Construction of Single Phase Induction Motor | Electrical Machine Theory

The theory of single phase induction motor and Construction of single phase induction motor is shown in this article, which is more helpful to strong your knowledge on Electrical Machine.

Single phase induction motors are in very wide use in industry, especially in fractional horse-power field.

They are extensively used for electric drive for low power constant speed apparatus such as machine tools, domestic apparatus and agricultural machinery in circumstances where a three phase supply is not readily available.

There is a large demand for single-phase induction motors in sizes ranging from a fraction of horse-power up to about 5 H.P. Though these machines are useful for small outputs.

they are not used for large powers as they suffer from many disadvantages and are never used in cases where three-phase machines can be adopted.

The main disadvantages of single-phase induction motors are:

✓Their output is only 50%of the three-phase motor, for a given frame size and temperature

rise.

✓They have lower power factor.

✓Lower-efficiency.

✓These motors do not have inherent starting torque.

✓More expensive than three-phase motors of the same output.

The magnetic field produced by the stator coils is pulsating, through varying sinusoidal

with time.

Ferrari pointed out that such a field can be resolved into two equal fields but rotating in opposite directions with equal angular velocities.

The maximum value of each component is equal to half the maximum of the pulsating field.

Split-phase Motors

Since the single-phase induction is not self-starting, means must be provided to create an initial torque, But the initial torque is only possible if a rotating flux is created in the stator.

It is known that a rotating flux is produced when there is a difference of 90 between

the currents of two stationary coils.

If the stator possesses two fluxes hauling a large phase difference the result is a rotating flux.