Fault Diagnosis Based on ANN for Turn-to-Turn Short Circuit of Synchronous Generator Rotor Windings

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1 J. Electromgnetic Anlysis & Applictions, 2009, 3: doi: /jem Published Online September 2009 ( 187 Fult Dignosis Bsed on ANN or Turn-to-Turn Short Circuit o Synchronous Genertor Rotor Windings H. Z. MA, L. PU Electricl Engineering Deprtment, Hohi University, Nnjing, Chin. Emil: hhumhz@163.com, pu.ln@hotmil.com Received Mrch 15 th, 2009; revised June 8 th, 2009; ccepted June 26 th, ABSTRACT Rotor winding turn-to-turn short circuit is common electricl ult in stem turbines. When turn-to-turn short circuit ult hppens to rotor winding o the genertor, the genertor terminl prmeters will chnge. According to these prmeters, the conditions o the rotor winding cn be relected. However, it is hrd to express the reltions between ult inormtion nd genertor terminl prmeters in ccurte mthemticl ormul. The stisctory results in ult dignosis cn be obtined by the ppliction o neurl network. In generl, the inormtion bout the severity level o the genertor ults cn be cquired directly when the ulty smples re ound in the trining smples o neurl network. However, the ulty smples re diicult to cquire in prctice. In this pper, the reltions mong ctive power, rective power nd excittion current re discovered by nlyzing the genertor mm with terminl voltge constnt. Depending on these reltions, novel dignosis method o genertor rotor winding turn-to-turn short circuit ult is proposed by using ANN method to obtin the ult smples directly, without destructive tests. Keywords: Genertor, Rotor Winding, Turn-to-turn Short Circuit, ANN, Dignosis 1. Introduction The sttisticl mteril orm Chin Electric Reserch Institute indicted tht the rotor winding turn-to-turn short circuit is common electricl ult in genertor [1,2]. However, minor turn-to-turn short circuit will not ect the norml opertion o genertor unit, so it is oten ignored. But i this ult develops, something serious will pper, such s remrkble incresing o rotor current, higher temperture o winding, decesing o rective power, distortion o voltge, vibrtion o genertor unit nd mny other mechnicl ults. Thereore, estimtion o the erly signs o ilure severity nd its develop trends cn be mde bsed on the identiiction o the ult s erly signls, nd this tsk hs grdully become importnt in condition-bsed mintennce o genertors [2,3]. At present, there hve been mny scholrs studying in the monitoring o rotor winding turn-to-turn short circuit worldwide [2 5]. Albright proposed dierentil serch-coil test method: Its dignosing eect is good or genertor under on-lod nd three phse short circuit, but * This work project ws supported by Ntionl Nturl Science Foundtion o Chin (No ), Chin Eduction Ministry s Foundtion Progrm or Excellent Young Techers in Universities nd Importnce Nturl Science Foundtion o Hohi University. one-time loction is diicult to mke under lod nd it is not sensitive to minor turn-to-turn short circuit. Russin scholr B. T. Crsmn proposed to detect turn-to-turn short circuit bsed on the circulting current in sttor prllel brnch, but this method depends on the structure o sttor winding. Trvelling-wve method bsed on online dignosing technique or rotor winding turn-to-turn short circuit is immture. The lternting impednce method nd loss method re oten-dopted in experiment, but the method cn not give n ccurte conclusion in monitoring miner rotor winding turn-to-turn short circuit ll the time. Further more, it is diicult to relize with the ection o the ctors like slot wedge etc. [6 8]. This pper nlyses the ult mechnism nd mm (mgnetomotive orce) or genertor rotor winding turn-to-turn short circuit. It discovers tht when the mchine terminl voltge is in the condition o constnt, there exist certin reltions mong ctive power, rective power nd ield current. Thus it inds kind o experiment on the electricl engineering which does not need to crry on destructiveness experiment, but cn obtin ult smple. And then it mkes use o rtiicil neurl network to crry out ult dignosis or genertor rotor winding turn-to-turn short circuit.

