Utilization of Line Surge Arresters in Transmission Lines

Transcription

1 Utiliztion of Lin Surg Arrtr in Trnmiion Lin Htl Prnll Intituto Suprior Técnico, Av. Rovico Pi 1, Libo, Portugl Abtrct Surg gnrtd by lightning trok cn ld to filur in th upply of lctricity, thrfor thy hv brought vrl concrn in th dign nd oprtion of trnmiion lin du to th conqunc of th for th vriou componnt. Thi dirttion prnt th rult of th work prformd with th im of tudying th u of lin urg rrtr on trnmiion lin, uing th imultion progrm ATPDrw. Th phyicl phnomnon ocitd to lightning i xplind, wll th chrctriztion of th dichrg wvform nd th tblihmnt of n quivlnt lctric modl for it rprnttion. Th modl of th componnt of th lctricl ytm tht r conidrd rlvnt to th tudy of th lctromgntic trnint gnrtd by th incidnc of lighting trok wr lo nlyd. Auming tht th trok hit th top of th trnmiion towr nd conidring dichrg currnt with diffrnt pk vlu nd diffrnt chrctritic tim, vrl imultion wr prformd with th im of tudying th influnc of ground ritnc nd th djcnt towr in th volution of th voltg in th ph conductor nd in th inultor, nlyzing th bckflhovr wll. It i lo prformd th tudy of th voltg in th inultor whn lin urg rrtr r intlld. inlly, th intlltion of lin urg rrtr in uniform nd non-uniform lin w imultd, prforming th nlyi of th bckflhovr tht occur nd tudying th trtgy of th intlltion of thi dvic tht ld to th rduction of bckflhovr. It w found tht th intlltion of lin urg rrtr in thr ph of on of th circuit whn uniform lin r conidrd ld to bt rult. In non-uniform lin, th intlltion of rrtr in th trnmiion towr tht hv th hight grounding ritnc nd in th djcnt towr prnt ignificnt rduction in bckflhovr, liminting bckflhovr in on of th lin circuit. Kyword: Lightning Strok, Trnmiion Lin, Bckflhovr, Grounding Ritnc, Lin Surg Arrtr, ATPDrw I. Introduction A trnmiion lin i dignd to nur n inultion lvl highr thn th mximum intntnou voltg. Th inultion lvl i lctd bd on urg tht r prdictbl to occur, whthr thir ourc r intrnl or xtrnl. Intrnl origin urg rfr to tho producd by witching or diconncting oprtion. On othr hnd, th xtrnl urg r gnrlly cud by lightning flh. Whn lightning trik componnt of th powr ytm currnt of high mplitud nd hort durtion i injctd to tht powr ytm, cud by th tblihmnt of n lctric rc through n ionizd chnnl formd btwn thundrcloud nd th point of impct, clld rc of rturn. Th currnt prviouly mntiond produc wv tht trvl through th conductor pth nr th impct point, which i ocitd with chrctritic impdnc, clld urg impdnc. Thi phnomnon produc ovrvoltg which mplitud corrpond to th product of urg impdnc with th intntnou vlu of th dichrg currnt. Lightning dichrg r rponibl for ignificnt numbr of intrruption in lctricity upply, bcu whn lightning trok hit trnmiion towr, th ovrvoltg gnrtd cn ld to th bckflhovr of th inultor, lding to lin oprtion filur. Thrfor, lightning inducd ovrvoltg um high importnc for dimnioning th inultion of high voltg lctricl intlltion. To minimiz th ffct of dichrg, ground wir r trtgiclly plcd in th trnmiion lin. Th ground wir r normlly connctd to rth t ll towr crting prfrntil pth for th dichrg of th lightning currnt. Howvr, th xitnc of thi wir do not xclud th poibility of dirct dichrg on th ph conductor, by hilding filur, or th pprnc of lctric rc t inultor tring, cuing problm