Which relay is used to detect and protect internal faults of a transformer?

Which relay is used to detect and protect internal faults of a transformer? Correct Answer <span style="">Buchholz</span>

Buchholz relay:

Buchholz relay is a gas actuated relay and it is used to detect and 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

Additional Information

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.