow te downstream ZMTC to ave reasonable magntude to better llustrate te metod. Te total lengt of outgong feeders of te swtcng staton s 23 km. Te dstrbuted feeder model s employed wen computng te transent sgnals. Te fault ncepton angle was set at 9. Te samplng frequency of ZMTC sgnals s set as 6kHz and all ZMTCs used are preprocessed by a 2kHz low pass flter. A quarter cycle data wndow s used Fg.2. Te smulated dstrbuton network Te calculated results of te correlaton functons for faults n te tree sectons are lsted n Table, were ρ max s te maxmum correlaton coeffcent between ZMTCs of CB and and ρ 2max s maxmum correlaton coeffcent between and 2. It can be seen very clearly from te smulaton tat te maxmum correlaton coeffcent s close to for te ealty secton and a negatve value for te faulty secton. Terefore te faulty secton can be dentfed relably by calculatng and comparng correlaton functons of ts two end ZMTCs. Table Te calculated results of correlaton functons Case ρ max 2max ρ Fault At F n te frst secton At F2 n te second secton At F3 n te trd secton Fg. 3 sows te two end ZMTCs of secton and secton 2 respectvely for a fault at F2. It can be seen tat two end CIRED29 esson 3 Paper No 464

4 C I R E D 2 t Internatonal Conference on Electrcty Dstrbuton Prague, 8- June 29 Paper 464 ZMTCs of te frst secton, wc s ealty, ave almost dentcal waveforms and two end ZMTCs of te second secton, wc s faulty, ave smlar waveform but wt opposte polartes. (A) (A) Fg.3. Te smulated ZMTC waveforms (a) Te two end ZMTCs of te secton between CB and ( Two waveforms are overlapped); (b) Te two end ZMTCs of te secton between and 2 FIELD TRIAL REULT Te algortm was tested usng feld data from an artfcal fault wt te DA of a kv ralway dstrbuton network n Ganzou, Jangx provnce, Cna. Te network as an solated neutral. Te feeder montored s 6km long and segmented by 4 sectonalzng swtces, as sown n Fg.4. An nductance s placed at te remote end to compensate te capactve current. (A) - Fg.4 Te ralway dstrbuton feeder for feld tral Xaojang Tes (A) - Tes Datang (a) (b) Fg.. Te recorded ZMTCs of an artfcal fault (a) Te two end ZMTCs of te secton between Tes and Xaojang; (b) Te two end ZMTCs of te secton between Tes and Datang Te fault was placed near Tes taton. Te feeder was suppled by te Xnfeng substaton wt te crcut breaker CB2 n Longnan substaton beng open. Fg. (a) sows two end ZMTCs of te ealty feeder between Tes and Xaojang staton wose maxmum correlaton coeffcent s.96. Fg. (b) sows two end ZMTCs of te faulty feeder between Datang and Tes statons, wose maxmum correlaton coeffcent s -.9. Te test results demonstrate tat te faulty secton can be dentfed relably usng te correlaton metod. CONCLUION An eart fault locaton metod for dstrbuton automaton of non-effectvely earted networks s presented. It s based on te caracterstc of faulty feeder ZMTCs were te two end ZMTCs of a ealty secton ave smlar waveforms and te two end ZMTCs of a faulty secton ave smlar waveforms but wt opposte polarty. Te metod as satsfactory relablty and senstvty as t makes use of transent currents wc as muc larger magntude tan te steady state current and s almost unaffected by te Peterson col. It does not requre te measurement of zero mode voltage and terefore can be easly appled nto a practcal DA. REFERENCE [] Dstrbuton Automaton Workng Group, June 27. "Dstrbuton Automaton", IEEE Tutoral Course, UA. [2] Xue Yongduan, Xu Bngyn, Ma cong, Wang Tao, 28. "Practcal Experences wt Faulty Feeder Identfcaton Usng Transent gnals". Developments n Power ystem Protecton (DPP), [3] Cong We, Pan Zencun, Zeng Gang, et al.28. "tudy on ngle Pase to Ground Fault te Locaton Metod Based on Injecton gnal and GM ort Message", Developments n Power ystem Protecton (DPP), [4] Letonen M, Hakloa T, 996. Neutral eartng and power system protecton. Vaasa, Fnland: ABB Transmt Oy Publcaton. [] Xu Bngyn, Xue Yongduan, L Tanyou, Gale, P.F., 24. "Protecton and montorng of nonsoldly earted networks". Developments n Power ystem Protecton, RAI Centre, Amsterdam, Te Neterlands,vol.2, [6] Xue Yongduan, Xu Bngyn, Cen Yu, et al. 22. "Eart Fault Protecton Usng Transent gnals n Non-soldly earted Network". PowerCon, Kunmng, Cna. BIOGRAPHIE XU Bngyn was burn n 96 and awarded P.D by X an Jaotong Unversty, Cna, n 99. He studed n Te Cty Unversty, UK, from Oct. 998 to Oct., 99 as part of splt-p.d tranng program. He s now Carman of te board of Keu Power Automaton Co. Ltd., Cna and a regstered professor of andong Unversty of Tecnology. Hs researc nterests are fault locaton and CIRED29 esson 3 Paper No 464

5 C I R E D 2 t Internatonal Conference on Electrcty Dstrbuton Prague, 8- June 29 Paper 464 montorng of power networks and dstrbuton automaton. MA cong was burn n 98 and awarded P.D by andong Unversty, Cna, n Dec., 28. Hs researc nterests are power system protecton and fault locaton. CIRED29 esson 3 Paper No 464