Consider a dc motor at standstill. When a dc motor is at rest the speed of the motor is zero, therefore the back emf is zero.
In order to limit this heavy current, we use the starter in a DC motor.
How Starter Works?
If this motor is directly connected to the supply, it will draw a current of 400/0.5= 800 Amps.
The full load current of the same motor is 64 Amps. The starting current is therefore 12.5 times that of full load current.
This gives rise to heating and mechanical forces of 150 times full load values.
The resistance should gradually cut in steps as the motor gains speed and develop back emf.
Hence, the starter is essential for DC motors.