BEARING CURRENTS
2017-11-05
Motor bearings have a higher failure rate when the motor is run with a VFD. This is due to currents in the motor bearings. The classic solution to this problem is insulated bearings. Insulated bearings insulate the bearing using either ceramic balls or an insulating ring between the bearing and the motor frame. Another solution to this problem by the manufacturers of the Aegis bearing protection ring is shown below.
Running a motor off of a VFD shaft voltages appear.
- Voltage builds up until it exceeds the insulation level of the bearing’s oil film layer – the “break-down” voltage of the bearing.
- The voltage then arcs through the bearing creating an electrical discharge machining (EDM) pit.
- Thousands of pits per second may be created and over time the ball rolling over the disturbed surface can cause “fluting damage”.
Linqing Nine Star Bearing Science & Technology Co., Ltd
( Insulated bearing, Hybrid ceramic bearing and Brass cage DGBB)
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