Frequency Dependent Characteristics Of The Soil Dielectric Constant And Grounding Electrode Impact Resistance Reduction Measure

The tower grounding devices of transmission line are basic equipment thatmaintain safe and reliable operation of the power system, with the development of thepower system, the voltage class grows higher and the capacity of power systembecomes larger, then, operations and lighting transient current will have greater impacton grounding system, which brings new safety problems.Scholars at home and abroad have done a lot of research on the impulse currentdispersal regularity of grounding electrodes, but most people ignored the soil dielectricconstant varying with frequency which can affect the dispersal process. Cause of theydo lots of assumptions and approximate on soil spark discharge, their results have agreat difference compared with real result. In allusion to the problems mentioned above,this paper does an adequate consideration in soil dielectric constant varying withfrequency, and builds a frequency domain finite-element model of grounding electrodesbased on Maxwell differential equations; this model was used to analysis impulsecharacteristics of grounding devices adding short conductors. Systematically discussesfour factors’ effect on impulse characteristics of grounding device, which are thearrangement position and length of short conductors, the injection current amplitude andthe current frequency. In this paper, the main work and conclusions are as follows:①Select a kind of common soil-red soil to carry out the test and obtain the soildielectric constant under the condition of different water content and differentproportion of earth-rock. According to the experimental data, fitting the power functionrelation between the soil dielectric constant change with frequency.②Establish a finite-element model of grounding electrodes based on Maxwelldifferential equations. In this model, the frequency dependent characteristic of the soildielectric constant needs to be considered in frequency domain. It introduces therelation between the soil dielectric constant change with frequency, give fullconsideration to the impact dispersion process and analysis the impact of soil ionization.③Establish a finite-element frequency domain model of horizontal groundingelectrode and analyzing the impulse characteristics of grounding electrodes adding shortconductors. Then, come to the influence factors such as the short conductor arrangementlocation, the length of the short conductor, injection current amplitude and frequencyaffecting the impulse characteristics of grounding electrodes. ④Carry out the simulation test of horizontal grounding electrodes adding differentdensity of short conductors, getting axial current distribution along the groundingelectrodes. Comparing the simulation results with numerical calculation, it can verifythe effectiveness of the proposed model. Applied to an actual length of60m horizontalgrounding electrode, the numerical calculation shows that reasonable arrangement ofshort conductors can effectively improve utilization and dispersal of groundingelectrodes. It also can provide theory basis for the practical application in engineeringand has important reference value.