The Buchholz relay of the distribution transformer is installed on the connecting pipe between the high-voltage bushing riser of the main transformer and the oil pillow. The buoy F1 of the relay goes down and turns on the contact of the alarm circuit; when there is a big fault in the distribution transformer, there is a surge in the oil flow due to the generation of a large amount of gas. When the speed of the oil flow reaches 100cm/s, the buoy F2 acts to connect through the trip circuit. At present, the open kup baffle type gas relay is used in Ertan Power Plant, and its main structure is two open kups up and down and a counterweight. When the distribution transformer is in normal operation, both the upper open cup and the lower open cup are immersed in oil, and the moment generated by the gravity of the open cup in the oil is less than the torque generated by the counterweight, so the open cup tilts upward and the relay contacts do not operate. When a slight failure occurs inside the fuel tank, a small amount of gas rises and gradually gathers on the upper part of the relay, forcing the oil level to drop. Make the upper opening cup leak the oil surface. At this time, the float is reduced. The torque generated by the gravity of the open cup plus the weight of the oil in the cup is greater than the torque generated by the counterweight, so that the contact of the upper open cup is actuated and a light gas protection action signal is sent. When a serious fault occurs inside the oil tank of the distribution transformer, a large amount of gas and oil flow directly impacts the baffle of the lower opening cup, causing the lower opening cup contact to act, thereby tripping the heavy gas protection action.