ON THE PROCESSING OF THE RECORDED DATA FOR THE SF6 CIRCUIT BREAKERS FROM THE TRANSFORMATION SUBSTATION 110/20/6kV CRAIOVA SOUTH

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1 ON THE PROCESSING OF THE RECORDED DATA FOR THE SF6 CIRCUIT BREAKERS FROM THE TRANSFORMATION SUBSTATION 11/2/6kV CRAIOVA SOUTH Mri Brojboiu Virgini Ivnov University of Criov Fcultty of Electricl Engineering 17 Decebl Blv., 244, Criov, Romni Andrei Svescu S.C. RELOC S.A. 19 Decebl Blv., 2746, Criov, Romni KEYWORDS Circuit brekers, mintennce, SF6, bltion. ABSTRACT The ssurnce of the relibility for the trnsformtion substtions is one of primry gols of the mnufcturers nd distributors of electricity. Therefore, proper monitoring nd mintennce progrm is required. The circuit breker is complex device, subject to the therml nd mechnicl stresses during the norml or fult currents switching. The substtions re frequently equipped with SF6 circuit breker. The circuit breker components subjected to the therml stresses re the min contcts which suffer electricl erosion nd the nozzle which is subjected to the bltion process. The bltion process ppers becuse of the energy rdition which is trnsferred from the electric rc. As result of the bltion, the nozzle geometry, the gs pressure nd the electric withstnd re chnged. Bsed on the recorded dt from the trnsformtion substtion 11/2/6kV Criov South, the mss loss from nozzle, the dmissible number of disconnections nd the throt nozzle dimeter re computed. The grphicl representtions highlight the impct of the interrupted current, of the rcing time nd of the integrl I2t over the mentioned ones. Consequently, if the switching process nd the time rc vlue re controlled, the therml wer cn be limited nd the equipments users my provide mintennce progrm with miniml costs nd n incresing of the lifetime. INTRODUCTION The circuit breker is one of the most importnt nd complex equipment from the medium nd high voltge electric substtions hving the switching functions of the electricl circuit in the norml or fult conditions. Depending on the therml nd dynmic stbility of the electricl equipment from sttions, the commuttion must be crried out in prescribed period of time. Consequently, the filure or decommissioning of circuit breker hs undesirble effects on the opertion of the power sttion, thereby providing progrm of monitoring, dignosis nd mintennce of the circuit breker it is bsolutely necessry. The progrm of monitoring, dignosis nd mintennce hs the purpose to increse the lifetime of the equipment nd to reduce the opertion nd mintennce costs. From the mintennce costs of the electricl sttions, 4% re dedicted to the circuit breker mintennce, menwhile 6% re dedicted to the generl revisions ( Milthon S. et ll, 25). Therefore, the predictive mintennce systems bsed on the continuous monitoring of the circuit breker led to the significntly reducing of the costs. The predictive mintennce system hs the dvntge to be crried out during the opertion of the equipment. A lrge number of references in the field re dedicted to the nlysis of the functioning nd monitoring of the circuit brekers (Milthon S. et ll, 23), (Richrd, T., 24), (Thnpong, S. 26). The power sttions from Criov South re equipped with oil circuit breker or, becoming frequently fter upgrding, with SF6 circuit brekers. The use of this gs hs reduced the frme sizes nd increse performnce s of switching. The medium voltge SF6 circuit brekers re designed of the self blst principle. This type of circuit breker genertes gs flow by mens of piston nd cylinder ttched to the moving contct. When the circuit breker is in close position the gs pressure from the puffer cylinder is equl to the pressure of filling gs. During the disconnecting opertion, the SF6 gs is compressed