Answer Posted / birla cellulosic, kharach
Inrush current in any inductive circuit is due to absence
of back emf and back emf is created by secondary circuit as
in case of motor and transformer. this back emf creates a
counter flux which opposes the main flux so when any
transformer is charged its back emf is absent initially so
primary will take excess current because there is no flux
to oppose it so we can say its total impedence is low
initially after some cycles back emf (counter emf) is
created which opposes the main flux and hence flow of
current decreases to its normal. in case of motor its rotor
is short circuited so when rotating magnetic field is
stablished it generated emf in rotor and since rotor is
stationary initially rate of cut of magnetic field is
maximum and so the generated emf in rotor is more initially
so large current will flow in short ckted rotor and since
it is like secondary cirkt of motor, so stator will also
take more current. when rotor starts rotating its relative
speed gap starts decreasing and hence rotating flux cutting
rotor will decrease so emf induced in rotor will decrease
and so the rotor current will decrease and stator current
will also decrease becoz it act like primary winding of
transformer and when rotor achieve its full speed current
will become normal.
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