CHAPTER 5: SETPOINTS 5.4 PROTECTION ELEMENTS
GEK-106310-AF F650 DIGITAL BAY CONTROLLER 5-49
5.4.2.2 IEC curves
This family of curves follows the European standard IEC 255-4, and the British standard BF142 for IEC Curves A, B and C,
IEC Long-Time Inverse and IEC Short-Time Inverse. The formulas that define these curves are as follows:
Where:
t = Operation time in seconds
Dial = multiplying factor
I = Input current
Itap = Current pickup value
K, E = constants defined by the standard
T
RESET
= reset time in seconds (assuming 100% of power capacity and that the reset is activated)
t
r
= characteristic constant.
Table 5-23: Constants for IEC curves
8.0 129.432 56.221 23.538 14.387 10.465 8.410 7.196 6.418 5.889 5.513
10.0 161.790 70.277 29.423 17.983 13.081 10.513 8.995 8.023 7.361 6.891
IEEE Inverse
0.5 3.220 1.902 1.216 0.973 0.844 0.763 0.706 0.663 0.630 0.603
1.0 6.439 3.803 2.432 1.946 1.688 1.526 1.412 1.327 1.260 1.207
2.0 12.878 7.606 4.864 3.892 3.377 3.051 2.823 2.653 2.521 2.414
4.0 25.756 15.213 9.729 7.783 6.753 6.102 5.647 5.307 5.041 4.827
6.0 38.634 22.819 14.593 11.675 10.130 9.153 8.470 7.960 7.562 7.241
8.0 51.512 30.426 19.458 15.567 13.507 12.204 11.294 10.614 10.083 9.654
10.0 64.390 38.032 24.322 19.458 16.883 15.255 14.117 13.267 12.604 12.068
IEC Curve Shape Name K
E tr
IEC Curve A IEC Curve A 0.140
0.020 9.7
IEC Curve B IEC Curve B 13.500
1.000 43.2
IEC Curve C IEC Curve C 80.000
2.000 58.2
IEC Long-Time Inverse IEC Long-Time Inv 120.000
1.000 120.0
IEC Short-Time Inverse IEC Short-Time Inv 0.050
0.040 0.5
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