i have one transformer 1000kva, 11/.433kv. we are using
200/5 amp. ct unit for measuring purpose, & one 800 amp.
V.C.B Unit for the same t/f operate, i wants to known the primary
current of T/F is only 53 amp. why we used 800 amp.
V.C.B ? & 200/5 amp. CT Unit.

Answer Posted / 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.

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