Dielectric faults occur in the winding due to turn-to-turn insulation breakdown.
It is the insulation between the turns of the winding.
Insulation breakdown commonly occurs due to high current and voltage which are high above the rated values.
The breakdown of the insulation results in the flashover of the winding turns and cause a short circuit.
Deterioration of oil may occur due to the result of prolonged overloading of the transformer.
Excessive oil temperature produces the formation of sludge, water, and acids.
Moisture entering the oil as a result of the breathing action greatly reduces its dielectric strength so that breakdown from coils or terminal leads to tank or core structure may take place.
EXAMIANS