Question { 5650 }

Why is the diffrential protection in DG. What if the CT
polarity is reversed while connecting for the same type of
protection? How polarity can be made ok?

Answer

Diffrential protection is used to protect internal fault
like winding faults,it is used to protect the the
equipments like Generator,Transformer and bus bars.

If CT polarity changed in Directional type releys it will
give trip command when normal operating condition.

Brfore giving connection we must read name plate details to
avoid polarity change.

Question { 16758 }

what is the difference in inductance and resistance.both
oppose the flow of current but how.resistance having + ve
power in both cycle while inductance having both power.

Answer

Resistance will produce electrical quantity in to heat,but
inductance will store electrical energy as a magnetic
energy.

While currrent flowing in resistance that will be in phase
with voltage so it will produce positive power in both cycle
(+P=+V * +I ,+P=-V * -I),but in inductance current will
lag the voltage by 90deg,so power will produced positive
and negative sign alternatively.