Transmission line pilot protection principle based on integrated impedance

Based on the ratio between the sum of two terminal-voltage phasors of the transmission line and that of two terminal-current phasors of the same line, which is defined as integrated impedance in this study, a novel transmission line pilot protection principle is proposed. When an external fault of the transmission line occurs, the imaginary part of the integrated impedance which reflects the capacitance impedance of the line is negative and with a great modulus. When an internal fault of the transmission line occurs, the imaginary part of the integrated impedance of faulty phase which generally reflects the impedance of the system source and the line is either positive or negative and with a relatively small modulus. According to such a characteristic, the external fault and the internal fault of transmission line can be distinguished. The criterion proposed in this study is not affected by the capacitive current. It can be applied to the line with or without shunt reactor. Moreover, the threshold of the criterion can be easily set. Simulation results of electro-magnetic transient program (EMTP) and dynamic physical test data both verify the high sensitivity and reliability of the proposed principle.