in th continuity of rvic. Th u of lin urg rrtr on trnmiion lin to prvnt bckflhovr of th inultor tring h bn tudid ovr th yr. Th rrtr prvnt bckflhovr by mintining th voltg t th inultor blow thir mximum cpbility. In gnrl, for lin without ground wir, th plcmnt of lin urg rrtr in ll towr i n ltrntiv. or lin protctd with ground wir, th rrtr r intlld in rmot loction whr mintnnc i difficult or whr thr i high oil ritivity (nd, rocky trrin). Currntly, th urg rrtr r ud in trnmiion lin to improv rlibility of rvic. Howvr, du to conomic ron, it i not poibl to quip ll towr with th dvic. Thrfor, it i ncry to tudy th bt trtgy for plcmnt of urg rrtr to nur crtin lvl of protction gint lightning. Thu, it i primordil th undrtnding of th phnomnon tht r ocitd with bckflhovr, wll with thir intlltion. Sinc, in c of doubl circuit lin, it i not dirbl to hv both circuit oprtion filur, th urg rrtr cn hv vry importnt rol in prvnting thi itution, bcu propr intlltion of rrtr cn ld to ignificnt rduction of bckflhovr, liminting thm in on of th lin circuit. 1

2 In thi work i prtndd to undrtnd th phnomn tht r ocitd to bckflhovr, wll th influnc of lin urg rrtr utiliztion. or th imultion prformd in th tudy it w ud th ppliction ATP, which hv grphic procor, ATPDrw. II. Lin Surg Arrtr A. Stt of Art Th litrtur uggt tht th lin urg rrtr hould b intlld t th towr which hv highr ground ritnc [2], wll t towr tht r intlld t locl pk or high ltitud loction [3]. In [4] i propod to intll lin urg rrtr t towr tht combin high xpour to lightning with high ground ritnc. According to [2], dpnding on th vlu of th ground ritnc, th rrtr hould b intlld in mor thn on ph, it i hown in Tbl I. It i lo propod tht th configurtion of th rrtr plcmnt to b uniform long th ction of th lin, vn if th ground ritnc i diffrnt in om towr. Tbl I Lin Surg Arrtr Plcmnt Configurtion [2] Ground Ritnc, R T (Ω) R T 10 Surg Arrtr Plcmnt No rrtr 10 < R T 20 On ph 20 < R T 40 Two ph R T > 40 Thr ph Currntly in Portugl thr r two trnmiion lin which r protctd with lin urg rrtr, Sin-Tun nd Rcri-Cnl. Arrtr r intlld in fiv towr of Sin-Tun lin. Dpit hving tudi don, thr in t lrg utiliztion of th dvic. B. ZnO Surg Arrtr Th lin urg rrtr hould ct n opn circuit t powr ytm frquncy, limit ovrvoltg blow th inultion lvl of th trnmiion lin nd rturn th ytm to it norml oprting mod o tht trnint ovrvoltg r upprd. Conquntly, urg rrtr hould hv vry high ritnc whn th ytm i in norml oprting mod nd rltivly low ritnc during trnint ovrvoltg. Bd on thi it cn b concludd tht it V-I chrctritic mut b non-linr. Th dvic r ntilly md of on or mor prk connctd in ri with on or mor non-linr ritor. Uully thr r incorportd ritnt nd cpcitiv voltg dividr to nur propr ditribution of th voltg pplid to th vriou lmnt. In norml oprtion, th prk inrtd btwn th non-linr ritor r not diruptd nd rducd intnity currnt dtrmind by th voltg dividr go through th urg rrtr connctd btwn th ph conductor nd rth. Th modrn urg rrtr u mtl oxid vritor (MO) with highly non-linr V-I chrctritic. Th vritor r contitutd by powdr of zinc oxid (ZnO) nd trc of othr mtl oxid unitd in crmic mold. It chrctritic do not rquir th u of prk. Thu, th lctricl bhviour of th dvic i only dtrmind by th block of MO. Thr r two typ of zinc oxid rrtr (ZnO) for urg protction. Th firt typ do not includ prk