Although the transformer is overloaded, the degree of overload is not significant, and before overload, the transformer load is light, the top oil temperature of the transformer is not high, and the hot spot temperature of the transformer winding will not reach a harmful level. This type of overload is allowed by the transformer

2. Limit overload

The overload degree of the transformer is relatively high, causing the top oil temperature to rise. The hot spot temperature of the transformer winding may reach a harmful level, but it has not yet reached a dangerous level. At this time, although the transformer can continue to operate, it will reduce the insulation strength and threaten the safety of the transformer, affecting its life This overload must be limited

3. Overloading is prohibited

The overload degree of the transformer is relatively high and the time is long, causing the top oil temperature of the transformer to exceed the allowable value, and the hot spot temperature of the transformer winding has reached a dangerous level If the transformer continues to operate at this time, the insulation oil around the hot spot will decompose and produce bubbles, resulting in a serious decrease in insulation strength, which may cause major faults in the transformer. This overload must be prohibited

When the transformer is operating under overload, special attention should be paid to the following points:

(1) Closely monitor the temperature of transformer windings and top oil temperature

(2) When all cooling devices of the starting transformer have defects or the cooling efficiency does not meet the requirements, overloading operation of the transformer should be prohibited

(3) For transformers with on load voltage regulating devices, it is advisable to avoid using on load voltage regulating devices to adjust the tap when the degree of overload is high

(4) The main transformer can operate under normal overload and accident overload conditions The allowable value for normal overload should be determined based on the load curve of the main transformer, the cooling medium, and the load carried by the main transformer before overload The operation of accident overload and normal overload must be carried out without any abnormal phenomena in the main transformer If the main transformer has damage to the cooler, severe oil leakage, or serious defects in the body protection, overload operation is not allowed