Asynchronous motor(Induction Motor) Starters | 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 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
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