Home Electrical Machine What is The Function of a Buchholz Relay?

What is The Function of a Buchholz Relay?


We all know about the Buchholz relay. Buccholz relay work as the protector of the transformer. Today we will discuss on Buchholz relay and what is the function of a Buchholz Relay.

What is the function of a Buchholz Relay

What is The Buchholz Relay?

Buccholz relay is a protective device that is used for transformers drowned in oil (more than 500 kVA power rating). It is a kind of oil and gas actuated protective relay. It is used for internal protection of transformers like insulation problems, insulation failure of turns, etc.

Buccholz Relay

Work Principle of Buchholz Relay/What is The Function of a Buchholz Relay?

  1. Buchholz relay gets activated when it can detect any problem inside the transformer. For example, insulation failure of winding turns, excessively heated core, overload, or short circuit.
  2. This excess heat creates gas by separating transformer insulating oil. 
  3. The gas flow is dependent on the level of fault. More the level of fault, more the level of gas flow.
  4. Gas bubbles go upwards to the conservator. 

Structure of Buchholz Relay

  1. There is a chamber full of oil in the Buchholz relay. 
  2. There are two floats. One is in the upper part and the other one is on the lower part. 
  3. The upper float has a mercury switch. The switch is connected to an alarm circuit. And the lower float is connected with the trip breaker.

How Buchholz Relay Shows Its Work?

  • When there is any fault inside the transformer, the fault current produces heat.
  • Produced heat cause oiliness/crack and makes gas bubbles.
  • These bubbles go upwards and get stored in the Buchholz relay. 
  • Gas collected by the Buccholz relay displaces oil inside the relay and this displacement is equal to the amount of collected gas by the relay.
  • The contact of mercury switch connected with upper float gets closed for the displacement of oil. And the switch is connected to an alarm circuit. 
  • So, when any fault arises the alarm gets activated. 
  • The amount of collected gas indicates the level of fault.
  • For a small fault, the gas amount is not enough for moving the lower float. That’s why their float is not affected during small faults.
  • Big faults like the line-to-earth produce excessive heat and gas. Big faults like the line-to-earth short circuit produce excessive heat and gas.
  • This gas flows to the upper and lower part.
  • Its speed is enough to move the lower float.
  • The lower float will isolate the transformer from the supply line with the help of a connected breaker.
Relay Function

Advantages of Buccholz Relay 

  1. Buccholz relay indicates internal faults by producing heat and helps to avoid big faults. 
  2. Transformers fault level can be determined easily.
  3. If any big fault occurs, buccholz relay disconnects the transformer from supply line.

This is all about what is the function of a Buchholz relay, if you have any questions, please leave a comment.

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