As the name indicates, starters are used to start or stop a motor. It consists of an electromechanical switch and protection devices (overload and/or short-circuit protection).
Why should we need a starter?
An induction motor draws 5-10 times its rated current during start. In order to reduce the starting current, we need a starter. If we don’t use a starter, inrush currents may heat up the motor winding and the life of motor may reduce.
Comparison of three phase induction motor starters
| Method | Starting current | Starting Torque | Pros | Cons |
|
Direct-on-Line (DOL) | 5-10 times the full load current | 5-10 times the full load torque | Economical and Higher starting torque. | High in-rush current |
|
Star-Delta Starter | 2-3 times the full load current | 2-3 times the full load torque | Inrush current can be reduced to one-third when compared to DOL. | Starting torque will reduce |
|
Auto-transformer | 2-3 times the full load current | 2-3 times the full load torque | Inrush current can be reduced to one-third when compared to DOL. | Starting torque will reduce |
|
Soft starter | 3-5 times the full load current | 1.5-2.5 times the full load torque | Inrush current can be reduced. Starting torque can be controlled. | Starting torque will be less |
|
Variable Speed drive | 1.1-1.5 times full load current | 1.5-2.5 times the full load torque | Speed and torque control, communication and Energy saving. | Higher cost |
thanks for providing useful information
this wasnt the best tbh