Abstract:  A pilot protection algorithm of transmission line based on the fault total content of line both terminals was proposed. According to the exact analysis of  the pilot impedance characteristics based on the fault conponent, this algorithm adequately described the computing result influenced by the load component under various operation condition,and established the reasonable protection tripping setting value. It does not set special protection starting unit; at any time of system running, when the result is less than the protection tripping setting value, the fault is determined as the internal and the protections at line’s two terminals may cooperatively trip; otherwise, the protection is blocked whether the fault occurs or not. The algorithm may ensure the stable and reliable results, has strong ability of resisting transition resistance, shows sensitive operating reaction characterictics and possesses selfselecting phase capacity. It builds 1 000 kV 500 km line model on electromagnetic transients program (EMTP), uses the dynamic model data from Lanzhoudong to Xianyang 750kV, executes the simulations under different faults. The simulation results indicate that this algorithm can correctly judge the aforesaid various fault states.

Key words: transmission line, fault total contents, pilot impedance, twoterminal electrical quantities, amplitude criterion