in the cvity between puffer cylinder nd the piston. The switching rc occurs between the sttionry contct nd the moving contct nd it is develops inside of the blowing convergent- divergent nozzle from PTFE with lower therml conductivity. A successful current disconnecting depends on the interction between the switching rc, the rdited energy from rc, the bltion of the nozzle mteril nd the pressure of the gs flow. During the period of the current disconnection, in norml or fult regime, occurs the therml wer of the circuit breker components which re in contct with the switching rc (Richrd, T., 24), (Bng, H, 212), (Bogtyrev, N, 213),( Murtovic, M, 213), (Weizong W.I., 213). The components which re directly exposed to the rditive or conductive energy trnsferred from the switching rc re the electricl contcts nd the blowing nozzle. As result of the therml wer, fter one opertion time or Proceedings 28th Europen Conference on Modelling nd Simultion ECMS Flminio Squzzoni, Fbio Bronio, Cludi Archetti, Mrco Cstellni (Editors) ISBN: / ISBN: (CD)

2 fter cumultive number of disconnected currents, these components must be replced. In the reference (Brojboiu, M. et ll, 213) the spects of the contct electro erosion re presented nd mss loss from the contcts becuse of the therml erosion is computed. It is well known tht there is n dmissible limit of the therml wer beyond which the circuit breker opertion cnnot be ssured nd this fct requires the replcement of the used components. Hving in view the therml wer of the circuit breker, the on line monitoring of the disconnections number, the rcing time nd the disconnected current vlues llow the estimtion of the circuit breker condition nd therefore mintennce pln cn be set out. Concerning the nozzle wer, during the opertion, becuse of the electric rc presence, the bltion phenomenon of the nozzle mteril occurs. The electric energy rc is minly bsorbed by SF6 gs. An importnt prt of this energy is bsorbed by the contcts nd nozzle. The energy bsorption produces heting, melting nd mteril vporiztion, this being the min cuse of the therml wer. Following the bltion phenomenon occurs the incresing of the nozzle throt dimeter nd consequently the chnging of the gs flow. In the sme time, the mixing of the PTFE vpors (C2F4) with the SF6 gs ppers. The influence of the vpors over the dielectric brekdown of the hot ws nlyzed in the reference (Weizong W.I., 213) The PTFE vpors modify the properties of the quenching rc medium. Therefore, the quenching of the electric rc depends on the bltion intensity of the nozzle mteril. Consequently, the nozzle bltion hs significnt influence over the composition of the gs or residul plsm between the min contcts, fter the rc quenching. The withstnd voltge of the gs - C2F4 vpors mixture is reduced in comprison with the one of the cold gs. The vlues of the criticl electric field for vrious percentges of the PTFE vpors mixed with gs t gs pressure of.4mp were experimentlly determined. Due to this fct, the re ignition of the electric rc cn occurs nd therefore disconnection filure cn hppens. At the sme time, the controlled bltion of the nozzle cn produce the gs overpressure ssocited with the movement of mechnicl piston (Ce-Yoon B., et ll, 26). The severity of the therml wer or the nozzle bltion depend on the mplitude of the disconnected current vlue, the electric rcing time, the integrl I2t, the constructive solution of the circuit breker nd the recovery voltge mplitude rc (Richrd, T., 24). There re lrge number of prmeters tht should be monitored to evlute the circuit breker condition during the opertion time. Concerning the min contcts of the circuit breker, the monitoring ssumes the evlution of the therml erosion, electric rc durtion, cumultive disconnected