Microgrids (MGs) are very attractive for electrical power generation/consumption owing to increased reliability and resiliency, however, protection against different short-circuit faults is a major challenge in implementation. This paper proposes a simple algorithm for on-line estimation of apparent resistance per-phase of a three-phase ac power line. The idea is to compare the estimated apparent resistance with the real resistance per-phase of the power line. Then, any reasonable difference between the two resistances will indicate a short-circuit fault occurrence along the line; hence, the line has to be tripped immediately. This pilot-based unit protection scheme presents salient advantages when applied to protect the power lines in the meshed MGs. Effectiveness of the proposed protection scheme is verified by simulation in the MATLAB/SIMULINK environment using a test MG with inverter-based distributed generations. The results confirm reasonable performance of the protection scheme for the meshed MGs with various topologies under both the grid-connected and islanded modes of operation and with different faults including the symmetrical/asymmetrical short-circuit faults, high impedance short-circuit faults, and close-in-internal short-circuit faults.
