Two Minute Tips  

Rotor Evaluation Using MCEMAX® – Fp Frequency

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.

Fp Frequency

Pole-pass frequency (Fp) sideband evaluation is one of the more established methods of rotor evaluation utilizing the current signature analysis test. The slip between the rotating rotor and stator magnetic fields creates a modulation of the stator current at Fp. Fp is calculated by multiplying the number of poles times the slip. Slip is equal to the difference in frequency of the stator and rotor rotating magnetic fields. Performing an fast-fourier transform (FFT) of the stator current produces a spectrum plot in the frequency domain, which allows isolation of the Fp as a sideband around the line frequency. Differential amplitudes between the Fp sideband and line frequency less than 36dB indicates possible advanced stages of rotor bar defects.

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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.