变压器和应涌流分析

Research on sympathetic inrush in operating transformer

以2台单相变压器并联运行为例,利用励磁涌流偏向时间轴一侧的特点,解释了和应涌流的产生机理及其变化特点,指出和应涌流产生的本质原因是由于合闸变压器励磁涌流流过系统电阻使得其他变压器工作母线电压偏移,导致铁芯饱和造成的。初步分析了系统电阻、线路阻抗、空投变压器不同剩磁以及运行变压器二次侧负载对和应涌流的影响,讨论了和应涌流对变压器差动保护和后备保护的危害,其非周期分量长期作用引起的电流互感器局部暂态饱和以及差流中二次谐波含量降低是造成差动保护误动的主要原因。提出了相应的防范措施:在条件允许的情况下将电流互感器从P级更换为TP级以防止其暂态饱和;在满足灵敏度要求的前提下适当提高发电机及变压器差动保护的定值;尽量避免可能产生和应涌流的运行操作;正确整定变压器电流距离保护的各段定值;利用二次谐波分量构成零序二次谐波制动判据防止差动保护误动;寻求更可靠的主保护原理或完善纵差保护原理。

Taking two single-phase transformers in parallel as example,the principle and characteristics of sympathetic inrush are explained according to the fact that the inrush current leans to time axis. The sympathetic inrush is essentially caused by the deviation of bus voltage and the consequent core saturation of adjacent transformer during the inrush current of the energized transformer running across the system resistance. The influence of system resistance,line impedance, different residual fluxs of no- load transformer and secondary load of operating transformer on sympathetic inrush are analyzed and the harm of sympathetic inrush to transformer differential protection and back- up protection are discussed. The local transient saturation of current transducer caused by the permanent effect of nonperiodic component of sympathetic inrush and the decrease of secondary harmonic in differential current are main factors resulting in the misoperation of differential protection,and corresponding countermeasures are proposed：change current transducer from P rank to TP rank to prevent its saturation if possible;increase settings of generator and transformer differential protection while the sensitivity is satisfied;try to avoid the operation causing sympathetic inrush; correctly set sect settings of transformer current distance protection;apply secondary harmonic to form the zero- sequence secondary harmonic triggering criterion to avoid the misoperation of differential protection;find out more reliable main protection principle or improve the principle of longitudinal differential protection.