Effects of electric fields generated by direct lightning strikes on ground to underground cables

The initial electric field distribution in soil is fundamental to the prediction of lightning caused breakdown to underground cables. The effect of electric fields due to direct lightning strikes on ground to underground cables were showed in the form of the safety depth of buried cables, the impacting current to cables and the overvoltage dropped XLPE insulator cable. The electric field distribution is calculated in homogeneous soils and direct buried cables. The lightning strike current magnitude impacted to cable is evaluated using equivalent circuit model that used characteristic impedance of cable in soil instead of underground cable and soil resistance instead of soil ionized. ATP/EMTP is used to model and simulation for analysis the overvoltage between core and sheath by used the cable data in 22 kV and 33 kV distribution systems PEA, Thailand. The result shows that the safety depth of underground cable installation from lightning flash point, the lightning current magnitude that insulation puncture and the numbers of cables damage.