A new method of switching on parallel medium resistance to select the fault line instantaneously when the single-phase earth fault occurs in the arc suppression coil grounded system is proposed.

When the neutral point is earthed by an arc extinguishing coilparallel resistance in high tension network of mine, the power frequency resonance over-voltage, linear harmonic over-voltage and arc earthing over-voltage can be efficiently controlled.

By analyzing the working principle of arc suppression coil earthing,in view of fault line selection and earthing over-voltage problems exsisting in arc suppression coil earthing system,the earthing method of arc suppression coil with parallel resistance was proposed and the arc suppression coil working principle was analyzed in detail.

The diode saturation current density J0,diode quality factor A,series resistance Rs and shunt resistance rsh are deduced using Matlab.

Base on the structural characteristic of GIS, the mechanism and effects of disconnector with shunt resistor to depress VFTO are simulated and analyzed in this paper.

Consequently,the principle of fault line selection under the arc-suppression coil parallel connecting the mid-resistance grounding was analyzed,and lots of single-phase-to-earth tests are carried out respectively on the metal slab,sand soil,floor slab,gravel pile,asphalt slab in 35 kV system.