Introduction Shaded pole motor is one of the types of s […]
Shaded pole motor is one of the types of single phase induction motors, which are used for producing a rotating stator flux in order to make the single phase induction motor a self starting one. Let us discuss the constructional details, diagrams and working of shaded pole motors in detail.
Like any other motors the shaded pole induction motor also consists of a stator and rotor. The stator is of salient pole type and the rotor is of squirrel cage type.
The poles of shaded pole induction motor consist of slots, which are cut across the laminations. The smaller part of the slotted pole is short-circuited with the help of a coil.
The coils are made up of copper and it is highly inductive in nature. This coil is known as shading coil. The part of the pole which has the coil is called the shaded part and the other part of the pole is called unshaded part.
Now let us consider that an alternating current is passed through the excited winding which surrounds the pole. Due to the presence of shading coil, the axis of the pole shift from unshaded part to shaded part. This shifting effect is equivalent to the physical movement of the poles, which is nothing but the rotation of poles. So the rotor starts rotating in the direction of the shift from unshaded part to shaded part.
Now let us discuss why the axis shift occurs when current is passed through the winding and how the shading coil aids in producing the shift.The current carried by stator winding produces alternating flux. The distribution of flux through the poles is greatly influenced by the shading coils.
When the alternating current through the coil increases, it induces a current in the shading coil. The direction of current in shading coil is such as to oppose the cause producing it (from Lenz law). The cause is the alternating current. So the flux in the shading coil decreases and it opposes the main flux. Hence the flux mostly crowds or shifts towards the unshaded part of the pole. So the magnetic axis lies along the middle of the unshaded part.It is denoted as NC in the picture below.