VI.C CIRCUIT BREAKERS DMS #84474 Pge of 28 Revsed :
GUIDE FOR DETERMINATION OF CIRCUIT BREAKER LOAD CURRENT CAPABILITY RATINGS PENNSYLVANIA-NEW JERSEY-MARYLAND INTERCONNECTION PLANNING AND ENGINEERING COMMITTEE TRANSMISSION AND SUBSTATION DESIGN SUBCOMMITTEE R. W. Alexnder PP&L P. M. Blm Publc Servce Electrc nd Gs Compny A. Mnnrno Publc Servce Electrc nd Gs Compny J. W. Burds PJM Interconnecton, L.L.C. B. A. Chernsky GPU Energy J. R. Dsey, Jr. Conectv G. Nbet Bltmore Gs nd Electrc Compny K. P. McHugh PECO Energy Servces M. V. Thden Chrmn Potomc Electrc Power Compny DMS #84474 Pge 2 of 28 Revsed :
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TABLE OF CONTENTS SUBJECT PAGE TABLE OF CONTENTS 3 SCOPE AND PURPOSE 4 BACKGROUND 4 DISCUSSION OF RATING METHOD 4 DEFINITIONS 5 AMBIENT TEMPERATURE 6 NORMAL RATINGS 7 EMERGENCY RATINGS 7 CURRENT TRANSFORMER AND CONNECTED EQUIPMENT LIMITATIONS 7 BUSHINGS & CONNECTIONS 7 DETERMINATION OF RATINGS 8 MAINTENANCE REQUIREMENTS 9 TABLE I- - TEMPERATURE LIMITATIONS FOR CIRCUIT BREAKERS 0 TABLE II - CIRCUIT BREAKER RATINGS ANNEX I - FORMULAE AND SAMPLE CALCULATIONS 2 PART A CIRCUIT BREAKER RATING FORMULAE 2 PART B CURRENT TRANSFORMER RATING FORMULAE 5 PART C SAMPLE CALCULATIONS 7 BIBLIOGRAPHY 24 DMS #84474 Pge 4 of 28 Revsed :
SCOPE AND PURPOSE Ths gude presents prncples nd procedures to be used n estblshng norml nd emergency lod current crryng cpbltes for crcut brekers ffectng the PJM Interconnecton. It does not consder close nd ltch, three-second nd nterruptng cpbltes. The resultng rtngs cn be used for selectng the most economcl nmeplte rtngs for new crcut brekers. Crcut brekers bult under stndrds lsted n the References of ths report re ncluded. Ths gude ncludes methods for determnton of rtngs of ll crcut breker current trnsformers except ol-flled woundtype current trnsformers. Recognton s mde tht exceptons such s those lsted n the subhedng enttled Current Trnsformer nd Connected Equpment Lmttons my be necessry for specl condtons. Crcut breker nd crcut breker prts terms used n ths report nclude current trnsformers unless they re specfclly excepted. BACKGROUND The recognton tht vrous desgn of brekers cn crry dfferent norml nd emergency currents led to the estblshment of rtngs bsed on breker cpbltes, opertng procedures, physcl envronment, nd specl condtons. These vrbles resulted n wdely dfferent methods of rtng nd produced dfferent rtngs for dentcl crcut brekers. Accordngly, the gol of common crcut breker rtng perod for ll PJM Compnes hs been pursued for some tme nd s now requred for proper PJM rtng dmnstrton. DISCUSSION OF RATING METHOD The rtng methods estblshed by ths report represent compromses n the vrous fctors nd consder provsons of ANSI Stndrd C37.00-979, C37.00b-985, nd C37.00-99X-D.2 (02/98). The method developed s bsed prmrly on the followng:. Ambent temperture ( ). b. Temperture rse s functon of the.8 power of the current. c. Mxmum temperture determned to be cceptble for vrous crcut breker components under norml nd emergency condtons. d. Acceptble ccelerted deterorton of some crcut breker prts under emergency condtons. DMS #84474 Pge 5 of 28 Revsed :
