Single phase induction motors are widely used in small-scale domestic and commercial applications. There are relatively simple in construction. Today we are going to discuss the Single Phase Induction Motor Operating Principle and its features. Stator construction of the single phase induction motor consist of a single winding disposed of in slots. The rotor construction is same as of squirrel cage type laminated and with axially spaced parallel aluminum or copper conductor bars laid in the rotor slots.
Double Revolving field Theory
This theory makes gives of the idea that an alternating uniaxial quantity can be represented by two opposite rotating vectors of half magnitude.
Accordingly and alternating sinusoidal flux can be represented by two revolving fluxes each equal to half the value of alternative flux and each rotating Synchronously in opposite directions.
Single Phase Induction Motor Operating Principle
A three-phase induction motor due to the nature of supply a rotating magnetic field will be produced and thereby a self-starting torque will be generated. But a Single Phase Induction Motor Operating Principle does not develop and self-starting torque but it does develop a torque when running.
For an example, if we consider the magnetic field produced by stator winding which varies sinusoidal ( because the voltage applies varies sinusoidally ) along the horizontal axis.
As the flux is varying there will be an induce emf in the rotor bars in the motor, due to transformer action.
There will be force produce due to rotor current and stator magnetic field. Forces on top half conductors are downwards, the whole force act on the bottom half of conductors are upward.
Therefore the net torque produced by this forces is zero and the motor will be at standstill. Since the magnetic field is pulsating the rotor will vibrate without rotating.
If an external push is given it will continue to develop a torque in the given direction of the external push. This known that if a single phase of a three-phase induction motor is open the motor continues a run and at slightly reduced speed.
Therefore the net torque produced by this forces is zero and the motor will be at standstill. Since the magnetic field is pulsating the rotor will vibrate without rotating.
If an external push s given it will continue to develop a torque in the given direction of the external push. This knew that if a single phase of a three-phase induction motor is open the motor continues a run an at slightly reduce speed.
