不同相位补偿方式下变压器差流特性研究

Research on Characteristics of Transformer Differential Current for Different Phase Compensation Methods

研究了励磁涌流条件下,不同相位补偿方式对变压器差动保护差流二次谐波含量的影响.从推导空载合闸磁链表达式出发,分析影响励磁涌流的因素,理论分析了Y→△与△→Y两种相位补偿方式对变压器差动保护中差流的二次谐波含量影响的差异,并重点分析了出现对称性涌流情况下的二次谐波含量.在此基础上,对比研究了这两种电流相位补偿方式对二次谐波比励磁涌流识别判据的影响.根据现场录波数据,通过实际数据分别计算分析了相电流及两种相位补偿方式下所得差流的二次谐波比.理论分析和实际计算表明,经Y→△相位补偿后出现的对称性涌流,其二次谐波含量并不低;△→Y相位补偿方式下采用分相闭锁保护也存在问题,也不宜利用未经补偿的相电流计算闭锁判据中的二次谐波比.

The influence of different phase compensation methods on the ratio of second harmonic in differential current for transformer is investigated under magnetizing inrush. Firstly, the flux linkage expression of switching on without load is deduced and influencing factors of inrush current are analyzed. Then this paper compares the differences between two phase compensation methods of Y→△ and △→Y, with an emphasis on the analysis of the ratio of second harmonic of symmetric inrush. Using inrush waveform of a real transformer, the ratio of sec-ond harmonic of phase current and that of differential current under two kinds of phase compensation methods are calculated respectively. Furthermore, based on the calculation results, the effect of two kinds of phase compen-sation methods on the inrush current identification is proved. The analysis and calculation results show that the ratio of second harmonic of symmetric inrush caused by phase compensation methods, from star to delta, is not low. Moreover, the split - phase blocking scheme should not be adopted for differential protection of from delta to star compensation. Using the phase current without compensation to calculate the ratio of second harmonic is in-advisable too.