When a large motor (or critical one) fails, a postmortem of the motor is never a bad idea. It should be standard operating practice. But while that work is being done at the motor shop, what about the new motor that took its place?
If that motor has faulty power factor (PF) correction capacitors (either stand-alone or as part of a PF-corrected drive), you may see a repeat performance of motor failure — especially if the original failure was due to overheated windings.
While the main response team is swapping motors, a secondary team should be assessing those capacitors.
PF capacitors hold a great deal of energy, so simply disconnecting them doesn’t assure safety. Anyone assigned to this task must be fully trained in working with PF capacitors and must also be wearing the appropriate PPE per NFPA 70E.
The assessment begins with a visual inspection, but will be followed up with an infrared inspection an hour after the motor has been returned to service. Other components of the assessment include measurements of current, capacitance, and PF.
