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1接地系统的选择与等电位连接(1)目前,各地都明确地求施工现场必须采用三相五线系统即TN-S方式供电。就是在变压器的中性点引出两根线,一根作为工作中性线(N),一根作为专用的保护线(PE),这样三相不平衡电流不再流经PE线,避免了用电设备外壳的电位升高。TN-S系统可采用剩余电流动作保护,这种保护直接反映接地故障电流,灵敏度高,动作电流可以整定得很小。但是,因为系统固有的缺点,变压器中性点对地电位(变压器低压侧中
1 grounding system selection and equipotential connection (1) At present, all over the construction site must explicitly use three-phase five-wire system that TN-S power supply. It is in the neutral point of the transformer leads two lines, one as a working neutral (N), one as a special protection line (PE), so that three-phase unbalanced current no longer flows through the PE line, to avoid the use of Electrical equipment shell potential. TN-S system can be used residual current protection, this protection directly reflects the ground fault current, high sensitivity, the operating current can be set very small. However, due to the inherent disadvantages of the system, the transformer neutral to ground potential (in the low voltage side of the transformer