What
is a Buchholz relay ?
Buchholz relay is used for the protection of oil-immersed
transformers from all kinds of internal faults. It is installed in the pipe
connecting the conservator to the transformer tank.
Buchholz Relay Construction
It is an oil filled container having two hinged
floats, one at the top and other at the bottom. Each float has a mercury switch
resting on it. The upper mercury switch is
connected to an alarm circuit and lower one is connected to an external trip
breaker.
Buchholz
Relay Working Principle
Whenever a fault occurs inside a transformer, such as
excess core heating, insulation failure of turns etc. , heat is produced. This
heat decomposes the transformer oil into gases such as H2 ,CO ,CO2
etc. The amount of gases produced depends on the intensity of the fault.
The gases so produced tends to flow in upward
direction towards the conservator which
is placed on the top of the transformer tank. In their way to the conservator,
they are trapped in the buchholz relay, installed in the pipe connecting the
transformer tank to conservator.
Buchholz relay Working
There are two cases under which the relay operates –
minor faults and serious faults. Lets understand buchholz relay operation
taking each case separately.
- In case of slow-developing or minor faults, small amount of gas is produced. This gas rushing towards the conservator, has too little power to tilt the lower hinge and therefore is collected at the top of buchholz relay. As collected gas increases, an equivalent volume of oil is displaced and therefore the upper float is lowered. This closes the mercury switch and hence alarm gets activated.
- When a serious fault occurs in the transformer, an enormous amount of gas is generated in the transformer tank. This large amount of gas has enough strength to tilt the lower float and therefore the mercury switch connected to the trip circuit is closed and hence the transformer is disconnected from the supply.
This explains the buchholz
relay function.
