Influence of Mechanical Load on Electrical Erosion of Air-Conditioning Motor Bearings

Abstract

Rolling bearings are critical supports in variable-frequency air-conditioning motors. Inverter-induced common-mode voltage produces shaft voltage and bearing current; when the voltage exceeds the dielectric strength of the grease film, electric-discharge machining (EDM) damage occurs. To reduce repeated background description and focus on the load-coupled mechanism, this study takes a 6204 deep-groove ball bearing as the object and combines point-contact elastohydrodynamic lubrication (EHL), Romax simulation, and breakdown-voltage testing. The core innovation is a quantitative correlation analysis linking minimum oil-film thickness, grease-film breakdown voltage, and radial mechanical load. When the radial load increased from 750 N to 1550 N at 920 r/min, 40 deg C, 100 N axial load, and 10,000 Hz excitation, the measured breakdown voltage decreased from 21.040 V to 11.139 V, corresponding to an absolute drop of 9.901 V, a 47.1% reduction, and an average sensitivity of -1.24 V per 100 N. The results show that mechanical load is negatively correlated with oil-film thickness: increasing the load compresses the lubricant film, lowers the breakdown voltage, and aggravates electrical-erosion damage. Increasing rotational speed strengthens hydrodynamic film formation, thereby increasing the film thickness and breakdown threshold. Low-speed, heavy-load operation constitutes a high-risk regime for bearing electrical erosion.