DC Motors
Motor starter are essential for

Avoiding excessive starting current
Preventing fuse blowing
Starting the motor
Accelerating the motor

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DC Motors
If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens

Nothing will happen to motor
Motor will come to stop
This will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
This will make armature to take heavy current, possibly burning it

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