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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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. @0 t( Y- H& ~6 q3 T) S' dInternational standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT.$ z6 \' r" \6 Y1 m& A
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The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):! D# x9 c* _$ v; y
5 U8 s1 K, r9 V9 gT : direct connection of a point with earth (French: terre);
2 s, B2 r# ` u1 AI : no point is connected with earth (isolation), except perhaps via a high impedance.
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{/ _/ M# r* k( K( q$ U9 {( YThe second letter indicates the connection between earth and the electrical device being supplied:
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6 P2 H. j g# `6 ~& YT : direct connection with earth, independent of any other earth connection in the supply system;
, w3 o/ d, V6 iN : connection to earth via the supply network 7 H+ \5 A: c' r& l+ F6 k
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: |. g2 t3 _$ P% G5 ^6 u Q/ Y( n! oThe 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:( b. d! Z3 o; J( S$ M
0 b5 Y, b- v! d, l; ITN‑S : PE and N are separate conductors that are connected together only near the power source.
) v- J) l# s1 YTN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor. ' k6 P5 Z& ^& A- @
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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