Answer / vinit patil

You are right, you should fight with your electricity board
regarding the HT Metering CT ratio. You should actually
required 100/5 ratio.
But while deasigning VCB it is always prfarable to go on
higher side because it can sustain the heavy short circuit
current. One thing should be noticed that the protection
CTs should be as per the Primary current of the ransformer.

Answer / a k kataria

Well given the rating of transformer as 1000 kva, CT ratio
should have been 100/5. As far as VCB current rating is
concernd,these are generally made for universal
applications and are generally 630 Amps onwards 'cause in
the eventuility of fault ,heavy currents are to be taken
care of.More over increase in the rated current capacity of
breaker adds little to the cost compared to other
components of the breaker.There fore capacity of VCB is OK.

Answer / krishna chaitanya

first u must know that transformer transforms with
no change in power. As its 11 kv on primary side as
per funda you can calculate primary current 53 amps.
P = vi cos fi. A 100/5 ratio ct is enough to measure.
But its always advisable to select equipments with
larger than required ratings. Sometimes u'l see a
300/5 ratio ct.
and vcb, 800 amp vcb is for load. There'l be another
breaker at secondary of transformer with larger than
this amp rating. 800 vcb is provided for a particular
load control.
checkchaitu@yahoo.com

Answer / b2

Transformar steap down the voltage so current grow up high
so we are use 200/5 amp. ct & 800 amp.V.C.B

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