One of the maintenance department’s most significant efforts to foster sustainability at the more than 300 buildings it services is a testing program for HVAC motors controlled by variable frequency drives (VFDs). Many of the buildings have their own maintenance managers. Whenever such a manager requests testing on a motor in his/her building, technicians from maintenance headquarters use portable oscilloscopes and voltage measuring probes to determine whether or not shaft voltages are present — voltages which cause electrical discharges through the motor’s bearings.
If harmful discharge levels are detected, the maintenance department may recommend the installation of a bearing-protection device that bleeds off the damaging currents. In this case, the university chose an AEGIS SGR Bearing Protection Ring. The shaft grounding ring redirects VFD-induced shaft voltages by providing a very-low-impedance path from shaft to frame, bypassing the motor bearings entirely. Conductive microfibers line the entire inner circumference of the ring in two rows, surrounding the motor shaft. A protective channel in the ring allows the fibers to flex without breaking and keeps out debris.
Read the complete article at Sustainable Facility