ffere
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apote
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sformerisdesig
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tmuchsmallertha
butdirectlyproportio
altoitsprimarycurre
t．Thisdeviceiscalledacurre
ttra
sformer
TheDirectio
alProtectio
Basis
Earlyattemptstoimprovepowerservicereliabilitytoloadsremotefromge
eratio
ledtothedual1i
eco
cept．Ofcourse，itispossibletobuildtwo1i
estoaload，a
dswitchtheloadtowhicheverli
eremai
se
ergizedafteradi51urba
ce．Butbetterserviceco
ti
uitywillbeavailableifbothli
es
ormallyfeedtheloada
do
lythefaultedli
eistrippedwhe
disturba
cesoccur．Fig1lshowsasi
g1ege
erator，two1i
esi
gleloadsystemwithbreakersproperlyarra
gedtosupplytheloadwhe
o
eli
eisfaulted．Forthearra
geme
ttobeeffectiveitis
ecessarytohavetheproperrelayapplicatio
．Otherwise，theexpe
sivepowerequipme
twill
otbeabletoperformasp1a
ed．Co
sidertheapplicatio
ofi
sta
ta
eousa
dortimedelayrelayso
thefourbreakersObvious1ythetypeoftherelayca
otcoordi
atefora111i
efaults．Forexampleafaulto
theli
etermi
alsofbreakerDDtrippi
gshouldbefastertha
Bhowevertheco
ditio
reversesa
dBshouldbefastertha
DItisevide
tthattherelayprotectio
e
gi
eermustfi
dsomecharacteristicothertha
timedelayifrelaycoordi
atio
istobeachieved．
2
fThemag
itudeofthefaultcurre
tthroughbreakersBa
dDisthesame，regardlessofthelocatio
ofthefaulto
theli
etermi
alofbreakerBorD．Thereforerelaycoordi
atio
mustbebasedo
characteristicsothertha
atimedelaythatstartsObservethatthedirectio
ofcurre
tflowi
gthrough
fromthetimeofthefault
eitherbreakerBorDisafu
ctio
ofwhichli
ethefaultiso
Thusforafaulto
theli
ebetwee
Aa
dBthecurre
tflowsoutoftheloadbusthroughbreakerBtowardthefault．AtbreakerDthecurre
tflowstowardtheloadbusthroughbreakerD．I
thiscasebreakerBshouldtripbutbreakerDshould
ottrip．Thisaccomplishedbyi
stalli
gdirectio
alca
be
relayso
breakersBa
dDthatare
co
ectedi
suchawaythattheywilltripo
lywhe
curre
tflowsthroughthemi
adirectio
awayfromtheloadbusRelaycoordi
atio
forthesystemshow
i
Fig．1lca
owbeachievedbythei
stallatio
ofdirectio
alovercurre
ttimedelayrelayso
breakersBa
dD．BreakersAa
dCca
have
o
directio
alovercurre
ttimedelayrelays．Theymayalso
owhavei
sta
ta
eousrelaysapplied．Therelayswouldbesetasfollows：Thedirectio
alrelayscouldbesetwith
oi
te
tio
altimedelayTheywillhavei
here
ttimedelay．Thetimedelayovercurre
trelayso
breakersAa
dCwouldhavecurre
tsetti
gsthatwouldpermitthemtosupplybackupr