Study On The Novel Line Selection Of Singel-phase-grounded In The Small Current Earth System

In our country,there are non-directly-grounded system including no-grounded system and Pterson-coil system in middle voltage distribute net system.. It has one adventage in non-directly-grounded system:When single-phase permanent earthing occurs,it's line voltage is still symmetrical, though power supply isn't influenced. On the other hand,the fault current is rather small,so it's difficut to find the fault line.In this paper, deep research has been made in the novel small current selection. It's aim is to find the deficiency of existing method ,to improve selection strategy. As a abasis, mechanisms and features in single-phase to earth fault that occurs on neutral non-grounded power system are distinction of fault component between fault circuit and normal circuit are listed. Effect of Peterson -coil on single-phase to earth is also discussed.In this paper,after all kind of selection method has been deep analyzed, a new method is given in neutral non-grounded power system that resistance are in parallel with neutral point when a single phase to ground occur. In this case ,fault current become bigger ,so small current selection can accurately choose fault line..