DSH 659 Problem of setting a current applied to ACB of high current rating in in

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DSH 659

Problem of setting a current applied to ACB of high current rating in instantaneous tripping * I4 H' J0 ?. P, W5 N; @# O

8.3.3.1.2

60947-2(ed.4)

' w9 j. y5 h( ^! nStandard-
' G/ a$ p8 t$ Q4 p% {/ \IEC 60947-2 (2006-04, 4th Ed.)
  `+ H9 m( o. j9 `- S2 }Sub clause(s):
% j! `1 g2 R1 w5 h( W+ `( F8.3.3.1.2
* ?, {) `5 A& E5 e4 d$ R2 \  ^9 dSheet:
& \2 Y" c7 Z7 K8 iDSH 659
$ I+ }! f" i  h. b7 A# iSubject:
Problem of setting a current applied to ACB of
high current rating for instantaneous tripping.
' @' C/ F. u7 b. R# mKey words:
Trip limits &
: g6 z% ~/ `* {; v! B+ s- [characteristics
7 O. s  ?8 Y$ v% D+ O4 cApproved at
the 45th CTL
Plenary
Meeting in
Prague in 2008
) I. l9 j6 e) CQuestion:
According to 8.3.3.1.2, when the over-current opening release is a built-in part of the
circuit breaker, it shall normally be verified inside the corresponding circuit breaker.
For example, in case an air circuit-breaker (ACB) has a rating of 6300 A with an
8 q+ d  M% L+ u" W! ainstantaneous trip release up to 16 In, do we have to apply 80640 A (16 In x 80 %)
and 120960 A (16 In x 120 %) to the main circuit of ACB by use of a high power
7 z# v/ Z2 ]" e4 J0 t1 Ctesting facility when performing the trip test of SEQ. I?
8 z) t) C/ n% ~# ~" DRationale:
" s; ]3 A) ~9 g6 ^It is not so easy to conduct the instantaneous trip test using the high currents
mentioned above, because to do so a high power testing facility is required. In
. M2 v0 M5 F, n  e$ Naddition ACBs often have several ratings, which are determined by the specification
of the CT in combination with the trip unit, and the trip unit is usually the same for all
models.
, x: g; v, u3 g/ P2 j/ f9 rSo some accredited testing laboratories have performed this test by applying the
/ ^! d; h0 g! r' v6 q5 Zsecondary current of CT (normally 5 A) to the input of an overcurrent release. This
' z, j/ h* Q5 P% w9 M. j- \release is connected to operating mechanism of contacts to check the mechanical
opening of an ACB. But by use of this method, we bypass possible problems such
- q' @% M& d# ^0 s" Pas CT saturation, thermal and EMC influence on ACB, especially on single-pole
, q( D& w( _  e0 W) Oconnection.
' }2 d: |8 X% x5 ?Decision:
The secondary current of the CT (reduced current, 5 A, for example) may be used
for trip tests of ACBs integrated with electronic OCR for all ratings of In, but only for
! W$ q* _1 o$ P3 Bsub-clause 8.3.3.1.2 of SEQ I.
But in addition, followings items shall be verified to fully cover the safety aspects of
% f9 X+ F: Q" m. |the standard:
1. The conformity of the performance (at least turn ratio and composite error)
of the CT or Rogowski coil, if any, shall be verified by specifications, test
reports or certificates. All CTs of the circuit-breakers of the given frame
) N* @+ \+ V% _; osize have to show the same performance characteristic.
) `3 H, S( a3 Z, _0 `% A$ I* ?2. The single pole short-circuit test with a current equal to 80 % of the
maximum current setting of the instantaneous release and equal to 120 %
of the maximum current setting of the instantaneous release shall be
- X/ d+ h' m8 F7 r& Z9 U, wperformed at any convenient voltage with the current in the main poles of
( \$ ]% w$ B8 b+ v( v; H% mthe circuit-breaker. The other tests required by the standard may be
, {% X( a" }& i4 k& Oconducted by use of a simulated input signal to the tripping unit.


7 X% t6 g+ b, e# Q