Method for judging internal fault of transformer using excitation property

Abstract

Technical scheme of the invention is as follows. If it is supposed that L1, L2 are as inductances of windings at primary side and subsidiary side; R1, R2 are as resistances of windings at primary side and subsidiary side. Relation between terminal voltage u1 of a winding of transformer, current i1 of flowing into the winding and mutual inductance chain of transformer is as U1 - R1í‡i1 - Lí‡di1/dt = dPhi/di. In the mutual inductance chain, cancellation between i1 and i2 is carried out. Thus, the differential current is as excitation surge current. Advantages are: raising action speed of differential protection of transformer, discriminating each internal fault in transformer by using less time, reducing harms on transformer and running system from faults of transformer, and increasing safety and stability of power system.

Description

technical field The invention relates to the field of microcomputer relay protection for power systems, and more precisely, the invention relates to a method for distinguishing excitation inrush current and internal fault current of a transformer. Background technique Transformer is one of the important electrical equipment in the power system. With more and more ultra-high voltage long-distance power transmission systems being put into operation, there are more and more large-capacity transformers, which put forward higher requirements for the reliability and rapidity of transformer protection. Due to the limitation of the conditions, the traditional transformer main protection is realized only by the amount of current. In view of the successful application of the current differential protection principle in many electrical equipment, the current differential protection is also applied in the transformer protection and plays an important role. effect. However, because the...

AI Technical Summary

Problems solved by technology

However, because the current-based differential protection has defects in principle for double-winding or multi-winding transformers coupled by magnetic circuits (that is, for impure circuits, Kirchhoff's current law is not applicable), resulting in no-load closing of transformers. When the gate or external fault is removed and the excitation inrush current is generated during the voltage recovery process, the differential protection will malfunction, so people have to work on how to correctly identify the internal fault current and excitation inrush current of the