Electric and Hybrid Vehicles by Tom Denton

Author:Tom Denton
Language: eng
Format: epub, pdf
Publisher: Routledge

6.2 Construction and function of electric motors

6.2.1 AC motors: basic principle

In general, all AC motors work on the same principle. A three-phase winding is distributed round a laminated stator and sets up a rotating magnetic field that the rotor ‘follows’. The general term is an AC induction motor. The speed of this rotating field and hence the rotor can be calculated:

where n speed in rpm, f frequency of the supply and p number of pole pairs.

6.2.2 Asynchronous motor

The asynchronous motor is often used with a squirrel cage rotor made up of a number of pole pairs. The stator is usually three-phase and can be star or delta wound. The rotating magnetic field in the stator induces an EMF in the rotor which, because it is a complete circuit, causes current to flow. This creates magnetism, which reacts to the original field caused by the stator, and hence the rotor rotates. The amount of slip (difference in rotor and field speed) is about 5% when the motor is at its most efficient.

Key Fact

An asynchronous motor is often used with a squirrel cage rotor.

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