What are steps to be taken when Buchholz Relay Operates in a Transformer?

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This Article describes the Standard Operating Procedure we need to carryout in case Buchholz Relay Alarm or Trip Operates in Power Transformer.

Answer:

When the Buchholz Relay Operates, we need to carry out following steps:

  1. If only Alarm has Operated, we need to take a Shutdown on the Transformer and do the necessary Isolations.
    Alarm indicates that there is an unusual gas buildup inside the transformer tank, the issues may be less severe but still need attention. This could signal problems like hot spots, partial discharges from damaged insulation, or core faults.
  2. If there is Trip, it indicates that quick Oil flows inside the Transformer Tank, it often means there’s a big problem, like a short circuit between windings. This quick change makes a lot of gas form quickly and sends a strong pressure wave through the oil, causing the relay to trip to avoid major damage.
  3. Check the Buchholz Relay for any Oil Leakage.
  4. Collect the gasses in a bottle and try to analyze it by taking the Flame test.
    If the Gas is Flammable, it’s a Severe Fault
    From the nature of the Gas collected from the Buchholz Relay, following Fault analysis can be carried out:
            Colorless & Neutral: Air trapped in Oil or Insulation
            White: Gas of decomposed Paper and Cloth Insulation
            Yellow: Gas of decomposed Wood Insulation
            Gray: Gas of Overheated Oil due to burning of Iron Portion  
            Black: Gas of decomposed Oil due to Electric Arc.
  1. Check the Transformer Oil Level.
    A low oil level can stop the relay from working correctly and cause an alarm.
    Low Oil level is a common issue. It can happen because of leaks in the transformer tank, connecting pipes, or not filling the oil enough during maintenance.
  2. We need to check if there is Gas in the Tank or these are only air bubbles.
    Due to Vibrations or during Maintenance, as air is not released properly, air bubbles get trapped in buchholz relay.
    Release the air.
  3. Carry out Magnetic Balance Test and IR Test. If results are Ok, the Transformer can be charged.
  4. Carryout out DGA. Looking at any gas that has accumulated can give more information. Different faults create different gasses. For example, arcing creates acetylene, while overheating may produce methane. This study, called Dissolved Gas Analysis (DGA), provides important clues about what type of fault it is, where it is, and how serious it might be.
Frequently Asked Questions:

What is a Buchholz Relay?

Buchholz Relay is a Gas Operated Relay (Mechanical Protection)  which provides Mechanical Protection for Oil Immersed Transformer of rating greater than 500 KVA.
They are mainly used to detect Slow developing Incipient Faults inside the Transformer at an early Stage.
Main Buchholz Trip Relay (30A)

Who Invented Buchholz Relay?

Ans: Max Buchholz of Germany invented Buchholz Relay in 1921

Where is Buchholz Relay Installed?

Ans: It is installed in the Pipe connecting Main Tank and Conservator Tank, at an Angle of about 5 to 7 deg. It is Mounted as per IS 3638.

Buchholz Relay is used for which type of Faults?

1) Internal Faults such as:
i) Internal Short Circuit
ii) Inter Turn / Winding Fault
iii) Core Fault

Position Setting: T/L (Transport/Lock) ans S (Service)

Explain the Buchholz Relay Construction?

It has two main parts: a float switch for detecting gas and a baffle plate for sensing quick changes in oil flow. These parts work together to find and fix different issues.

  1. Upper Bucket/Element : When the Bucket is lowered, the Mercury Switch also moves with it and shorts the Contacts.
  2. Contacts:
  1. Alarm (Top Float)
  2. Trip (Bottom Float)

3)  Inspection Glass:

Explain the Working of the Buchholz Relay?

The relay works by sensing unusual gas buildup or changes in oil flow inside the transformer tank.

Buchholz Relay is completely filled with Oil, all the time


Whenever there is a fault, it makes gas bubbles. These Gas  bubbles rise through the transformer oil from the Main Tank and get trapped in the Upper Portion of the Buchholz Relay, causing the oil level to drop. As the oil level drops, the float goes down too. This float is connected to a mercury switch. When the oil level gets to a certain point, the Inclined Position of the Switch changes to Horizontal Position, the Contacts get shorted and the Alarm is actuated.

The lower Bucket does not change its position, because when the Gas reaches the Upper inside wall of the pipe, it will escape to the Conservator.

When a major Fault occurs in the Transformer, the Gas generation is Violent and causes the Oil to rush through the Connecting Pipe to the Conservator.

In the Relay, Oil Surge hits the Flap fitted on the Lower Float (Located in front of the Hole for Oil passage) and causes the Rotation of the Float, operating the Mercury Switch connecting to it which is used to Trip the Transformer.


What are the precautions to be taken with Buchholz Relay?

  1. Buchholz Relay Mechanical Lock to be taken in Service, during the process of Oil topping in the Transformer.
  2. Enough Oil level to be maintained in the Transformer, so that the Buchholz Relay do not operate due to Low Oil level in the Buchholz Relay.

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