Vertical motors run on variable frequency drives are susceptible to electrical bearing damage and premature failure. When any motor, vertical or horizontal, is run on an inverter, the drive’s output causes a capacitive voltage on the motor shaft that can discharge through the bearings, causing electrical damage and premature failure. This has brought grief to more than one water treatment plant; you can read one of their stories here.
GE Power Conversion is aware of this problem, so they offer their Ultra™ Vertical Pump Motors with an AEGIS® Shaft Grounding Ring as an option. AEGIS® shaft grounding gives VFD-produced shaft voltages a low-impedance path to ground, drawing damaging current away from the bearings, and so protecting them against electrical damage.
For more on GE Ultra™ Vertical Pump Motors, see this brochure. To learn how AEGIS® shaft grounding helped with a Kansas treatment facility’s chronic bearing failure problem, read this case study. And for fuller background on electrical bearing damage due to VFDs, see the AEGIS® Bearing Protection Handbook.