Method to Identify Transformer Sympathetic Inrush Based on Time-domain Variation Characteristics of Aperiodic Component

The analysis of maloperation cases indicates that mal-operations of the transformer differential protection caused by sympathetic inrush usually occur under the combined action of sympathetic inrush and current transformer (CT) saturation. The process and characteristics of the mal-operation caused by sympathetic inrush are analyzed. According to the wave characteristics of sympathetic inrush that firstly increases to maximum gradually and then decays slowly, a new sympathetic inrush identification method is proposed, based on the calculation of the fundamental component increment of transformer differential current. The new method can identify sympathetic inrush quickly and reliably and adopt effective measures accordingly before sympathetic inrush makes CT saturated. The simulation and dynamic simulation experiment verifies the validity and feasibility of the method.