Buchholz relay

Lore & Background

Max Buchholz developed the relay in 1921. The device is mounted on oil-filled power transformers and reactors equipped with an external overhead oil reservoir called a conservator. It is connected to the oil piping between the conservator and the main oil tank, allowing gas evolved in the main tank to flow upward toward the relay.

The relay operates by detecting gas accumulation or rapid oil flow. Slow gas buildup from overload lowers the oil level, activating a float switch for an alarm. Rapid gas from an electrical arc moves oil into the conservator, operating a vane switch that trips a circuit breaker. The relay includes a test port for gas sampling to identify faults.

Reader's Guide

The Buchholz relay has been a key protective device in oil-filled transformers since the 1940s, used in both stationary power systems and electric trains operating on AC electrified lines. Its ability to detect slow gas accumulation and rapid oil flow helps prevent overheating and short circuits. The relay's design, governed by standards like DIN EN 50216-2, allows for up to four switches to send alarms or isolate equipment. By enabling gas sampling, it aids in diagnosing internal faults such as arcing or leaks, contributing to transformer safety and reliability.

Did You Know?

• The Buchholz relay was first developed by Max Buchholz in 1921.
• It is also known generically as a 'gas detector relay'.
• The relay can detect both slow gas accumulation from overload and rapid gas from electrical arcs.
• Buchholz relays have been used in electric trains with up to 25,000 volts AC supply.