low and medium voltage distribution systems

7/28/2019 Low and Medium Voltage Distribution Systems

1/5

thepowertoprote

ct

ASK THE EXPERTS

Low And mEdium voLTAg

diSTRibuTion SySTEmS

the per t prtect

ASK THE EXPERTS

Arc Flash Hazars a Hh

Resstace gr

ASK THE EXPERTS

gr Staby a

Eerecy Pwer Systes

ASK THE EXPERTS

netral gr Resstrs

-des a Applcat

PRoduCT guidE

Hh Resstace gr

Systes

ASK THE EXPERTS

Syste gr

-det a dferet Types

CoRPoRATE mAnuAL

i-gar Crprat

i-gARd LiTERATuRE

.ar.c


2/5

thepow

ertopro

tect

L a me vltae dstrt Sstes

Electrcal strt sstes ca eerall e classe as l ltae (208 lts t 4,160 lts) a eltae (4,160 lts t 13,800 lts) a hh ltae (ae 13,800 lts). y ca ral class e

ltae (mv) r (earth) sstes t r cateres: sll re, lresstace re

(LRg); hhresstace re (HRg) a slate etral (re) sstes.

wth the sll re sste, there s tetal peace the etraltearth path. istea, theetral s sll cecte t earth. The phasetr ltae reas cstat r a r alt, a

there are er hh alt crret s, reslt extese aae. The prtecte ece clsest t the alt

st trp a slate the crct as ast as pssle. The cst repar s hh e t extese eerec repars.

i the alt s a rtat ache, the there s a hh psslt cre aae a replaceet csts. Als,

the cst asscate th the te ca e ers.

wth LRg, the r alt crret s ctrlle a rall lte t etee 25A a 1000A. The ltae

tr the alte phases creases t the phasetphase ltae leel, s st se aeqatel

rate slat sstes a sre sppress eces. Als, the r alt st e etecte a slate.

Sce the r alt crret s saller a ctrlle, r alt rela stll has the reqreet ast

trpp. bt, etter te/crret crat ca e achee th ths tpe r sste. daae

at the alt pt s als rece a ths the ateace a repar csts are als rece. The etral

r resstr ees t e shrt te rate (tpcall 1030 secs), as the alt ll e cleare the

prtecte rela clsest t the alt.

wth HRg, the r alt crret s the 10A rae. The tet here s t all the sste t perate

tht trpp ee th a phasetr alt e phase. whe a r alt es ccr, l a

alar s rase. Ths perts te t lcate the alt hle per ctt s atae. Ths als alls repars

t e e at a schele sht the alt eqpet. daae at the alt lcat s sall.

wth the slate etral (re) sste, there s tetal cect the sste t r.

i eect, the three phases the sste at. whe a r alt ccrs, the alt crret s ctrte

the sste capactace t earth the alte phases. Ths s sall sall a the sste ca e perate

tht trpp. Sce the sste s at, the r alt s a arc r terttet tpe, there s psslt

sstatal traset erltaes, hch ca e sx t eht tes the phase ltae. These trasets te

case a sseqet alre elsehere a ths rase the psslt a phaseteartht phase alt, lea

t hh alt crret a extese aae.

Fr stat serce at strt ltaes less tha 15kv, per ctt s er prtat. Here, l

sze the etral r resstr s that the let thrh r alt crret s hher tha the et crret

r the strte capactace. i the lettrh r alt crret s less tha 10 A, the ths l e hh

resstace r. i ths crret ere re tha 10A the t l e l resstace r.

it s rare t hae stat serce ltae that s hher tha 15kv. i the ltae s hher tha ths, the the sae

rle as te ae l appl, except the alt shl e etecte a slate trpp the alte eeer

at the clsest prtecte ece.

