Based on the field implementation of energizing 750 kV no-load transformer located in Wubei substation within the 750 kV interconnection project of Xinjiang power grid and Northwest power grid,the mechanism of system power frequency voltage sag caused by energizing no-load transformer was analyzed and it was proposed that the inrush current and the short-circuit capacity of the interconnected power grid were the main factors influencing the voltage sag due to energizing no-load transformer.Using EMTP tools,...