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

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DSH 659 + N% n1 M5 a; d' S3 T* L. u

Problem of setting a current applied to ACB of high current rating in instantaneous tripping

8.3.3.1.2

60947-2(ed.4) 2 W& M' g: f& Y0 k0 A, M! x  L# r

Standard-
. n3 U* s1 U2 P; ]! sIEC 60947-2 (2006-04, 4th Ed.)
Sub clause(s):
) \6 R5 e0 O) o8.3.3.1.2
9 C- j+ @0 u* {. Q% \* t: y* _( iSheet:
DSH 659
Subject:
& }6 C$ Q) ^' L6 z# ZProblem of setting a current applied to ACB of
. w( O1 P# s0 T1 s& Bhigh current rating for instantaneous tripping.
5 m/ Q9 `: j2 m, sKey words:
Trip limits &
characteristics
Approved at
the 45th CTL
Plenary
Meeting in
Prague in 2008
! k- i$ ]( @9 {" w- yQuestion:
' C9 c2 D) k. W7 e, lAccording to 8.3.3.1.2, when the over-current opening release is a built-in part of the
/ x6 T' \4 G9 q" z0 Vcircuit 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
instantaneous trip release up to 16 In, do we have to apply 80640 A (16 In x 80 %)
3 I; d- _/ J% Z; a8 Land 120960 A (16 In x 120 %) to the main circuit of ACB by use of a high power
testing facility when performing the trip test of SEQ. I?
Rationale:
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
addition ACBs often have several ratings, which are determined by the specification
, l7 m, {1 O+ |5 e4 I5 i) Y' Qof the CT in combination with the trip unit, and the trip unit is usually the same for all
; Q* ?5 B& ?' _, I) pmodels.
$ e  u/ T: L8 S1 U* h/ H9 {; E2 qSo some accredited testing laboratories have performed this test by applying the
- n  E3 F: j* i5 n* m: ~: B6 Vsecondary current of CT (normally 5 A) to the input of an overcurrent release. This
5 n  H6 a3 R$ G- urelease 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
! t. U9 A% S- I5 w5 f+ ias CT saturation, thermal and EMC influence on ACB, especially on single-pole
connection.
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
, X: ]2 @9 V* U7 D# Msub-clause 8.3.3.1.2 of SEQ I.
: D' y/ F  {$ r( q% Q5 mBut in addition, followings items shall be verified to fully cover the safety aspects of
6 x, j5 C( h; C/ G9 Sthe standard:
6 ?( p2 D9 ~+ L0 a( a" c7 l1. The conformity of the performance (at least turn ratio and composite error)
: L. E7 ?# r$ g, r4 wof 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
size have to show the same performance characteristic.
2. The single pole short-circuit test with a current equal to 80 % of the
" A6 c* N% T! B: J% U2 hmaximum current setting of the instantaneous release and equal to 120 %
. d6 V3 Q/ i: L8 c( C: @. I* yof the maximum current setting of the instantaneous release shall be
performed at any convenient voltage with the current in the main poles of
8 J, x, p( X/ Lthe circuit-breaker. The other tests required by the standard may be
4 f* P  P+ C  Q; Y9 pconducted by use of a simulated input signal to the tripping unit.

2 P6 a/ u) [4 X  T2 X* s