Impulse Characteristics On Grounding Devices Of Transmission-line Tower Based On Spark Discharge Equivalent Radius

Reducing impulse grounding resistance of transmission poles is the important measure to improve the thunder-resisting level and thus improve the operational reliability of transmission line. Accurately determining the impulse resistance of ground electrode for transmission poles is the foundation to achieve this measure. Domestic and foreign researchers published a lot of papers about impulse characteristics of grounding devices. But they were in a number of assumptions, ignoring the impact of soil spark discharge. And some simplified mathematical models on simple structure of the grounding devices were presented. The impulse characteristics of grounding devices in this way are very different with the actual.To address the above issues, a new equivalent model based on spark discharge equivalent radius is presented in this paper. This model can simulate the high frequency of lightning current and spark discharge. And the various parameters of the formula is given in the paper. Then two simulation models based on ATP-EMTP are established on the basis of the above model. One is a equivalent circuit model ofπtype. It can be a very good simulation based on spark discharge. The other is a equivalent circuit ofπtype with control module. It not only can simulate spark discharge, but can simulate the time-varying characteristics of various parameters under the lightning current. Impulse grounding resistance is calculated by using the two models. It shows that the two results are very close after comparing them.The results calculated by using the first model are compared with authoritative data from the field test, simulating experiment and numerical calculation. The comparative results show that the results of the model are very close to the real situation.Then the paper does a lot of simulation calculation by using the model and calculation method. And the paper detailedly analyses the impulse characteristics of grounding devices under the lightning current. Firstly, I get a lot of calculation results of radiation-type, box-type and mesh-type grounding devices. And I discuss the influences of different factors on the impulse grounding resistance, such as impulse current magnitude, geometrical dimension of grounding devices, soil resistivity, and so on. Secondly, two improved grounding devices are presented based on the common grounding device. And the impulse grounding resistances are calculated under different impulse current magnitude and soil resistivity. The grounding resistance has declined. Although the resistance decline is very small, the improved grounding devices cover a smaller area. Finally, the concept of actual impulse grounding resistance R(t) is presented. Its characteristics in various factors are studied and compared to the traditional impulse grounding resistance Rch.