Oil Immerse Type Transformer Protection

Devices Provided with the Oil-Immersed Transformers

• Gas detector relay (63P): This device, generally known as a “Boucholz relay,” is used with conservator-type transformers. It is mounted on the pipe connecting the highest part of the transformer tank and the conservator. It operates in two stages and has two sets of contacts. The first stage detects the slow accumulation of gas generated from an incipient or minor fault, such as damaged winding or core insulation, loose connections, etc.

The second stage operates on the sudden rise in oil pressure in the main tank caused by faults of a major nature, such as internal flash overs, short circuited turns, etc. The first stage is used for alarm, and the second stage is used for trip.

• Sudden gas-pressure relay (63SP): This device is used with sealed-tank transformers. It is mounted in the space above the oil and operates on the rise of pressure due to internal faults. The device is wired to trip and disconnect the transformer from the power source.

• Winding over temperature (49): This is a temperature-measuring device submerged in the transformer oil but also surrounded by a heater that is connected to the secondary of a current transformer in the winding. This is calibrated to measure the winding hot-spot temperature and has two to four adjustable temperature set points. These set-point contacts are wired to start the pumps or fans of a forced-cooled transformer, give an alarm, and trip the primary circuit breaker at the appropriate temperature level.

• Oil temperature (23Q): This device measures the oil temperature and has two, three, or four adjustable set points; it functions in the same manner as the winding-temperature device 49W.