Question { 6436 }

can a 50 Hz transformer work satisfactorily if placed under 60
Hz,what are the prices and losses that will arise

Answer

well flux will depend on ratio of voltage and frequency ..
so as the frequency will increase flux will decrease .. so
the magnetising current required will be more.. so there
may be decrease in power factor and also losses will be
more.

Question { Bhel, 17050 }

For the same power rating,which motor is bigger in size,AC or DC?

Answer

I think DC motor is bigger then AC in size..because as the
voltage is increased, the commutation, and sparking at
brushes increases.

Question { 7326 }

why transformers rating are in KVA

Answer

copper losses depends on current and iron losses depends on
voltage. Total transformer loss depends on volt-ampere (VA)
and not on phase angle between voltage and current i.e., it
is independent of load power factor. That is why
transformer's rating is in KVA