DEFINITIONS Followng re defntons of terms used n ths report for use n determnng PJM crcut breker rtngs. Rted Contnuous Current (Nmeplte Rtng) (I r ) Mxmum current n mpere t rted frequency devce cn crry contnuously wthout ny prt exceedng ts lmt of observble temperture rse. Rted Contnuous Current (Nmeplte Rtng) of Current Trnsformer Tp (Itp r ) Mxmum current n mperes t rted frequency specfc tp of current trnsformer cn crry contnuously wthout the current trnsformer exceedng ts lmt of observble temperture rse. Adjusted Rted Contnuous Current of Crcut Breker (I) Rted contnuous current of crcut breker corrected to lmt of observble temperture rse usng specfc temperture rse by test. Note: I = I r when specfc temperture rse test dt s not vlble. Adjusted Rted Contnuous Current of Current Trnsformer Tp (Itp) Rted contnuous current of specfc tp of current trnsformer corrected for connecton on reduced tp nd to lmt of observble temperture rse. Norml Current Rtng (I ) Current whch cn be crred contnuously wthout ny crcut breker prt exceedng ts norml llowble mxmum temperture. Emergency Current Rtng (I e ) Current whch cn be crred for specfed perod of tme, t selected mbent temperture, wthout ny crcut breker prt exceedng ts emergency llowble mxmum temperture, e.g, e8 = 4 to 8 hour emergency current, nd e4 = 0 to 4 hour emergency current. Short Tme Emergency Current Rtng (I s ) Short tme emergency currents whch cn be crred for less thn 4 hours, e.g. I s.25 s the current whch cn be crred for ¼ of n hour (5 mnutes). Lmt of Observble Temperture Rse ( r ),.e., the llowble hottest spot temperture rse t rted current. Mxmum vlue of observble temperture rse of ny prt of crcut breker s lmted by C37.00-979 nd C37.4 953. Vlues re lsted n Tble I of ths report. Actul Ambent Temperture ( ) Actul mbent temperture expected. DMS #84474 Pge 6 of 28 Revsed :
Test Observble Temperture Rse ( ) Actul stedy-stte temperture rse bove mbent temperture of ny prt of crcut breker when tested t rted contnuous current. Lmt of Totl Temperture (mx),.e. the llowble hottest spot totl temperture Mxmum temperture whch ny crcut breker prt cn wthstnd contnuously. Vlues from C37.00-979 nd C37.4 953 re lsted n Tble I of ths report. Emergency Allowble Mxmum Temperture (mx e ) Mxmum temperture whch ny crcut breker prt cn wthstnd for vrous emergency rtng durtons, e.g., mx e8.= 8 hour mxmum temperture, mx e4.= 4 hour mxmum temperture, etc.. Temperture Due to Intl Contnuous Current ( ) Totl temperture due to ntl contnuous current t mbent. Utlzed n clculton of short term rtngs less thn four hours. Temperture Reched f I s were ppled contnuously ( s ) Totl temperture reched f the short term current I s were to be ppled contnuously t mbent. Utlzed n clculton of short term rtngs less thn four hours. Therml Tme Constnt ( τ ) Tme requred, n hours, for the temperture of crcut breker prt to chnge from the ntl vlue to the ultmte vlue f the ntl rte of chnge were contnued untl the ultmte temperture ws reched. (Assumed to be /2 hour mnmum for ll crcut brekers nd current trnsformers n ths report). Contnuous Therml Current Rtng Fctor (RF) [Pertnng to Current Trnsformers Only] The specfed fctor by whch the rted contnuous current of ny current trnsformer tp cn be multpled to obtn