During normal operation of the relay, its interior is filled with transformer oil, and the split cup (float) is in the upwardly inclined position shown in Figure 1. When there is a slight fault inside the transformer, the gas generated by the decomposition of the transformer oil accumulates in the air chamber at the upper part of the relay, forcing the oil level to drop, and the split cup 3 then drops to a certain position. The magnet 6 on it causes the dry spring contact 10 to engage, connects the signal circuit, and sends an alarm signal. If the oil level in the oil tank drops, it also acts on the signal circuit to send an alarm signal. When a serious fault occurs inside the transformer, the pressure in the oil tank will momentarily rise, causing oil surges to occur, triggering the damper 5. When the damper rotates to a certain limited position, the magnet 6 on it causes the dry spring contact 10 to engage, connecting the trip circuit, and directly cutting off the power supply of the transformer without prior warning, thereby protecting the transformer.