Abstract: The feed circuit fault at the low voltage side of the transformer could cause a serious damage to the transformer and cause a power shut down to a large area of the mining area.An interphase fault occurred by the single phase flashover fault due to a line damaged by thunderstrike had made a serous accident of the insul ation damage to a 110 kV transformer.The fault recorded wave, the dispatching and comprehensive automatic background SCADA and the information provided by SOE were applied to analyze the development process of the accident and anti short circuit capacity of the transformer. Based on the related stipulations of the ISO standard and the national standard, the failure cause of the transformer was found.According to the fault causes, the prevention measures and the method to test and identify the transformer damaged or not were provided to the repair and maintenance of the related electric equipment.The implementation of those measures and method could eff ectively improve the safety of the mine electric power supply.