mre recetl hr r has ee prpse. Here, a crret lt ece s parallel th a resstr,

sch as a resstr l resstace a the ther hh resstace (5A). i the eet a teral earth alt

the statr the eeratr, a ast act eeratr r eretal rela pes the crret lt

ece ( ths case the l resstace r path) a ths alls the hhresstace (5A letthrh)

resstr) t ctrl a ler the alt crret, ths rec the statr aae case the teral r

alt ater the eeratr has ee slate a hle t s sl . wtht t hs rect crret, the

eeratr l cte t ee eer t t he alt hle t s c t a stp. The reslt l e extese

statr r aae at the r alt lcat.

netral Earth Resstr

Q. what s r ace chs resstaceetral earth he e hae t se l r hh resstace?Als, h ee crret prtect resstace earth?

A. Hh resstace earth s se 3phase, 3re strt sstes p t 5 kv (letle), here:

(a) at t ata serce ctt p earth alt (.e. t trp alte eeer earth alt); a

() the sste char crret s less tha 6 A; a

(c) the etral earth resstr s sze r a aperae etee 110 A. Tpcall, 25 A s se r sste ltaes p t690 v; 510 A s se r sste ltaes ae 690 v, p t 5 kv; a

() the etral earth resstr letthrh crret s eqal t r hher tha the sste char crret.

Lresstace earth s se e ltae sstes ae 1 kv, here the sste char crret s hher tha

6 A. dstrt sstes ae 5 kv st t e hh resstace earthe ee the char crret s less tha 6 A; the

sle except t ths rle s a tlt eeratrtrasrer t, here a 15 kv eeratr eerates tlt per a ees

rectl a stepp trasrer r trasss ths case the 15 kv sste char crret s s l that hh resstace

r th a 510 A resstr a e se. istral strt sstes ae 5 kv st trp earth alt, rer

t a escalat the earth alt t a phasetphase alt, at the pt alt. The sste char crret a the

ltae t r are lare eh that the rsk escalat s t hh. S, lresstace earth s se t lt the

earth alt crret, tpcall th the rae 50400 A t all r the earth alt t e sese a selectel trppe

le a earth alt rela. Hh crret (400 A) st e se resallcecte CTs are se t sese the earth alt

r the earth alt rela. Ler crrets ca e se (50200 A) a crealace CT s se r pt t a rela th seste

earthalt eatre. Lresstace earth s etter tha sl earth (Tn) ecase s lts the earth alt crret t a s ae

ale, there rec arc ash cets a eqpet aae earth alt.

T prtect starcecte trs, a eeer earth alt rela shl e set t trp at 1020% resstr letthr crret. 10% s

the , t a lea t sace trpp, hece ca e crease t 20% case sace trpp ccrs ths ca

e easl ajste at css te. Ths sett alls captre earth alt that ccr the statr clse t

the etral pt (th 1020%), here the ltae t re the earth alt ll l e 1020% rate, hece the crret

ll e 1020% resstr letthr rat. The trp sett shl e eqal t r hher tha the sste char crret t

a sace trpp alte eeers, hse earth alt sesrs ll sese each ther eeers ctrt t

sste char crret r earth alts elsehere the sste. S the sste char crret a 15 kv sste s

15 A, the the earth alt pckp sett cl e 20 A, sa, s a crealace CT a seste earth alt rela.

The the resstr shl e 10 tes ths, r 200 A.

T prtect eltacecte trasrers, the alt crret r a elta s 50%, ecase atter here

the earth alt s lcate the , t ll alas e etee 50100% the leetral ltae, hece the earth alt

crret ll e at least 50% resstr letthrh crret. Therere, a earth alt pckp sett 2050% s acceptale.

Fr selectt, earth alt pckp setts er the rae 2060% resstr letthrhcrret eeers s acceptale.

Fr ackp prtect, earth alt pckp setts er the rae 5080% resstr letthrh crret the earth

resstr are acceptale.

Fr hhresstace r, etral earth resstrs st e cts t rate.

Fr l resstace r, etral earth resstrs are rate r 10 secs t. Earth alts are trppe le

etee 100 s t 1 sec.

o parallel eeratrs, se a sle etral earth resstr cecte t the parallel s thrh a zza earth

trasrer.


