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Principle and origin of shaded pole motor

2020/08/17

        The shaded pole motor is the simplest one of the unidirectional AC motors, usually using a cage-shaped skew-slot cast aluminum rotor. It is divided into salient pole shaded pole motor, hidden pole shaded pole motor according to the different structure of stator.

        The shape of the stator core of the salient-pole shaded pole motor is a square, rectangular or circular magnetic field frame with protruding magnetic poles. Each magnetic pole has one or more auxiliary short-circuit copper rings, namely shaded pole windings. The concentrated winding on the salient poles serves as the main winding.

         The stator core of the hidden pole shaded pole motor is the same as that of the ordinary single-phase motor. Its stator winding adopts distributed winding, and the main winding is distributed in the stator slot. The shaded pole winding does not need to short-circuit the copper ring, but is wound with thicker enameled wire Distributed windings (short-circuit automatically after being connected in series) are embedded in the stator slots (about 1/3 of the total number of slots) and act as an auxiliary group. The main winding and the shaded pole winding are spaced at a certain angle.

          When the main winding of the shaded pole motor is energized, the shaded pole winding will also generate an induced current, which causes the magnetic flux of the part of the stator pole covered by the shaded pole winding and the uncovered part to rotate in the direction of the covered part.

         Shaded pole AC motors are widely used in small household appliances such as electric fans, exhaust fans, heaters, etc. due to their simple structure, low manufacturing cost, and low operating noise. Shaded pole motors have only main windings and no starting windings. No additional winding and starting capacitor are needed. However, there is a pair of short-circuit rings at each of the two poles of the stator, which is also called "electrode shaded pole circle". When the motor is energized, the main magnetic pole part generates a magnetic field. This magnetic field is pulsating and the motor will not rotate. However, a short-circuit current is generated in the short-circuit loop, so that the magnetic field generated by the covered part of the magnetic pole is lagging behind the uncovered part, so the magnetic poles form a rotating magnetic field, and the motor rotor starts to rotate. In fact, this short-circuit loop is equivalent to the start winding of the motor. This is the origin of the shaded pole motor.