中文摘要：

TA饱和一直是影响变压器差动保护可靠性的重要原因。目前已有的比率制动特性和时差法等方法，在一定程度上提高了保护躲避区外故障的能力，但无法及时处理区外故障转区内故障的情况。通过分析发现：当外部故障且TA饱和时，绝大部分采样点在满足动作条件的情况下，其饱和TA的二次电流变化趋势与差流的变化趋势相反，而在内部故障情况下，上述规律则不满足。由此提出利用饱和二次电流和差流采样值变化轨迹，动态地定是否发生故障发展，有利于进一步提高差动保护的可靠性。仿真结果证实了所提方法的有效性。

英文摘要：

The TA saturation has always been the main problem to degrade the reliability of the differential protection of power transformer. The percentage restraint characteristic and the method using operation time difference between startup element and differential protection can enable the protection to immune to the external fault to some extent. However, they cannot deal with the developing fault from an external one to an internal one, It is disclosed that the change of most samples of the secondary current of the saturated TA is inversely proportional to the change of the differential current for an external fault accompanied by the TA saturation, In contrast, this law will not untenable for an internal fault. Therefore, the locus of the change of the saturated secondary current with the differential current are utilized to dynamically discriminate if the an external fault develops to an internal fault. In this case, the reliability of the differential protection can be improved. The simulation results testify the effectiveness of the proposed methods,