Designing an Optimal Lightning Protection Scheme for Substations Using Shielding Wires

Transcription

1 Engineering, Tecnolog & Applied Science Reserc Vol. 7, No. 3, 217, Designing n Optiml Ligtning Protection Sceme for Substtions Using Sielding Wires Abolfzl Kodddi Electricl Engineering Deprtment Amirkbir Universit of Tecnolog Tern, Irn.kodddi@ut.c.ir Mommd Hssn Nzri Electricl Engineering Deprtment Amirkbir Universit of Tecnolog Tern, Irn nzr@ut.c.ir Seed Hossein Hosseinin Electricl Engineering Deprtment Amirkbir Universit of Tecnolog Tern, Irn osseinin@ut.c.ir Abstrct An optiml ligtning protection sceme for substtion using sielding wires is investigted in tis pper troug computer softwre nlsis. An economic pproc is utilized b coosing resonble trde-off between protection, te number of sielding wires nd te eigts of tem from te ground. Tis stud is initill pplied to simple two-wire sstem nd ten extended to smple substtion. Te solution for ec problem is executed in MATLAB nd 3-D reliztion is sown. Kewords substtion protection; ligtning stikes; sielding wires; computer id nlsis I. INTRODUCTION Fults nd dmges in substtions re te culmintion of sundr fctors ec of wic pl significnt role in te sielding filures mong wic ligtning is one of te most importnt one. Tis penomenon s probbilistic event m cuse severe consequences like power suppl interruptions nd economic losses [1 5]. Terefore, ligtning protection sstem is required for reducing te probbilit of fult ginst direct ligtning stroke to te objects nd buses witin te substtions [6, 7]. For more illustrtion on te ligtening progress penomenon, brief description is presented in [8]. In te ligtening, te stepped leder moves towrd ert in stopping steps of bout 5 meters. After ec step, te stepped leder puses, ten proceeds long one or more pts. Te time for ec step is bout 5μs ner te bse of te cloud but decreses to bout 13μs s it pproces te ert. Te velocit of te stepped leder is slow, bout.1% of te speed of ligt. As tis stepped or downwrd leder reces ner te ert, n upwrd leder or return stroke strt progressing to meet te downwrd leder. Te speed of tis stoke is bout 1 to 3% of ligt wic mkes it possible to be observed b nked ee. Te mplitude of tis upwrd cnnel is more tn 2 ka wit medin vlue of 33 ka. Te totl lengt of te downwrd leder or te upwrd cnnel is bout 5 to 6 km. Te bove description illustrtes te mecnism of te first stoke of ligtning fls. One fls m consists of up to 54 stokes; owever, te verge is tree stokes per fls In order to ppl protection to te equipment, tree different metods cn be utilized: sielding wires, msts nd combintion of tese two. Ec of te forementioned metods for sielding substtion s its own dvntges nd disdvntges. However, te ppliction of sielding wires is muc more recommended due to its wide rnge of protection re [9]. In ddition, te pproc wic is pplied for ligtning protection cn be obtined from vrious equtions, suc s Young s equtions, Love s equtions, Brown- Witeed, IEEE-1992 nd IEEE-1995 [8], [1]. For Young s equtions onl smll modifiction for te vlue of te strike distnces is required nd for Love s equtions nd IEEE-1995, tere is no need for n djustment. However, utilizing Brown- Witeed nd IEEE-1992 needs significnt cnges in te vlue of different strike distnces. In tis pper, for te cse of generlit, Young s equtions re emploed. MATLAB is emploed in tis pper for simultion. Te economic spect of te design is lso considered nd trde-off between cost nd level of securit is proposed. Tus, tis pper pplies specific criteri for cieving te design wit minimum possible cost. II. METHODOLOGY Different distnces re used for defining te strike distnce: (1) Te strike distnce to te sielding wire or sielding mst, r s (2) te strike distnce to te object to be protected,, nd (3) te striking distnce to te ground, [11]. All of tese distnces re sown in Figure 1. Tis figure lso specifies te res on wic ligtning strokes will be terminted. Te following equtions ve been derived from te electromgnetic model to clculte te strike distnce equtions [8]: r r r r (1) s s g c c g in wic γ s nd γ c re coefficients wic will be defined b Young s equtions:.32 rg 27I 444 s for 18 m oterwise s 1 (2) c for 18 m oterwise c Kodddi et l.: Designing n Optiml Ligtning Protection Sceme for Substtions Using Sielding

