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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 5 J6 T: _3 q, e/ |% V
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5 \* C4 [2 r8 X5 t6 lInternational 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):9 X- ~! P; ~ k0 T, f, |& n- e
4 D/ p |/ s; x- D- ]! JT : direct connection of a point with earth (French: terre);
! q, `, Y4 C: I6 z. {I : no point is connected with earth (isolation), except perhaps via a high impedance.
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' u; u/ ~) _4 y6 O+ NThe second letter indicates the connection between earth and the electrical device being supplied:6 J. S+ J6 _( c5 @) o* {
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T : direct connection with earth, independent of any other earth connection in the supply system;
. i; _2 D$ u4 N5 dN : connection to earth via the supply network 8 O/ C/ h- I( }3 e$ n
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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:
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# O" L. [# O5 K! ~TN‑S : PE and N are separate conductors that are connected together only near the power source. % F7 x( q& f6 B: ?+ Q. V
TN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor. 7 \& u* s8 I, c( N7 a$ ~, T: y$ G
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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