Dear All,
In a 400V power system, ratio of three current transformers
installed incoming switchgear is 4000/1. Maximum three
phases short circuit current of this system is 48kA. One CT
is installed on neutral of upstream transformer (6/0.42kV,
solidly earthed) for 51G protection. Would you please inform
me about the correct CT ratio of this current transformer
(on neutral)??
Thanks a million
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Answer Posted / k.prakashchandra
Further you can not expect much earth fault current in
neutral earthing as the voltage is only 230.Unless the phase
comes in contact with earthed metal part or welding is done
on the ground, this current will be too low to be picked up
by ct.As the power supply points are provided with fuses
,the relay may not get a chance to act at all.
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