the prmry current tht cn be crred contnuously wthout exceedng the lmt of observble temperture rse. AMBIENT TEMPERATURE Snce mxmum crcut breker temperture s functon of prevlng mbent temperture,, the vlue of mbent temperture s mportnt for determnton of rtngs. For short-tme ntervls the mxmum expected mbent temperture s of prme mportnce. Temperture records surveyed by the PJM Compnes resulted n greement on use of the followng tempertures whch re consstent wth those used for ll PJM equpment rtngs. Rtng Durton Summer Wnter (Aprl thru October) November thru Mrch Norml contnuous 30 C Dly 0 C Dly Emergency 8 Hours or Less 35 C Dly 0 C Dly NORMAL RATINGS The norml current rtng of crcut breker s tht current whch cn be crred contnuously wthout ny crcut breker prt exceedng ts norml llowble mxmum temperture. The prme consdertons n defnng the norml current rtng of crcut breker re mbent temperture nd lmt of observble temperture rse. The norml current rtng s clculted by compenstng the djusted rted contnuous current (rted contnuous current f temperture rse from het run test s not vlble) for specfc mbent temperture. EMERGENCY RATINGS DMS #84474 Pge 7 of 28 Revsed :
Emergency rtngs for durtons of four hours to eght hours re bsed on operton up to the emergency llowble mxmum temperture for the lmtng crcut breker prt. Emergency llowble mxmum temperture lmts of 0 C nd 5 C bove the norml llowble mxmum temperture re utlzed for rtngs of eght hours n durton, nd for rtngs of four hours nd less durton, respectvely. These temperture lmts my results n slghtly ccelerted deterorton of some crcut breker prts but wll not ffect crcut breker nterruptng cpblty. Emergency rtngs for durtons of less thn four hours re determned bsed on the crcut breker therml tme constnt whch s functon of the het storge cpcty of the crcut breker. Lodng pror to pplyng emergency rtngs ssumed to be 00% of the norml rtng for the prevlng mbent temperture. Although rtngs cn be ncresed by ssumng pre-lod current less thn 00% of norml rtng, ths type of rtng s dffcult to supervse. CURRENT TRANSFORMER AND CONNECTED EQUIPMENT LIMITATIONS When current trnsformers hve Clss A nsulton, contnuous therml current fctor of.0, nd re connected on tp equvlent to or greter thn the crcut breker rted contnuous current, they wll not lmt the crcut breker norml or emergency rtng. Appendx II contns method for determnng the rtng of current trnsformer when connected on tp whch hs rtng lower thn tht correspondng to the rted contnuous current of the crcut breker. When determnng current trnsformer therml rtng ll ccessory equpment connected to the secondry must be checked for therml cpblty. BUSHINGS & CONNECTIONS Pror to 964, mx for bushngs ws lmted to 70 C, nd ths should be utlzed for brekers mnufctured pror to ths tme. Snce 964, crcut breker emergency rtngs hve been descrbed s requrements of ANSI stndrd C37.00 (Applcton Gude for AC Hgh-Voltge Crcut Brekers). Brekers purchsed to meet ths stndrd should contn bushngs, tht would operte to the emergency condtons descrbed. The crcut breker mnufcturer should be contcted to determne bushng cpbltes. Untl recently the overlod cpblty of bushngs hs not clerly been defned. Bushng stndrds hve ndcted tht