Improvements in the operation of a distance relay during resistive faults

Distance relays provide good dependability for bolted faults but they can face problems detecting resistive faults, specially in short lines. The fault resistance can also affect the security of the relay. This paper explains the concept of the apparent resistance. The influence of the remote infeed with load flow and non-homogeneity of the system on both Quadrilateral and Mho characteristics is described. The effect of the ground resistance on the phase to earth loops during a phase-phase-ground fault is also reviewed. The paper describes the most common polarization methods used for the reactance line to compensate the load flow and non-homogeneity of the system. It describes an adaptive polarization method that provides good security and dependability for any type of resistive fault. Special conditions are considered: faults during open pole conditions, cross-country faults and evolving faults. Real events and RTDS cases are considered. The paper also provides a guide for setting the resistive reach of a distance relay, based on the line impedance, the VT and CT errors, the phase selector used, the type of load flow and non-homogeneity compensation, general reactance line tilting, load encroachment, resistive limiter algorithm (based on ohms / phase or ohms / loop), etc. Examples from real installations are included.