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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.$ j* S! s/ q& I3 v) A# {
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The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):! ?( j" y: A- z
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T : direct connection of a point with earth (French: terre); 4 ]. c# m: h z0 b- M# l8 W
I : no point is connected with earth (isolation), except perhaps via a high impedance.
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6 i5 r P% k! w+ g2 j* b' u" FThe second letter indicates the connection between earth and the electrical device being supplied:
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8 o' T( n7 |2 J/ {4 BT : direct connection with earth, independent of any other earth connection in the supply system; ! s, U. ]9 t9 k9 W
N : connection to earth via the supply network D+ E. h1 ^) E4 k( L) q# H
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: L1 g1 v' b) I) H& v5 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:/ \, w0 Y [* i
% C3 v+ K2 i; M: e+ R3 nTN‑S : PE and N are separate conductors that are connected together only near the power source.
' l% b- u. Z7 h9 \- X: z1 B, [2 mTN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor.
7 \, ^4 W1 {# f% j- [- p, Y0 eTN‑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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