For contactors energized with alternating current, a small part of the core is surrounded with a shading coil, which slightly delays the magnetic flux in the core.
2.
Low-power synchronous timing motors ( such as those for traditional electric clocks ) may have multi-pole PM external cup rotors, and use shading coils to provide starting torque . " Telechron " clock motors have shaded poles for starting torque, and a two-spoke ring rotor that performs like a discrete two-pole rotor.
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