Owing to the influences of such factors as the earth resistivity on the zero module parameter， the stable space module is adopted to calculate energy for energy balance protection. In general， EHV and UHV transmission line protection needs to correctly select and switch off the faulty phase when single line-to-ground fault occurs. As the energy balance protection based on spatial modules 1 and 2 does not possess the natural phase selecting function， a new algorithm for energy balance protection based on three modules in space is proposed， making it possible to switch off the faulty phase should single line-to-ground fault occur.