Field Measurement Studies on Shunt Coefficient of Lightning Shield Line

The shunt coefficient of lightning shield line is an important parameter, which needs to be considered when we are designing or reforming the substation grounding network, however, it is difficult to be calculated. This paper is to introduce a method to measure the shunt impedance of lightning shield line with a substation transformer to calculate the shunt coefficient of lightning shield line. This study is to establish a mathematical model by studying the distribution of the three parts of the maximal grounding short-circuit current which are the current flowing into the ground and flowing through the transformer neutral point and the lightning shield line, in additions, simplifying the mathematical model considering the influencing factors of the shunt impedance of lightning shield line. Besides, deriving an easier and more practical approximate calculation formula of shunt coefficient of lightning shield line from the mathematical model, combined with the field measurement done in Jiangxi province, furthermore, by analyzing the measured data, this study also found out the relationship between the shunt coefficient of lightning shield line and its influencing factors such as the average grounding resistance of towers, the average space distance, the grounding resistance of the contra lateral substation.