Based on a typical case that the backup protection of high voltage side tripped earlier than the backup protection of low voltage side when two-phase short circuit fault took place at the transformer low voltage side, this paper analyzes the characteristics of the currents of high voltage side and low voltage side when two-phase short circuit fault takes place at the transformer low voltage side. Considering the situations of other kinds of faults at the transformer low voltage side, this paper finds out the difference of sensibility of backup protections between the high voltage side and low voltage side. The paper finds that the provision DL/T584-2007 3~110 kV operation setting regulations of relay protection equipments of power network in the standards of the power industry is inappropriate. Hereby, this paper gives an advice on the setting of transformer’s backup protection:the setting sensibility of backup protections of high voltage side must assort with that of the low voltage side, and the fit coefficient must be not less than 1.15.This proposal effectively promotes the reliability of transformer’s backup protection of high voltage side and low voltage side.%就一例典型的变压器低压侧两相短路故障引起变压器高压侧后备保护先于低压侧后备保护动作的事故案例，分析了变压器低压侧两相短路故障时变压器高、低压侧电流的特性，并结合变压器低压侧其他故障情况，得出变压器高压侧后备保护和低压侧后备保护灵敏度的差异性。发现电力行业标准DL/T584-2007《3～110 kV电网继电保护装置运行整定规程》的规定不合适。特此对变压器后备保护整定提出一点建议：高压侧后备保护与低压侧后备保护的定值灵敏度要配合，且配合系数应不小于1.15。该建议有效提高了变压器高、低压侧后备保护的可靠性。
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