With a new hurricane season underway many of us review our property susceptibility to unwanted water intrusion. The same mentality should be underway to review our electrical assets susceptibility to water contamination. Liquid contamination has an amazing ability to find a way into our electrical systems. Unfortunately, without the right technology, when water contaminates our electric motors, the indications can be intermittent and misleading. This can result in the repair and replacement of a symptom and not the root cause. Nuisance trips and worse, equipment failures can result from the water penetration. Variable frequency drive (VFD) failures can occur as a result of an intermittent motor ground and if not aware of the root cause we will continue to replace the VFD without correcting the actual root cause. In troubleshooting the failed drive, a simple insulation test might clear the motor when in fact it is contaminated with water. Clearing the motor and replacing the drive would likely result in the same nuisance trips and eventual failure of the drive again.
Insulation analysis is primarily performed with the motor deenergized using tools such as a steady DC voltage for insulation resistance and polarization index measurements, high frequency AC voltage for insulation capacitance measurements, and variable DC voltage for step voltage testing. Depending on your application and power distribution, insulation can be evaluated while the motor is running using measurements like line-to-ground voltage measurements and spectral and time domain analysis.
To see a detailed discussion about Insulation Fault Zone Analysis and Troubleshooting view the Insulation Tips – Todd and Noah Podcast at https://www.youtube.com/watch?v=4fOfJ4Jv4e0