bushng ppled n crcut breker must be desgned to operte stsfctorly t rted condtons wthout exceedng the temperture rse lmttons of the nsulton utlzed. In recent yers (989-999) work hs been ongong to determne the therml performnce of pprtus bushngs, however, fnl stndrd hs not been ssued. When ssued, the stndrd s expected to pply only to recently mnufctured bushngs. Some gudnce cn be obtned from pper publshed n 978 (see bblogrphy) whch descrbes the mthemtcl modelng tht cn be used s the bss for lodng gude. Connectons must lso be consdered when determnng crcut breker lodng cpbltes. Snce 964, ANSI bushng stndrds hve ndcted tht externl bus or cble connectons under norml condtons should not operte wth more thn 30 C rse (e.g. totl temperture of 70 C t 40 C mbent) t norml rted currents. Desgn exceedng these levels would both deterorte the bushng under norml condtons nd could further elevte temperture rses under emergency condtons. DETERMINATION OF RATINGS Crcut breker rtngs cn be determned s follows: ) If no nformton s vlble on crcut breker mterls or the yer of mnufcture, the followng mnmum rtngs from Tble II cn be ppled. Mnmum Rtng of All Crcut Breker Mterl Clsses (Percent of Crcut Breker Adjusted Rted Contnuous Current) Rtng Durton Wnter Summer (%) (%) Norml 2 07 Emergency, 4 to 8 hours 28 DMS #84474 Pge 8 of 28 Revsed :
Emergency, 0 to 4 hours 3 5 Emergency, 5 mnutes, (.25 hours) 7 35 These mnmum rtngs do not consder lmttons of current trnsformers:. Wth 80 C rse nsulton becuse only smll number re n servce. 2. When connected to reduced tp. 3. When connected equpment s thermlly lmtng. These mnmum rtngs do not consder lmttons of bushngs nd ther externl connectons. b) If crcut breker mterls nd/or the yer of mnufcture s known, refer to Tble I nd then determne rtngs from Tble II. c) If crcut breker mterls nd yer of mnufcture re known nd temperture rse dt from het run tests s vlble, refer to Tble I nd then determne rtngs from Appendx I or II. DMS #84474 Pge 9 of 28 Revsed :
MAINTENANCE REQUIREMENTS Stsfctory performnce of crcut brekers crryng lods bsed on rtngs estblshed by ths report re dependent upon dequte mntennce. The requred frequency nd extend of mntennce wll be determned by severty of short crcut current, frequency of crcut breker operton nd pplcton of emergency lodngs. The blty of crcut breker to crry norml, emergency or short crcut currents my be mpred f the crcut breker s not properly mntned. DMS #84474 Pge 0 of 28 Revsed :
Crcut Breker Component Descrpton TABLE I TEMPERATURE LIMITATIONS FOR CIRCUIT BREAKERS Lmt of Observble Temperture Rse t Rted Current r ( C) Lmt of Totl Allowble Mxmum Temperture mx ( C) Emergency Allowble Mxmum Temperture Rtng mx e ( C) 8 Hours or Less mx e8 4 Hours or Less mx e4 Brekers mnufctured pror to 964 Contcts n ol, ol nd bushngs 30 70 80 85 2 Contcts n r or gs 35 75 85 90 3 Averge Wndng Temperture Rse of Current Trnsformer wth 55 C Rse (Clss A) Insulton 4 Averge Wndng Temperture Rse of Dry-Type Current Trnsformer wth 80 C Rse (Clss B) Insulton Brekers mnufctured 964 nd lter 2 Copper Contcts, Copper-to- Copper Conductng Jonts, Externl Termnl Connected to Bushng 55 95 05 0 80 20 30 35 30 70 80 85 2 Top Ol 40 80 90 95 3 Hot Spot