Transformer Buchholz Relay
Working principle and Connection diagram.

  1. Buchholz relay.
  2. Connection diagram.
  3. Working principle.
  4. Why buchholz relay is used?

1- Buchholz Relay:

Buchholz relay is known as oil and gas actuated protection relay. It is safety device which is used above 500 KVa capacity of transformers. It is installed between the conservator and main tank. It is not required for small rating transformers below 500 KVA.

Buchholz relay:schematic diagram and working principle.

When the fault is occurred inside the transformer then the gas will generate in oil tank and it will travel to the conservator side where Buchholz relay is installed before conservator. After detecting fault the buchholz relay provides tripping signal to the HT panel breaker.

1. Major fault occurred in transformer tank and generating gas in tank than it will provide alarm and trip protection.

2. Oil level going to down than it will provide protection alarm and trip condition.

2- Connection diagram:

Buchholz relay:connection, wiring diagram  and working

3- Working principle:

1- During Fault Condition:

When any internal fault occurs in main tank due to failure of winding insulation or core heating than oil temperature will increase fastly and oil will start evaporating form as gas. Gas will move upside and will enter inside the relay resultant gas float valve will move to upside. For alarm closing condition. After closing alarm contact supply breaker will be tripped.

2- During Loss of Oil Condition:

any leakage or loss of oil in main tank is protected by the lower float of gas protection relay. If the oil level is low or any leakage of oil than low side float will move down side and will connect the trip contact and finally breaker supply will be tripped

4 - Why buchholz relay is used?

Oil Transformer is a costly equipment. Due to over heating, overload or short circuit in the oil tank, resultant winding insulation may be failure or explosion in oil tank then a gas is generated and it flows to the conservator side. So prevention for winding and explosion in tank, The buchholz relay is is installed in the middle of tank and conservator.
When a fault is occurred in a tank then due to high pressure gas the buchholz relay is activated and a signal of alarm and tripping is sent to the transformer incomer breaker. So in this way the oil transformer can be prevented by buchholz relay.
Buchholz relay has two important features which is mentioned in below.

  • Due to any fault in transformer oil tank then it provides alarm and tripping signal for protection.
  • Loss of oil level in tank then it provides alarm and tripping signal for protection.

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