Electric Motor Bearing Failure and Use of the Proper VFD Cable

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Electric Motor Bearing Failure and Use of the Proper VFD Cable

What causes bearing failure to occur between the variable frequency drives (VFD) and electric motors?  What can be done to minimize the potential for failure?

ball bearing

For starters, the ball bearing is the connection between the shaft and the motor frame.  There are two rings: an inner ring (which is in contact with the shaft) and an outer ring (which is in contact with the motor frame).  The shaft turns due to electromagnetic interaction between inductors on the shaft and inductors on the frame. When the shaft turns, it drives the machine.

The problem lies in the connection between the VFD and the motor.  The VFD send power to the motor and some signal contents reflect off the motor and move back towards the VFD.  The reflected waves collide with the upcoming waves and this causes high voltage spikes.  The high voltage spikes cause strong electric fields which then influence the motor.

The voltage spikes and strong electric field then produce a high frequency flux around the stator.  If this frequency flux becomes high enough to overcome the impedance of the bearings’ oil film, a current starts to flow.  The end result is spark erosion.  Tiny metal particles of steel balls and rings melt and the bearing eventually fails.

LUTZE Driveflex VFD XLPE A216

However, LUTZE has come up with the perfect solution and that is to minimize the electric field.  A symmetrical construction results in a smaller electric field. The DRIVEFLEX® A220 is the most capable solution thus far of preventing bearing currents.  It connects all three earth wires and connects the cable shield to PE on both cable sides.

So, there you have it! LUTZE has created the solution to your bearing current problems with the DRIVEFLEX® A220.

LUTZE presented this information in an educational session at our recent Product and Technology Expo.  Check out the full presentation here.

Are you interested in learning more about this VFD cable solution?  Contact your French Gerleman Account Manager or contact us.