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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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International standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT.# ^5 S# q2 N9 I5 [6 k' E5 V
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The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):
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6 X/ g& i% @1 PT : direct connection of a point with earth (French: terre); . c+ J1 C4 l, L5 w9 _
I : no point is connected with earth (isolation), except perhaps via a high impedance.
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! O; ]& V8 T0 M6 [: X0 zThe second letter indicates the connection between earth and the electrical device being supplied:
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T : direct connection with earth, independent of any other earth connection in the supply system; & Z l6 k: C- T: _& ]! W: Y5 V' t
N : connection to earth via the supply network 2 o% e& \9 |7 r! v
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1 {" n8 w, I. P# yThe 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:; K! q( n$ O. Q0 W! H" f! T( {
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TN‑S : PE and N are separate conductors that are connected together only near the power source. P4 N# V* p5 X
TN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor.
) [" E& ? N$ j7 G+ |; t& P$ dTN‑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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