A novel UHV transmission line pilot protection principle based on integrated impedance

Based on the ratio between the sum of two terminals voltages phasor of the transmission line and the sum of two terminals currents phasor of the same line, which is defined as integrated impedance in this paper, a new ultra high voltage (UHV) transmission line pilot protection principle is proposed. When an outer fault occurs, the integrated impedance reflect the capacitance impedance of the line, its imagine part is negative, and the absolute value of its imagine part is large, when an internal fault occurs, the imagine part of the integrated impedance of the faulty phase is either a positive figure or a negative figure with small mode, According to such a characteristic, whether there is fault in line or not can be distinguished. The new criterion does not need compensating capacitance current, can be applied in the line with or without shunt reactor. Also, it can be easily set. Simulation with EMTP data shows that the presented principle has high sensitivity and reliability.