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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 7 A3 Q9 K4 ]. G4 d- c
7 d1 T. P) ^( `" M, x7 v& H
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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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; N2 f& V3 ^( K$ zThe first letter indicates the connection between earth and the power-supply equipment (generator or transformer):
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T : direct connection of a point with earth (French: terre);
2 Y R# s" C% u2 MI : no point is connected with earth (isolation), except perhaps via a high impedance. - R2 Y6 b/ T, i+ w7 G
: @# U2 j5 O+ _: xThe second letter indicates the connection between earth and the electrical device being supplied:8 f" @" p. w+ B7 O ?7 O
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T : direct connection with earth, independent of any other earth connection in the supply system;
R/ g; x1 Z! B9 r/ }5 [3 K! kN : connection to earth via the supply network
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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:( w" P4 C9 R+ H6 H
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TN‑S : PE and N are separate conductors that are connected together only near the power source.
. P& P' v2 L/ f9 m2 s5 g+ jTN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor. ' J9 w# _2 D4 W. U* z- d7 J/ i
TN‑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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