in it contitution, which i dirctly connctd to th ph conductor. Thi typ of urg rrtr h th dvntg of not hving dly in borbing th ovrvoltg nrgy. Th othr typ prnt prk in it compoition, which r inrtd btwn th rrtr nd th ph conductor, lo functioning n inultor btwn thm. Th prk rrtr only oprt whn lightning trik th trnmiion lin or towr, bing out of rvic in vry othr itution, including witching ovrvoltg. Thi mn tht thr i currnt going through th rrtr during vry mll priod of tim, corrponding to th dichrg tim. Thi typ of urg rrtr h biggr liftim nd mor rlibl oprtion thn th othr typ. Th non-linr chrctritic of th urg rrtr i formd by xponntil gmnt nd ch gmnt cn b pproximtd by qution (1). (1) Whr i nd v rprnt th urg currnt nd voltg, rpctivly, nd p, q nd V rf r th componnt contnt. A. Study Dt B C III. Study Dt nd Modlling In thi work i prformd tudy of th 150 kv Sin- Tun lin, which i doubl circuit lin with th configurtion prntd in ig. 1, clld cro configurtion. ig. 1 - Sin-Tun 150 kv lin ph configurtion - cro configurtion. Th grounding ritnc of th lin undr tudy r rprntd in ig. 2. 2

3 Grounding Ritnc (Ω) Towr ig. 2 - Sin-Tun lin grounding ritnc. Bd on th figur prntd it w dcidd to tudy on ction of th lin tht h vry high grounding ritnc: towr Th nxt tp conit in dtrmining th dichrg currnt to crry out th tudi. [1] propo concv wvform for th dichrg currnt rprnttion, which prmtr follow log-norml ditribution who probbility dnity i givn by qution (2). / 1 2 (2) Whr M corrpond to th vrg vlu nd β to th logrithmic tndrd dvition. Th xprion of th probbility ditribution i givn by th qution (3). 1 2 / To clcult th ditribution prmtr tht llow obtining th dichrg currnt, tht r th pk vlu, ri tim, hlf-wv tim nd growth rt, it i ncry to trnform th log-norml ditribution in norml ditribution, uing chng of vribl. 1 2 / Bing th chng of vribl givn by (5). ln / (5) Stting th vlu of P(X ) th clcultion of X i don by uing th invr function of rror, bing implmntd uing mthmticl progrm (MATLAB), nd thn obtin X. Th prmtr of th probbility ditribution to clcult th prmtr tht chrctriz th dichrg currnt r prntd in Tbl II, clcultd ccording [1]. (3) (4) Tbl II Ditribution prmtr [1] Prmtr M β Pk Vlu 61 ka 1.33 ka Ri Tim 4.7 µ 0.49 µ Growth Rt 29.4 µ 0.55 µ Hlf-wv Tim 30.2 µ 0.93 µ Th chrctritic prmtr of th dichrg currnt obtind for 80, 60, 40, 20, 10 5% probbility of bing xcd i prntd in Tbl III. Tbl III Dichrg currnt prmtr Hlfwv Probbility Pk Growth Ri Tim (%) Vlu Rt Tim In th imultion only lin ction r rprntd. Th rmining lin i implmntd uing infinit lngth lin connctd to powr ourc intndd to impo th lin voltg. Th mot ignificnt prmtr of th ourc i th voltg ngl, bcu it influnc th vlu of th voltg tht will b t th inultor tring, which i givn by (6). (6) Bd on th bov qution, th wort c corrpond to th lowr ph bcu thy hv th lowr coupling fctor with th ground wir. It i conidrd tht d R S T circuit h th wort c cnrio. Th vlu of th voltg ngl in both circuit t th momnt of th dichrg r prntd in th Tbl IV. Tbl IV Voltg ngl t th momnt of dichrg. Ph Voltg Angl S -60º R 60º T 180º T 180º R 60º S -60º Th tudy c of th 150 kv Sin-Tun lin prntd in thi work r rprntd in Tbl V. 3

