A transmission line pilot protection principle based on the composite impedance of individual phase is proposed. The individual phase impedances are calculated from the fault total content differences of the voltages and currents at both terminals of the line
and then used for judging if the fault is occurs at the line.If the fault is outside of the protected area
the individual phase impedances just equal to the positive sequence impedance of whole length of the transmission line
while they will obviously differ from the determined value in case of the fault inside of the protected area
which refers an amplitude criterion. The proposed protection with independent phase selection possesses identity of reliable performance
sensitive operation
and strong adaptation. The EMTP simulation and the dynamic simulation test results indicate the effectiveness of the presented principle.
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