Ol t Ponts n Contct wth Hot Prts, Slver (or Equl) Contcts or Conductng Jonts n Ol 4 Averge Wndng Temperture Rse of Current Trnsformer wth 55 C Rse (Clss A) Insulton 5 Slver (or Equl) Contcts or Conductng Jonts n Ar or Gs, Hottest Spot of Bushng Metl Prts n Contct wth Clss A Insulton or wth Ol 50 90 00 05 65 05 5 20 65 05 5 20 6 Averge Wndng Temperture Rse of Dry-Type Current Trnsformer wth 80 C Rse (Clss B) Insulton 0 50 60 65 Adpted from ANSI C37.00-979, C37.00b-985, nd C37.4-953 2 Unless ndcted otherwse by mnufcturer contcts nd conductng jonts n other thn ol or r re ssumed to be t 65 C hottest spot rse nd 05 C hottest spot totl temperture per ANSI C37.0b-985 DMS #84474 Pge of 28 Revsed :
TABLE II CIRCUIT BREAKER RATINGS (% OF ADJUSTED RATED CONTINUOUS CURRENT) Allowble Mx. Temp. Rtng Durton Norml Ambent Adjusted 70 C 75 C 80 C 85 C 90 C 95 C 05 C 0 C 20 C 50 C Mnmum Rtng of ll tempertures 5 W 2 S 3 W 2 S 3 W 2 S 3 W 2 S 3 W 2 S 3 W 2 S 3 W 2 S 3 W 2 S 3 W 2 S 3 W 2 S 3 W 2 S 3 47 7 4 5 36 3 32 29 0 27 09 23 08 2 07 9 06 4 05 2 07 8 Hrs. 60 25 52 2 47 9 42 7 38 5 35 4 30 2 28 25 0 8 07 28 4 Hrs. 66 32 58 28 52 25 47 22 42 20 39 8 33 6 3 5 28 3 2 09 3 5 5 mnute 200 6 73 200 6 64 200 6 57 200 6 52 93 47 86 43 75 37 7 35 63 3 3 48 7 35 Notes:. CAUTION: The rtngs n ths tble do not nclude lmttons of bushngs, nd/or current trnsformers connected on reduced tps or lmttons of equpment connected to current trnsformers. ANSI lmts lodng beyond nmeplte to 200%. 2. Wnter mbent temperture s 0 C for ll rtng durtons. 3. Summer mbent tempertures re 30 C for contnuous norml rtngs nd 35 C for rtng durtons of 8 hours or less. 4. These emergency rtng fctors re bsed on breker hlf-hour therml tme constnts, per ANSI C37.00-979. For tme constnts other thn one-hlf hour, specl clcultons cn be mde s outlned n Appendx II. 5. Mnmum rtngs lsted do not nclude 20 C nd 50 C becuse of the lmted number of bushng current trnsformers tht use 80 C rse nsulton. DMS #84474 Pge 2 of 28 Revsed :
ANNEX I - FORMULAE AND SAMPLE CALCULATIONS PART A - CIRCUIT BREAKER RATING FORMULAE.0 Correcton of Rted Contnuous Current (Bsed on fctory temperture rse test only) When crcut breker test temperture rse s less thn gurnteed, rtngs my be djusted s follows for ech mterl clss. I = Adjusted rted contnuous current I I r n r = I r = Rted contnuous current (crcut breker nmeplte rtng) = Test observble temperture rse t rted contnuous current r = Lmt of observble temperture rse t rted contnuous current n =.8 for crcut brekers For subsequent clcultons the djusted rted contnuous current (I) should be used when test dt s vlble. When test dt s not vlble, use rted contnuous current (I r ). Note: ANSI nomenclture utlzes (I r ), moreover I = I r when temperture rse tests re unvlble. 2.0 Clculton of Norml (Contnuous) Current Rtngs (Bsed on ctul mbent temperture) Wnter nd summer norml rtngs my not be equl to rted contnuous current but cn be determned s follows: I qmx- q = I qr I = Norml current rtng = Ambent temperture mx = Allowble mxmum temperture (mx = r + 40 C) n 3.0 Clculton of Emergency Rtngs of 8 Hour Durton Wnter nd summer emergency rtngs of 8 hour durton cn be determned s follows: I e8 = Emergency rtng for 8 hour durton I mx - n e8 e8 = I r DMS #84474 Pge 3 of 28 Revsed :
