This paper proposes a new scheme for backup protection of transmission lines with a limited number of phasor measurement units (PMUs). In the presented methodology, the PMUs is located optimally in a way that all faults would be observable. The network is divided into a few zones with 1, 2 or 3 transmission lines. Following this, the nearest bus to the fault location named as the faulted bus is selected through the voltage data measured by PMUs. A faulted area including the suspected zones, the zones connected to the faulted bus, is then identified. The faulted zone is subsequently recognized by using the phase deviation between the positive- (negative-) sequence voltage of the faulted bus and the positive- (negative-) sequence of the input current to the suspected zones. The faulted line is finally detected based on the type of the faulted zone and corresponding algorithm. The effectiveness of the presented scheme is assessed under several fault situations in MATLAB/Simulink platform. Simulation results demonstrate that the proposed method detects the faulted line accurately for all fault conditions. Moreover, the proposed scheme protects the shunt-compensated transmission lines as properly as the uncompensated ones without using the pre-fault data.

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