2 188 Fult Dignosis Bsed on ANN or Turn-to-Turn Short Circuit o Synchronous Genertor Rotor Windings 2. Cuses o Rotor Winding Turn-to-Turn Short Circuit The cuses o rotor winding turn-to-turn short circuit minly include mnucture nd opertion. For exmple, the mounting o rotor end winding is not irm; spcer block becomes loose; the trimming o leding wire soldered joint is not good; there re remining metl scles inside rotor protective ring; the dynmic orces such s centriugl orce cuse displcement deormtion o high-speed rotting rotor winding; the choking o rotor winding cuses locl overheting, which mkes turn-to -turn insultion to burn down. Otherwise, while the genertor is operting or converting rom the sttic stte to the dynmic stte, due to the brsion o the turn-to-turn insultion or the reltive disloction cused by the reltive motion between the turns in rotor, the turns my contct ech other. When this ult hs developed to certin extent, the turn-toturn shot circuit will hppen. As result o the emergence o this, the Eective mgnetic ield o genertor will decrese, nd the genertor rective power will be ected. Those led to imblnce in the mgnetic circuit which cuses vibrtion, nd then monopole potentil nd monopole current will be produced to mgnetize the genertor sht seriously. In ddition, prtil over heting in ult point my be extended to grounding ult in rotor windings. 3. Mm Bsed Anlysis o Electromgnetic Chrcteristics o Genertor Rotor Winding Turn-to-Turn Short Circuit 3.1 Anlysis o Mm under Rotor Winding Turn-to-Turn Short Circuit Sptil distribution o mm in rotor windings is shown in Figure 1 Just like Figure 1(b), while the genertor units re operting normlly, the sptil distribution o Mm is trpezoidl-like, ignoring the minor intermittent o mm which is cused by the grooves. The mm will loss prtilly, while short-circuit hppens in rotor windings. This kind o loss will result in prtil loss o shorted mgnetic pole, so tht the verge nd mpliy o shorted mgnetic pole will decrese s shown in Figure 1(c). Thereore, the sptil distribution o mm in the turn-to-turn short circuit cn be considered s tht in demgnetiztion. So the equivlent eect o short-circuit cn be considered s mm with the opposite direction dding on the min mm o short circuit. The mm o rotor winding under norml condition is represented by F 0, the mm cused by short-circuited turns is represented by F, ter short circuit, the rotor mm is F F F 0 F 1 Figure 1. Sptil distribution o mm in rotor windings F F F F F E 0 E U j Ix I r Figure 2. Mgnetic-electronic potentil vector o genertors considering sturtion The mm-em vector digrm o non-slient poles genertor considering sturtion is shown in Figure 2. The ir-gp mm undmentl component F is estblished by exciting mm undmentl component F 1 nd r- mture rection mm undmentl component F, i.e. F F 1 F (1) F Reduced to the exciting mm wve, it cn be got: F F F where, F wi, w is the turn number o rotor winding; is exciting current; the phse ngle o, smller thn the ormer vlue. 1.35wk 1 wi F p I I (2)

3 Fult Dignosis Bsed on ANN or Turn-to-turn Short Circuit o Synchronous Genertor Rotor Windings 189 in time-spce vector digrm is the sme s I, w 1 is the series number o sttor winding phse, is the coeicient o sttor winding. Suppose terminl voltgeu, ctive output P nd rective output Q re invrints, then sttor current I nd power ctor ngle become invrible. And x hs little reltion to the sturtion level. E U I (r jx ). Then the ngle between E nd I is unchngeble. So tht the ngle between F nd F will not chnge. Becuse o this, F is unchngeble. I the working condition o genertor beore nd ter rotor winding ult remins unchnged, in order to stisy the ir-gp composite lux condition, I will increse, but wi does not chnge, rom this it cn be see: the reltion betweenu, P, Q, I not only mniest the stte o the rotor winding, but lso relects the eective turn number o the rotor winding. 