CHAPTER 6: SETPOINTS
S3 PROTECTION
350 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
6–59
IAC Curves
The curves for the General Electric type IAC relay family are derived from the formulae:
where: T = trip time (seconds), M = multiplier setpoint, I = input current, I
pu
= pickup current
setpoint, A to E = constants.
Table 7: GE Type IAC Inverse Curve Constants
Table 8: IAC Curve Trip Times
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
0.20
0.612 0.356 0.223 0.175 0.150 0.135 0.124 0.115 0.109 0.104
0.40
1.223 0.711 0.445 0.351 0.301 0.269 0.247 0.231 0.218 0.207
0.60
1.835 1.067 0.668 0.526 0.451 0.404 0.371 0.346 0.327 0.311
0.80
2.446 1.423 0.890 0.702 0.602 0.538 0.494 0.461 0.435 0.415
1.00
3.058 1.778 1.113 0.877 0.752 0.673 0.618 0.576 0.544 0.518
IAC Curve Shape
A
B
C
D
E
IAC Extreme Inverse
0.0040
0.6379
0.6200
1.7872
0.2461
IAC Very Inverse
0.0900
0.7955
0.1000
–1.2885
7.9586
IAC Inverse
0.2078
0.8630
0.8000
–0.4180
0.1947
IAC Short Inverse
0.0428
0.0609
0.6200
–0.0010
0.0221
Multiplier (TDM)
1.5
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
IAC Extremely Inverse
0.5
1.699 0.749 0.303 0.178 0.123 0.093 0.074 0.062 0.053 0.046
1.0
3.398 1.498 0.606 0.356 0.246 0.186 0.149 0.124 0.106 0.093
2.0
6.796 2.997 1.212 0.711 0.491 0.372 0.298 0.248 0.212 0.185
4.0
13.591 5.993 2.423 1.422 0.983 0.744 0.595 0.495 0.424 0.370
6.0
20.387 8.990 3.635 2.133 1.474 1.115 0.893 0.743 0.636 0.556
8.0
27.183 11.987 4.846 2.844 1.966 1.487 1.191 0.991 0.848 0.741
10.0
33.979 14.983 6.058 3.555 2.457 1.859 1.488 1.239 1.060 0.926
IAC Very Inverse
0.5
1.451 0.656 0.269 0.172 0.133 0.113 0.101 0.093 0.087 0.083
1.0
2.901 1.312 0.537 0.343 0.266 0.227 0.202 0.186 0.174 0.165
2.0
5.802 2.624 1.075 0.687 0.533 0.453 0.405 0.372 0.349 0.331
4.0
11.605 5.248 2.150 1.374 1.065 0.906 0.810 0.745 0.698 0.662
6.0
17.407 7.872 3.225 2.061 1.598 1.359 1.215 1.117 1.046 0.992
Multiplier (TDM) Current (I/Ipickup)
1.5
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
