TRC-2018 Learning Zones 21:35
by Glenn Eyle and Ken Bates, EMCOR Government Services
The drive to go green and consume less energy has, especially in facilities operation, has increased the regularity of variable frequency drive (VFD) installation to new and existing mechanical systems. The drive’s capability to adjust the speed of a motor on a mechanical reduces power consumption. By making VFDs more accessible and field serviceable, they have become a nearly standard, go-to choice for an assured return-on-investment in facilities energy conservation projects. It is important to know the harm the VFD can cause, how to diagnose it, and how to mitigate the damage it generates. The cost-saving, energy reducing benefits of VFDs come with one significant adverse effect on the induction motor’s roller element bearing: fluting! This paper seeks to describe the fluting phenomena, the grooving damage created by the VFD, and the technology that has been developed to address it. There is no way to determine when this fluting will occur, but it absolutely will occur. At NASA’s Jet Propulsion Laboratory, we have a robust PT&I program that actually measured and recorded fluting after VFDs were installed on the facility before it even had a name. Our Vibration Analyst learned of fluting, and how to mitigate it, by installing a shaft grounding protection ring, from a Vibration Institute Conference in 2012. However, even after installing the protection ring on motors, we have continued to detect bearing failures. This failure led us to research available technology to validate the operation of the shaft grounding protection ring before and after installation. After researching viable ESD measuring devices, we selected the Electrostatic Discharge Pen. Based on documented PT&I finds here at JPL, this paper will make the case that this pen is an affordable, rapidly responsive solution to discerning the arcing that occurs before its damage is done to the motor bearings.
