Abstract

The motor bearing is prone to discharge breakdown under the output common mode voltage of PWM inverter. The breakdown voltage threshold can be calculated quantitatively by finite element numerical calculation, but it is related to motor operating conditions, surface roughness and lubricant particle impurities and other parameters. In this paper, the breakdown voltage thresholds of bearing oil film under different parameters are analyzed. Firstly, a lubrication micro-zone model is built for the oil film breakdown region to determine the oil film breakdown voltage threshold. Quantitative analysis of the change of the voltage threshold of the motor under different conditions shows that low speed, large load and high temperature conditions will decrease the breakdown voltage threshold, and it is easier to produce discharge breakdown current. Then the influence of bearing surface roughness and particle impurities on the breakdown threshold of oil film is analyzed. It shows that larger bearing surface roughness or bubbles mixed in grease will make bearing more prone to breakdown. Finally, combined with the above analysis, the bearing current suppression measures are given.

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