Buchholz Relay: Its construction, working and Usage

A Buchholz relay is the protection device which is installed in oil transformers for protecting it against different faults. It is installed in the pipe which connects the conservator tank to the main tank of the transformer.

What is it made up of?

The Buchholz relay has two sections.
  • Alarm section: The upper one which connects to a float and alarms the system in case of small faults.
  • Tripping section: The lower one which trips the circuit in case of dangerous menacing faults.

How it works?

For lower faults: The heat generated during smaller faults decomposes a small part of transformer oil to hydrogen gas. This hydrogen gas rises to conservator tank. While making its way through the pipe it passes through Buchholz relay and is entrapped in the upper alarm section (Since it is lighter).
For menacing faults: Heavy faults in the main tank generate a large amount of hydrogen gas which forces the oil to the conservator tank. During its journey, the oil switches the tripping section and opens circuit breakers.

When to Use it and when not to use it?

Buchholz relays are expensive and are often uneconomical for kVA’s smaller than 800. Since they require oil immersion we can only utilize them with oil immerses transformers.
Let’s now understand the in-depth working of Bucchollz Relay in this Electrical Engineering video:

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