Study On Designing Configuration Of Grounding Electrode Based On Controlling Electric Field Distribution In Soil

The grounding electrode with excellent impulse grounding properties can provideeffective protection for electrical utility, as well as effectively reduce the rate of outagesdue to lightning strikes. Currently, problems in the design of ground electrode in Chinaare following:(1) Regard power frequency grounding resistance as the sole indicator ingrounding design;(2) Rely on engineering experience excessively;(3) Lack of impulsegrounding experiment, the numerical calculation based on certain assumptions andsimplify. Furthermore, impulse characteristics of grounding electrode depend upon theelectrode structure, size, lightning current parameters, soil resistivity, etc, for one thing,factors such as lightning current parameters, soil resistivity can’t be controlled, foranother, oversize of grounding electrode is not practical. Consequently, reasonable andeffective optimization design structure of ground electrode aimed at improving impulsecharacteristics, which is not only the basis of calculations and theoretical research inlightning protection, but also is an important prerequisite for reliable as well as secureoperation of power system.According to the above issues, methods of simulation experiment and numericalcalculation are adopted in combination. A needle structure grounding electrode isproposed in this work based on "end effect" of impulse current leakage regulation firstly,analyze on impulse grounding characteristics of the above configuration groundingelectrode is carried out on simulation experiment platform built before. Secondly,impulse characteristics calculation model was established based on finite elementmethod(FEM), investigate of reasonable configuration layout via a series of FEMcalculations. Conclusions obtained in this paper are following:(1) The measure of adding needle shaped conductor can reduce impulse groundingimpedance effectively, even at the premise of the same length of conductor. Under thesoil resistivity of ρ=115Ω m, during the whole range of current amplitude inexperiment, the average resistance reduction of the two configuration electrodes are16%and14.36%respectively, while the soil resistivity increase to ρ=1000Ω m,impulse impedance reduction of needle shaped grounding electrode is more significantthan under low soil resistivity.(2) With the purpose of controlling electric field distribution along groundingconductor, as well as increasing the strong electric strength region, a variety of needleshaped grounding electrode as sample in simulation experiment were designed. The simulation results show that comparing with any other cases, electric field distributionin soil along grounding conductor is more homogeneous with needle shaped conductorat the middle of the electrode, impulse impedance of which is smaller too. Electric fielddistribution along grounding conductor becomes more unhomogeneous while length ofneedle shaped conductor increasing whereas the location remain the same.(3) To a single grounding electrode with10m length, impulse impedance is notdisturbed by location of needle shaped conductor which was arranged within the middleinterval instead of the end, what’s more, range of the interval is described as distancefrom current injection point d. Specifically: d is0.5m~9.5m,2m~8m and4m to6mwith length of needle conduct are0.1m,0.5m and1m respectively, the impact of needleshaped conductor upon impulse impedance could be neglected. Furthermore, the aboverange almost not be affected subject to amplitude of impulse current. Detail study revealthat in order to achieve excellent impulse performance, appropriate distance S betweenneedle shaped conductors with0.5m and1m length should be0.5m~1.0m and1.0m~1.6m, respectively.