A novel transmission line pilot protection principle based on current model recognition

Due to the distributed capacitance, the conventional current differential protection has unsatisfying performance. Considering matrix pencil algorithm can accurately analyze the composition of fault transient currents, a novel pilot protection principle using only current data is proposed in this paper to solve the above problem. This principle adopts model recognition concept. Firstly, the theoretical expression for external fault is derived which describes the ratio between the sum and difference of two terminal fault component currents, and the expression is defined as the standard model. Then the model error function is established while the function measures the extent to which actual fault data accord with the standard model. When an external fault occurs, fault data correspond with the standard model and the model error equals zero. When an internal fault occurs, fault data do not correspond with the standard model and the model error is greater than zero. Therefore, external fault and internal fault are distinguished. This new principle is immune to the distributed capacitance and has high reliability without using voltage data. Moreover, the principle possesses fast operation speed and high sensitivity. Electromagnetic transient program (EMTP) simulation results verify the effectiveness of the proposed principle.