When the volume of the transformer oil expands or decreases with the temperature of the oil, the oil pillow acts as a regulating oil, and the transformer tank is often filled with oil. In order to make the transformer body and the lower part of the casing immersed in the oil, the operation of the transformer is ensured, and the design size of the casing can be reduced. The transformer oil is only in contact with the air in the oil pillow, the contact surface with the air is reduced, the oil is damp and the oxidation opportunity is reduced, the oil temperature in the oil pillow is lower than the oil temperature in the oil tank, and the oxidation speed is slowed down, which is beneficial to slowing the aging of the oil. . If there is no conservator, the oil surface fluctuation in the fuel tank will bring the following unfavorable factors. First, the exposed core and the coil part will affect the heat dissipation and insulation when the oil level is lowered. Second, as the oil surface fluctuates, the air is discharged and sucked in from the joint cover. Due to the high temperature of the upper layer, the oil is quickly oxidized and damp. The oil level of the oil pillow is smaller than the oil level of the oil tank, so that the contact surface of the oil and air can be reduced to prevent the oil from being oxidized and dampened excessively. Third, the oil of the conservator rarely participates in the circulation in the fuel tank. Its temperature is much lower than the temperature of the upper oil in the fuel tank, and the oxidation process of the oil is also slower. Therefore, the conservator can prevent oil.