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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.
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The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):7 X% F# N% _8 f
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T : direct connection of a point with earth (French: terre);
5 E0 x( j2 V. @, U( m+ i2 h8 LI : no point is connected with earth (isolation), except perhaps via a high impedance.
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The 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;
( w7 E& D5 R! Z/ L ^' \& vN : 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:+ c* p( F" s4 O& s) J5 Y- K" _
- g2 y0 y+ g0 YTN‑S : PE and N are separate conductors that are connected together only near the power source.
& j# v! E% e5 \1 n& g' jTN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor. : M4 n, p7 ]8 @% F7 Q! z( G c
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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