Prediction of Mechanical Shaft Failures Due to Pulsating Torques of Variable-Frequency Drives

• Published in: IEEE transactions on industry applications Vol. 46; no. 5; pp. 1979 - 1988
• Main Authors: Song-Manguelle, Joseph, Schröder, Stefan, Geyer, Tobias, Ekemb, Gabriel, Nyobe-Yome, Jean-Maurice
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.09.2010; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Cement; Damping; Electric potential; Error detection; Failure; Failure analysis; Frequency; Harmonics; Inverters; liquid natural gas (LNG); Mathematical analysis; mechanical resonance; Mechanical sensors; medium voltage; mining; Motors; multilevel inverter; oil and gas; pulsating torque; Pulse inverters; Pulse width modulation inverters; pulsewidth modulator; Rotating shafts; Shafts; Studies; Testing; Torque; torque harmonics; torsional vibration; Voltage
• ISSN: 0093-9994; 1939-9367
• DOI: 10.1109/TIA.2010.2057397

Mechanical damage of rotating shafts has been reported for several years from various high-power applications. This paper shows that the variable frequency drive incorporated in a rotating shaft is one of the main root causes of mechanical-shaft failures. Simple analytical relationships show that the frequencies of the motor air-gap torque have a more significant impact on the mechanical-shaft failure than their magnitudes. Effects of mechanical damping are analytically derived and analyzed. Motor air-gap torque is successfully reconstructed using only the motor's voltage and current, thus avoiding torque sensors, which are subject to failure and errors. Simple relationships between frequencies of current harmonics and frequencies of motor pulsating torques are proposed. For pulsewidth-modulated inverters (two and multilevel), possible drive operating points that might excite the shaft's eigenmodes are predicted. Simulation results of four interleaved three-level neutral-point-clamped converters are analyzed for validation purposes. Experimental tests up to 35 MW are performed on a compressor test bed. The presented results confirm the accuracy of the proposed approach, which is particularly valuable for multimegawatt drive applications.