Why Starting Current of Induction Motor High.? ANS:Starting current of induction motor is as high as 5 to 7 times the normal full load current. Therefore different starting methods such as star delta starter, auto transformer starter and other starting methods are employed in order to reduce the starting current. Induction motor can be compared to an transformer with the secondary short circuited. Primary winding of the transformer can be compared to the stator winding of the induction motor and the rotor winding is considered as the short circuited secondary winding of the transformer. When 3 phase voltage applied across the stator winding high inrush currents magnetize the air gap between the stator and rotor and induces emf into the rotor of the induction motor. During this instant current in the rotor windings is high and this rotor current produces a field which in turn produces torque to rotate the motor. Once the rotor starts picking up the speed, current drawn by the machine decreases. The time required for staring of the motor depends on the time required for the acceleration which depends on the nature of the connected load.
Posted on: Fri, 06 Sep 2013 11:45:09 +0000
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