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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 T6 e5 M0 i3 m; Y& y
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The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):. C. n7 a6 k; ?* Y
7 g( s* }/ g1 L& \- c. j- N* KT : direct connection of a point with earth (French: terre); & Z7 K9 v$ q5 P( L3 u
I : no point is connected with earth (isolation), except perhaps via a high impedance. : B; e- X% k/ }2 {. z2 A
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The second letter indicates the connection between earth and the electrical device being supplied:8 Z. i' ^: z6 c) `
. Q: }2 ?6 F" U' r8 \' ?T : direct connection with earth, independent of any other earth connection in the supply system;
3 i/ F9 e3 P: n8 N; q- z) ~N : 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:- j! {3 F" i* M: n
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TN‑S : PE and N are separate conductors that are connected together only near the power source. ) q4 e2 J N: V
TN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor.
/ o- _7 o8 }2 B: E; 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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