Ground potential rise influence near HV substations in urban areas

When the grounding system of a high voltage substation is connected to uncoated metallic shielded cables, they act as a part of the grounding system, and have large influence on the potential distribution around the substation. National and international regulations define the potential contour 430 V as a border of the GPR zone of influence on telecommunication installations in case of faults to ground inside a high voltage substation or on a connected power line. However, if the substation is in a highly urbanized area, the potentials are equalized due to large and complex underground metallic networks. In such cases, as more suitable to define the protection measures are potential differences that may cause overvoltages in the telecommunication lines. A computer model of the substation grounding system and all connected uncoated metallic sheathed cables is developed. This model is used to estimate the GPR zone of influence to the consumer installations in urban environment. The effect of the equalizing of potentials by other buried metallic networks, typical for urban environment, is included in the model based on measured potentials in a small number of specified points