Why is starter necessary for a three-phase induction motor?

Answer Posted / subhakanta sahu

As we know at the time of starting an induction motor the rotor is stand still hence the slip is 1.if slip is 1 the rotor induced voltage is maximum hence drives maximum current in the rotor circuit.This rotor current current has impact on stator current(As per LENZ's law).This is the reason why an induction motor takes high current at starting(About 5 to 7 times the full load current).

This high current causes voltage fluctuation,unwanted power loss & unwanted stress to the system or equipment.So it has to be reduced by using different starting methods.

There are two possible ways to limit the starting current
1.Reduce the applied voltage.
2.Increase the rotor resistance.

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