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发表于 2007-7-10 18:05:52
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来自: 中国河南南阳
仅供参考
Terra Neutral-Combined-Separate ; E- c% l2 ?5 _# S1 p
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International standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT.
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, F. {1 K* P* L8 IThe first letter indicates the connection between earth and the power-supply equipment (generator or transformer):2 {- Q2 K) _& X8 v" w
- v6 Z; M4 }3 H! rT : direct connection of a point with earth (French: terre);
+ y# v. Q2 O: CI : no point is connected with earth (isolation), except perhaps via a high impedance.
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The second letter indicates the connection between earth and the electrical device being supplied:- _2 x% H: @) h9 O2 J+ C7 X
& U# P; j: T8 B& f6 u/ _4 R2 }T : direct connection with earth, independent of any other earth connection in the supply system;
7 b( J' o! N; [, m6 H# i6 F) p( f1 N3 bN : connection to earth via the supply network + B! o8 t6 j1 ?) D# h; [
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The conductor that connects the exposed metallic parts of the consumer is called protective earth (PE). The conductor that connects to the star point in a three-phase system, or that carries the return current in a single-phase system, is called neutral (N). Three variants of TN systems are distinguished:5 I7 y. C- ^2 p
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TN‑S : PE and N are separate conductors that are connected together only near the power source.
3 ?# h# h: h+ W5 K. DTN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor.
3 U, \; V K! e$ S4 M( Q# G, f" yTN‑C‑S : Part of the system uses a combined PEN conductor, which is at some point split up into separate PE and N lines. The combined PEN conductor typically occurs between the substation and the entry point into the building, whereas within the building separate PE and N conductors are used. In the UK, this system is also known as protective multiple earthing (PME), because of the practice of connecting the combined neutral-and-earth conductor to real earth at many locations, to reduce the risk of broken neutrals - with a similar system in Australia being designated as multiple earthed neutral (MEN). |
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