湖南省柘溪水电站扩建工程接地设计

Grounding Design for Expansion Project of Zhexi Hydropower Station in Hunan

柘溪水电站扩建工程的地质基础浅表层为薄风化石夹砂予，浅表层以下为灰色带状砂质板岩与细砂岩夹燧石状石英岩、灰色细砂岩与长石石英砂岩互层，土壤电阻率较高（约1000～5000Ω·m），接地网的设计难度极大。文中采用上、下库水下接地网，充分利用电站构筑物与水工建筑物中的钢筋，埋设至地下含水层的长接地极，对主厂房、副厂房、主变场、220kV开关站及出线场等重要部位采用不等间距布置均压网等措施，较好地解决了该接地网的设计难题。计算分析表明，这些措施能有效改善接地网的地电位分布，降低接触系数；接地网的工频电位升为1950V，满足规程要求；可节省钢材约16．9％～22．2％，并减少施工量和投资。

At where the expansion project of Zhexi Hydropower Station is constructed, slightly weathered rock mixed with sand is found at the shallow surface layer, and below the layer there is interbedded grey belt sandy slate and fine sandstone mixed with flinty quartzite as well as interbedded grey fine sandstone and feldspar - quartz sandstone. Therefore, the design of grounding grid meets great difficulty as the soil has a relatively high electrical resistivity of 1000--5000Ω·m. In order to solve the problem, underwater grounding grid is provided for both the upper and the lower reservoirs. Reinforcing steel bars of station structures and hydraulic structures are embedded to long ground electrode at the underground water layer. Voltage equalizing network is arranged in unequal spacing for such important places as main power house, auxiliary power house, main transformer field, 220kV switchyard, and outgoing line field. Computational analysis indicates that these measures can help lower contact factor by efficiently improving ground potential distribution of the grounding grid, boost power frequen- cy potential of the grid to 1950V as required, and reduce engineering work load by saving 16.9% --22.2% steel products.