Short-duration high voltages (commonly called “spikes” or “transients”) can penetrate motor winding insulation and cause premature failure.
Motor winding insulation resistance testing, if performed regularly and trended, can predict failure if the damage from a particular instance is small enough that repeated episodes accumulate until failure occurs.
This cumulative effect is the normal failure mode, though windings may fail from a single incident. This is why a multi-pronged maintenance solution is in order.
The sources of damaging transients often are inside a given facility, but you can’t ignore lightning. A lightning protection system will help avoid a direct strike and even protect you from flashovers.
To protect your facility from induced voltages coming in through the electrical service or generated from inside the facility, you need a well engineered system of transient protection. This will consist of layers of protection.
The specification for protective devices in a given layer is based upon the voltage levels being let through by each previous layer of protection. No single device can provide complete protection down to your nominal voltage. You need to carefully map out which layers of your distribution system will get which voltage band of protection.
Then, eliminate internal transients wherever possible. Motors themselves are often sources of transients, notably when left to start across the line. A soft starter on every large motor saves energy, reduces motor wear, and helps protect the entire distribution system from damage.
The soft start function is built into variable frequency drives (VFDs), but use a power analyzer around each VFD to ensure that its settings are actually giving you a good soft start that sufficiently reduces transients.
Switching power supplies produce transients. So look at solid state loads (as a group, if individual ones are small) to see if they are generating large enough transients to warrant corrective action.
This spike protection reduces the need for replacing motors, but you need to monitor and maintain the lighting protection system, surge arrestor(s), surge protective devices, soft starts, VFDs, and other equipment used to protect your motors.
Power monitoring systems can help with this, but always include this equipment in your electrical testing program.
