A Technical Research On 220KV Substation Grounding Net Reconstruction

In order to insure electric power system safety, stability, economy operation, it needs a better and high quality grounding net for substation or power plant. In our company, existing grounding net has been constructed for a very long time and has some Ground-Potential-Rise and Heat-Stability problems.This thesis is focused on the two critical problems of Ground-Potential-Rise and Heat-Stability. A soil model has been put forward to simulate and analyze characteristic of the soil according to real data of soil resistance rate and related grounding net data. In order to verify model's correctness, a field real grounding net has been set up according to model parameters. It is found out that model is effective after comparing data from model simulation and real data. On the other hand, to evaluate and calculate Grounding Net related data, the fault current contributions from all connected substations and the transformer circulating currents in the grounding system. are modeled accurately with the fault current distributions analyzation.The maximum GPR (Ground Potential Rise) and the maximum GPD (Ground Potential Difference) of the station (between two points of the grounding system) of the station (at the fault location) during a worst-case phase-to-ground fault on a 220 kV bus are computed. The maximum acceptable touch and step voltages are calculated with certain criteria and excessive touch and step voltages inside and outside the station during a 220KV bus fault at all possible locations are evaluated to determine if standard is satisfied. Based on the analysis and calculation, the paper developed several reconstruction grounding net design strategies. A final economy grounding net design has been proposed.