The transformer overload operation is common in electric system.It is also a normal operation. The transformer accident happened in recent years which has growth trend.From these accidents, the main reason is overload.It is harmful for power grid and influence on safe operation.

The overload transformer include normal overload and accident overload.
normal overload. The load of transformer usually change in the operation.That means the load diagram has the peak and the low ebb.When it overload in peak,the damage of insulation aging will increase.When in overload in low ebb,it will decrease.The overload of normal aging calls normal overload.It usually has following situation.The partial transformer failed to work out of repairing or breakdown.The operation way has been changed which make partial transformer overload.The user load increase and the new transformer can not use immediately.
The accident overlaod has following case.The certain transformer happen accident which overload can not cut off or transfer to other transformer substation that force the else transformer overload.When the one or more happen accident, the partial overload will transfer to one or more transformers.The accident overload may appear high multiple current which make winding temperature high.It is dangerous for insulation safety. Once it happen,you must reduce overload immediately or shorten the operation time. When system happen accident, the top priority is to supply  power ceaselessly.The acceleration of transformer insulation is the second.The differences between accident overload and normal overload which lose the transformer aging.The insulation aging rate is higher than normal overload.When it confirm accident overload,it also consider the temperature too high to enlarge accident. The operation load rate influence on transformer overload. To make sure the installed capacity of transformer which consider transformer overload capacity. When transformer require overload that need to cooperate with overload capacity.