Abstract:

This paper analyzes the principle of transformer saturation.Residual magnetism is an important factor behind the transformer saturation.With residual magnetism,the transformer is operated in non-linear regions and be saturated in turn.Then this paper analyzes a recent case.A permanent line error appeared in a 220 kV double-circuit.Another circuit CT was saturated and the line was mis-protected after the reclosing failure.Non-faulty lines were found to possess a large penetrating non-periodic component due to the inconsistent opening and closing characteristics of the switches on both sides of the line.As residual magnetism was produced on the CT of one side,the line was severely saturated and incorrect protection operation was taken.Through the analysis of this case,the relevant countermeasures and treatment methods are introduced,and a reference for the subsequent treatment of similar incidents are provided.

Key words: current transformer, magnetic saturation, remanence, differential protection