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

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DSH 659 / P1 {, \+ k6 s0 s

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

8.3.3.1.2

60947-2(ed.4)   t4 p' g' Z! X# h' j

Standard-
$ g8 M, }# i7 \+ v) nIEC 60947-2 (2006-04, 4th Ed.)
Sub clause(s):
. k7 `+ h2 s+ Z) e: y# m8.3.3.1.2
Sheet:
' K) E1 I1 l1 @0 o* M4 _DSH 659
Subject:
' S5 t! ~& C0 Q- nProblem of setting a current applied to ACB of
2 r8 e9 g% @! {high current rating for instantaneous tripping.
Key words:
Trip limits &
characteristics
Approved at
the 45th CTL
Plenary
Meeting in
2 w5 D( }7 Q2 g0 ?Prague in 2008
Question:
According to 8.3.3.1.2, when the over-current opening release is a built-in part of the
( B7 O5 p% j4 W; q9 tcircuit 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
* G- S: M6 y( w& A; s2 minstantaneous trip release up to 16 In, do we have to apply 80640 A (16 In x 80 %)
% v  Y" b2 y& T8 `" E& K  yand 120960 A (16 In x 120 %) to the main circuit of ACB by use of a high power
; n3 K+ ^, ]1 Atesting facility when performing the trip test of SEQ. I?
Rationale:
( p* t6 w3 w$ T; |It is not so easy to conduct the instantaneous trip test using the high currents
/ u& }" L$ [! p6 u% n$ wmentioned 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
) o, a, l" r0 |0 q% lof the CT in combination with the trip unit, and the trip unit is usually the same for all
  M' D" `: }) ^! w$ |models.
/ a! @5 l" u) P6 L: t% fSo 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
$ y+ ]. X. A1 A* k; lopening of an ACB. But by use of this method, we bypass possible problems such
7 J' @, i% t4 ~7 O4 was 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
sub-clause 8.3.3.1.2 of SEQ I.
But in addition, followings items shall be verified to fully cover the safety aspects of
the standard:
0 Q# N: Y8 V( U1. The conformity of the performance (at least turn ratio and composite error)
' I$ G( P% I( p( U% T6 dof the CT or Rogowski coil, if any, shall be verified by specifications, test
$ A8 U3 F7 c$ D/ l" lreports or certificates. All CTs of the circuit-breakers of the given frame
6 y8 D, A1 v" y' Q( R0 j/ Ysize have to show the same performance characteristic.
2. The single pole short-circuit test with a current equal to 80 % of the
( ^1 F- G) f" o5 V' |7 `maximum current setting of the instantaneous release and equal to 120 %
of the maximum current setting of the instantaneous release shall be
6 ~$ f) A- Z: ?: F8 Z: \9 Rperformed at any convenient voltage with the current in the main poles of
the circuit-breaker. The other tests required by the standard may be
) \( m) J/ r) n& zconducted by use of a simulated input signal to the tripping unit.
* f7 N( G! T+ w- c