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 / D5 e1 x* x$ b% z

8.3.3.1.2 ! o1 ^0 j5 v* T( n4 J

60947-2(ed.4)

5 j. M  w) v( vStandard-
IEC 60947-2 (2006-04, 4th Ed.)
" o' _8 s7 s9 D/ R6 y9 QSub clause(s):
. g7 ?: l3 R( U1 M( m8.3.3.1.2
Sheet:
, x) ^8 `3 S; R9 d# {& S4 }1 vDSH 659
9 w2 a" g* C" WSubject:
$ _6 j5 Z* P. u/ wProblem of setting a current applied to ACB of
) h1 ?5 R3 K/ K6 g( S+ M$ e' lhigh current rating for instantaneous tripping.
Key words:
8 {9 x% v+ N! q# l" G! ?6 |Trip limits &
characteristics
Approved at
the 45th CTL
Plenary
% X7 Q- Q1 m% C3 g# r* V: @9 w) XMeeting in
Prague in 2008
Question:
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
# }( c, ^( E4 z  T" S) tinstantaneous 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
testing facility when performing the trip test of SEQ. I?
; z. \% Z" H0 L+ x' [. VRationale:
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
& a% z0 l$ H, g" K5 q, x1 Cof the CT in combination with the trip unit, and the trip unit is usually the same for all
models.
4 e7 s7 w$ V) }$ WSo some accredited testing laboratories have performed this test by applying the
4 ]5 Z" y* x2 T8 L- X$ bsecondary current of CT (normally 5 A) to the input of an overcurrent release. This
. t, p, ], Y$ e( T5 irelease 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
' w$ f8 a5 U/ |$ g- ]0 J4 ]) {as CT saturation, thermal and EMC influence on ACB, especially on single-pole
connection.
* A* J3 q8 G; K. e$ s! P) ?. q2 {Decision:
The secondary current of the CT (reduced current, 5 A, for example) may be used
1 c7 a6 z( b  g, o' `; ^+ Sfor trip tests of ACBs integrated with electronic OCR for all ratings of In, but only for
sub-clause 8.3.3.1.2 of SEQ I.
2 W3 {) ?. c, o2 k* l4 QBut in addition, followings items shall be verified to fully cover the safety aspects of
& J9 Q4 o1 n: Vthe 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
! y% w; c; w. p; M. |6 \# B1 oreports or certificates. All CTs of the circuit-breakers of the given frame
- s4 N8 N1 y+ ~' O$ K- lsize have to show the same performance characteristic.
' N4 r6 o$ s% I7 ]9 }2. The single pole short-circuit test with a current equal to 80 % of the
3 T$ s; Z$ b. J/ Vmaximum current setting of the instantaneous release and equal to 120 %
# h2 n2 H; q+ s0 ^* w1 C* |of the maximum current setting of the instantaneous release shall be
" M% b( F3 O  j6 eperformed at any convenient voltage with the current in the main poles of
2 l  E- `- a; B8 h8 f2 wthe circuit-breaker. The other tests required by the standard may be
, r) B1 e2 j- Q' o, _2 N4 D( Xconducted by use of a simulated input signal to the tripping unit.

, P' t: U5 Z; w5 Q
) g" k1 l' Y' e0 f, T' \9 u- a( x