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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
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. R# B' U% q$ `" t1 h$ l5 f5 fInternational standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT.
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The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):
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+ G: L/ {1 c/ u: LT : direct connection of a point with earth (French: terre);
. b* R# O7 l$ kI : no point is connected with earth (isolation), except perhaps via a high impedance. 2 w, r/ `# k3 m! ]' R
+ y- i! o! f- A6 w& ~The second letter indicates the connection between earth and the electrical device being supplied:8 k- p1 `0 U/ `- ~
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T : direct connection with earth, independent of any other earth connection in the supply system; # Y" Q1 N/ P( [% Q3 w9 j
N : connection to earth via the supply network
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/ e+ m* @# A9 D2 l9 G, {: L# JThe 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:( C- `: Q% ~& H
- j! y1 Z! _8 i2 W6 `' j( vTN‑S : PE and N are separate conductors that are connected together only near the power source. 6 C& n: `: X8 b
TN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor.
$ W* n0 T$ w; q( vTN‑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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