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| DSH 395. W& Q j! e! w7 p% F
: ^' y. H5 R8 ^" l4 n4 z1 \. O" B
| Separation of TNV-3 and SELV circuitry$ E, C" L4 `4 g" W) i: R, W8 B4 B
| 2.3.2! U% B& w; h& |% _/ A i0 t3 ^
| 60950(ed.3)7 a) L6 f6 e9 p5 `. o
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/ Z7 m6 l. y" I! n3 M; SStandard(s):3 u3 M, G$ q2 G$ h
IEC 60950 (1999) 3rd Ed.
' s U7 V) I# C) wSub clause(s):# L/ @: r' x7 i6 e
2.3.29 J4 k9 i5 O8 ]' R" e& h+ b6 Z
Sheet No., }8 H8 r& e7 |+ H. a$ N* @. W" K" j
395: f+ p+ T! \, P$ |; S
Subject:
6 F& g2 e& a. G3 ~0 Q6 l4 w2 p2 nSeparation of TNV –3 and SELV7 `/ }! @* P+ G U$ |
circuitry- O' c6 W8 Y! u) ~ B+ D8 f2 E2 p& L
Key words:- l6 `* S% }! S8 k
- Separation of TNV-3 circuit2 [) j6 n4 O# R% r* o T3 v. |
and SELV circuit
' _5 s: {7 B, |+ |1 ?3 K* ?Decision taken at the 39th6 e2 e! |* k) H( d5 e1 @
meeting 2002, Y' N% G- \; h1 f7 z6 P/ g
Question:+ `' J( c& L& O% B5 {. l! y
1. Is it permitted to demonstrate that a TNV -3 circuit is adequately separated from a SELV circuit by
|/ q! @1 x, D4 i8 Xmeans of single fault testing, in the situation where the spacings do not meet the requirements for basic7 k, ^/ E2 o% o; J# A6 U) j
insulation? (The dielectric strength test is still required under Subclause 6.2.1.)# S# w3 c/ R" ?, d7 K
2. If so, is it required under the compliance paragraph to short circuit the insulation between the TNVcircuit) B H0 F8 x- {3 U8 Z/ b" U. g
and the SELV circuit at all points which do not meet the criteria for basic insulation, before
; m# v6 ^/ [6 j' \; D7 `' Acarrying out the tests?
. a9 J; Z& s$ K$ D/ z9 ?3. If short circuiting the insulation before carrying out fault tests results in the equipment passing the tests,
2 H, {0 ?% Q' _% z4 \. z1 dwhereas carrying out the fault tests without short circuiting the insulation would result in the equipment' T# C, C! p4 a+ r. \. w
failing the test, should the insulation be short circuited?3 `- c7 i1 i3 c
Rationale:
- I6 f% S/ a( D; m* u1. Paragraph 1 of Sub-clause 2.3.2 requires that separation between a TNV-3 and a SELV circuit be such
8 T3 @% Z6 P" u4 V/ ~ Ythat in the event of a single fault, the SELV circuit remains below TNV-3 limits. Paragraph 2 of Subclause
V: a2 J6 i0 F; o2.3.2 states that basic insulation will achieve this, but other solutions are not excluded.$ f8 a) [* g2 O. U5 Y# ~
Equipment is not required to meet either Paragraph 2 or 3. It can meet the single fault conditions stated
4 M+ Q( }* g" K2 o" xin Paragraph one and in the compliance paragraph.
" K# x% N) u' P2. According to the compliance paragraph, before carrying out the single fault tests, insulation which does$ n! w/ I. O5 u( c G+ S. d; S& G
not meet the requirements for basic insulation is short circuited. Presumably this does not mean that
! r2 x% W! k; J" p q$ qshort circuits are to be applied between all tracks and components in the entire TNV-3 and SELV0 ^/ `3 p* d3 e; S% \" \5 Q: M
circuitry which do not meet basic insulation, but that the insulation at the point where the TNV-3 circuit
2 K+ V5 U: a& Z' n- U* wmeets the SELV circuit is short-circuited.
5 h M2 `1 {# Z6 F5 e; u3. It is possible to envisage a situation where short circuiting the insulation between TNV-3 and SELV
5 }, w) p3 N7 o+ ^could cause the TNV-3 voltages to be lowered. Fault tests under this condition would not represent the
7 U4 V+ S, h4 f. `9 }+ uworst case possible fault condition
: [! ]4 T$ c i$ f Q+ e. f8 VDecision:; l+ c. L8 {9 J1 a+ _0 v/ ]: A
1. It is permitted to demonstrate compliance with Subclause 2.3.2 by means of single fault testing.4 K4 G, a! q+ d1 Q5 S
The limits in 2.3.1.b) shall not be exceeded in normal or single fault conditions.
7 S( o u/ w5 r6 ~% R. E: d: K2. Before carrying out single fault testing of components and insulation, insulation between TNV-3 and
w$ T3 s# k0 g z3 mSELV circuits not meeting the requirements of Basic insulation should be short circuited if this results in# E: w2 I; l! _3 ?; Q! Q
a worst case voltage measurement at accessible parts of SELV and TNV-1 circuits, and at accessible
) G3 I& \' c; ?# n% G0 ~) Cconductive parts during subsequent fault testing. E9 i7 F( S; P. D
3. If the single fault test would be more severe if carried out without short circuiting the insulation, the test0 O3 z0 J: ^- {
should be done without short circuiting the insulation.
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