mx e8 = Emergency (8 hour) llowble mxmum temperture 4.0 Clculton of Emergency Rtngs of 4 Hour Durton Wnter nd summer emergency rtngs of 4 hour durton cn be determned s follows: I e4 mx - n e4 = I r I e4 = Emergency rtng of 4 hour durton. mx e4 = Emergency (4 Hour) llowble mxmum temperture DMS #84474 Pge 4 of 28 Revsed :
5.0 Clculton of Emergency Rtngs of Less Thn 4 Hour Durton Wnter nd summer emergency rtngs of less thn 4 hour durton cn be determned s follows: ( C ) I -40 = mx + I r For PJM rtngs n ths gude t s ssumed tht the ntl lod I s equl to I r the rted lod. Therefore the equton bove reduces to: ( mx-40 C ) = + n I s s mxe4 - = + t - -e τ s - = Ir mx-40 C n = totl temperture due to ntl contnuous current t mbent. s = totl temperture reched f I s were ppled contnuously t mbent. I s = Emergency rtng of less thn 4 hour durton t = Rtng durton (hours) τ = Therml tme constnt of the crcut breker (hours) τ, The therml tme constnt of crcut breker, preferbly should be obtned by test or t cn be conservtvely used s.5 hours (30 mnutes). DMS #84474 Pge 5 of 28 Revsed :
PART B - CURRENT TRANSFORMER RATING FORMULAE The current trnsformer s desgned to llow operton n the hgher temperture envronment of crcut breker. For smplfcton of clculton of current trnsformer rtngs, the ssumpton s mde tht the temperture rse of the current trnsformer wth the contnuous therml current rtng fctor ppled s equl to ts llowble mxmum temperture less the mbent temperture of the r surroundng the crcut breker..0 Correcton of Rted Contnuous Current for Operton on Any Tp Usng the current trnsformer tp settng, the djusted rted contnuous current of the tp my be determned s follows: I r Itp=Itp r Itpr n RF Itp = Adjusted rted contnuous current of specfc current trnsformer tp under consderton I r = Rted contnuous current (current trnsformer nmeplte rtng) Itp r = Rted contnuous current of specfc current trnsformer tp under consderton RF n = Contnuous therml current rtng fctor (Mnufcturer should be consulted for vlue of the contnuous therml current rtng fctor. Assume.0 f not vlble.) =.8 for current trnsformers Note: If temperture rse dt from het run test s vlble for current trnsformer, the djusted rted contnuous current of the tp my be determned usng the formule n Annex I, Prt C, 2.0, Determnton of Current Trnsformer Rtngs. 2.0 Clculton of Norml (Contnuous) Current Rtngs Wnter nd summer norml rtngs for current trnsformers cn be determned s follows: mx I Itp = r n DMS #84474 Pge 6 of 28 Revsed :
3.0 Clculton of Emergency Rtngs Wnter nd summer emergency rtngs for current trnsformers cn be determned s follows: 8 Hour Durton = mx - e8 Ie8 Itp r n = mx - e4 Ie4 Itp r Less Thn 4 Hour Durton = mx-40 C + ( ) n s mxe4 - = + t - -e τ I s s - = Itp mx-40 C n DMS #84474 Pge 7 of 28 Revsed :
