Shaded Pole Electric Motor
A shaded pole motor is a single phase induction motor provided with an auxiliary short-circuited winding or winding’s displaced in magnetic position from the main winding. There are a number of different construction methods used, but the basic principle is the same. The shading coil consists of low resistance copper links embedded in one side of each stator pole, and are used to provide the necessary starting torque. When the current increases in the main coils a current is induced in the shading coils that opposes the magnetic field that is building up in part of the pole pieces they surround. When the main coil current decreases, that in the shading coil also decreases until the pole pieces are uniformly magnetized. As the main coil current and the pole piece magnetic flux continue to decrease, current in the shading coils reverses and tends to maintain the flux in part of the pole pieces. When the main coil current drops to zero, current still flows in the shading coils to give the magnetic effect which causes the coils to produce a rotating magnetic field which makes the motor self-starting.
Used where the power requirements are small such a in clocks, instruments, hair dryers, small fans, etc.