Two Minute Tips  

Rotor Evaluation Using MCEMAX®: Pole-Pass Frequency (Fp)

Noah Bethel | Vice President-Product Development, PdMA Corporation

Six independent methods of rotor evaluation can be used from the MCEMAX technology to analyze the condition of a squirrel cage AC induction motor: Pole-pass frequency (Fp) sidebands around line frequency, 5th harmonic, demodulated Fp frequency, Rotor Influence Check (RIC), In/Rush-Start/Up, and average inductance. Over the next six tips we will discuss each of these methods in detail and provide examples.

Pole-Pass Frequency (Fp)

Rotor bars on the rotor of a squirrel cage induction motor act as a shorting mechanism to the magnetic flux emitted from the steel rotor laminations. When one or more of the rotor bars break, the magnetic field in the vicinity of the broken bar will intensify. The resulting higher reflected impedance onto the stator windings will also elevate the stator inductance readings as measured by the MCEMAX. Monitoring the trend of the stator inductance is an ideal method to monitor the degradation in rotor bar health. To view a case study in trending stator inductance to troubleshoot an AC induction rotor click on the link below

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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.