1. Direct On Line Starter

1. It is simple and cheap starter for a 3-phase induction motor.
2. The contacts close against spring action.
3. This method is normally limited to smaller cage induction motors, because starting current can be as high as eight times the full load current of the motor. Use of a double –cage rotor requires lower staring current( approximately four times) and use of quick acting A.V.R enables motors of 75 Kw and above to be started direct on line.
4. An isolator is required to isolate the starter from the supply for maintenance.
5. Protection must be provided for the motor. Some of the safety protections are over-current protection, under-voltage protection, short circuit protection, etc. Control circuit voltage is sometimes stepped down through an autotransformer.