DETECTING AND PREVENTING ELECTRICAL BEARING DAMAGE IN VFD DRIVEN MOTORS THROUGH SHAFT VOLTAGE MEASUREMENT AND ANALYSIS

摘要

The bearings in electric motors operating on variable frequency drives (VFD) are vulnerable to shaft voltages that are capacitively coupled from the motor's stator to the rotor and may be of sufficient amplitude to cause electrical discharges in the motors bearings. These high energy discharges produce an electrical discharge machining (EDM) effect in the motor's bearings that cause fusion craters, pitting and fluting and premature bearing failure. The shaft voltages may be detected and measured using an oscilloscope and a shaft voltage probe that touches the motor's shaft while it is running. The waveforms may then be analyzed to determine if there is a potential for bearing discharges or if bearing discharges are in fact already occurring. Testing the VFD driven motor early in its life cycle will allow potential problems to be detected and a shaft grounding ring implemented as mitigation on the motor. Incorporating shaft voltage measurements into preventative maintenance programs will help prevent unplanned downtime and improve equipment reliability and sustainability.