保护接地和保护接零（Protective earthing and protective zeroing）.docVIP

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保护接地和保护接零（Protective earthing and protective zeroing）.doc

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保护接地和保护接零（Protective earthing and protective zeroing）

保护接地和保护接零（Protective earthing and protective zeroing） DOC documents may experience poor browsing on the WAP side. It is recommended that you first select TXT, or download the source file to the local view. Protective earthing and protective zeroing For the purpose of protecting the personal safety, the earthing of the metal casing of the electric equipment is not grounded or connected to zero. It is called protective earthing and protective zero connection. A protective grounding and neutral in three-phase power supply system in electrical equipment when received on the system for insulation damage of the casing is charged, if the person standing on the ground by hand touch shell, because of the distributed capacitance between the transmission line and the ground, will have a current through the body and the distributed capacitance returned to the power supply, the electric shock, as shown in figure 6-7-13. In general, this current is not large. However, if the grid is widely distributed or the grid insulation strength drops significantly, the current may reach a dangerous level, which requires safety measures. Figure 6-7-13 no motor protection grounding shell a collision situation Protective earthing is the reliable connection of metal casings of electrical equipment with enough thick metal wires to the ground. Electrical equipment using grounding protection measures, equipment through the wire shell has good contact with the earth, when the human body touches the charged shell, the body is equivalent to a parallel branch grounding resistance, as shown in figure 6-7-14. Because the body resistance is far greater than the grounding resistance, the electric current is very small, and the electric shock accident is avoided. Figure 6-7-14 equipped with a motor grounding protection against shell case Protective earthing is applied to neutral ungrounded power distribution systems. Two, zero protection (a) protect the concept of the so-called zero zero connection protecti