Two-tier protection mechanism: Light gas (gas accumulation) triggers an alarm signal, while heavy gas (oil flow surge) triggers a trip protection. These two levels of protection cover the entire protection chain, from early-stage faults to severe faults. Invented by Max Buchholz in 1921, this mechanical relay has become an essential component in transformer protection systems worldwide. The Buchholz relay provides early warning. Internal faults refer to the faults that occur inside the case, including phase-to-phase short-circuit faults of windings, inter-turn short-circuit faults of one-phase windings, short-circuit faults between windings and iron cores, and disconnection faults of windings.