Buchholz Relay:-
When we discuss about protection of transformer we come across buchholz relay first.What Is A Buchholz Relay?.Buchholz Relay is the major safety device of transformer.it is pipe like construction between the top of the transformer main tank and the conservator,employed in gas and oil operated transformer(rated >500 kVA).it prevents transformer from internal faults such as impulse breakdown of the insulating oil, insulation failure of turns,over heat of coils due to failure of windings etc.
Construction & Working of Buchholz Relay:-
Buchholz relay consists of an oil filled chamber with one inlet from transformer tank and one outlet to conservator. There are two hinged floats, one at the top of oil level and other at the bottom in the oil chamber. Each float is connected by a mercury switch. The upper float mercury switch which is connected to an alarm circuit and that on the lower float is connected to an external trip breaker. The schematic construction of a buchholz relay is shown in the above fig.
Working Principle Of Buchholz Relay:-
Whenever there will be a minor internal fault such as impulse breakdown of the insulating oil, insulation failure of turns,core heating,over heat of coils due to failure of windings etc high amount of heat will be produced this heat heat decomposes the transformer insulating oil which results in production of gases like hydrocarbon gases, CO2 and CO.this gases occupies the area aboove the oil level which results in decrease in oil level.when oil level fall down to certain height alarm circuit will be energized.
Trip circuit will be energizes when phase to earth short circuit happens,baffle plate or lower float will be closed.This switch energized the trip circuit of the circuit breakers associated with the transformer and immediately isolate the faulty transformer from the rest of the electrical power system by inter tripping the circuit breakers associated with both LV and HV sides of the transformer. This is functioning of buchholz relay.
Advantages & Uses Of Buchholz Relay:-
1.Buchholz relay identifies the internal faults of transformer due to heating and it helps in avoiding the major faults by simple mechanical phenomenon.
2.Severity and type of the fault can be determined without even dismantling or disturbing the transformer.
3.If a major fault occurs, the transformer can be isolated automatically with the help of buchholz relay to prevent accidents.
