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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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* }# y \6 v6 WInternational standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT.7 s# j8 L% V) O8 s
( n+ f2 ~/ Q' \3 XThe first letter indicates the connection between earth and the power-supply equipment (generator or transformer):9 N+ N9 Q C6 [+ q" I
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T : direct connection of a point with earth (French: terre); / A7 N. N3 v& T9 P( n# p
I : no point is connected with earth (isolation), except perhaps via a high impedance. 5 R* Y& J$ b5 ~. B$ a2 M1 A/ O2 z
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The second letter indicates the connection between earth and the electrical device being supplied:
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( U4 ~% R9 m6 D$ J: s. z6 Q3 TT : direct connection with earth, independent of any other earth connection in the supply system; & z0 y2 d D* {2 A% C
N : connection to earth via the supply network
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7 Z" v+ J7 ~$ o, n3 WThe 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.
3 o' T! b8 L9 N0 a; ]5 B( S" v9 L. \TN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor.
0 [% V: @3 S- x9 ]6 q$ nTN‑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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