At the time of 1st
charging of
transformer, there
were huge inrush
current, so why at
that diffrential relay
are not operated? Why?

Answer Posted / vinod

During the first charging of transformer the magnetising
inrush current is second harmonic, differential relay is
provided with second harmonic trip by pass with sufficient
time. Also 87 relay having 5 th harmoninic by pass during
lightning surges.

Is This Answer Correct ?    5 Yes 1 No



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