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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.* b: A) y" e5 P7 `# C
# Q; k8 F6 O* ?4 _" q4 s& LThe first letter indicates the connection between earth and the power-supply equipment (generator or transformer):: y! R! c' `" ?# m4 M7 I
c, I9 V5 W* y/ j& MT : direct connection of a point with earth (French: terre);
, W- H0 Y2 p" k3 I9 cI : 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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, r& n0 p3 C& `! Z- sT : direct connection with earth, independent of any other earth connection in the supply system;
) |. }. d: }; {N : 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:
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; R( V: z- |/ J4 X! WTN‑S : PE and N are separate conductors that are connected together only near the power source. 8 L9 r. ~* ]( J. z
TN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor.
/ Z9 p. P; D3 U( W1 J. D9 ETN‑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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