(A) High voltage surges
(B) Overload faults
(C) Incipient faults
(D) Earth faults
Answer: (C) Incipient faults
Explanation:
Incipient faults:
Incipient faults are one among the internal faults of power transformers.
Incipient faults are not serious at the starting but they gradually develop into hazardous faults.
These faults leads to insulation deterioration.
The incipient faults in transformers are due to the following reasons:
Contamination of the insulating oil in the transformer.
Core bolt insulation failure.
Rust or other materials on the core.
Short circuits in the lamination.
Moisture content in the insulating oil.
Effects of incipient faults:
Incipient faults causes mechanical stresses to the transformers.
These stresses gradually affect the insulation system of the transformer.
So the protection schemes of transformers are very much essential in order to prevent the winding faults resulting from the insulation failure.
Generally, Buchholz relay is used for protecting transformer against incipient or internal faults.
Buchholz relay:
Buchholz relay is a gas actuated relay and it is used to protect the transformer against all internal faults
It is a gas actuated device
It is placed between the main tank and the conservator
It is used in the transformer having the rating higher than 500 kVA
It causes alarm for minor fault and tripping for a major fault
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