3.2 Impct o Exciting Current on Rotor Winding Turn-to-Turn Short Circuit Dignosis The reltion betweenu, P, Q, I cn mniest the stte o the rotor winding. The exciting current i 0 o genertor under norml opertion cn be clculted by the mthemticl Eqution, nd then compred with mesured exciting current i c, the existence o rotor winding turn-to-turn short circuit cn be determined, urthermore ic i 0 the clcultion o reltive devition % i 0 100% cn be used to estimte the severity o the ult. 4. ANN Dignosis Method or Genertor Rotor Winding Turn-to-Turn Short Circuit Recently it is minly ccording to the mesurement o the genertor terminl prmeters which nmely genertor ctive power P, rective power Q, the genertor terminl voltge U, current I, ield voltge nd other genertor prmeters, uses ormul clcultion to cquire the ield current I 0 which opertes under normlly lows, nd then compre the mesurement o ctul electric current I with I 0 to dignose rotor Winding Turn-to-turn Short Circuit ult o genertors. This kind o method needs to consider the inluence o mgnetic ield sturtion, nd it needs ccurte mthemtics model nd the prmeter o genertor in the mentime. The prmeter o genertor will lso hve vriety chnge long with the operting wy nd the vriety k w chnge o operting conditions. The ccurcy o online recognition is not very high, thereore there exists certin error mrgin. The rtiicil neurl network (ANN) does not need ccurte mthemtics model nd the detiled prmeters o genertor, nd it hs no intererence to the opertion o genertor in the mentime. It only needs to mesure the genertor terminl prmeters ccurtely, nd depends on gret del o trining smples. Through suicient network trins, dignosis cn be directly crried out o the ults operted under dissimilr wys. By hving ulty smple, we cn not only dignose the ults, but lso estimte the seriousness o short-circuit. The terminl voltge U o genertor is generlly rted voltge, which could be supposed to be constnt. According to the nlysis o the bsis genertor mgnetic ield, certin P, Q will correspond to certin F, nmely certin o wi. So the reltion o P, Q nd I cn relect the turn-to-turn short circuit ult, with the genertor prmeter P, Q, I s the ANN importtion, nd circles o turn-to-turn short circuit hve the percent o totl number o ull circles % s the output. The key o the ult dignosis which crries on with ANN to is to obtin the trin smples. The selection o norml smples cn tke in vrious smples in normlly opertion in the P-Q digrm o genertor, but in the ctul power sttion or gurnteeing the ergodicity o smples, we could detect the genertor prmeters with long hours t norml opertion conditions. In order to estimte the severity o genertor ults nd the number o short-circuit turns, the ulty smples o genertors re needed. Reltively speking, to cquire the smples o the genertors under norml opertion condition is still esy, but to obtin genertor ult smples is usully very diicult. The generl method is to do destructive experiment in dynmic simultion lbortory, short connecting severl turns o the rotor windings o genertor ctitiously. This kind o method cn brely be crried out on the engineering. This pper uses the method o blncing the mm to obtin ult smple o the genertor under turn-to-turn short circuit o rotor winding. Suppose turn-to-turn short circuit ult occurs to genertor t the rted condition, beore nd ter the short-circuit, P, Q,U re constnt. By nlysing the mgnetic ield we cn know the mgnetic ield wi will mintin constnt, nd suppose the short-circuit turns o the totl rotor winding number is %, ter the ult, the ield current is: where, I N 1 I I N (3) 1 % the rted vlue o the ield current.

4 190 Fult Dignosis Bsed on ANN or Turn-to-Turn Short Circuit o Synchronous Genertor Rotor Windings Chnging the number o short-circuit turns, we will get series o ulty smples. And lso we cn cquire ulty smples under dierent opertion conditions. 5. Simultion To veriy the credibility o this method, we cn dopt culturl heritge [9] genertor prmeters, see Tble 1; nd then tke its norml operting smples. The rted operte conditions o the ult smple cn be seen in Tble 2. In Tble 2, α % is the short-turns s percentge o the totl rotor winding turns number. We cn crry out network trining, nd then crry out ult dignosis; the ult smples cn be seen in Tble 3. From Tble 3, α%(ctul) is the ctitiousness number o short-turns s percentge o the totl number o rotor winding turns in dynmic simultion lbortory. %(emultion) is the number o short-turns simulted by computer s percentge o the totl number o rotor winding turns. The bck propgtion rtiicil neurl network(bp) is used here, nd the ctive unction dopts S type unction. The BP network dopts 3 lyers. As it is shown in Figure 3, the irst lyer hs three importtion nodes, hide lyer hs our nodes, nd exporttion lyer hs one node. The genertor prmeters contin