Why Is The Transformer Able To Operate Under Condition Of Normal Overload And Accident Overload?

Overload operation means that the isolation transformers are in excess of the ruled current value in the on the nameplate while operating.It is caused by the increase in urban consumption, leading to an increase in temperature rise, the accelerated insulation aging and the shortened service life. The insulation life of transformer is related to the temperature. When the temperature exceeds a certain value, the insulation will be aging rapidly and even damaged. Therefore transformers are not allowed to operate under overload.

Overload Can Be Undivided Into Normal Overload And Accident Overload.

Normal overload

Normal overload doesn’t have an impact on the transformer life. The transformer load is changing constantly and it keeps below the rated value while operating under the normal overload. The transformer may overload instantaneously during the peak load. During the low load the operating temperature is a bit lower and the transformer is underload which is  is beneficial to prolong its service life. That way the loss during the low load is small and  it can make up for the loss during the peak load. The judging basis of normal overload is the principle of transformer insulation equivalence. If there is no significant change in total service life, that is the normal overload. The temperature rise is related to the environment temperature.For example, it is cold in winter and the heat dissipation is fast. Therefore, normal overload is the moderate overload operation during the peak load or in the winter under the premise of not damaging the transformer insulation and not shortening its service life.There is a special rule that the overload can not exceed the 30% of the rated overload in winter and 15% of the rated overload in summer while the transformer is operating.

Accident overload

Sometimes some one among the transformers running in parallel suddenly breaks down and it needs to be withdrew from running. Its load will be shared with rest transformers. At that time the transformers are allowed to operate under the big overload and that is the accident overload.

There are special regulations on the times of the rated overload and the overload permissible time as below: