Industrial Power Engineering Handbook

4

Starting of Squirrel Cage Induction Motors

Contents

Direct on-line starting (DOL)

Reduced voltage starting

Star/delta (Y/Δ) starting

Autotransformer (A/T) starting

(a). Open transient condition

(b). Closed transient condition

Soft starting

List of formulae used

Further reading

An induction motor can be regarded as a transformer with a small air gap in the magnetic circuit. When at rest, having no induced back e.m.f., it can be regarded as a transformer with a short-circuited secondary. A squirrel cage induction motor therefore draws a very high starting current, as noted in Section 1.2.1. However, it reduces substantially in a slip-ring motor due to the high impedance of the rotor circuit.

The starting of an induction motor does not ...