Why Neutral Busbar CT & transformer neutral CT connected
with phase CT in Restricted Earth Fault?
Answer Posted / vinod g
In Restricted earth fault protection Three phase CT is
parralleling (shorting all S1 andshorting all S2 together)
and paralleel conection with Neutral Relay and CT. IN
Healthy conditon current in all the three phase will be
balanced and summation will be zero. During earth fault out
side CT area summation of phase CT currents and Neutral CT
zero, so relay will not pick up. When earth fault inside
the transformer the current in the CT will differ and Relay
will pick and trip the tranformer breaker,so it is clear
that REF is for Transformer Winding protection and Bushing
CT is normally using for phase CT
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