State the function of overload coil and No volt coil in dc motor starter.

State the function of overload coil and No volt coil in dc motor starter.
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Answer :

Function of Overload Coil: When DC motor is overloaded, the overload coil carries the overload current and produces strong magnetic field to attract a plunger, which short the terminals of no-volt coil. The no-volt coil current then becomes zero, its magnetism is lost and it releases the starter handle so that by spring tension it goes to off position and motor is disconnected from the supply. Thus the dc motor is protected from overload.

Function of No-volt Coil: When supply fails, the no-volt coil current becomes zero, its magnetism is lost and it releases the starter handle so that by spring tension it goes to off position and motor is disconnected from the supply. On recovery of supply, one has to restart the motor using the starter. Thus the dc motor is prevented from restarting automatically on recovery of supply without starter and protected.
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