PART C - SAMPLE CALCULATIONS.0 Determnton of Crcut Breker Rtngs eincludes current trnsformer lmttons) Snce ll crcut brekers my contn more thn one mterl clss, t wll be necessry to determne rtngs for ech mterl clss nd select the lmtng rtng for the pproprte condtons. Assume 200 mpere nmeplte ol crcut breker wth slver contcts, 200/5 mpere mult-rto bushng current trnsformers wth Clss A nsulton, contnuous therml current rtng fctor RF of.33 nd connected on the 200 mpere tp. Temperture rses from het run test dt re s follows: Observble Temperture Rse, Component C Bushng Termnl (Slver Plted) 50.4 Contcts (Slver-to-Slver) 43.5 Top Ol 28.0 Adjusted Rted Contnuous Current (Bsed on fctory temperture rse test only) For the 200 mpere (I r ) ol crcut breker, the djusted rted contnuous current should be determned for ech component. I I r.8 r = r I ( C) ( C) (mp.) Bushng Top Termnl 50.4 65 382 Contcts 43.5 50 296 Top Ol 28.0 40 463 DMS #84474 Pge 8 of 28 Revsed :
For the 200/5 mpere mult-rto bushng current trnsformer on the 200 mpere tp, the djusted rted contnuous current should be determned. I r Itp=Itp r Itpr.8 RF.8 200 =200.33 200 Itp=596 Ambent Adjusted Norml Contnuous Current Rtngs (Bsed on djusted current rtngs evluted from fctory temperture rse test) For ll prts except CT: I mx- = I r.8 For CT: mx I Itp = r.8 I (mp.) Summer Wnter I or Itp r mx =30 C =0 C (mp.) ( C) ( C) Bushng Top Termnl 382 65 05 496 706 Contcts 296 50 90 434 682 Top Ol 463 40 80 656 996 CT 596 55 95 75 2032 Contcts re lmtng for summer nd wnter rtngs. DMS #84474 Pge 9 of 28 Revsed :
Emergency Rtngs of 8 Hour Durton (I = nmeplte current rtng, Itp = Nmeplte current of CT wth RF of.33) For ll prts except CT: For CT: I mx -.8 e8 e8 = I r = mx - e 8 Ie8 Itp r I e8 (mp.) Summer Wnter I or Itp r mx e8 =35 C =0 C (mp.) ( C) ( C) Bushng Top Termnl 200 65 5 346 566 Contcts 200 50 00 388 663 Top Ol 200 40 90 432 763 CT 596 55 05 824 262 Bushng top termnl s lmtng for summer nd wnter rtngs. Emergency Rtngs of 4 Hour Durton (I = nmeplte current rtng, Itp = Nmeplte current of CT wth RF of.33).8 For ll prts except CT: For CT: I mx -.8 e4 e4 = I r = mx - e 4 Ie4 Itp r.8 I e4 (mp.) Summer Wnter I or Itp r mx e4 =35 C =0 C (mp.) ( C) ( C) Bushng Top Termnl 200 65 20 392 607 Contcts 200 50 05 446 74 Top Ol 200 40 95 50 824 CT 596 55 0 896 2224 Bushng top termnl s lmtng for summer nd wnter rtngs. Emergency Rtngs of 5 Mnute Durton (I = nmeplte current rtng, Itp = Nmeplte current of CT wth RF of.33) DMS #84474 Pge 20 of 28 Revsed :
Assumes.5 hour (30 mnute) crcut breker tme constnt wth t =.25 nd τ =.5. For ll prts except CT: ( mx-40 C ) = + s mxe4 - = + t - -e τ I s s - = Ir mx-40 C.8 For CT: I s s - = Itp mx-40 C.8 I s.25 (A) Summer Wnter I or Itp mx mx e4 =35 C =0 C (A) ( C) ( C) ( C) s ( C) I s ( C) s ( C) I s Bushng Top Termnl 200 05 20 00 50.8 654 75 89.3 22 Contcts 200 90 05 85 35.8 77 60 74.3 236 Top Ol 200 80 95 75 25.83 892 50 64.3 2400 CT 596 95 0 90 40.8 2295 65 79.3 2968 Note: s s the fnl temperture reched f the.25 hour (5 mnute) rtng ws ppled contnuously. Bushng top termnl s lmtng for summer nd wnter rtngs. DMS #84474 Pge 2 of 28 Revsed :
