A practical guide to understanding bearing damage related to PWM drives

The performance and reliability of AC adjustable speed drives (ASDs) is continually improving. One of the key reasons for improvement has been the advent, development and use of pulse width modulated (PWM) drives utilizing faster switching devices, primarily insulated gate bipolar transistors (IGBTs). As with many other developments, improvements in some areas may cause problems in others. An increased bearing failure rate in motors is one of the negative effects of these types of drives. To mitigate bearing current damage in motors, as well as in loads and other auxiliary equipment attached to the motor shaft, it is important to understand how these currents are generated. In addition to theoretical explanations, actual field cases and solutions are reviewed.