2 Engineering, Tecnolog & Applied Science Reserc Vol. 7, No. 3, 217, Were I is te design current in ka nd r s, nd re strike distnces in meters. Design current is n importnt fctor tt igl ffects te output prmeters of te design. For prcticl designs, te design current vlue for voltges below 23 kv is usull considered to be 5 ka nd for voltges bove 23 kv is considered to be 1 ka [8], wic is te vlue used in tis pper. In substtions, te eigt of devices cn vr from zero to te eigt of te sielding wires. Tus, te loction of te objects nd wires sould be determined in suc w tt minimum number of sielding wires cover te entire re of te substtion. Ec sielding wire s specific protection zone. For instnce, consider single wire s depicted in Figure 1. Te ctul re of te finl protective zone depends on te number of sielding wires tt ve been emploed. In order to clrif tis issue, two cses re investigted s follows. Also te equtions folculting te orizontl protective distnce between two sielding wires cn be evluted b (5) nd is depicted in Figure 4. R r ( r R ) R R pc c s c c c pc Rpc = (5) Strike to wire Strike to object Strike to ground r s Strike to ground Fig. 2. Protective zone of single wire ( upper view ) R pc Fig. 1. Strike distnces ( front view ) A. One Sielding Wire In tis cse one sielding wire will be used in order to protect specified zone. Assume tt tere is n object wit eigt nd sielding wire t eigt. Now if te position of te object from te sielding wire is known, wit te following equtions, te eigt of te sielding wire m be determined (see Fig. 1). R r ( r ) R po c g g po r r s Were in tese equtions is te distnce from te sielding wire to te object (Figure 2). (3) Fig. 3. S g mc Protected zone of te two sielding wires Te minimum eigt of te protection level is in te middle of te distnce between two wires s sown in Figure 3 nd it cn be derived b setting te R pc equl to zero in (5), tt is: r r R (6) mc c s c However, it sould be mentioned tt if te distnce between two wires increses, te vlue of te mc equls to zero nd te configurtion wic is depicted in Figures 3 nd 4 will not old true, but te equtions cn be utilized. B. Two Seilding Wires Te sielding zone wic is introduced b two sielding wires is sown in Figure 3. Te igligted zone in tis figure sows te protected re b two sielding wires. Hving n object wit te eigt of, te orizontl distnce of te protection,, will be clculted s it follows: r ( r ) r ( r ) (4) c g c g Fig. 4. r s Rpc c R c S g Protective zone between two sield wires Kodddi et l.: Designing n Optiml Ligtning Protection Sceme for Substtions Using Sielding

3 Engineering, Tecnolog & Applied Science Reserc Vol. 7, No. 3, 217, To clrif nd visulize te sielding protection re b two wires, 3-D reliztion of Figure 4 is depicted in Figure 5. Heigt(m) Dept (m) Fig Sielding wires Stnds 5 Horizontl distnce (m) 3-D visuliztion of sielding protection zone C. Economic Anlsis Te overll cost of te design sould be clculted in cost effective mnner. So, softwre sould be emploed to solve te problem wit specific tecnicl nd economic constrints (number of wires nd eigt re considered s prmeters). As te eigt of te wires increses, te number of tem decreses. An eqution tt cn be pplied for economic constrint cn be defined s follows. CostFunction.N. H ($) (7) Were α is constnt wic trnsfers te number of wires, N, into monetr unit ($/number) nd β is noteonstnt wic trnsfers te eigt of te wires (in meter) into monetr unit ($/eigt). A person wo is expert in tis field sould define tese constnts in order to ve resonble nd economic solution. III. SIMULATION RESULTS A. Cse Stud Informtion An smple substtion cn be nlzed b te lgoritm utilized for tis pper. For instnce, consider substtion wic its front view is sown in Figure 6. Te first prt is 345 kv trnsformer wic its eigt is 3 feet (pproximtel 1 meter) or second prt 5 kv EHV gs circuit breker [12] After determining te position of te second wire, tis process continues until te protection re of te lst wire reces te end of te defined re. Te process wic s been mentioned owever, bove will solve problem for specific eigt. Next step is to increse te eigt of te wires nd ten repet te sme process. As te eigt of te wires increses, te number of tem will decrese. Terefore, te economic criteri will be considered for te finl sceme selection. Heigt (m) Fig. 6. Front view of te smple substtion C. Simultion Results In te first prt of te simultion, te minimum eigt of te wires is selected nd te lgoritm clcultes te complete protection s depicted in Figure 7. As it ws stted before, tis design s been performed in w tt ll equipment s t lest one meter mrgin from te sielding re provided b te wires. In tis cse five sielding wires ve been used nd te eigt of te wires is 11.5 meter from te ground. Te 3-D reliztion is sown in Figure 8. Heigt (m) B. Simultion Algoritm At te first stge, te lgoritm puts two wires in te beginning nd te end of te specified re t minimum cceptble eigt. Ten it proceeds to clculte te sielding zone between tese two wires. It is obvious tt tese plcement cnnot gurntee te full protection of te equipment between tem. Ten, it brings one of te wires closer to te oter one in order to increse te eigt of te protection level between tem. Tis process continues until te position of te second wire reces position ensuring tt ll of te equipment between tem will be completel protected. Te usen define te specific mrgin between te igest prt of te equipment nd te protection level defined b sielding wires. In tis problem, te forementioned mrgin is set one meter bove te igest equipment. Heigt (m) Fig Fig. 8. Protection level provided b wires 4 5 Widt(m) D Reliztion of sielded re 5 1 Dept (m) Kodddi et l.: Designing n Optiml Ligtning Protection Sceme for Substtions Using Sielding

