Countermeasure to Prevent Transformer Differential Protection From False Operations

Abstract

The reliability of the transformer differential protection is under threat from multiple interferences, including the inrush condition, the current transformer saturation condition, and the arc fault condition. For improvement, a new method is proposed to discriminate fault conditions and other non-fault conditions. Firstly, the proposed method identifies the unidirectional inrush via unidirectional index, since only it exhibits unidirectional characteristic. Then, the remaining signals are classified by the quartering-based similarity index. The quartering-based similarity index is obtained by quartering segmented fitting to overcome the drawback of overall fitting. Simulation results indicate that the proposed method is able to effectively avoid misjudgments caused by aforementioned interferences. Actual experimental tests, field data tests, and comparison analyses demonstrate its engineering adaptability and superiority.

Keywords

• Curve fitting
• current transformers
• fault currents
• fault detection
• inrush current
• protective relaying