Earthing Transformers for Power Systems

EARTHING TRANSFORMERS FOR  POWER SYSTEMS

ABSTRACT:-

 Normally power systems and net works are operated under variable complex stresses.n  power systems t!e "aults are not avodable even a"ter takin# utmost care at every sta#e"rom plannin# to maintainance. T!e #roundin# o" a circuit reduces potential stresses under "ault condition. $ower "eedin# "rom delta delta or i" t!ere is no accessibility "or star  connected trans"ormers occasionally s!orted to #round is very common-un-intentional #roundin# occurs any w!ere "rom t!e "eedin# system to utili%ation e&uipment T!e main ob'ective o" #roundin# neutral is to make a s!ort circuit current su""icient in ma#nitude "or t!e relay action. T!is article restricted to %i#-%a# type wit! oil "illed trans"ormers. T!e neutral point is usually available at every volta#e level "rom #enerator to trans"ormers. n t!e absence o" a power trans"ormer o" suitable capacity( connection and desi#n a separate #roundin# trans"ormer can be used . T!ey are inductive devices intended primarily to provide a neutral point "or #roundin#  purpose. T!e main purpose o" t!is paper is to discuss about t!e di""erence between )art!in# trans"ormer and $ower trans"ormer and to discuss about t!e desi#nin# o" eart! trans"ormers.

NTR*+,CT*N:A trans"ormer is a device w!ic! electroma#netically trans"ers A.C. volta#e "rom one level to anot!er level. An eart!in# trans"ormer is a trans"ormer primarily to provide a neutral point "or #roundin# purpose. T!e sole duty o" t!e #roundin# trans"ormer is to pass #round current durin# an eart! "ault.( and it carries no use"ul load. T!e desirable &uantities o" an eart!in# trans"ormer are low %ero impedance and low losses no load losses.

/,NCT*N */ )ART0N1 TRANS/*R2)RS:•

Apart "rom providin# an easy pat! to #round current durin# an eart! "ault( t!e "ollowin# additional "unctions are also to be ac!ieved

•

0oldin# t!e neutral s!i"t wit! in t!e limits

•

$ermittin# t!e circulation o" unbalanced load current in t!e neutral

•

To limit t!e current durin# line to eart! "aults

•

To eart! t!e system

•

To provide sin#le p!ase line to neutral load

•

Can be used wit! resistance 3reactance3arc suppression coil

C*2$ARS*N

B)T4))N

)ART0N1

AN+

$*4)R 

TRANS/*R2)RS:T!e selection any trans"ormer mainly by two "actors-namely( primary volta#e and load ./or an eart!in# trans"ormer load is s!ort time or s!ort duty   only at t!e time o" "ault (normally "rom a "ew seconds to one minute COMPARISION CHARACTERISTICS 2.29MVA (S.C) 6.6KV 600 Amps(ET@)

)T5

2MVA110.!""KV #$%& 1 (PT@)

$T5

$urpose

To provide a neutral point Raidin# "or eart!in# volta#es

or

lowerin#

67A ratin#

S!ort time

Continuous

7olta#es in #eneral

,p to 88kv

0i#!er volta#eseven 9967 and above

 No o" windin#s

*ne3two

*ne3two3t!ree

+irection o" power "low

,ni direction

B-directional

S.C wit! stand duration

;sec.to ; min

9 sec

times normal "ew !undred amperes to "ew current t!ousand amperes