Influence of transmission line tower grounding impedance to the line flashover rate

The paper presents a mathematical model for analysing impulse characteristics of complex grounding grids in uniform and two-layer soil. The model is based on the grounding grid equivalent circuit with lumped parameters, described by a system of differential equations. The effect of the mutual couplings of the grounding grid elements can be comprised by the so-formed model. The established model has been successfully checked experimentally for the square grounding grid. A grapho-analytical approach to the evaluation of the transmission line tower impulse grounding impedance model is described. The proposed model is convenient for practical application. It is incorporated into the present lightning overvoltage computation program. The methodology of the line flashover rate estimation is illustrated at the example of 400-kV overhead lines.