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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.+ \9 y" \% R( U- f: f' M
5 A H. D( I7 I8 C/ Z/ {7 R7 O* f0 KThe 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);
3 ?; A$ {# E/ C3 @% F" lI : no point is connected with earth (isolation), except perhaps via a high impedance. ! T3 I; X/ o$ V2 d0 h
( ?7 `. G! M0 p. I+ VThe 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; ( ^$ x9 n4 c+ c$ ]
N : connection to earth via the supply network
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1 e" s6 M$ w* M6 S* D9 sThe 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:7 t- y) y N) z. ?. q
) X' Y9 x+ C4 RTN‑S : PE and N are separate conductors that are connected together only near the power source.
9 X# V3 I) ^! Y5 `TN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor.
# ]' v/ T6 R9 U0 ]! I' q( j5 r8 P6 oTN‑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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