EPRI Statistics
Based on statistical data compiled by the Electric Power Research Institute (EPRI), 47% of motor failures are   due to electrical faults/failures.  The 47% can be further broken down into rotor problems (10%) and winding problems (37%).  Mechanical faults may sometimes have root causes that are electrical in nature.

Winding defects can occur due to insulation age, contamination, power surges, thermal overload, damaged wire/materials, vibration and other causes.  The begin as energy crossing an insulation fault (such as moisture or contamination), which isolates at least one turn.  This generates additional stress and heat across the defect, which progresses until an arc is drawn and the winding fails.

About Winding Faults
There are four basic types of winding faults.

• Between turns in a coil
• Between coils in a phase
• Between coils in different phases
• Between a coil or phase and ground

Only about 5% of electrical faults begin as a fault to ground.  The other three fault types may or may not propagate into a ground fault  as the failure becomes advanced.  The short term result of these faults is reduced efficiency (and higher operating costs).  Symptoms include higher operating temperatures, perhaps nuisance tripping, and reduced motor life.  As faults advance, power and torque may decrease.  The longer-term result is always motor failure.

Testing Options
Megohm Insulation testing will only detect faults to ground.  Since only 5% of motor faults begin as ground faults, the majority of faults will go undetected using this method alone.

Surge testing requires the application of high voltages and currents, and can be a destructive test, actually generating faults.  This aspect, combined with the size of surge testing equipment makes it inappropriate for troubleshooting and predictive maintenance testing.

Resistance and inductance-only (RLC) test methods don’t provide enough information for reliable fault detection and troubleshooting.

ALL-TEST PRO® MOTOR GENIE® is your best, most economical choice, for fault detection and troubleshooting.

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