Analysis of Grounding Impedance Computation for Grounding Grid of Substation in Operation
Chenghuan Tian · Gao dianya jishu · 2013
Topology structure of a grounding grid in substation will change due to the overhead grounding wire of transmission lines or two-end grounded power cables connected with the grounding grid.Consequently,the measured grounding impedance of a grid will be different from the actual value of the main grounding grid of substation in operation.Therefore,on the basis of the idea of field-circuit coupling theory,we put forward a step-by-step method to calculate the grounding impedance of substation in operation.The accuracy of the calculation method and the correctness of the model were validated by an example analysis and comparison.An analysis of the main factors affecting the calculation shows that the current injection point and the amount of overhead grounding wires have considerable influences on the grounding impedance calculation.Moreover,the impact of grounding wire and tower on the calculation accuracy under three different conditions are compared,and the results indicate that the current injection point should not be in the corners of a grounding grid when measuring the grounding impedance of substation in operation;if there are many lightning lines,it is necessary to consider the impact of the terminal tower on the measurement results.