currents nd the contct resistnce. The monitoring of the nozzle implies the supervision of the inner dimeter of the nozzle throt, the incresing pressure in the puffer chmber nd the criticl electric field vlue. THE PROCESSING OF THE RECORDED DATA The medium voltge SF6 circuit breker, whose dt were recorded (Svescu A. 213), is Flurc FG3 type, is instlled in the trnsformer substtion 11/2/6kV Criov South - Ghercesti. The min rted vlues of this circuit breker re: rted voltge 24kV, rted current 125A, rted breking cpcity 25kA. The dt were recorded using the protection system F65 Generl Electric nd cn be used for ll equipment from trnsformtion substtions (oil or SF6 circuit brekers). Such protection system is ble to store the lst 2 events of the protected equipment. For circuit brekers, recording contins the collected dt in rnge of time between one to two seconds. On this rnge of time, the currents, the voltges nd the operting stte of the circuit breker (connected/disconnected/rar) re grphiclly represented on every moment of time. The recorded dt cn be visulized by mens the SIGRA4 progrm which is prt of the DIGSI softwre. The recording of vrition in time of the interrupted current is shown in Figure 1. The current vlues re cquired from the secondry of current trnsformer with trnsformtion rtio 2/5. The rcing time is mesured from the moment of time when the current flls below the vlue of 1A, t this vlue of rcing time, the post-rc currents occur between the min contcts of the circuit breker. In the recording from figure 1, the time durtion of the rc is of 24,3ms. Figure 1: The Recorded Interrupted Currents vs. Time L1,L2, L3 Phses of the SF6 Circuit Breker In the Figure 2 the recording of the vrition in time of the voltges on the three L1,L2, L3 phses is shown. The recorded voltges re corresponding to the recorded interrupted currents. In this cse, the trnsformtion rtio of the voltge instrument trnsformer is of 1/5. Tht mens the voltge vlue in the moment of occurrence of the current interruption is bout 22kV. The recorded interrupted currents vlues on three phses of the circuit breker nd the rcing time vlues re shown in Tble 1.

3 South hs been processed in order to observe the dependencies between the mss loss from PTFE nozzle t the fult currents interruption nd the electric rc energy, the integrls Gidt nd Gi2dt. The computtion of the electric rc energy ws performed with formul: W = U I t (1) Figure 2: The Recorded Voltges vs. Time L1,L2, L3 Phses of the SF6 Circuit Breker Tble 1: Recorded Vlues: Interrupted Currents, Arcing Time / Computed Vlues: Mss Loss, Integrl I2t No. I L1 I L2 I L3 t m L1 I2t1 5 [A] [A] [A] [ms] [mg] [A2s] The recorded dt using the SIGRA 4 progrm must be combined nd processed in order to mke conclusions on the opertion system nd the circuit breker stte. Tht could help to increse the relibility of the electricl sttion. Becuse the circuit brekers must interrupt the fult currents throughout lifetime, their ging is due to the therml nd mechnicl stresses of the blowing nozzle nd the min contcts between the electric rc occurs. The therml wer or cumultive electroerosion of the min contcts is used s criterion to evlute the electricl endurnce of the circuit breker. Additionlly, for the SF6 circuit brekers is very importnt to ssess the cumultive wer of the blowing nozzle. Accordingly to (Thnpong, S. 26), the totl dmissible electroerosion vlue of the min contcts nd of the nozzle is depending on two prmeters: the mximum breking current I scmx nd the dmissible number of disconnections of the fult currents N dm. In the works (Brojboiu, M. et ll, 213), (Svescu, A.,213) the computtion of the mss loss from the min contcts depending on the recorded dt in the oil circuit breker from medium voltge substtion