ctive power, rective power, exciting current, nd ll these prmeters re normlized vlues. Tble 3 shows the results simulted by MATLAB. According to this, the ctul results conirmed the BP network dignoses. In word, this method hs relized the direct cquisition o ult s seriousness nd the solution o ult smples cquisition which re diicult to get. In prticulr process, the current I nd the terminl voltge U o sttor windings re mesured by CT (Current Trnsormer) nd PT(Potentil Trnsormer), nd the exciting current I is mesured by current converter. Here, select the CT nd PT used to mesure system prmeters s the mesure equipment. The genertor cpcity nd voltge level decide the selection o them. And the hll current converter produced by Swiss compny LEM is used to mesure I in rotor winding. The prmeters I ndu re used to clculte both the ctive power P nd rective power Q. Ater trining, this method is pplied to ll kinds o lod. By mesuring I ndu o norml genertor in ll running sttes, we cn obtin the corresponding P nd Q by clculting. The trining o ANN needs P, Q nd I to obtin the reltionship mong the prmeters( P, Q nd I ) in ll the running sttes. 5. Conclusions While ANN is pplied to the ult dignosis o genertor, the most diicult prt is the cquirement o the Figure 3. Schemtic digrm o ANN Tble 1. Prmeters o synchronous mchine Model number MJF-30-6 Rted Voltge/V 400 Rted Current/A 43.3 Fctor 0.8 Rotor Current/A 2 w /turn 100 P(*) Active Tble 2. Dignostic ptterns in neurl trining Q(*) Rective I (*) Exciting Current α % Short-turn Number s Percentge o Totl Winding turns Number Tble 3. The comprison between the output o the neurl network nd the ctul output P(*) Active Q(*) Rective I (*) Exciting Current %(ctul) Short-turn Number s Percentge o Totl Winding Turns Number %(emultion) Short-turn Number s Percentge o Totl Winding Turns Number ult smples mong trining smples. This pper nlyses genertor turn-to-turn short circuit o rotor winding ult nd ccording to the certin opertion o genertor, nmely ctive power P, rective power Q, terminl voltgeu keep constnt, nd the ield current I in reses, but the mm F wi mintins constnt.

5 Fult Dignosis Bsed on ANN or Turn-to-Turn Short Circuit o Synchronous Genertor Rotor Windings 191 Fulty smples re obtined through direct clcultion, turn-to-turn short circuit ult o rotor winding is dignosed by mking use o rtiicil neurl network, nd we could obtin seriousness level o ult inormtion directly. Tht method cn void dmge experimenting nd it is convenient in engineering. The shortcoming o this method is tht it could not locte the ulty position. Ater dignosing nd conirming the existence o the ult, i we ssist it with other wys such s trveling wve method, loction o ult cn be crried out. REFERENCES [1] W. J. Wng nd L. Gui, Present sitution nd improvement o rely protection or lrge sized genertor trnsormer set o 600~1000MW, Hudin Technology, Vol. 30, No. 1, pp. 5 8, [2] W. Q. Li, Prevention nd ult dignosis o turbogenertor, Beijing: Chinese electric power publisher, [3] S. Wn, H. M. LI nd Y. G. LI, Anlysis o genertor vibrtion chrcteristic on rotor winding inter-turn short circuit ult, Proceedings o the CSEE, Vol. 25, No. 10, pp , [4] H. W. Fng, C. L. Xi nd J. Xiu, Anlysis o genertor electro-mgnetic torque on rmture winding inter-turn short circuit ult, Proceedings o the CSEE, Vol. 27, No. 15, pp , [5] G. G. Mo, Resons o ilures occurred in lrge cpcity turbogenertors in Chin, System Technology, Vol. 24, No. 11, pp. 1 7, [6] R. J. Streiel, R. J. Mrks II, nd M. A. EI-Shrkwi, Detection o shorted-turns in the ield winding o turbine -genertor rotors using novelty detectors development nd ield test, IEEE Trns on Energy Conversion, Vol. 11, No. 2, pp , [7] A. S. Kulkrni, M. A. El-Shrkwi, R. J. Mrks II, G. Andexler, X. Jin, nd I. Kerszenbum, Development o technique or on-line detection o shorts in ield windings o turbine-genertor rotors: Circuit design nd testing, IEEE Trns on Energy Conversion, Vol. 15, No. 1, pp. 8 13, [8] S. E. Guttormsson, R. J. Mrks II, nd M. A. EI-Shrkwi, Ellipticl novelty grouping or on-line short-turn detection o excited running rotors, IEEE Trnsctions on Energy Conversion, Vol. 14, No. 1, pp , [9] D. W. Auckl, I. E. D. Pickup, nd R. Shuttleworth, Novel pproch to lterntor ield winding inter-turn ult detection, IEE Proc., Gener., Trnsm., Distrib., Vol. 142, No. 2, pp , 1995.