4 Engineering, Tecnolog & Applied Science Reserc Vol. 7, No. 3, 217, Selecting deferent cost function constnts is vrible tt cn be depended on te vrious fctors bsed on te region in wic te sielding design is performed, suc s monetr fctors or vilbilit of specific mterils. According to tis, tble wit different constnts nd teionsequent costs bsed on (7) is provided (Tble I). Tis tble is bsed on te first scenrio in wic te eigt of te wires is te minimum possible eigt nd five wires re emploed ccording to te computer softwre solution. Incresing te eigt of te wires leds to decrese in teir number. In tis problem, in order to protect ll te equipment wit just two wires, te finl result will be s depicted in Figure 9. Heigt (m) Fig. 1. Optiml sielding protection design TABLE I. COSTS OF THE FIRST SCENARIO ($) α β Heigt(m) Widt (m) Dept (m) Heigt(m) Fig D Reliztion of te optiml design Fig. 9. Protection wit two wires In tis scenrio, te finl cost of designing tis protection sstem is stted in Tble II. β TABLE II. COST OF THE SECOND SCENARIO ($) α Te optiml configurtion derived is bsed on α=4 nd β=1 wic re obtined b n expert in te region in wic te substtion s been locted. Te finl output of te lgoritm is depicted in Figure 1. In tis design, tree sielding wires ve been pplied nd te eigt of te wires from te ground is 15 meters. Tus, te totl cost of tis design is found to be te lowest. As finl step, 3-D reliztion of Figure 1 is depicted in Figure 11. IV. CONCLUSION In tis pper, n lgoritm s been developed in MATLAB in order to design ligtning sielding protection sstem for substtions using sielding wires. Young s equtions re emploed to determine te vlue of te different strike distnces in te design process. As significnt fctor in design, n economic constrint s been defined nd tis fctor determines te number of te sielding wires to be emploed nd teir eigt from te ground. Finll, te lgoritm s been pplied to smple substtion nd simultion results re sown nd discussed. REFERENCES [1] P. Sen, Understnding direct ligtning stroke sielding of substtions, Power Sst. Eng. Res. Center, PSERC Seminr, Colordo, November 6, 21 [2] F. A. M. Rizk, Modeling of substtion sielding ginst direct ligtning strikes, IEEE Trns. Electromgn. Compt., Vol. 52, No. 3, pp , 21 [3] K. L. V. Dung, Ligtning protection sstems design for substtions b using msts nd Mtlb, Interntionl Journl of Mtemticl, Computtionl, Psicl, Electricl nd Computer Engineering, Vol. 4, No. 5, pp , 21 [4] F. A. M. Rizk, Exposure of overed conductors to direct ligtning strikes: modeling of positive stremer inibition, IEEE Trns. Power Deliv., Vol. 26, No. 2, pp , 211 [5] S. Dedeoglu, S. Yilmz, Design nd implementtion of progrmmble ig-voltge impulse mesurement sstem, Turkis Journl of Electricl Engineering & Computer Sciences, Vol. 22, pp , 214 Kodddi et l.: Designing n Optiml Ligtning Protection Sceme for Substtions Using Sielding

5 Engineering, Tecnolog & Applied Science Reserc Vol. 7, No. 3, 217, [6] A. M. Mous, Sielding of ig-voltge nd extr-ig-voltge substtions, IEEE Trns. Power Appr. Sst., Vol. 95, No. 4, pp , 1976 [7] A. M. Mous, R. J. Weling, A surve of industr prctices regrding sielding of substtions ginst direct ligtning strokes, IEEE Trns. Power Deliv., Vol. 8, No. 1, pp , 1993 [8] A. Hilemn, Insultion coordintion for power sstems, CRC Press, 1999 [9] A. H. A. Bkr, C. K. Tn, A. Z. Abidin, P. J. Ki, H. Moklis, H. A. Illis, Comprtive Stud on substtion sielding due to direct ligtning strokes, J. Power Energ Eng., Vol. 2, No. 4, pp , 214 [1] A. Mous, A computer progrm for designing te ligtning sielding sstems of substtions, IEEE Trnsctions on Power Deliver, Vol. 6, No. 1, pp , 1991 [11] J. McDonld, Electric Power Substtions Engineering, CRC Press, 212 [12] IEEE Std , IEEE Guide for Direct Ligtening Stroke Sielding of substtions, 1996 Kodddi et l.: Designing n Optiml Ligtning Protection Sceme for Substtions Using Sielding