A preventive maintenance program at a New England Ivy League university demonstrates how the push for more sustainable green-building management has led to growing awareness of a chronic, widespread problem with HVAC motors — electrical bearing damage.
Variable-frequency drives (VFDs), also known as inverters, are widely used because they save energy, especially in applications with variable-torque loads. It’s widely recognized that because many centrifugal fans and pumps run continuously, their motors use less power if the speed is controlled by VFDs rather than a damper for flow control. But if downtime occurs, savings from efficiency increases vanish. Shaft currents induced by VFDs can wreak havoc with bearings, dramatically shortening motor life and causing costly repairs. To mitigate these currents and realize the full potential of VFDs, a reliable method of shaft grounding is essential.