3/5

2 QA

gr r Cgeerat 13,8kv

Q. i l lke t k at the ccept r r eeratrs 13,2 r 13,8 Kv; ths case shl the practce eetral resstace r sste, r a t e sll re?

The iEEE St. 1421991, the gree bk, Recee Practce r gr istral a Cercal Per Sstes,

es se rat at ths case; s ths the ral a the al pst?

A. me ltae stral eeratrs shl e lresstace re, t sll re. See sect 1.8 the iEEE gree bk(St. 1421991) r a scss eeratr r. Ather srce r e ltae eeratr r a prtects Sect 12.4 the iEEE b bk, St. 2422001, a Recee Practce r Prtect a Crat istral a Cercal

Per Sstes. Sll re eeratrs tpcall experece 2050% hher alt crret er r alts tha er threephase

alts.

The sae s t tre r trasrers. yet eeratrs are rall race l t thsta threephase lte alts, t r alts. geeratrs

shl t e sll re less the are rate r sl r t, rearless ltae leel. me ltae eeratrs are qte

expese a hae a l eler te; ther las are alas 3re, hece le the t resstace r. T lt r alt

crret, the are sall lresstace re th a etral r resstr rate 200400 A, 10 secs. T a statr r r

aae r a statr r alt a eeratr, a e techqe mv eeratr prtect, calle Hr gr, has ee eelpe

recetl. i at t the 200400 A ngR, a 10A ctst ngR s cecte t the eeratr etral. up eeratr r alt,

the aecte eeratr s eatel trppe le r the lare ngR; the stre aetc eer th the eeratr s sael schare

thrh the 10A ngR tht aa the statr. Ths r alt schee reqres a 51n r alt rela each eeer, a a 87gd

rectal r eretal rela the eeratr. The 87gd rela stshes etee teral a exteral r alts. Fr exteral

r alts, the 51n eeer rela selectel trps the alte eeer. Fr teral r alts, the 87gd rela trps the alte eeratr

le. backp r alt prtect s pre th a 51g rela the lare ngR, crate t all the prar 87gd a 51n relas t trp

rst. A alre the prar rela cases the ngR 51g rela t trp the eeratr(s) le, eeerz the strt sste.

Fr re etals the hr r schee, reer t the ll rpart artcle: iEEE Trasacts istr Applcats, Ja/Fe

2004, vl. 40, n. 1, gr a gr Falt Prtect mltple geeratr istallats mevltae istral a Cercal

Per Sstes, Pralla Plla et al.

Harcs

Q. H are harcs prce the HT sste se a plat? we se certrs a recters LT se l. H theseharcs teract th the HT trs?

A. HT a LT sta r hhtes a ltes, als k as eltae (mv) a lltae (Lv), respectel. Tpcall eltae trasrers pre per t the Lv sste r the mv sste. Trple harc crrets the Lv se et trappe the elta

(at least the alace prt the trple harcs ) a t the mv se. ntrple harc crrets (5th, 7th,

11th, 13th, etc) pass rht thrh the trasrers a the mv se. These ca teract th the mv trs t as: i there are

peractrcrrect capactrs the trs, the the harc crrets ca e attracte t the capactrs stea the tlt srce.

Harc resace ca ccr a the per actr crrect capactrs ca erheat, erae, a lse ther capactace er te. or,excesse harc crrets ca case excesse harc ltae strt thrh the peace the mv strt sste, cas the

trs t erheat. Ths es t alas ccr, t he t es, slts cle a harc lters at the a Lv stchars t keep

the trple harcs r ett t the mv sste; s atresatper actr crrect capactrs, hch hae et

reactrs t preet harc resace etee the capactrs a the per srce peace.

Hh Resstace gr

Q.Traset erltaes re electrcal sstes e t terttet r alt exst. The hh resstareces the ptetal erltae scatl. what at sre sppressrs? d the prtect a e lta

the erltae? d the prtect the sste th hhresstace r he the r resstace

crrectl a a capacte char crret s seeral tes hher tha the resstr crret?