Criov is presented. The recorded dt on the SF6 circuit breker from the trnsformtion substtion 11/2/6kV Criov where, the interrupted currents vlues nd the rcing time vlues re presented in Tble 1. The rc voltge drop U hs been computed bsed on the described lgorithm in (Hortopn, Gh., 198). Knowing the mximum vlue of the recovery voltge s function of mximum phse voltge, the mplitude fctor k, first phse fctor k f, the oscilltion frequency f, the following formul ws deduced: where: ( T/8 ) U =.77u e (2) u r mx rmx = U k k 2 / 3 (3) n f is the mximum vlue of the recovery voltge, rted voltge U n =24kV, T=1/f, f is the oscilltion frequency of the recovery voltge, is the time constnt. In the work (Rong, M., 25) it is estimted tht 4% from electric rc power is used for the nozzle bltion, the bltion rte being round of k b =15 17mg/kJ. The mss loss m b s function of the interrupted current vlue or the rc energy hs been computed with formul: m b = k.4 W (4) b The vrition of mss loss through bltion from PTFE nozzle depending on the interrupted currents vlues from three phses is shown in Figure 3. Mss loss [g] Interrupted current [A] Figure 3: The Mss Loss vs. Interrupted Current- L1,L2, L3 Phses

4 The processing of the experimentl results ws performed using Mtlb ppliction. By pplying lest squres pproximtion method to the recorded dt, using Mtlb ppliction, it ws possible to plot continuous curve (solid line) tht pproximtes the vrition of the mss loss from nozzle depending on the interrupted current. This Mtlb ppliction hs been pplied to ll the recorded nd computed dt which were processed in this work. Concerning the computtion of the integrl I2t, one integrtion Mtlb procedure hs been pplied. A sinusoidl vrition of interrupted current ws tken into ccount. 26) llow the estblishing of the one empiricl formul in order to estimte the limit mss loss depending on the dmissible number of disconnections. M lim = N (7) The dmissible number of disconnections (the llowble number of disconnecting opertions) is computed s function of the rtio between the interrupted current nd the mximum breking current of the circuit k=i/i scmx, I scmx =25kA, using the following formul (Thnpong, S. 26): t I2t = ( 2 I sin( t)) dt (5) In the Figure 4 the vrition of the loss mss depending on the integrl I2t is presented N dm = 4.4 k (8) Inner Dimeters Rtio [%] Mss loss [g] Integrl I2t [A2s] x 1 5 Figure 4: The Mss Loss vs. integrl I2t From this figure, the incresing of the mss loss ccording to the incresing of the integrl I2t vlues cn be noticed, s it is expected. Using the vlues of nozzle mss loss nd for known geometry of the nozzle, the inner rdius of the nozzle throt fter bltion r ws clculted using the following formul: 2 r = ri + L1 ( m / / h) (6) where r i nd h re the vlues of the internl rdius nd the height of the throt nozzle respectively, mesured for the circuit breker under mesurements. For the PTFE s the mteril of the nozzle, the density vlue is tken s =22kg/m 3. In the Figure 5 is grphiclly represented the vrition of the rtio of the inner dimeter fter bltion to the initil inner dimeter, depending on the mount of the mss lost from the throt nozzle. The lrge vlues of the rtio for reduced vlues of the mss loss cn be observed. The experimentl determintions crried out in reference (Thnpong, S Mss loss [g] Figure 5: Inner Rdius Rtio [%] vs. Mss Loss [g] In the Figure 6, the vrition of the dmissible number of disconnections depending on the rtio k, for the recorded current vlues of the L1 phse, is shown. Admissible disconnections number Rtio k=i/iscmx Figure 6: The Admissible Number of Disconnections vs. k=i/iscmx From the grphicl representtion, the decresing of the dmissible number of disconnections s the rtio k increses cn be noticed.

