Introduction: –
Shaded pole motor is a type of single-phase motor. This motor is designed for very low HP like 1/25 to 1/6 HP. This type of motor has also low torque.
Internal structure and principle: –
This type of motor has single coil in stator. A cut is applied on the pole section and inserted a thick copper strip in that slotted pole section. These strips are short circuited which is called shading winding.
Shaded pole motor has squirrel cage type rotor. And this rotor works like multiphase induction motor.
A figure is given below. According to figure you can see four pole shaded motor is displayed. And a coil which is winded on all these four poles in series connection.
When we give single phase AC supply an alternating flux is generated. This alternating flux cuts the shaded winding. Resultant, a emf will induced.
As we know that shaded coil is short circuited. That’s why a heavy current will induced across shaded winding. This heavy current produced its own flux which is opposite of main field flux.
During this whole activity, magnetic axis will shift towards unshaded part of pole. Thus, due to shifting of the magnetic axis rotor stator, rotor start to move and rotor’s moving direction is unshaded pole to shaded pole.
We should remember that shaded winding is highly inductive. That’s why when main winding or exciting winding’s current increases, a current is induced in shaded winding. This current is a heavy current and this current is opposing the induced flux. Thus, the exciting current is increase and flux density on shaded part is decrease. And when exciting current decreased, the flux density of shaded part is increased.
According to the figure 1 assume that exciting current increasing towards O to A. Consequently, an emf is induced in the shading winding. As we know that, resistance of shading winding about to negligible. That’s why a heavy current will flow through the shading winding.
That heavy current is flowing in the shading winding is in opposite direction of exciting current. Thus, maximum flux will shift towards unshaded part. And magnetic axis displaced towards ND1 which is unshaded middle part.
Now assume that exciting current is on peak. Means of exciting current is situated between A & B point. In this condition, the changes in exciting current are minimum. That’s why zero emf and a current will induce in shading winding. In this condition induced flux by exciting current is at maximum point. And flux distribution is uniform on whole pole. Thus, magnetic axis will shift towards ND2.
Now assume that exciting current changes B to C and exciting current decrease same speed as we noticed on the first process (O to A). In this condition heavy current flows in the shading winding . And this heavy current opposes the exciting current. Resultant, flux strength will increase on the side of shading part. And magnetic axis shifts towards ND3.
Thus, we can see that, in the positive half cycle of exciting current, N-pole will shift unshaded point to shaded point. And in the next half cycle of exciting current is also acting previous process. Thus this process will continuously running.
Uses of shaded pole motor: –
Motor is using that field where we need fractional horse power like 1/250 HP to 1/6 HP. So, we use this motor in this application which is given below.
- Small fan
- Hair dryer
- Electric watch
- Blower
- Toys etc.
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