The Insulation Margin of UHV Transformer Lead Exit at Low Temperature

The main insulation materials of ultra-high voltage (UHV) transformers and UHV shunt reactors include the transformer oil, insulating paper, insulating paperboard, and other paper components. In the extreme cold ambient, the properties of those insulating material will change because of the temperature decreases. Therefore, under extremely cold conditions, when the transformer is put into operation from a cold standby state, it must ensure that the internal electric field performance of the transformer meets safety requirements firstly. In this paper, the insulation structures of key parts of UHV transformers are investigated in the view of insulation margin under extremely low temperature conditions.