High Frequency Bearing Currents

Variable Frequency/Speed Drives (VFD / VSD) used to control AC motors can produce high frequency voltages that may ultimately appear on the machine shaft. These voltages are the result of capacitive coupling of the VSD PWM voltage to the motor shaft. The voltages on the shaft can be sufficient to cause arcing currents to flow through the motor bearings to ground. 

These discharging currents can cause heating and even melting of the surface of the bearing raceways. The damage caused by bearing currents can lead to premature failure of the motor drive as well as costly maintenance and down time. 

PEM have a range of probes for engineers to monitor these currents, directly measuring the bearing current, which ultimately can be used to evaluate the effectiveness of steps taken to mitigate against bearing currents.