What is Buchholz Relay ? | working ,construction | Electronicsinfos

What is Buchholz Relay?

    Buchholz Relays is a Gas Operating Relay that is used for the Internal protection of the Transformer is called Buchholz Relay. This is mounted on the power transformer to protect it from Dielectric Failures. 

    This is located between the conservator and the main tank of the transformer. Buchholz relay used with immersed oil transformer. For Economic consideration, the Buchholz relay is not used in transformer under a rating of 500 KVA.

    what is buchholz relay in transformer
    What is Buchholz Relay? 

    Construction of Buchholz Relay

    There are two main elements of Buchholz Relay one is float and another Element is a baffle plate. There are two floats in the upper element one is connected to the Trip Circuit that works when any emergency condition occurs and another float is connected to the alarm circuit that generates an alarm signal. 

    The Float is attached with a hinge in such a way that it can move up and down easily. The movement depends on the oil level. 

    The lower element consists of a mercury switch and baffle plate that change their direction when oil is entering with high pressure.

    What is Buchholz Relay ? | working ,construction | Electronicsinfos

    Working Principle of Buchholz Relay

    Buchholz relay is working on the principle of gas actuating relay. When any Internal fault occurs due to the Decomposition of insulating oil. The oil bubbles are produced in the oil. 

    This bubble is moving toward the conservator and strikes the upper relay chamber. The b1 float tilt due to the movement of bubbles and external Mercury contacts C1 is close. when c1 closes the alarm is operated.

    When heavy Faults occur in a transformer due to the heavy current passed in the oil, the decomposition process starts and the oil changes into gases. These gases strike with the lower float and c2 contact is close. 

    after that circuit is trip and the transformer is disconnected from the main supply. This relay is only operated when the temperature reaches up to 150 degrees.

    Advantages of Buchholz relay

    Buchholz relay is a protective device used in oil-immersed transformers to protect them from faults such as internal short circuits, insulation failure, and other related issues including

    1. The Buchholz relay can detect faults at an early stage. This helps to prevent severe damage to the transformer.
    2. Buchholz relay is a highly sensitive protective device. This allows for quick and accurate detection of faults.
    3. Buchholz relay can also detect the presence of moisture or other contaminants in the transformer oil. This can help to prevent oil degradation.
    4. Buchholz relay is easy to maintain and can be checked periodically for faults or other issues.
    5. Buchholz relay is used in outdoor and indoor operations.
    6. Buchholz relay is a highly secure relay.
    7. Buchholz relay can work with both types of temperatures (Internal and External).
    8. Buchholz relay is a corrosion-free relay.

    Disadvantages of Buchholz relay

    1. The relay may sometimes give false alarms, which can lead to unnecessary shutdowns or maintenance activities.
    2. The Buchholz relay requires regular maintenance and testing to ensure that it is functioning properly.
    3. The relay is designed to work with oil-filled transformers, so it may not be compatible with dry-type transformers.
    4. The Buchholz relay is typically more expensive than other types of protective devices.


    In conclusion, the Buchholz relay plays a critical role in oil-filled transformers. It protects from internal faults and gas accumulation. The Buchholz relays have a dual function of alarm signalling and tripping making. 

    it is a vital component of transformer protection schemes. Its sensitivity to small gas and oil flow variations enables early fault detection.  

    Frequently Asked Questions (FAQs)

    What is a Buchholz relay?

    A Buchholz relay is a protective device used in oil-filled transformers and protects from internal faults such as overheating, insulation breakdown, or gas accumulation.

    How does a Buchholz relay work?

    It operates based on the principle that internal faults in a transformer. These variations are detected by the Buchholz relay which triggers an alarm.

    What are the main functions of a Buchholz relay?

    The main functions include detecting internal faults, providing alarm signals for maintenance personnel, and tripping the transformer to prevent further damage during severe faults.

    What types of faults can a Buchholz relay detect?

    It can detect faults such as insulation breakdown, arcing, overheating, partial discharges, and gas generation.

    What are the components of a Buchholz relay?

    A Buchholz relay consists of a float assembly, oil chamber, gas collection chamber, trip mechanism, alarm contacts, and a test valve for manual testing.

    Can a Buchholz relay be used in all types of transformers?

    Buchholz relays are primarily used in oil-filled transformers. They are not typically used in dry-type transformers.

    Are there alternatives to Buchholz relays for transformer protection?

    Yes, There are alternative protection schemes such as gas and temperature monitors, dissolved gas analysis (DGA), and online monitoring systems.

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