Motor Starter is a safety device which enables a safe current to be supplied at the time of starting and during running conditions protection has been given to the motor against over voltage and under voltage difficulties. When the DC motor is stationary, then no back emf is produced in the armature.
If now full voltage is supplied across the stationary armature at the time of starting, the motor will draw excessive current due to the very small value of armature resistance. This excessive current will blow out the protective fuses and it may cause burning out of the armature windings and heavy flash over across the commenter, so avoid the excessive current which may cause damage of the motor, a high resistance is inserted in series with the armature terminal during the time of starting which limit the starting current to a safe value and to get the required starting torque.
Function of Motor Starter:
The functions of a motor starter are:
i. To limit the starting current to a safe value.
ii. To protect the motor against failure of supply.
iii. Protection is given to the motor from taking overload current.
iv. Giving facilities for starting and stopping the motor.