Types and comparison of induction motor starters

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 current5-10 times the full load torqueEconomical and Higher starting torque.High in-rush current

Star-Delta Starter
2-3 times the full load current2-3 times the full load torqueInrush current can be reduced to one-third when compared to DOL.Starting torque will reduce

Auto-transformer
2-3 times the full load current2-3 times the full load torqueInrush current can be reduced to one-third when compared to DOL.Starting torque will reduce

Soft starter
3-5 times the full load current1.5-2.5 times the full load torqueInrush current can be reduced. Starting torque can be controlled.Starting torque will be less

Variable Speed drive
1.1-1.5 times full load current1.5-2.5 times the full load torqueSpeed and torque control, communication and Energy saving.Higher cost
Sharing is caring

This Post Has One Comment

  1. nexa electrical supplies

    thanks for providing useful information

Leave a Reply