Factors of insulation failure and remedies

Insulation failure is the loss of the insulating property of a material so that it can no longer withstand the applied voltage. It usually results from several stresses acting together over time.

Factors responsible for insulation failure

1. Electrical stress: lightning and switching overvoltages, temporary overvoltages, and long-term partial discharges in voids that slowly erode the insulation (treeing).
2. Thermal stress: overloading, poor cooling and hot spots raise temperature; insulation ages faster (roughly half life for every 8–10 °C rise) and thermal runaway may occur.
3. Mechanical stress: vibration, short-circuit forces, thermal expansion and bending cause cracks and voids.
4. Environmental factors: moisture, dust, salt and industrial pollution, UV radiation, which reduce surface resistance and cause tracking and flashover.
5. Chemical action: oxidation of oil, acids and sludge formation, attack by ozone and nitric acid produced by corona.
6. Manufacturing defects and ageing: voids, impurities, poor impregnation, and the natural deterioration of material with time.

Possible remedies

Regular condition monitoring (insulation resistance, tan δ, DGA of oil, PD measurement) helps detect weakening insulation before a breakdown happens.