The Buchholz relay is a protective device used in transformers to detect and protect against certain types of internal faults. It is specifically designed to protect the transformer from internal faults that can occur within the transformer windings.

1. Types of Internal Faults:
The Buchholz relay primarily protects the transformer from various types of internal faults, including:

- Insulation Failure: Insulation failure can occur due to aging, overheating, or mechanical stress. This can lead to short circuits or ground faults within the transformer windings.

- Core Faults: Core faults can occur due to mechanical damage or insulation breakdown within the core. This can cause an imbalance in the transformer, leading to excessive heating and potential damage.

- Overheating: Overheating of the windings can occur due to excessive loading or poor cooling. This can result in insulation breakdown and internal faults.

2. Operation of Buchholz Relay:
The Buchholz relay operates based on the principle of gas accumulation. It is installed in the connecting pipe between the transformer tank and conservator. The relay consists of two float-operated switches and a gas collection chamber.

- Normal Operation: During normal operation, the oil level in the conservator is constant, and the float switches in the Buchholz relay remain in their normal positions. The relay is in a standby mode, not affecting the operation of the transformer.

- Internal Fault: When an internal fault occurs within the transformer, such as insulation failure or core fault, it causes the generation of gases, primarily hydrogen. These gases accumulate in the gas collection chamber of the Buchholz relay.

- Gas Accumulation: As the gases accumulate, they displace the oil in the gas collection chamber, causing the float switches to tilt. The tilting of the float switches triggers an alarm or trip signal, indicating the occurrence of an internal fault.

- Protection Action: The alarm or trip signal from the Buchholz relay can be used to initiate protective actions, such as isolating the transformer from the power system or initiating a fault investigation.

In conclusion, the Buchholz relay protects the transformer from various types of internal faults, including insulation failure, core faults, and overheating. It operates based on the accumulation of gases generated during internal faults and triggers an alarm or trip signal to initiate protective actions.