single phase induction motor construction
single phase induction motor is similar to the three phase induction motor in physical appearance except that single phase motor has two windings in the stator and three phase induction motor has three winding in the stator.
Single phase induction motor is widely used below the rating or size of 03 HP. Single phase induction motor is widely used in the homes, offices and in the buildings where power requirement is low. Single phase induction motor is mostly used in the home appliances like washing machines, fans, coolers, drill machines and pumps etc. because of the low cost of the motor and low maintenance cost
single phase induction motor construction
in the Single phase induction motor construction motor has mainly two parts same as three phase induction motor:-
Stator- In the single phase induction motor construcction stator is the stationary part of the motor. The single phase induction motor has two windings namely- starting winding and the running winding. Single phase supply is given to the stator of the single phase induction motor.
Rotor- rotor of the single phase induction motor is the rotary or rotating part of the motor. Rotor of the single phase induction motor is of the squirrel cage rotor. The rotor is connected to the load through the shaft.
The stator and rotor of the single phase induction motor are not electrically connected but are magnetically coupled to each other with uniform gap between stator and rotor. The stator slots are distributed uniformly so a single phase double layer winding is employed.
A simple single-phase winding would produce no rotating magnetic field and no starting torque. It is therefore necessary to split the stator winding into two parts, each displaced in the space on the stator to make the motor self-starting.
Working of the single phase induction motor
When single phase AC (Alternating Current) supply is given to the winding of the single phase induction motor the alternating current starts flowing through the stator winding or the main winding. This alternating current start producing an alternating flux is called main flux. the main flux also links with the rotor conductors and hence cut the rotor conductors.
According to the faradays law of electromagnetic induction emf get induced in the rotor. As the rotor circuit is closed one so, the current start flowing in the rotor. This current is also called the rotor current.
The rotor current produces its own flux is called rotor flux. Since this flux is produced due to the induction principle so the motor working on this principle got its name as induction motor.
Now there are two fluxes one is main flux and another is called rotor flux. These two fluxes produce the desired torque which is required to the motor to rotate.
Double field revolvvving theory
According to the double field revolving field theory
Any alternating quantity can be resolved into two components, each component have magnitude equal to the half of the maximum magnitude of the alternating quantity and both these component rotates in opposite direction to each other.
e.g- A flux, φm/2 and –φm/2
each of these components rotates in opposite direction i.e., if one φm/2 is rotating clockwise direction then the other φm/2 rotates in anti-clockwise direction.
When a single phase AC supply is given to the stator winding of the single phase induction motor it produces flux of magnitude φm.
According to the double field revolving theory, this alternating flux φm is divided into two components of same magnitude i.e- φm/2. Each of these components will rotate in opposite direction with the synchronous speed Ns.
Let us call these components of flux as forward components of flux φf and backward component of flux φb.
The resultant of these two components of flux at any instant of time gives the value of instantaneous stator flux at that particular instatnt.
i.e- φr= φm/2+ φm/2
or rotating flux, φr= φf + φb
now at starting, both the forward and backward components of flux are exactly opposite to each other. Also both of these components of flux are equal in magnitude.
So both the components cancel each other and hence the net torque experienced by the rotor at the starting is zero. So, the single phase induction motor are not self starting.
There are five methods for making a single phase induction motor self starting
As the single phase induction motor is not self-started, it can be started by anyone way of the following methods-
- Splitting one-phase into two-phase (split-phase motor)
- Using capacitor (capacitor induction motor)
- By shading the poles (shaded pole motor)
- Universal motor
- By repulsion (repulsion motor)