Motor bearing failure from VFD induced shaft to ground voltages in HVAC applications

Investigation into fan motor bearing failures on heating, ventilation and air conditioning (HVAC) air handlers, used to recirculate air within computer manufacturing clean rooms, has made it clear that these failures were caused by electric discharge current problems within the bearings when the motor was operated from a PWM inverter source. This is a newly identified mode of failure in this application; and as such, appears to be not fully understood by the manufacturers of the drives and motors. Although first noticed in clean room fans, there may be greater implications for HVAC designs and other industrial applications employing variable frequency drives (VFDs). This paper discusses efforts to discover the source of this failure, measurement techniques utilized, and proposed solutions for mitigation related to this application