Electrical Machine

AMERICAN INTERNATIONAL UNIVERSITY- BANGLADESH (AIUB)

ELECTRICAL MACHINE 2 ASSIGNMENT

UNIVERSAL MOTOR

Name: Tasfia Farzana Khan

ID: 09-13049-1

Sec: F

Dept: EEE

Course Teacher: A. Z. M. Shahriar Muttalib

A universal motor is a series wound electric motor that is designed to run on either AC or DC current. These motors are normally made in sizes ranging from 1/200 to 1/3 horsepower.

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The universal motor is mainly a DC series motor which is specifically designed to work on DC as well as on AC. A standard DC series motor has very poor characteristics when operated on AC mainly due to two reasons:

1. The reactance of armature and field windings limits the AC current to a much lower value than DC current.

2. If solid steel is used for the stator frame, AC flux will produce large eddy currents in the frame with consequent heating.

Hence to make the motor operable in AC power supply, certain changes are made. The reactance of the series field and the armature winding is reduced as much as possible. The reactance of the series field winding can be somewhat reduced by using fewer turns of heavier wire. However it would be impractical to eliminate the reactance voltage drop due to series field since that would eliminate the magnetic field. The reactance voltage drop of the armature winding can be eliminated by use of compensating winding. The compensating winding is connected in series with the armature winding. It is such arranged that ampere- turns of the compensating winding oppose and neutralize the ampere- turns of the armature winding. The compensating winding is displaced by 90 electrical degrees from the field winding. The compensating winding also improves commutation considerably. This is a great advantage since the field of the universal motor is weakened by the lowering of series field winding.

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Fig 1: Series motor with conductively Fig 2: Series motor with...