In order to effectively reduce the grounding resistance, substation ground grid in China's western region is often across vertical two-layer soil. For the sake of deriving the formula convenient for engineering use to calculate substation grounding resistance across vertical two-layer soil, substation ground grid across vertical two-layer soil is broken down into two independent ground grids. Its grounding resistance is regarded as a parallel resistance of two independent ground grids grounding resistance. The independent ground grid image is equivalent to the same layer uniform soil grid according to image method principle. Then DL/T 621—1997 standard and IEEE std80—1986 standard recommended formula for calculating the grounding resistance of same layer uniform soil grid is adopted to derive a simple computational formula for the substation grounding resistance across vertical two-layer soil according to parallel circuit principle. Results of calculation example show that the accuracy of the derived simple computational formula can meet the requirements for engineering design.%为有效降低接地电阻,我国西部地区的变电站地网常跨越垂直双层土壤.为导出便于工程使用的跨越垂直双层土壤的变电站地网接地电阻计算公式,将跨越垂直双层土壤的变电站地网分解成2个独立地网,其接地电阻视为这2个独立地网接地电阻的并联电阻；根据镜像法原理将分解后的独立地网镜像等效为同层均匀土壤地网,然后运用DL/T 621-1997标准和IEEE std80-1986标准推荐的同层均匀土壤地网的接地电阻计算公式以及并联电路原理,推导出跨越垂直双层土壤的变电站地网接地电阻简易计算公式.算例计算结果表明,推导所得简易计算公式的精度能够满足工程设计的要求.
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