Phase distance relaying algorithm for unbalanced inter-phase faults

This study presents a new fault impedance estimation algorithm for inter-phase faults for the purpose of phase distance relaying of extra high voltage (EHV) and ultra high voltage (UHV) transmission lines. The principle is based on the assumption that the fault arc path is predominantly resistive, and the phase angles of the unmeasured fault point voltage and fault arc path current are equal. This is used to construct the fault impedance estimation equation, which naturally prevents the effects of fault arc path resistance, load current, power swing and load encroachment. PSCAD (simulation software) simulation shows the validity of the proposed algorithm.