The Research And The Safety Assessment On The Grounding Grids

A good grounding system is the fundamental guarantee for the safety of powersystem, therefore a thorough study of grounding technology is critical in powersystem design. Furthermore, parameter calculation, optimal design and safetyassessment of grounding grids are important component parts of grounding design.Since traditional methods regarding grounding system parameter calculation rely onempirical formulas, they may involve errors and can’t show the distribution of thewhole surface potentials, step voltages and touch voltages.So they don’t satisfy thehigh precision required nowadays. Given the fact that equidistant grounding grids areapplied in some substations with large surface potential gradient,they scatter flowspoorly,the grounding effect will be substantially improved if we put verticalgrounding electrodes into grounding grids. At present, the safety assessment ofgrounding grids is still accustomed to using grounding resistance as the soleindicators. With modern power grids to the high pressure,large capacity andlong-range direction, the grounding grids need more accurate and comprehensivesafety assessment methods.This paper introduces the Green function and the complex image algorithm in thecontext of layered soil model,and the model is in constant current field. In particular,by using a two-layer model of soil with uniform conduction for each, this paperderives a analytical formula of resistance coefficient between the two conductors withany angle. Then the optimal design of grounding grids including vertical groundingelectrodes is studied. The impact of electrodes, in term of their relative position, totalnumber and length, on the overall grounding resistance and maximum contact voltageare analyzed systematically.Grounding resistance alone can not profile the overall characteristics of groundgrids, and the safety assessment should include more comprehensive aspects. Thispaper points out the factors that should be considered to ensure the safe operation ofthe ground grids. It also proposes a safety assessment method of ground grids, inwhich such considerations as grounding resistance, potential distribution, touchvoltage, step voltage and the electrical connectivity between the ground deflectors areinvolved. In a specific grounding grid, this paper calculates the grounding parameterssuch as the grounding resistance, the maximum contact voltage and the surface potential distribution.Then we analyze the grounding parameters and rearrange thevertical electrodess of the originsl grounding grids.In comparison of the data beforeand after the improvements, it is proved the effectiveness in reduction of theresistance and the pressure.