低压配电系统TN、TT、IT的比较（Comparison of TN, TT and IT in low voltage distribution system）.docVIP

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低压配电系统TN、TT、IT的比较（Comparison of TN, TT and IT in low voltage distribution system）.doc

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低压配电系统TN、TT、IT的比较（Comparison of TN, TT and IT in low voltage distribution system）

低压配电系统TN、TT、IT的比较（Comparison of TN, TT and IT in low voltage distribution system） According to the current national standard low voltage distribution design specification (GB50054) definition, the low-voltage distribution system is divided into three kinds, namely TN, TT, IT three forms. Among them, the first capital letter T means that the neutral point of the power transformer is earthed directly; the I indicates ungrounded neutral grounding of the power transformer (or through high impedance grounding). The second capital letters, T, indicate that the enclosure of the electrical appliance is directly grounded, but is not connected to the grounding system of the power grid; the N indicates that the outer shell of the electrical equipment is connected to the neutral line of the system. TN system: the neutral grounding of the power transformer, the exposed part of the equipment is connected with the neutral line. TT system: neutral grounding of power transformer, protective earthing of electric equipment enclosure. IT system: ungrounded neutral power transformer (or through high impedance grounding), and electrical equipment, enclosures, electrical equipment enclosures using protective grounding. 1 and TN systems The neutral grounding of the power transformer of power system can be divided into three kinds according to the different ways of connecting the exposed part of the electrical equipment and the system: the TN - C system, the TN - S system, and the TN - C - S system. The following are described separately. 1.1, TN - C system Its characteristic is: the power transformer neutral point ground, protects the zero line (PE) and works the zero line (N) to share. (1) it is the neutral line using neutral grounding system (zero line) as a return conductor of fault current, when the electrical equipment line touch shell, the fault current through the zero line back to the point, because of the short circuit current, so it can be used to cut off the power supply overcur