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

8.3.3.1.2

60947-2(ed.4)

" Y) ^3 g' ~5 n) |Standard-
IEC 60947-2 (2006-04, 4th Ed.)
Sub clause(s):
- x+ K( s& d& l+ \6 u1 |6 ]- w8.3.3.1.2
Sheet:
DSH 659
Subject:
Problem of setting a current applied to ACB of
high current rating for instantaneous tripping.
" T" z2 P6 k8 _  c  [2 D9 IKey words:
5 }3 L9 ~1 V: v4 iTrip limits &
characteristics
3 }) J% X8 @$ X9 CApproved at
the 45th CTL
Plenary
7 B: W; E$ P2 NMeeting in
Prague in 2008
. I- ^+ s" Y5 G9 y% j9 n8 oQuestion:
: L  @) p8 S# G* ~# `According to 8.3.3.1.2, when the over-current opening release is a built-in part of the
: `$ U  P3 {4 {6 i# v: Bcircuit breaker, it shall normally be verified inside the corresponding circuit breaker.
3 @- n8 v  e8 i  Q6 }0 sFor 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 %)
- G  K& b4 M; A) X, I# I; U$ hand 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?
, c* e% @  h% N" `Rationale:
8 P4 m5 v7 n9 A$ m2 s( DIt is not so easy to conduct the instantaneous trip test using the high currents
6 s0 F! s2 x  vmentioned 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
/ s# l* I+ x0 o; v9 J2 R. ]/ G& Eof the CT in combination with the trip unit, and the trip unit is usually the same for all
' A7 J: |! U3 z: a, z% Z7 nmodels.
So some accredited testing laboratories have performed this test by applying the
secondary current of CT (normally 5 A) to the input of an overcurrent release. This
release is connected to operating mechanism of contacts to check the mechanical
! Q5 c9 a1 G7 j& v( i4 @2 aopening of an ACB. But by use of this method, we bypass possible problems such
as CT saturation, thermal and EMC influence on ACB, especially on single-pole
connection.
( H. B1 ?' _) W  f  KDecision:
, v* S% ~2 O& f8 x  G7 CThe 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
- T) W& D4 q" wsub-clause 8.3.3.1.2 of SEQ I.
$ X. Y; G1 G8 L- n: `/ W5 mBut in addition, followings items shall be verified to fully cover the safety aspects of
the standard:
- }9 b6 V4 f) V1. 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
3 F* I; `: E% T, e( V% O0 ^; xreports 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
, N( W+ v& R) U' x- ]$ `maximum current setting of the instantaneous release and equal to 120 %
& W" p+ y$ E+ b: w- m$ Wof the maximum current setting of the instantaneous release shall be
performed at any convenient voltage with the current in the main poles of
7 H  g- U9 K; dthe circuit-breaker. The other tests required by the standard may be
+ `0 P( V8 g8 S7 U5 j9 mconducted by use of a simulated input signal to the tripping unit.
8 V% R9 M2 [* v' I