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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., _$ X1 O: j: ^
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The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):2 S8 N' T! J/ F
- L6 o/ x% J6 `: sT : direct connection of a point with earth (French: terre); , C/ p4 u& c- @/ o6 r( B1 o. ~+ _
I : 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:- M) Z5 T* o# Q; B" e! @, m
, p( i4 @9 Y! d! ~9 q2 H! WT : direct connection with earth, independent of any other earth connection in the supply system; 4 L, S1 ` [6 t
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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TN‑S : PE and N are separate conductors that are connected together only near the power source.
3 ~$ s, t- W ]TN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor. 4 E* w- t* A7 g' 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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