2.0 Determnton of Current Trnsformer Rtngs The followng exmple llustrtes the mpct on emergency rtngs tht results from utlzng reduced tp on CT. Compre these rtngs to the prevous exmple (Annex I, Prt C,.0) nd note the CT wll become the component lmtng crcut breker emergency rtngs. Assume the crcut breker n the bove exmple hs 200/5 mpere mult-rto current trnsformers wth Clss A nsulton, contnuous therml current rtng fctor (RF) of.33 nd s connected on the 800 mpere tp. Adjusted Rted Contnuous Current I r Itp=Itp r Itpr.8 RF 200 Itp=800 800.8.33=332 mp. Ambent Adjusted Norml Contnuous Current Rtngs (Bsed on djusted current rtngs evluted from fctory temperture rse test) mx I Itp = r.8 I o o = 30 C summer; 0 C wnt er. I I ( ) ( ).8 wnter =332.27=696 mp. summer =332.09=46 mp. Emergency Rtngs of 8 Hour Durton (I = nmeplte current rtng, Itp = Nmeplte current of CT wth RF of.33) = mx - e 8 Ie8 Itp r.8 I e 8 95- = 332 55 05- = 332 55 o o = 35 C summer; 0 C wnt er. Ie8 ( ).8 wnter =332.35=804 mp. DMS #84474 Pge 22 of 28 Revsed :
Ie8 ( ) summer =332.4=523 mp. Emergency Rtngs of 4 Hour Durton (I = nmeplte current rtng, Itp = Nmeplte current of CT wth RF of.33) = mx - e 4 Ie4 Itp r.8 I e 4 0- = 332 55 o o = 35 C summer; 0 C wnt er. Ie4 Ie4 ( ) ( ).8 wnter =332.39=856 mp. summer =332.8=582 mp. Emergency Rtngs of 5 Mnute (.25 hour) Durton ( mx-40 C ) = + s mxe4 - = + t - -e τ I s.25 s - = Itp mx-40 C.8 DMS #84474 Pge 23 of 28 Revsed :
( ) Summer = 35 C = 0 C-40 C + 35 C= 05 C s 0 C-05 C = + 05 C.25 - - e.5.8 7.7-35 I = I =.097I 0-40 C s.25 tp tp Is.25 ( summer ) =332.09=46 mp. ( ) Wnter = 0 C = 0 C-40 C + 0 C = 80 C s 0 C-80 C = + 80 C.25 - -e.5.8 56.24-0 I = I =.505I 0-40 C s.25 tp tp Is.25 ( ) wnter =332.50=2005 mp. DMS #84474 Pge 24 of 28 Revsed :
ħ BIBLIOGRAPHY. ANSI Stndrds C37.04-979 (R988) Rtng Structure for AC Hgh-Voltge Crcut Brekers on Symmetrcl Current Bss. 2. ANSI Stndrd C37.06-97 Schedules of Preferred Rtngs nd Relted Requred Cpbltes for AC Hgh-Voltge Crcut Brekers Rted on Symmetrcl Current Bss 3. ANSI Stndrd C37.09-964 Test Procedures for AC Hgh-Voltge Crcut Brekers 4. ANSI Stndrd C37.09-979 (R988) IEEE Stndrd Test Procedure for AC Hgh- Voltge Crcut Brekers Rted on Symmetrcl Current Bss. 5. ANSI Stndrd C37.00-979 (R988) Applcton Gude for AC Hgh-Voltge Crcut Brekers 6. ANSI Stndrd C37.00b-985 IEEE Stndrd for Emergency Lod Current-Crryng Cpblty 7. ANSI/IEEE Stndrd UNAPPROVED DRAFT SUBJECT TO CHANGE C37.00-99X- D.2 (02/98) IEEE Applcton Gude for AC Hgh-Voltge Crcut Brekers Rted on Symmetrcl Current Bss 8. ANSI Stndrd C37.4-953 Alterntng-Current Power Crcut Brekers 9. ANSI Stndrd C37.6-97 Schedules of Preferred Rtngs for AC Hgh-Voltge Crcut Brekers Rted on Totl Current Bss 0. ANSI Stndrd C37.9-953 Test Code for Power Crcut Brekers ħ. ANSI Stndrd C57.3-993 Requrements for Instrument Trnsformers 2. ANSI Stndrd C76.-943 Apprtus Bushngs nd Test Code for Apprtus Bushngs 3. ANSI Stndrd C76.-964 (R970) Amercn Stndrd Requrements nd Test Code for Outdoor Apprtus Bushngs 4. ANSI Stndrd C76.-976 IEEE Generl Requrements nd Test Procedure for Outdoor Apprtus Bushngs 5. PJM Report Gude for Determnton of Current Trnsformer Rtngs, June, 998, by Trnsmsson nd Substton Desgn Subcommtte. 6. Method of Predctng the Therml Lodng of n Ol Crcut Breker Proceedng, Insttuton of Electrc Engneers, Vol. 2, No. 5, My, 965, pp. 986-994. 7. McNutt, W. J. nd Esley, J. K., Mthemtcl Modelng A Bss for Bushng Lodng Gudes, IEEE Trnsctons on Power Apprtus & Systems, Vol. PAS-97, pges 2393-2404, November/December, 978. Orgnlly Issued: DMS #84474 Pge 25 of 28 Revsed:
Orgnlly Issued: DMS #84474 Pge 26 of 28 Revsed: