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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 9 k. I+ |1 H+ V1 c2 s; T+ T
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International standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT.1 D1 O$ ] s2 u) y e/ b
( ~3 U4 z2 A/ e: h* U
The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):
3 R/ l& N- |$ ~
x. Z3 D& w8 B* p1 e8 g3 zT : direct connection of a point with earth (French: terre);
) m d$ Z+ I' t& N4 \& oI : no point is connected with earth (isolation), except perhaps via a high impedance.
$ Q9 d- }7 A8 W5 S3 B' j5 D
: y W- @8 @# z+ P5 TThe second letter indicates the connection between earth and the electrical device being supplied:
2 `* ^4 Z7 @. G% R% x+ n
2 D* [6 w% M0 i+ a3 JT : direct connection with earth, independent of any other earth connection in the supply system; 0 X0 d4 z7 S% N/ n
N : connection to earth via the supply network
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& q6 H; `+ Z: m+ ]! EThe 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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TN‑S : PE and N are separate conductors that are connected together only near the power source.
" T& K# t- n$ s4 e, Y; DTN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor.
+ W# [. K. |2 m( S% X- qTN‑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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