Abstract: This paper analyzes one rectifier transformer abnormal trip at one salt chemical enterprise in Jiangxi province. By inspecting the field equipments including the transformer, CT, breaker protection cabinets, junction box, and microcomputer integrated protection devices etc, find that the microcomputer integrated protection device was fault. The current and voltage samples inside the devices were error. This made the device act wrongly. After dealling with the fault, the normal production of the enterprise was restored