4 Tbl V C tudid for non-uniform lin Tbl VII C tudid for uniform lin C I pk (ka) Towr Hit by Lightning Uniform Lin Th m dichrg currnt prntd in Tbl III r ud to prform th tudy of uniform lin. Howvr, it i ncry to tblih critrion for th lction of th grounding ritnc to b imultd. ig. 3 how th probbility of th grounding ritnc of Sin-Tin lin bing xcdd. Prtobbility of th vlu b xcdd (%) Grounding Ph tht C I pk (ka) Ritnc (Ω) lhovr T, T T, T', S' B. Modlling Lightning Currnt Onc th chrctritic prmtr of th dichrg currnt r clcultd, it i poibl to rcontruct tht currnt wv in ATPDrw, by uing currnt ourc with prlll ritnc, which h th purpo to rprnt th lightning pth impdnc hown i ig. 4. Thi ritnc vlu i tkn to b 400 Ω. ig. 4 - Lightning tok modl ud in ATPDrw ig. 3 - Probbility of th vlu of th grounding ritnc bing xcdd. Th critrion tblihd for lcting th grounding ritnc i bd in th prviou figur. Th ritnc tht hv 30, 20, 15, 10, 5, 2 1 % probbility of bing xcdd wr lctd, prntd in Tbl VI. or thi imultion it w conidrd tht th ction of th lin h 17 towr, 16 pn of mtr ch, connctd to 20 km lin t it nd tht ubquntly connct to voltg ourc of 150 kv with th ngl dcribd in Tbl IV. Tbl VI Grounding ritnc vlu ud for uniform lin tudy Probbility (%) Grounding Ritnc (Ω) Grounding Ritnc (Ω) Th c tht wr tudid in thi work r prntd in Tbl VII. Trnmiion Lin Th lin prmtr vry with frquncy nd ATPDrw offr poibility to u vriou frquncy dpndnt lin modl to rprnt ovrhd trnmiion lin. In thi tudy JMrti modl w lctd. Th ground wir i rprntd ph wir connctd to th top of th towr. Towr or implifiction purpo nd inc th tudy of th diffrnt towr modl r not th im of th tudy, th towr wr rprntd by hort-circuit. Grounding Ritnc Th grounding ritnc i rprntd by linr ritnc. Inultor Th inultor tring wr rprntd by high vlu ritnc in prlll with low vlu ritnc tht i connctd in ri with voltg controlld witch, which only conduct whn th voltg cro it trminl xcd th vlu prntd in qution (7). 4

5 (7) Whr l d corrpond to th inultor lctrod, E 0 to th lctric fild, which vlu i tkn to b 750 V/km nd V(t) to th intntnou voltg vlu. ig. 5 prnt th modl ud in ATPDrw. 900 [kv] T S R ig. 5 - Inultor tring modl ud in ATPDrw. Lin Surg Arrtr Th lction of th pproprit lin urg rrtr i don bd on th rrtr Mximum Continuou Oprting Voltg (MCOV), which i clcultd by th qution (7). 1.1 (1) 3 Whr V m rprnt th lin voltg lvl. Th multiplictiv fctor driv from th fct tht during th lin oprtion th voltg of th lin cn gt vlu 10% bov of th lin voltg lvl. Th urg rrtr r rprntd in ATPDrw by MOV block, ig. 6, modlld by currnt dpndnt xponntil ritnc, which follow qution (1) [u] 60 contornmntoinv ro.pl4; v:top v:top -T (f il x-v r t) -S -R v :TOP ig. 7 - Inultor voltg of RST circuit in th towr hit by th dichrg. 12 [ka] T R [u] 60 contornmntoinv ro.pl4; c:top c:top -T (f il x-v r t) -S -R c:top ig. 8 - Inultor currnt of RST circuit in th towr hit by th dichrg. S ig. 6 - Surg rrtr modl ud in ATPDrw. 900 [kv] 680 S or th imultion, ABB PEXLIM R urg rrtr wr ud, which chrctritic i prntd in Tbl VIII. Tbl VIII Surg rrtr chrctritic TOV Mx. Ridul Voltg (kv) Rtd MCOV (kv) with Currnt Wv 8/20 µ Voltg, (kv) for 1 U r (kv) 5kA 10kA 20kA 40kA c IV. Study of Bckflhovr in Uniform Lin without Lin Surg Arrtr In ig. 7 to ig. 10 r rprntd th voltg nd currnt in th inultor for both RST nd R S T circuit for th imultion of th c from Tbl VII [u] 60 contornmntoinv ro.pl4; v:top v:top -S' (f il x-v r t) -T' -R' v:top ig. 9 Inultor voltg of R'S'T' circuit in th towr hit by th dichrg. 11 [ka] S R [u] 60 contornmntoinv ro.pl4; c:top c:top -S' (f il x-v r t) -T' -R' c:top ig. 10 Inultor currnt of R'S'T' circuit in th towr hit by th dichrg. R T T Whn lightning hit towr, it potntil incr bcu big portion of dichrg currnt i conduct by th grounding ritnc of tht towr, bing th rmining 5

