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

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DSH 659 4 c5 o9 @+ q2 j+ E3 n9 j( i

Problem of setting a current applied to ACB of high current rating in instantaneous tripping : d. @, }) y0 }  ]7 d+ Y

8.3.3.1.2

60947-2(ed.4) 4 l- D# ~* [! Y2 u/ R

; r6 I$ T$ ^9 @4 R' sStandard-
0 q" f4 d7 @: |/ A: o/ TIEC 60947-2 (2006-04, 4th Ed.)
9 p6 ~( l7 C! F* ^7 lSub clause(s):
0 A8 e0 y# @% j8.3.3.1.2
Sheet:
% H0 Y9 s( Z; }( GDSH 659
% s$ O3 {4 X. j  @Subject:
Problem of setting a current applied to ACB of
; T" X7 `  q- H! L" g' T1 w% ]1 uhigh current rating for instantaneous tripping.
Key words:
# v3 y% C: x5 K9 o3 P3 C* O2 H' [Trip limits &
characteristics
Approved at
the 45th CTL
Plenary
Meeting in
Prague in 2008
" p; u# L* T3 D( Q' z1 ZQuestion:
- j) j* ~# x( @+ o! f- yAccording to 8.3.3.1.2, when the over-current opening release is a built-in part of the
8 Q/ e. ]+ Z2 t6 ]circuit breaker, it shall normally be verified inside the corresponding circuit breaker.
2 g2 z: |% V3 o! a  R" c0 K- 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 %)
and 120960 A (16 In x 120 %) to the main circuit of ACB by use of a high power
. H  K9 s% m9 H2 f( P% V, Atesting facility when performing the trip test of SEQ. I?
3 i9 }/ m! D. h' y; ZRationale:
/ i, a0 Y4 t+ V8 r) nIt 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
! P9 @2 E# Z8 |2 w0 V( iaddition ACBs often have several ratings, which are determined by the specification
2 M- ], b% r% Y3 W, R7 xof the CT in combination with the trip unit, and the trip unit is usually the same for all
6 E+ }: a9 Y8 t! M+ K2 Amodels.
So some accredited testing laboratories have performed this test by applying the
3 R, b% K7 ~- C  D& G) fsecondary current of CT (normally 5 A) to the input of an overcurrent release. This
6 a/ j$ ~  ^' I5 |/ r# v, K  Yrelease is connected to operating mechanism of contacts to check the mechanical
) x# E$ r9 [+ K' Z9 H0 topening 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
. n( y( \. e* ^$ ^3 \connection.
Decision:
The secondary current of the CT (reduced current, 5 A, for example) may be used
  Z& `  D' K, Y& m- e: qfor 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
) X* c3 P5 A5 q+ g$ L, N9 tthe standard:
# f  c/ s3 F! g5 {% t1. The conformity of the performance (at least turn ratio and composite error)
# D$ s6 g% w2 y4 J/ zof 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
1 o1 k/ B1 L' Osize have to show the same performance characteristic.
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 %
3 M/ ]- j3 g3 e( v6 {3 Eof the maximum current setting of the instantaneous release shall be
performed at any convenient voltage with the current in the main poles of
the circuit-breaker. The other tests required by the standard may be
conducted by use of a simulated input signal to the tripping unit.
1 q" F  v8 R% C3 g# W0 M