5 CONCLUSIONS The lifetime nd the SF6 circuit breker performnces depend on the bltion intensity nd the chnges in the nozzle throt geometry, which re produced by the rditive nd conductive energy of the electric rc. If the rcing time durtion cn be controlled nd restricted in order to void the lrge vlues, the therml wer of the contcts or the nozzle bltion cn be limited. Consequently, the intervl between mintennce ctivities cn be extended. REFERENCES Bng, H.; Lee,Y. S.; Ahn, H. S.; Choi J. U.; Prk, S. W A Study on Het Trnsfer by Electric Arcs nd Performnce Prediction in Gs Circuit Breker. Recent Advnces in Communictions, Circuits nd Technologicl Innovtion. Pris. Ndezhd, B.; Brtlov, M.; Aubrecht, V.; Holcmn, V Men Absorption Coefficients for SF6 + PTFE Arc Plsms, Electrorevue, ISSN , Vol.4, No.1, APRIL 213. Brojboiu, M.; Ivnov V.; Svescu, A Concerning the Monitoring of the Electric Contcts Electroerosion of the Circuit Brekers from Medium Voltge Sttions of CEZ Criov, Annls of the University of Criov, Serie Electricl Engineering, nr.37, ISSN , pp Himnshu, J,; Anjni, P.; Ghnshym, P Optimiztion of High Voltge Arc Assist Interrupters, Interntionl Journl of Scientific & Engineering Reserch, Vol. 4, Issue3, Mrch-213, ISSN Hortopn, Gh. 198 Aprte Electrice, Editur Didctic si Pedgogic, Bucuresti. Silv, M.; Jrdini, J.; Mgrini, L. 25. On-line condition monitoring system for in-service circuit breker, PEA. Deprtment of Electricl Energy nd Automtion Engineering, Polytechnic School of the University of So Pulo, Brzil. Silv, M.; Jrdini, J.; Mgrini, L. 23. An experience in circuit breker on-line condition monitoring system design, PEA - Deprtment of Electricl Energy nd Automtion Engineering Polytechnic School of the University of So Pulo, Brzil. Murtovic, M.; Kpetnovic, M.; Ahmethodzic, A.; Delic, S Clcultion of nozzle bltion intensity nd its influence on stte of SF6 gs in therml chmber, Solid Dielectrics (ICSD), 213 IEEE Interntionl Conference on, June 3 - July 4 213, Bologn. Richrd, T. Controlled Switching of High Voltge SF6 Circuit Brekers for Fult Interruption, Thesis for the degree of licentite of engineering. Mingzhe, R.; Qin, Y.; Chunduo, F. 25. Simultion of the Process of Arc Energy-Effect in High Voltge AutoExpnsion SF6 Circuit Breker, Plsm Science nd Technology, Vol. 7, Issue 6, pp Svescu, A The mintennce of the 2kV circuit breker- clssicl nd modern constructive solutions, Thesis for the degree of licentite of engineering, University of Criov, Bilterl greement for prcticl trining with CEZ Criov. Suwnsri, T. 26. Investigtion on No-lodMechnicl Endurnce nd Electricl Degrdtion of Circuit Breker Model under Short Circuit Current Interruption, Thesis. Weizong, W. I Investigtion of the dynmic chrcteristics nd decying behviour of SF6 rcs in switching pplictions, Thesis submitted to the University of Liverpool. AUTHOR BIOGRAPHIES MARIA BROJBOIU is currently working s Professor t the University of Criov, Electricl Engineering Fculty, Deprtment of Electricl Energetic nd Aerospce Engineering. Before tht, she worked s design engineer t the Electroputere holding the Reserch nd Development Center. She is Doctor in Science Technique Electricl Engineering. She teches the courses Electricl Equipment, Electrotechnologies nd Industril Systems Engineering. She published 5 books nd 92 scientificl ppers for different ntionl nd interntionl conferences nd symposiums. VIRGINIA IVANOV ws born in Vel, Dolj, Romni, She ws grduted in Electricl Engineering t University of Criov, Romni, in 1986 nd Doctor in Electricl Engineering in 24. From 1986 to 1998 she worked s resercher with the Reserching Institute for Motors, Trnsformers nd Electric Equipment Criov. In 1998 she joined the Fculty for Electricl Engineering, Deprtment of Electricl Equipment nd technologies. She is concerned with reserch ctivities in monitoring nd modeling of electricl equipments. ANDREI SAVESCU. He grduted bchelor studies in 213 t the Fculty of Electricl Engineering t the University of Criov nd currently he is ttending the Mster's progrm "Energy qulity nd electromgnetic comptibility in electric systems". Since July 213 he works s design engineer t RELOC SA compny from Criov, which hs s business line the mintennce nd repir of locomotive s well s designing nd construction ctivities concerning the new locomotive models.