6 currnt trnmittd by th ground wir to th djcnt towr nd ubqunt pn. Aftr th dichrg incidnc, th voltg of th inultor incr rult of th towr nd th ph potntil incr (bcu of ground wir coupling). Whn bckflhovr occur th voltg cro th inultor dcr to pproximtly zro nd currnt circult cro th ir gp, hown in ig. 8 nd ig. 10. A ph flhovr impli th dcr of th towr potntil nd th incr of th ph potntil. Towr potntil dcr bcu nw pth of conduction i inrtd, th ph wir. Ph conductor potntil incr rult of ph coupling. It i obrvd in th prntd wv tht th ph tht don t flhovr hv dcr in thir inultor voltg whn othr ph flhovr. Thi occur bcu th towr potntil dcr i biggr thn th ph potntil incr. If th dichrg currnt h not rchd it pk, th towr nd ph potntil incr gin, wll th voltg cro th inultor, hown in ig. 7 nd ig. 9. Aftr th bckflhovr, th potntil of ph i pproximtly qul to th towr potntil. In th figur prntd it i poibl to viuliz tht th wv hv two ocilltion with diffrnt priod, on with 3 µ nd othr with 12 µ. Th firt ocilltion i jutifid by th rflction of th djcnt towr (th pn h mtr, corrponding to propgtion tim of 1.5 µ) rult of th portion of th currnt tht i trnmittd by th ground wir to tho towr. Th cond ocilltion i xplind by th flhovr tht occur in nighbouring towr. To undrtnd thi phnomnon it i prntd Tbl IX. Thi tbl rprnt th flhovr in th towr nd in th ph. Th hdd column rprnt th towr hit by th lightning Tbl IX lhovr in uniform lin for c 2 C 2 R 0 = 80 Ω, I pico = 55 ka T T i th phnomnon tht i obrvd in ig. 10, t 25 µ th currnt of th inultor in ph T incr, tht corrpond th flhovr in th towr N-4, which occur t 19 µ, plu th propgtion tim of th 4 pn. Aftr 12 µ th currnt incr gin, bing thi incr mllr. Thi phnomnon i obrvd bcu th rflction trvl gin through th ph conductor to th ph tht h uffrd flhovr nd com bck. Sinc th flhovr in th ph T nd T occur in th immditly djcnt towr, th trvl tim i much lowr, o it i only obrvd th currnt growth, followd by it dcr. To bttr undrtnding of th nighboring towr ffct th vlu of th mximum potntil of th towr tht i hit by th lightning r prntd in Tbl X. Tbl X Mximum voltg vlu in th towr hit by th dichrg in on towr c nd in uniform lin c I pk (ka) Mximum Voltg in th Towr Hit by th Dichrg (MV) Mximum Voltg in th Towr Hit by On Towr Uniform Lin th Dichrg Rduction (%) In Tbl X it i poibl to obrv tht th towr potntil dcr, which i xplind by th nw conducting pth providd by th ground wir nd th rflction of th djcnt towr, which do not xit in th itution of only on towr. V. Study of Bckflhovr in Uniform Lin with Lin Surg Arrtr To undrtnd th ffct tht urg rrtr cu th ig. 11 i prntd. It illutrt th voltg cro th ph S inultor whn c 2 i imultd, with nd without rrtr intlld. In ig. 12 th currnt tht circult through th rrtr in c 2 whn th dvic r intlld in ll ph of th circuit R S T r rprntd. S A it i poibl to obrv in th tbl bov, in T ph th flhovr occur in th towr tht i hit by th lightning, N, nd in towr tht r 4 pn prt, N-4. Th flhovr of th m ph in othr towr triggr rflction tht propgt through th ph wir. Whn tht rflction rch th towr N, th currnt uffr big incr. Tht 6

