CHAPTER 5: SETPOINTS S4 ELEMENTS
745 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL 5–61
IEC curves:
For European applications, the relay offers the four standard curves defined in IEC 255-4
and British standard BS142. These are defined as IEC Curve A, IEC Curve B, IEC Curve C, and
Short Inverse. The formulae for these curves are:
(EQ 5.8)
where: T = trip time (in seconds), M = multiplier setpoint, I = input current,
I
pickup
= pickup current setpoint, and K, E = constants.
10.0 13.509 7.574 4.776 3.818 3.324 3.020 2.815 2.666 2.554 2.465
Table 5–6: IEC (BS) inverse time curve constants
IEC (BS) curve shape K E
IEC curve A (BS142) 0.140 0.020
IEC curve B (BS142) 13.500 1.000
IEC curve C (BS142) 80.000 2.000
IEC short inverse 0.050 0.040
Table 5–7: IEC curve trip times (in seconds)
TDM Current ( I / I
pickup
)
1.5 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0
IEC curve A
0.05 0.860 0.501 0.315 0.249 0.214 0.192 0.176 0.165 0.156 0.149
0.10 1.719 1.003 0.630 0.498 0.428 0.384 0.353 0.330 0.312 0.297
0.20 3.439 2.006 1.260 0.996 0.856 0.767 0.706 0.659 0.623 0.594
0.40 6.878 4.012 2.521 1.992 1.712 1.535 1.411 1.319 1.247 1.188
0.60 10.317 6.017 3.781 2.988 2.568 2.302 2.117 1.978 1.870 1.782
0.80 13.755 8.023 5.042 3.984 3.424 3.070 2.822 2.637 2.493 2.376
1.00 17.194 10.029 6.302 4.980 4.280 3.837 3.528 3.297 3.116 2.971
IEC curve B
0.05 1.350 0.675 0.338 0.225 0.169 0.135 0.113 0.096 0.084 0.075
0.10 2.700 1.350 0.675 0.450 0.338 0.270 0.225 0.193 0.169 0.150
0.20 5.400 2.700 1.350 0.900 0.675 0.540 0.450 0.386 0.338 0.300
0.40 10.800 5.400 2.700 1.800 1.350 1.080 0.900 0.771 0.675 0.600
0.60 16.200 8.100 4.050 2.700 2.025 1.620 1.350 1.157 1.013 0.900
0.80 21.600 10.800 5.400 3.600 2.700 2.160 1.800 1.543 1.350 1.200
1.00 27.000 13.500 6.750 4.500 3.375 2.700 2.250 1.929 1.688 1.500
IEC curve C
0.05 3.200 1.333 0.500 0.267 0.167 0.114 0.083 0.063 0.050 0.040
0.10 6.400 2.667 1.000 0.533 0.333 0.229 0.167 0.127 0.100 0.081
0.20 12.800 5.333 2.000 1.067 0.667 0.457 0.333 0.254 0.200 0.162
0.40 25.600 10.667 4.000 2.133 1.333 0.914 0.667 0.508 0.400 0.323
0.60 38.400 16.000 6.000 3.200 2.000 1.371 1.000 0.762 0.600 0.485
0.80 51.200 21.333 8.000 4.267 2.667 1.829 1.333 1.016 0.800 0.646
1.00 64.000 26.667 10.000 5.333 3.333 2.286 1.667 1.270 1.000 0.808
IEC short time
0.05 0.153 0.089 0.056 0.044 0.038 0.034 0.031 0.029 0.027 0.026
0.10 0.306 0.178 0.111 0.088 0.075 0.067 0.062 0.058 0.054 0.052
Table 5–5: ANSI curve trip times (in seconds)
TDM Current ( I / I
pickup
)
1.5 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0
TM
K
II
pu
⁄()
E
1–
----------------------------
×=
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