Mitigating VFD-Induced Electrical Damage to AC Motor Bearings

Overview:

Due in part to an increased focus on energy savings, the use of pulse-width-modulated variable-frequency drives (VFDs) to control AC motors has grown dramatically in recent years. However, shaft currents induced by VFDs can destroy motor bearings, leading to costly downtime and lost production. Without some form of mitigation, destructive voltages build up until they find a path to the motor frame (ground). All too often, these voltages discharge through the bearings, causing damage that can result in bearing noise, bearing failure, and subsequent motor failure. The challenge facing system designers and engineers is to cost-effectively mitigate this damage.