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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 ) [+ i I# a+ B% G) f1 N
; `& W) N7 N0 r9 l& k1 V: [$ S
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% ^/ \' \( K, ^/ J, y6 J4 o+ k1 G5 GInternational standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT.
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7 F# [1 \; Q; ~/ E0 EThe first letter indicates the connection between earth and the power-supply equipment (generator or transformer):
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T : direct connection of a point with earth (French: terre);
J, h3 ]- Z. t! B/ YI : no point is connected with earth (isolation), except perhaps via a high impedance. 2 b5 k6 r& H" L( Z- n- Q
( m4 K) T: q# K7 u4 CThe second letter indicates the connection between earth and the electrical device being supplied:/ M' K& a8 K9 C8 j' V/ |) G
9 N) i5 J6 S3 t9 D
T : direct connection with earth, independent of any other earth connection in the supply system;
" [7 l' d# V. A1 s% l3 XN : connection to earth via the supply network , o1 \ _% J9 M1 p
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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:( `3 n2 [1 D6 s! f4 N. {
2 X' V5 v3 H. y1 T4 @; d. p, NTN‑S : PE and N are separate conductors that are connected together only near the power source. 9 j: x/ g; G, V& d6 p/ ?- Y
TN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor. 1 }' Z4 _. ~" t. G. |+ K5 B5 n
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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