电机轴电流问题中轴承等效电容和电阻的计算模型

Modeling of Bearing Capacitance and Resistance in Motor Bearing Current Problem

在PWM逆变器供电交流电动机运行中,轴电流问题影响着系统安全。预测轴电压和轴电流需要确定轴承的等效电容和电阻。该文通过分析轴承受到应力作用发生的弹性形变推导了轴承滚球与滚道之间的赫兹接触面积与油膜厚度的计算公式,继而得出轴承电容的计算公式。通过该模型分析了轴承电容与电机轴承温度、电机转速和轴承受力之间的关系。推导了轴承等效击穿电阻的计算公式,指出该等效电阻会随着油膜击穿点数的增大而减小。对一台变频供电2.2 kW感应电机进行轴电压和共模电压测量,结果表明所提出的计算模型是合理的。

The bearing current problem affects operation safety of the PWM variable frequency drive system. Precise calculations of capacitance parameters of bearings are very important to predict the shaft voltage and the bearing current. Combined with the elastic deformation and fluid mechanics analysis,the formula of thickness of the grease film and the Hertz contact area between balls and bearing races were obtained, then the bearing capacitance calculation model was derived. The relationships between the bearing capacitance and temperature,force and speed of the motor were analyzed. The equivalent bearing breakdown resistance calculation model was developed. The model shows that the resistance decreases with the rising of the breakdown numbers. The shaft voltage and the common voltage of a 2.2 kW induction motor fed by a PWM inverter were measured. The results verify the proposed model is reasonable.