7 900 [kv] [m] 0.10 (f il Dcrrgdor.pl4; x-v r v:top3 t) v:top -S' -S'3 ig Ph S' inultor voltg with nd without rrtr for c [A] T ig Currnt in rrtr intlld in ll ph of R'S'T' circuit for c 2. or th tudy of th bckflhovr in uniform lin with intlltion of urg rrtr th c 1 prntd in Tbl VII w imultd, for th configurtion of rrtr plcmnt givn in Tbl XI. Th rrtr r intlld in vry towr imultd, only in th circuit R S T, bcu thi circuit h th bt c cnrio rgrding th ngl of th lin voltg. Tbl XI Surg rrtr plcmnt configurtion imultd Configurtion 1 With Arrtr R S Without Arrtr [m] 0.10 Dcrrgdor.pl4; x-v r -PHAC -PHAA -PHAB (f il t) c:top3 c:top3 c:top3 No rrtr Configurtion 2 Arrtr in ph S Configurtion 3 Arrtr in ph S nd R Configurtion 4 Arrtr in ph S, R nd T Tbl XII to Tbl XV r prntd for bttr viuliztion of th rult. Th hdd column rprnt th towr hit by th lightning nd th hdd lin corrpond to th ph tht hv rrtr intlld. Tbl XII lhovr in uniform lin for c 2, no rrtr C 2 R 0 = 80 Ω, I pico = 55 ka No Arrtr T T S Tbl XIII lhovr in uniform lin for c 2, rrtr in ph S C 2 R 0 = 80 Ω, I pico = 55 ka Arrtr in ph S T T S Tbl XIV lhovr in uniform lin for c 2, rrtr in ph S nd R C 2 R 0 = 80 Ω, I pico = 55 ka Arrtr in ph S nd R T T S

8 Tbl XV lhovr in uniform lin for c 2, rrtr in ph S, R nd T C 2 R 0 = 80 Ω, I pico = 55 ka Arrtr in ph S, R n T T T S Bd on th tbl bov, it i poibl to conclud tht th intlltion of urg rrtr improv th lin prformnc by rducing th flhovr. Whn th dvic r intlld in mor thn on ph it i poibl to conclud tht th improvmnt i biggr. It i obrvd tht th flhovr in om ph do not occur in th towr immditly djcnt to th towr hit by th lightning. Du to th c 2 complxity, it w imultd c 1 nd th rult r prntd in Tbl XVI. Tbl XVI lhovr in uniform lin for c 1, no rrtr C 1 R 0 = 80 Ω, I pico = 39 ka No Arrtr T T S Th phnomnon mntiond hppn bcu whn lightning hit towr, th potntil of vry towr incr, wll of th ph. Whn ph flhovr, th potntil of tht ph incr or dcr o it cn qut th potntil of th towr. A w mov wy from th towr whr th flhovr h occurrd, th potntil of th ph mintin prcticlly it vlu, but th towr potntil dcr. Thrfor, in om c, th potntil of th ph i biggr thn th potntil of th towr nd it cu th flhovr of th inultor. Conquntly, it i concludd tht xit two typ of flhovr in uniform lin: flhovr cud by th potntil of th towr bing biggr thn th potntil of th ph, bckflhovr, or flhovr cud by th potntil of th ph bing biggr thn th potntil of th towr nd, in thi c, it cn t b clld bckflhovr. Th phnomn r rprntd in ig. 13 nd ig. 14, whr th firt corrpond to bckflhovr nd th cond to th othr typ of flhovr. 1.6 *10 6 Towr * Unif ormri80.pl4; v:top_n (f il x-v r t) v:t_n ig Towr nd ph (T') potntil in th towr N for th imultion of th c 2 without rrtr. 1.2 * Towr Ph Ph * Unif ormri80.pl4; v:top_n2 v:t_n2c (f il x-v r t) ig Towr nd ph (T') potntil in th towr N-2 for th imultion of th c 2 without rrtr. VI. Study of Bckflhovr in Non-uniform Lin In thi ction i wntd to tudy ction of Sin-Tun lin, conidring it non-uniform, i, conidring th nonuniformity of th grounding ritnc long th lin. Th tudy w prformd in th towr 69-81, for th c 1. Th urg rrtr in thi tudy r intlld in ll ph of R S T circuit, but it i nlyd d diffrnc of intlling tho dvic only in th towr with high grounding ritnc nd lo in th djcnt towr. Tbl XVII to Tbl XIX r prntd rult, whr th hdd column corrpond to th towr whr th lightning hit nd hdd towr rprnt whr th rrtr r intlld. 8

