In distribution systemsue of neutral ground is usually categorized into neutral unground, neutral ground via resistor, and neutral-point grounding via arc suppression coil. Differnent grounding ways decide various operating ways. With development of economy , over-head line which is the main way of past power grid has been replaced by cable running line. Meanwhile, some new e such as hermetic compact structure of SF6 swichgear, twisted polyethylene cable and zinc oxide arrester are more and more widely applied. Therefore, non-effective groundingue is unsuitable to present situation. As a result, to set