After an internal fault occurs in the transformer, the transformer oil is degraded by the heat and energy of the fault and gases such as hydrogen, methane, ethane, ethylene and acetylene are produced. If the fault is of high energy, the gas production rate is higher than the gas dissolution rate in the oil and the gas moves as insoluble to the conservator and gets trapped in the Buchholz relay on the way. And the relay alarm is activated. Generally, a high-energy fault such as an electric arc in