VDFs Save Energy
Controlling motors with variable frequency drives allows the motors to run at reduced speed. This can save huge amounts of energy in HVAC and other variable speed applications.
...But Damage Motors
VFDs’ pulsed output voltage is not balanced. Imbalanced input voltage induces a capacitive voltage on the motor shaft. The shaft voltage can discharge through the motor bearings, causing cumulative damage and often premature failure. The energy savings from VFD control can be wiped out by repeated motor failures.
Shaft Grounding
AEGIS® Shaft Grounding Rings electrically bond the motor shaft to the frame. Shaft voltage bleeds off through the ring instead of arcing through the bearings. Specifying AEGIS rings for motors on drives can lock in clients’ savings and help secure their loyalty.
Learn More
Here are some resources on the problem of VFD-sourced bearing currents and how to specify AEGIS to protect against them.
Resources:
- AHRAE SL-08-025 Shaft Grounding: A Solution to Motor Bearing Currents
- AEGIS Bearing Protection Handbook (registration required)
- White Paper: Specifying AEGIS Bearing Protection
- CSI Division 23 05 13 with added language specifying AEGIS for motors on VFD