A. The traset erltae case terttet r alt re sste s e t the strte capactathe three phases. The ate ca e 5 t 6 tes phase t phase ltae. The etral r resstr alls ths chare

a hls the etral ae r at phasetetral ltae ths all the ltae t r the alte p

crease r phasetetral ale t phasetphase ale a ths ll exst ctsl as l as the alt s preset. Sltae e the phasetphase ltae ate. Heer, er shrt rat trasets ca stll ccr a exst t

sch as thse case the lht strkes a stch.

Sre sppressrs are rall tee t clp a asr er shrt rat (llsec t crsecs) traset er

thse case lht strke a stch. The cat hale cts excesse ltae. Ther clpp ltae s a

cl e re tha 1.5 X the ral stea state peak ltae. S he TvSSs are apple HRg sstes the ee t e rat

ltae. The ll the clp trasets ae ther cts rat.

nER mevltae Sste

Q. Ths s relate t sz a etral earth resstrr 33kv sste. The a per trasrer rat s

132/33kv, 25/31.5mvA yn1. T trce sste earth

33kv se, a earth trasrer s trce. Rat

the earth trasrer s 33/0.433kv, 315kvA, Zn11.

T hae resstacere earth, nER s trce

the etral path earth trasrer. we l lke t

restrct the earth alt crret t 550A.

The qest s, hle eter the resstace ale

nER, shl e cser ttal peace the crct r

Srce rht p t the alt pt 33kv sste. what ll

e the pact e elect the zer seqece peace

per trasrer a earth trasrer?

A. yes, the ttal r alt crret s epeet p letetral ltae a peace etre retr path, hch

cles eerth ete.

Experece shs that at e ltae (a th a stral

sett), the ltae acrss the earth resstr qckl rses t

letetral ltae, cat that the peace the retrpath a trasrers are relatel sall cpare t peace

earth resstr. S es, t shl e csere t rarel es

t hae a lare pact.

Q. i a crretl ace th a eltatr a ee t cect a tal crc

teperatre the s. i hae a spl

240v as e t l hae access t

(415v Astrala) a at t se a tras

ltae r 415 240v. wl ths e sae c

s etral ths setp? i hae cect

the secar the 2407.5v

r t esre t s re prperl. is

et earth prles a trp crct reak

A. it s perectl sae t cect a slephasslat trasrer rate 415v prar, 240v

t the phases the 415v elta per src

a e earthe as hae e (that s the p

y ll t aect the earth sste the pr

the trasrer s t a attrasrer. The

etee the prar a secar s

trasrers ecples the earth (r

etee the prar a secar. Fr exap

the secar ll t case a r a

t rather a phase ercrret, hch t trp

prtecte eces.

mltple Trasrers 4157

the per t prtect


4/5

4

QA400kv/220kv itercect Trasrers

Q. what s the ecesst 33k reactrs the trasrers a hat are zza tpe trasrers?

A. Reactrs mv Sstes ca e se t as. 1) whe the aalale shrt crct crret r the etrk s t hh ae the capalt crct prtecte eces the reactrs the three phases ca pre the lt peace that reces theaalale shrt crct crret. The atal ltae rp trce ees t e csere. 2) Reactrs ca als e apple etee

etral a r t pre reactace r the sste. Ths pres a la r crret hch as t the lea

capacte crret ctrte the et strte le t r capactace r the t alte phases the eet a le

t r alt. i ths reactace s ae lare eh t exactl atch ths capacte crret the there l e zer crret the

alt cseqetl arc a er l alt aae. Heer, the reactace ca als case trasets a resace th the le

capactace. S stl resstace s se r earth.

A zza trasrer s a threephase attrasrer hch each le has t etcal cls a the are crss cecte t r a

star. Frst terals the three cls et cecte t three phases A, b, C. The Phase A sec teral ets cecte t the sec

cl phase b le; slarl, sec teral Phase b ets cecte t sec cl Phase C, a the sec teral Phase C

ets cecte t the sec cl Phase A. The es t these three sec s are cecte a star. Ths s the etral

Select Crtera r mevltae ngR

Q. i a sz a ngR r a 132kv/11kv, d11 40 mvA trasrer. The est tr cecte the 11 kv sste s5.3mw slpr tr a the sallest e s 300kw. i a lk r a l resstace earth sste. what shl e

the crret lt ale r the ngR? H t s arre at? what are the crtera?

