接地系统
一、接地基础 | Grounding Fundamentals
二、接地材料 | Grounding Materials
三、接地施工 | Grounding Installation
四、防雷保护 | Lightning Protection
五、接地测试 | Ground Testing
Substation Grounding Grid — Installation and Welding
Song, the substation grounding grid is critical — it protects personnel from touch and step potentials during a fault. What's the design?
宋工，升压站接地网很关键——它在故障时保护人员免受接触电压和跨步电压 危害。设计是什么样的？
宋工: The ground grid is a 60-foot by 80-foot mesh, buried 2 feet deep below the substation grade. The grid is made of 4/0 AWG bare copper conductors, spaced 10 feet by 10 feet. All cross- points are exothermically welded. Twenty ground rods — 10-foot copper-clad steel, 3/4-inch diameter — are driven around the perimeter.
接地网是60英尺×80英尺的网格，埋在升压站地面以下2英尺。用4/0 AWG裸 铜线，间距10英尺×10英尺。所有交叉点放热焊接。20根接地棒——10英尺长铜 包钢、3/4英寸直径——沿周边打入。
What's the target ground resistance?
目标接地电阻是多少？
宋工: IEEE 80 requires the grid resistance to be less than 1 ohm for this size substation. Based on the soil resistivity measurement — we got 85 ohm-meters — the calculated grid resistance is 0.62 ohms. That's with the GEM ground enhancement material around each rod.
IEEE 80要求这个级别的升压站接地电阻小于1欧姆。根据土壤电阻率测量 结果——85欧姆-米——计算接地电阻0.62欧姆。是加了GEM降阻剂后的数据。
工长: 网格已经按图纸铺好了。现在正在做交叉点焊接——用放热焊接,铜粉和氧化铜 的混合物在石墨模具里引燃。
The grid is laid per the drawing. Now doing the cross-bond welding — using exothermic welding, a mixture of copper powder and copper oxide ignited in a graphite mold.
宋工: (检查焊点) This weld is solid — full fusion, no porosity. The mold produced a clean connection with full cross-section. Make sure every cross-point is welded — no mechanical clamps underground, they'll corrode over time.
（检查焊点）这个焊点牢固——完全熔合、无气孔。模具产生的接头洁净、 全截面连接。确保每个交叉点都焊——地下不能用机械夹具，久了会腐蚀。
Show me the connection to the equipment — the transformer neutral and the switchgear ground bus.
给我看接到设备的连接——变压器中性点和开关柜接地母排。
宋工: We bring two 4/0 AWG ground leads from the grid up to each piece of major equipment — redundancy. The transformer neutral is solidly grounded through a disconnect link in the ground well so we can isolate it for testing.
每个主要设备从接地网引两根4/0 AWG接地线——冗余。变压器中性点通过接 地井里的可断开连接片直接接地，便于测试时隔离。
工长: 所有20根接地棒都打完了。每根棒与主网做了放热焊接。接地棒周围填了 降阻剂——可以进一步降低接地电阻。
All 20 ground rods are driven. Each rod is exothermically welded to the main grid. GEM is backfilled around each rod — that'll lower the resistance further.
Ground Resistance Testing — Fall-of-Potential Method
Song, the grid is buried. Now let's measure the ground resistance using the fall-of-potential method. Equipment ready?
准备好了。用四端子接地电阻测试仪。电流探针C1放在距接地网边缘300 英尺处——是接地网最长对角线的5倍。电位探针P1放在距C1的62%处——186 英尺。这是标准的IEEE 81测试布置。
Connected. Testing now... Reading: 0.71 ohms. Moving P1 ±10% and retesting — 0.72 and 0.69 ohms. Three readings are consistent — no soil stratification interference. Average: 0.71 ohms.
0.71 ohms — under the 1-ohm requirement. Pass. Let's also verify the soil resistivity.
OK. Using the Wenner method — four probes at 10-foot spacing. Inject current, measure voltage drop. Calculated resistivity is 82 ohm-meters — close to the 85 we used in design. Confirms the grid design is accurate.
Finally, let's run the step and touch potential test — inject a test current and measure at various locations around the substation. All readings must be below allowable limits. Per IEEE 80 with crushed rock surface: touch voltage < 650V, step voltage < 2,200V for a 0.5s fault duration.
Injecting 100A test current... Point A touch potential scaled to 312V, step potential 487V. Point B... All test points are within limits. Grounding system accepted!