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Special Application Motors: Wound Motor Rotors

Noah Bethel | Vice President-Product Development, PdMA Corporation

Special Application Motors

Many industrial applications require three-phase motors to operate at variable speeds. The basic three-phase induction squirrel cage motor is a constant speed motor. However, using starting resistors connected to a three-phase wound rotor circuit can provide high starting torque without drawing excessive current and allow a means to control/adjust speed during operation. On a wound rotor motor the stator acts as any three-phase induction motor stator would, creating a rotating magnetic field. On the rotor, an external three-phase resistance is connected through slip rings to the three-phase rotor circuit. On startup the external resistance is high, controlling rotor current and torque. Throughout the startup the external resistance will be reduced, often in stages using contactors to short out portions of the external resistance. This is especially effective for high inertia loads that require a long acceleration time. Wound rotor motors are typically found in cranes, hoists, compressors, conveyors, mixers, fans, blowers, mills, and pumps.

To watch a case study on a wound rotor motor visit the PdMA YouTube channel at:

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About the Author

Noah Bethel Vice President-Product Development, PdMA Corporation

Noah has over twenty-five years of broad operations and electrical systems maintenance experience in industrial, commercial, and military settings ranging from nuclear submarines to world class amusement parks. His experience includes high and low voltage, AC and DC, power generation, power distribution, motors, and motor controllers. Noah is currently in charge of product development for new and existing PdM technology at PdMA Corporation.

Noah is a graduate of the University of the State of New York and the Naval Nuclear Power School and Training Unit. He is a Certified Maintenance Reliability Professional, with field experience in motor circuit analysis, current signature, power analysis, thermography, vibration analysis, oil analysis and ultrasonic testing.