Research of one new adaptive mho relay

In this paper, a new mho relay based on the adaptive principle is proposed. The operation boundary of the new relay can be adjusted to adapt different earth-fault resistance automatically, and provide consistent relay zone coverage. Therefore the adaptive mho relay has a perfect performance for the protection of single phase-to-earth faults, especially the high impedance faults on transmission line. The performance of the relay has been verified on a simulated network using ATP program. The result shows that the new adaptive mho relay has excellent performance within the protective zone, and it can reflect inner single-phase faults with a high impedance of more than 800 Ω on a simulated 300 km long transmission line of 500 kV.