CHAPTER 6: SETPOINTS
S3 PROTECTION
350 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
6–35
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 6-7: GE Type IAC Inverse Curve Constants
Table 6-8: IAC Curve Trip Times
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
8.0
23.209 10.497 4.299 2.747 2.131 1.813 1.620 1.490 1.395 1.323
10.0
29.012 13.121 5.374 3.434 2.663 2.266 2.025 1.862 1.744 1.654
IAC Inverse
0.5
0.578 0.375 0.266 0.221 0.196 0.180 0.168 0.160 0.154 0.148
1.0
1.155 0.749 0.532 0.443 0.392 0.360 0.337 0.320 0.307 0.297
2.0
2.310 1.499 1.064 0.885 0.784 0.719 0.674 0.640 0.614 0.594
4.0
4.621 2.997 2.128 1.770 1.569 1.439 1.348 1.280 1.229 1.188
6.0
6.931 4.496 3.192 2.656 2.353 2.158 2.022 1.921 1.843 1.781
8.0
9.242 5.995 4.256 3.541 3.138 2.878 2.695 2.561 2.457 2.375
10.0
11.552 7.494 5.320 4.426 3.922 3.597 3.369 3.201 3.072 2.969
IAC Short Inverse
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