基于瞬时励磁电感频率特性判别变压器励磁涌流

基于变压器瞬时励磁电感基频分量的有无，提出了判别励磁涌流与内部故障的新方法。涌流时变压器铁心必然经历饱和与非饱和过程，瞬时励磁电感是时变、交替变化的，具有较大的基频分量；内部故障时，变压器铁心工作于线性区，瞬时励磁电感恒为常数，无基频分量。据此，可实现励磁涌流与内部故障的有效判别。但瞬时励磁电感很难精确求取，为方便计算，提出了等效瞬时电感的概念，论证了其基频特性的等效性。动模实验有力地证实了所提方法的可靠性与安全性。

DISTINGUISH INRUSH CURR ENTS FOR TRANSFORMERS USING FREQUENCY CHARACTERISTIC OF INSTANT ANEOUS EXCITATION INDUCTANCE

Based on the difference between the internal faults and magnetic inrush currents on the frequency characteristic of instantaneous excitation inductance, a novel method is proposed to distinguish internal faults from inrush currents for transformers. The cause of the inrush currents is the saturation of core in the transformer. The instantaneous excitation inductance varies alternately in one cycle under the inrush currents, in which fundamental frequency component is very significant. However, the transformer operates in the linear section of the magnetizing curve for the internal fault, in which the fundamental frequency component is nearly zero. So, it must be the inrush current for the transformer if the fundamental frequency component of the instantaneous excitation inductance is very large. For the sake of convenience in the computation, the equivalent instantaneous inductance is proposed, which is consistent with the instantaneous excitation inductance in the fundamental frequency characteristic. Experimental tests are carried out on a power transformer, and the results verify dependability, security and fast speed of operation when distinguishing internal faults from inrush currents.