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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 ( Z/ D8 l' [. B" O- o
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! i) O0 ~3 b( s2 Q! _International standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT.- M) z, Q$ y T$ j
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The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):% I6 p3 A4 E$ I2 D
# f( n8 |2 J, R/ z7 T% z( TT : direct connection of a point with earth (French: terre); , z0 \! u- c+ ?, G
I : no point is connected with earth (isolation), except perhaps via a high impedance. ! T+ V- q- J; t5 r7 ^( P0 u5 o
7 ~: l" l+ \0 n+ l) A( R$ _6 EThe second letter indicates the connection between earth and the electrical device being supplied:- F* b$ V. J/ y% C$ G
6 F! \" P! G6 l8 l4 wT : direct connection with earth, independent of any other earth connection in the supply system;
' @, ?- n3 m5 Y6 Q% fN : connection to earth via the supply network ' p. a1 g# Z1 m: L+ M/ {
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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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( x! ^: D/ @8 F) a. E; ?1 hTN‑S : PE and N are separate conductors that are connected together only near the power source. ; ]% d0 U) w* H" V
TN‑C : A combined PEN conductor fulfils the functions of both a PE and an N conductor. : m" Y g- q5 R( G
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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