9 Tbl XVII lhovr in non-uniform lin (towr 69-81) without rrtr C 1 I pk = 55 ka No Arrtr S R T T R S Tbl XVIII lhovr in non-uniform lin (towr 69-81) with rrtr in towr C 1 I pk = 55 ka Arrtr in Towr S R T T R S Tbl XIX lhovr in non-uniform lin (towr 69-81) with rrtr in towr C 1 I pk = 55 ka Arrtr in Towr S R T T R S In th tbl it i obrvd tht th intlltion of rrtr in th towr with high grounding ritnc nd in it djcnt towr, th flhovr in circuit R S T r limintd. Sinc th rult r vry complx, implifid nonuniform lin w imultd, whr only on towr, th towr tht i hit by th lightning h highr ritnc, whil th othr towr hv grounding ritnc of 22 Ω, to undrtnd whn it i ncry to intll rrtr in th djcnt towr to limint flhovr in R S T circuit. In Tbl XX r prntd th vlu of th grounding ritnc, for diffrnt lightning currnt, which nd th intlltion of rrtr in th djcnt towr, bid th towr with high grounding ritnc. Tbl XX Grounding ritnc vlu of th towr hit by lightning tht nd th intlltion of rrtr in djcnt towr. Grounding Ritnc of th Towr Hit by Lightning Adjcnt Towr Grounding Ritnc (Ω) (Ω) % I pk (ka) % % % It i poibl to conclud tht th dichrg currnt incr cu n incr in th diffrnc btwn th grounding ritnc of th towr hit by lightning nd th djcnt towr tht nd th intlltion of rrtr. VII. Concluion - Th volution of th voltg nd currnt in inultor prnt two typ of ocilltion. Th firt i jutifid by th rflction of th djcnt towr. Th cond i xplind nxt. A ph flhovr gnrt wv tht propgt through th ph wir. If th flhovr occur t ph loctd in th towr hit by lightning nighbourhood, th wv gnrtd propgt through th ph wir nd whn it rriv t th towr, th currnt tht circult in th ir gp of th inultor tht uffrd th flhovr incr. - In th tudy of uniform lin it w obrvd tht flhovr occur bcu two ron: towr potntil highr thn ph potntil (bckflhovr) or ph potntil highr thn towr potntil. - Lin urg rrtr intlltion ld to limittion of th pk of th inultor voltg, prvnting it flhovr. - Whn rrtr r intlld in ll ph of th circuit hving th bt c cnrio rgrding th ngl of th lin voltg, it i vrifid rduction of flhovr. - Th intlltion of rrtr in th thr ph of th circuit mntiond bov, t th towr with highr grounding ritnc nd t it djcnt ld to th limintion of ll flhovr in tht circuit. 9

10 - In th tudy of th implifid non-uniform lin it w concludd tht for highr dichrg currnt th vlu of th grounding ritnc of th towr hit by lightning nding intlltion of rrtr in djcnt towr to limint flhovr in R S T circuit i lowr. REERENCES [1] CIGRÉ Working Group 33.01, Guid to Procdur for Etimting th Lightning Prformnc of Trnmiion Lin, [2] Ocr Ktrup, Luiz Cr Zntt Jr., Lightning Prformnc Amnt with Lin Arrtr, Trnmiion nd Ditribution Confrnc, pp: 288, [3] Krthik Munukutl, Vijy Vittl, Grld T. HEydt, Dryl Chipmn, Brin Kl, A Prcticl Evlution of Surg Arrtr Plcmnt for Trnmiion Lin Lighntning Protction, IEEE Trnction on Powr Dlivry, Vol. 25, pp: 1743, [4] E. J. Triwicz,. Rimmr, A. S. Morchd, Trnmiion Lin Arrtr Enrgy, Cot, nd Rik Anlyi for Prtilly Shildd Trnmiion Lin, IEEE Trnction on Powr Dlivry, Vol. 15, nº 3, pp ,