Design of the shaded-pole motor

A shaded-pole motor is a single-phase induction motor provided with an auxiliary short-circuited winding displaced in magnetic position from the main winding. This auxilary winding (called a "shading coil") is used for producing the starting torque. The essential parts of a shaded-pole motor are the stator, carrying the main winding, the shading coil and the squirrel-cage rotor. Although a non-salient-pole or distributed winding can be used for the stator, it is usually built as salient pole type motor. The shading coil surrounds a portion about 1/4 to 1/2 of the whole pole. Usually iron wedges are used to bridge the adjacent pole tips to increase the leakage flux of the shaded poles in order to improve the motor characteristics. Sometimes these bridges are punched in one piece of the stator laminations. The squirrel-cage rotor is the same in construction as that used for polyphase induction motors. Although shaded-pole motors have been widely used in practice the esign of these motors is still based upon experience in many respects. P.H. Trickey has given an analysis of the electric circuits and performance calculations of shaded-pole motors (see reference 9 and 10), but only the special case of 90 electrical degrees between the effective centers of un-shaded portion of whole pole and shaded pole was considered.