Answer / thowsif_emerson_csm team

Inrush current or input surge current:-

It refers to the maximum, instantaneous input current drawn
by an electrical device when first turned on. For example,
incandescent light bulbs have high inrush currents until
their filaments warm up and their resistance increases.
Alternating current electric motors and transformers may
draw several times their normal full-load current when
first energized, for a few cycles of the input waveform.
Power converters also feature high inrush currents relative
to their steady state currents. This is typically the
charging current of the input capacitance. The selection of
overcurrent protection devices such as fuses and circuit
breakers is made more complicated when high inrush currents
must be tolerated. The overcurrent protection must react
quickly to overload or short circuit but must not interrupt
the circuit when the (usually harmless) inrush current flows

Answer / prashant

during starting of transformer actual flux change is twice
that of rated due which it gets saturated and high current
flows through the winding , dis current is called inrush
curent

Answer / m.venkatesh

hi! inrush current is initial current taken by an inductive
load when switch it on to supply

Answer / 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.

Answer / srv.26@rediffmail.com

inrush current is the current that is 7 to 10 times more
current than the rated current

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