A Study on the Improved Performance of Half-LENS-Half-MHO Relays

MHO type directional impedance relay has been widely used in HV and EHV systems for many years, but its misoperation under certain fault conditions has been a major problem. One such instance is that relays on unfaulted phases will misoperate during a close-in S-L-G fault with fault resistance. The other is the misoperation of MHO relay during a reverse fault with fault resistance.