A.C MOTORS

BY

DEEPAK ROTTI

ROLL NO: 017

K.L’S G.I.T BELGAUM

A.C motors  Electric motor driven by an alternating current.

Two basic parts – stator and rotor.

Advantages over D.C motors.

Types:

Induction motors

Synchronous motors

Further single phase and poly-phase motors

Principles Faraday's Law: Any change in the magnetic environment

of a coil of wire will cause a voltage (emf) to be "induced" in the coil.

Lenz's Law : The polarity of the induced emf is such that it produces a current whose magnetic field opposes the change which produces it.

Electromagnet

Induction Motors (asynchronous motor)

The electric current in the rotor needed to produce torque is induced by electromagnetic induction from the magnetic field of the stator winding.

Components – Rotor, Stator and windings.

Working –

Current passed through stator

Magnetic field induced emf in rotator

Magnetic field due to induced emf

Rotation due to couple formation

ROTOR

STATOR

SYNCHRONOUS MOTORS: The rotation of the shaft is synchronized with

the frequency of the supply current , the rotation period is exactly equal to an integral number of AC cycles.

Rotor is a electro magnet connected to A.C with slip contacts.

Components – magnetic rotor, stator & windings

Asynchronous

Rotor is not magnetic

For a given frequency speed decreases with increase load.

Self starting motor.

Efficiency high for high speeds.(above 600rpm)

Simple in construction and less price.

Synchronous

Rotor is magnetic.

For a given frequency speed is constant irrespective of load.

Not a self starting motor.

Efficiency high for low speeds.(below 600rpm)

Complex in construction and costly.

Thank you