安规网

标题: DSH 376 Backfeed protection [打印本页]
作者: 小米    时间: 2012-11-6 17:41
标题: DSH 376 Backfeed protection
DSH 376) N" [& c9 a1 d; |* d( u5 k- C

- Z$ T- e7 W3 j1 B) H  g$ W" N. G5 x3 b! Z
Backfeed protection
- d$ z6 Y( Q6 c, e  C) |% o  \5 U		-9 b* H4 a! E& K# C4 R. Z+ N
60950(ed.3)9 z& e8 c. h) E, E

+ p: J$ A; y1 {$ C2 R$ ?) W( B# ZStandard:
  K8 l* @" q/ K% YIEC 60950 Ed. 3
0 n; ?2 L2 I! t& N/ o) @. v5 pSub clause: --- Sheet n. 376
6 I/ u. \9 e0 }' ?3 w# ZPage 1(1)! t: t8 F# p+ a1 o5 L6 Z
Subject:  Z9 N- i* x8 n( j6 ?- w3 m
Backfeed protection9 |' K9 C+ `$ X
Key words:
( v6 x# G" K: e  n- Backfeed Protection% d2 w  F" w3 y* V& h* i5 C+ J* j4 `
Decision taken at
1 g! P) u. V2 I9 Y37th CTL4 j% N9 E; }' }5 `1 |: P
meeting/2000 further
6 g+ o/ g3 _( N5 L$ ato the trial period7 d9 }! k  `, l
consultation+ o  q! M( X& O$ _7 G9 x2 m# O' [: ^
Question:* J2 X6 g! z3 D
The product in question is a power supply to IEC/EN 60950 with an internal Battery Back Up- V/ V  S5 D4 g
Unit (BBU). The BBU provides 170Vdc, which is connected to the “output” of the mainsrectifier9 @! q/ R! d7 @6 h) [
bridge. The question is related to the backfeed protection to prevent potential risk of
- Z5 D" o6 K) P6 e3 h! p9 R6 velectric shock from being present on the mains supply terminals during interruption of the1 ?/ O; N3 Q, }  \  U
primary power or removal of the plugs from its socket.8 b  r( M  v' G, V$ L$ E4 J
Different interpretations have been experienced, and we are looking forward to a consensus.( Q  U2 q6 K  {& n" |5 l
Three alternatives may be listed as follows:
+ W) A) v2 u3 V) V1./ ?8 t% X% ^, D+ P4 m3 D6 Q
The BBU can be considered similar to parts of an Uninterruptible Power Systems (UPS), for
# `' F, L/ D* @& D  mwhich there is the European standard EN 50091-1. However this standard is not an IEC$ _  ]+ m4 Q, P7 H# H; l" w
standard and may not be applicable outside CENELEC. EN 50091-1 specifies requirements for
2 @) w9 Q1 \# R. j  V* _# Nbackfeed protection. Sub clause 2.1.5 states that such switching device shall be of an all pole3 p- g, S8 x% H7 O: ?: s
type having an air gap in each pole in accordance with EN 60950 Table 5 – Minimum
. R% _9 v9 A  ]: ~: e% Yclearances in secondary circuits and using the column headed “circuits not subjected to
8 L' m$ Z, t0 Ztransient overvoltage” – for reinforced insulation at the working voltage that is backfed (in this
% o! M* d2 S9 Q$ W$ m8 s5 Hcase 170Vdc).
. A1 M( }* \  T% s; n$ G9 @2.. _7 q# W* |! e" r; q2 J2 P- s
According to sub clause 2.2.6 (IEC 60950), it is likely to apply reinforced insulation between
" P" T) @. i4 _0 Q) h# e6 k9 Aunearthed hazardous voltage secondary circuit and unearthed accessible parts.
7 N: I- {; ~5 e: F- X, b; d" F3.  n  S# ?+ s4 c' i; J$ D
If the voltage on the mains plug does not exceed 60Vdc (or 42.2V peak) in the event of a
  i& _# w. B2 M6 F$ f: f( V& Wsingle failure, when the mains plug is disconnected and the battery provides 170Vdc to the
+ b2 o" ?1 @# T) G“output” of the mains rectifier bridge, no additional requirements for “backfeed protection”
' ?  R% ?. C+ f4 ^should be applicable.6 ~% W( M, [  ~3 [
Decision:' c% K$ p+ m" |* ~$ v- E, H
Interpretation Item 3 is the correct one
/ w2 t0 j7 s3 P$ o' Q" l5 t
' t3 q# @8 ~# z[attach]77180[/attach]
! B- J7 g8 Y' u2 M9 `% {
# {/ E7 |3 [3 q3 j, Z5 ~9 m9 Z% f. m" t/ Z




欢迎光临 安规网 (http://bbs2.angui.org/) Powered by Discuz! X3.2