Winding defects can occur due to insulation age, contamination, power surges, thermal overload, damaged wire/materials, vibration and other causes. They 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.
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
- Possible nuisance tripping
- Reduced motor life
As faults advance, power and torque may decrease. However, the longer-term result is always motor failure.
