What is the Role of Buchholz Relay in Transformers, Working Principle, Construction, and Its Applications

The Buchholz Relay was first implemented in the year 1921 by “Max Buchholz. This relay is a security device used in the fields like the transmission of power, as well as distribution. This relay had kept on some oil-filled transformers, and used as a protective device for die-electric failures in the transformer like current leakage, fractional discharge, hot spots and arcing are phenomena that deliver to oil degradation insulation acts by producing a hazardous flow of gas in the transformer tank. When the transformer was close, then it has a large economic impact on the power supply network operation. Thus, it is the aim to make sure an exact measurement of the transformer condition.

What is Buchholz Relay?

Buchholz relay is a security device which is normally used in large oil absorbed transformers. It is a kind of oil and gas activated security relay. The Buchholz relay purpose is to give the protection to a transformer from the different faults happening in the transformer like the Short circuit, inter-turn, core, incipient, etc. This relay will sense these faults and shuts the alarm circuit. The Buchholz relay diagram is shown below.

Buchholz Relay
Buchholz Relay

The main features of Buchholz relay include field proven consistency, No fake alarms, the design is robust, special design for OLTC applications, airtight transformers and transformers with conservator with a rubber bag, etc.

Buchholz Relay Working Principle

The Buchholz relay working principle and operation is very simple. The function of this relay depends on the mechanical phenomenon, that means it activates by mechanically. When there will be a small internal error in the transformer like insulation errors among turns, stop working on the core of the transformer, core high temperature, the transformer oil will be decayed in diverse hydrocarbon gases, Co, and CO2. The Buchholz relay gas analysis s generated due to a decay of transformer oil will build up in the higher part of the Buchholz container which reasons drop of oil level in it.

Working Principle of Buchholz Relay
Working Principle of Buchholz Relay

This means lowering the location of the float and thus rolling the mercury switch. The switches of the contacts stopped and an alarm circuit strengthened. Sometimes due to oil outflow on the major tank, air bubbles may build up in the upper part of the Buchholz container which may also source a drop of oil level in it and alarm circuit will strengthen. By gathering the accumulated gases from the pockets on the peak of the relay and by examining them one can expect the kind of fault in the transformer.

Different types of faults accompanied by a flow of oil which hits the baffle plate and sources the mercury switch of the minor element to shut. This switch thrilled the trip circuit of the circuit breakers allied with the transformer and without delay isolate the defective transformer from the remaining electrical power system of inter tripping the circuit breakers linked with both the sides of LV and HV of the transformer. This is how a Buchholz relay works.


Buchholz Relay Construction

The Buchholz Relay consists of two elements, namely the upper element, and the lower element. Where the upper element includes a mercury type switch linked to a float. Similarly, the lower element comprises of a mercury switch increased on a hinged kind flap situated on the straight line of oil flow. Here, the flow of oil from the transformer to the conservator which is in make contact with the other float.

Buchholz Relay Construction
Buchholz Relay Construction

How Does it Work?

Whenever a small fault happens within the electrical device, heat is made by the fault currents. The made heat causes decomposition of electrical device oil and gas bubbles are made. These gas bubbles run in the upward direction and obtain collected within the Buchholz relay.

The collected gas relocates the oil in Buchholz relay and therefore the displacement is similar to the amount of gas collected. The dislocation of oil causes the higher float to shut the higher mercury switch to connect an alarm circuit.

Hence, once a small fault happens, then the alarm will be activated. The collected quantity of gas specifies the harshness of the error occurred. Throughout minor faults, the making of gas is not enough to move the lower float. Hence, throughout small faults, the lower float will not be changed.

During main faults, like the section of earth short, the heat generated is high and an outsized quantity of gas is made. This massive quantity of gas can equally flow upwards, however, its motion is high sufficient to tilt the minor float within the Buchholz relay. During this case, the lower float can source the lower mercury switch which can trip the transformer from the supply.

Buchholz Relay Advantages and Disadvantages

The following are the pros of Buchholz relay.

  • This relay specifies inter-turn errors which occur due to heating of the core and assists in the prevention of strict faults.
  • The environment and harshness of the fault will determine without separating apart from the transformer by checking the air samples.

The following are the drawbacks of the Buchholz relay.

  • This sort of relay is applicable to an oil absorbed transformer.
  • This relay can detect only when the oil level is below.
  • This relay does not guard the connecting cables. So separate security is required for the cables.
  • It has the high response time.
  • The least operating time of the Buchholz relay is 0.1 seconds.

Buchholz Relay Applications

The different types of transformer faults can protect by the Buchholz relay and that is identified by an alarm. The applications of Buccholz relay include the following.

Buchholz Relay Applications
Buchholz Relay Applications
  • Buchholz Relay can use at the Entry of air bubbles in the oil
  • Insulation failure of the Core bolt
  • Buchholz Relay can use where the reduction of oil level will be low due to leakage
  • This relay can use in loose and bad electrical contacts
  • Bushing pierce
  • The short circuit between stage
  • Winding short circuit

Operating Conditions of Buchholz Relay

Buchholz relay works throughout three conditions

  • Whenever gas bubbles formed within the transformer due to severe error.
  • Whenever the amount of oil in the transformer drops.
  • Whenever oil in the transformer flows apace from the conservation tank to the major or from the major tank to the conservation tank.

Buchholz Relay Testing Procedures

The different types of Buchholz relay testing procedures include the following.

Leakage Test

The Buchholz relays can pack with oil at the 90 C temperature and at the force of bars and verified for the outflow after 30 minutes.

Electrical Test

The connections of earthing insulation can ensure at the 2000V voltage for 1 minute.

Functional Test

The testing of the Buchholz relay can be done on particularly designed PLC controlled testing unit, as well as all the contact systems reply conditions will be verified.

Precautions for Buchholz Relay Installation

  • The conductor connection must have a paper connection while contacting the terminals instead of rubber because it may damage by the coil.
  • The floats of the transformer must be check for air stiffness by, for instance, immersing them in warm oil to make a surplus force in them.
  • The connection pipe and relay cover should have 1.5-3 % slope and not have any projecting exterior to make sure clear of the gases into the conservator.

Thus, this is all about Buccholz relay, working, construction, etc. From the above Buchholz relay manual, finally, we can conclude that these relays are not responsive to external pressures.No servicing required throughout the function. Furthermore, any queries regarding this topic, please give your feedback by commenting in the comment section below. Here is a question for you, what is the function of the Buchholz relay?

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