A. i rece s lresstace r (LRg) e t the ltae a capact. At 11kv a 40mvA, the capact (mvA) catesthe sste s lare ( ters ttal leth all the eeer cales, hch are tpcall the reatest ctrtr t sste capacte

char crret) a the ltae ces hher ats sste capacte char crret. The ext larest ctrtr t sste

capacte char crret s sre arrestrs/capactrs eeratrs.

i l rece 200A as ths s ec the str staar. The ngR s etere tak the letetral ltae (11kv

/ 1.73 = 6.36kv) e esre crret (200A) t et hs (31.8hs). mst peple l all the alt t e the sste r 10

secs r less. S, the ngR l e rate r 200A / 10 secs. Jst ake sre that the prtecte rela schee clears the alt

th 10 secs.

i eeral, ler the alt crret; ler s the aae at the alt. Therere, t s esrale t keep the alt crret as l as pssle.

i mv trs are e prtecte the keep the alt crret l als helps ler the aae t the laats at the alt

pt the eet a alt the statr . i e cecte tr s the r ltae r the r alt reces as

the alt lcat es clser t the star pt hece r alt rela st e set seste eh t etect the alt a sfcet

Zza gr Trasrer

Q. i hae a applcat here i hae a 75KvA rtpe lht slat trasrer 480v threephase elta t phase elta.

The er es t lke the re elta sce there s reerece t r r lht r alts a

r reerece estalshe rer t esre a l lht se he a r alt ccrs. All the lht

slephase th ses the xtres. Rather tha replace the trasrer, i thh t l e cheaper t s

zza r trasrer, threephase re e tht a secar a attach t t the elta sec

75kvA trasrer. Ths l essece estalsh a r a e lht r alts a rect path ack t

i hae lteratre these tpe zza r trasrers t i cat ae h ca sell e

3kvA sze rae. Ca help? A t r klee s t hs a reasale applcat?

A. i hae see 277v lht apple 277/480v threephase rre sstes a 347v lht apple 347v/600v trre sste. Ass that lht s actall 480v, t l a se r alt ll ee sstatal r c

610 X se rat.

3kvA zza s a pssle pt t ca pre sfcet r crret t pe the se. T pssle spplers are Ha

Trasrers.

delta cecte s are te se s that th ees t e trppe the rst phase t r alt. A sall ct

zza th p t 5A r resstr ll pre stalt a all r crret t hch ca e etecte r

A alar s rase cat a r alt. whle th s trppe. The xtres are cecte t r thrh the r

carres the r crret ctsl a keeps the sae t tch.

Hr gr

Q. Fr the Hr eth, hat eqpet se t pe the l resstace r resstr?

A. y ca se a sle ple ac ctactr. we hae see these rate 15kv., 200A.

the per t prtectA cat ngR tr a r alt rela, t pres

ajstale pck p leel a ajstale ete te ela r the r

crret. i Resstace gre Sstes, the etral r resstr

s cstatl tre t esre that the 3phase 3re strt

sste reas alt ree. The igar SigmA s ese r se a

resstace re sste that reqres cts tr the

netral gr Resstr. A separatel te sesr easres the

r crret a the ltae acrss the ngR. The ales easre

are cpare th setts a trp a alars are cate he a


5/5

6 QA

Q. is ths a sse saller 12470 lt eeratr sets that are sll re? we hae seeral hsptals that hae three12470 lt eeratr sets (1.5 t 2.5mw ) that ca e parallele th the tlt.

A. Ths s er ch a sse he at t prtect a k s cecte e ltae eeratrs. As state thepresetat, mst e ltae eeratrs are t rate t thsta a sle phase t r alts. The srace cpaes

reqeste iEEE t speccall lk at h the ral e prtect as t aeqatel prtect the eeratrs. Ths s h the

Hr sste as eelpe.

