Explain the function of Buchholz relay and its position within the protection system of a transformer.

The Buchholz relay is a safety device mounted on oil-filled transformers to detect faults that occur inside the transformer tank. It is a gas-actuated relay, meaning it detects the accumulation of gas within the transformer. Its function is to provide early warning of developing faults, allowing for corrective action before major damage occurs. The Buchholz relay is typically positioned in the pipe connecting the transformer tank to the conservator tank. The conservator tank is a small tank mounted above the main transformer tank that allows for the expansion and contraction of the oil due to temperature changes. The Buchholz relay contains two floats or hinged buckets. The upper float is designed to detect the slow accumulation of gas. Minor faults, such as overheating or insulation degradation, cause the oil to decompose and release gases like hydrogen, methane, ethane, ethylene, and acetylene. These gases rise and accumulate in the Buchholz relay, displacing the oil and causing the upper float to tilt. This tilting action triggers an alarm, providing an early warning of a developing problem. The lower float is designed to detect sudden pressure surges caused by major internal faults, such as arcing or winding shorts. These faults generate a large volume of gas and create a pressure wave that travels through the oil. The pressure wave causes the lower float to move suddenly, triggering a trip signal that isolates the transformer from the system. The Buchholz relay is an important component of the transformer's protection system. It provides protection against a wide range of internal faults, from slow-developing problems to sudden, catastrophic failures. However, it is not a primary protection device for external faults. Other protection devices, such as differential relays and overcurrent relays, are used to protect against external faults. The Buchholz relay complements these devices by providing early detection of internal faults that might not be detected by other means. Regular inspection and testing of the Buchholz relay are essential to ensure its reliable operation. This includes checking for gas accumulation, verifying the float movement, and testing the alarm and trip circuits. Proper installation and maintenance of the Buchholz relay are crucial for protecting oil-filled transformers from internal faults.