Buchholz Relay

The correct answer is option C, the Buchholz relay. The Buchholz relay is a protective device used in electrical power transformers to detect and prevent major faults such as internal short circuits and oil leaks.

The Buchholz relay operates on the principle of gas accumulation in the transformer's oil conservator tank. It is mainly installed in oil-immersed transformers with a rating of 500 kVA and above. The relay is connected in the pipe between the main tank and the conservator tank of the transformer.

The Buchholz relay consists of two float chambers, each with a float and mercury switch. The upper float chamber is connected to the main tank and the lower float chamber is connected to the conservator tank. The relay is filled with oil and operates based on the gas produced during a fault condition.

When a fault occurs, such as a short circuit inside the transformer, the fault generates heat, which causes the insulation material to break down and produce gas. The gas rises to the top of the transformer tank and enters the Buchholz relay through the upper float chamber.

Now let's discuss the operation of the Buchholz relay in detail:

1. Minor Faults:
- If a minor fault occurs, such as a small internal fault or a slow oil leak, a small quantity of gas is produced. This gas accumulates in the Buchholz relay, causing the upper float to rise.
- When the upper float rises, it activates the mercury switch, which in turn sends an alarm signal to the control room or activates an alarm locally.

2. Major Faults:
- In the case of a major fault, such as a severe internal short circuit or a rapid oil leak, a large quantity of gas is produced. This gas rapidly accumulates in the Buchholz relay, causing the upper float to rise rapidly.
- When the upper float rises rapidly, it activates the mercury switch, which sends a trip signal to the circuit breaker, isolating the transformer from the system.
- Additionally, it also sends an alarm signal to the control room or activates an alarm locally.

The Buchholz relay plays a crucial role in preventing major transformer faults, as it can detect both minor and major faults. It provides an early warning system, allowing for maintenance or repair work to be carried out before the fault worsens and causes significant damage to the transformer.

It is used to sense the fault such as short circuit faults such as inter turn faults, incipient winding faults, and core faults. it recognized fault by different gases release due to fault.