Q. Ca exst e prae?

A. All eeratrs ca e prae. Ths prae ca e er sple r er cplexe t exst rastrctre.

Q. y et ltae escalat qckl at e ltaes a lare sstes ( sa 4160, 13.8kv). what at asste 2.4kv th 16 2 4mw eeratrs parallel, tlt? wl stll rece LRg a HRg (hr)?

A. vltae escalat s a threat re sstes a prl ese hhresstace re sstes. As ca see rthe re el the ltae tes t escalate th eer arc alt. whe a alt ccrs th the statr a eeratr, the

arc pheea s er apparet. The prle s th the sste capactace. All electrcal sstes cta t cpet strte

capactace. The capactace the the sste chares th eer restrk arc that ccrs.

Q. H sell atal cst t the Laa h l atst lk at rst cst sses? Ca the Hr e stalle Phases er

te?

A. The Laa ll t e le eter hether r t thehr r sste s applcale r arale. Ths sste ll e

se t prtect eeratrs that are scat captal expese a ll

e prtecte th that captal cst . The hr hhresstace

r sste s re expese tha the staar hhresstace

r sste a lresstace r sste. The prtat th

t keep s that the hr hhresstace re sste prtects

the eeratr at all tes. The cetal lresstace re sste

ale t aeqatel prtect the eeratr.

Q. i stres, eeratrs are rall r essetal per l. d e stll ee t r hr r, tprtect t r the r alt crret?

A. yes, The Hr r sste s eee t prtect the eeratr a electrcal strt sste.

Q. i a stll t sre hat the prpse hr s, h t jst the HRg, h shl e a LRg er ral crcstaces?

A. The hhresstace r sste ll rk er certa crcstaces. Resstr ll hae t e ese t lt the r altcrret t a ale that s larer tha the sste capacte char crret. i lare strt sste at e ltae, the capacte

char crret ll e t hh. i the capacte char crret s l eh a hae the ecessar eqpet t etect a

slate the alte eeer a reasale aer, the the hhresstace r sste ll rk.

Q. what ll happe, e se rple Cb trasrer & eeratr th?

A. Fr Ple reakers are se sll re sstes a t hh r lresstace re sstes. The etral s tstrte these ks sstes. i the 4th ple s se t slate the resstr r the etral, the the eeratr ll e let a

re state a ther prles ll arse r that scear.

Q. what sze eeratrs l eet r the hr apprach?

A. The Hr hhresstace r apprach ll rk all s cecte e ltae eeratrs. These erall tal t the perat a plat. The sze the eeratr s t that prtat.

Q. what s the saatae s l resstace etral r (400A) r each three 2500kw, 4.16kv perat parallel?

A. whe a r alt ccrs there ll e 1200 A. the r alt, 400 A thh each resstr. Ths ll cchere the alt ccrs. S the r alt ccrs the Statr , the the alt ll rea the eeratr ee

eeratr s le, th 400 A. aa the r the statr. The alt crret has rece r 1200 t 400 ecase t

eeratrs are electrcall slate r the alt. The Resstr cecte t the eeratr that s alte s stll cecte a c

the crct. Ths s the aae e preet th the Hr hhresstace re sste.

Q. H the ercrret prtecte eces cl e set t e aeqate r sstes that hae th l resstacresstace re srces?

A. i a Hr hhresstace re applcat the prtecte eces r the sste are ese t e aeqate resstace re sste. The presece the hhresstace re sste s l se t prtect the eeratr sh

ccr th the statr . Ths ct s etecte th the s eretal rela tr the eeratr a s

r r lresstace t hhresstace. All thrh alts are treate as l resstace alts.

Q. what s the phscal sze the Hr cpars t the HRg? Ca t e stalle rs?

A. The Hr s a lttle larer tha a lresstace sste a ch larer tha a hhresstace sste. it s fclt t cas the hhresstace a r a t e aeqate r the prpse a a lresstace ll case t ch aae.

the per t prtect

low and medium voltage distribution systems

Documents