The Buchholz relay is a gas-actuated protective relay used for liquid-immersed transformers.

It detects faults like core heating, inter-turn shorts, and loose connections before they lead to catastrophic failure.

Inspection intervals depend on the transformer capacity and environmental conditions (e.g., humidity, load cycles).

Functional testing includes verifying the tripping circuit of the circuit breaker.

Provides early detection of incipient faults.

Prevents major damage to the transformer windings and core.

Requires proper oil quality to avoid false trips.

Frequent inspection requires skilled personnel to avoid accidental relay damage.

Oil-filled power transformers

On-load tap changer compartments

Periodic maintenance of protection relays is critical to avoid 'fail-to-operate' conditions during actual faults.

Option A (Yearly) is generally considered too frequent for relay mechanical parts, while options C and D represent less conservative maintenance strategies.