4–158 889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL
PROTECTION CHAPTER 4: SETPOINTS
ANSI CURVES
The ANSI time overcurrent curve shapes conform to industry standards and the ANSI
C37.90 curve classifications for extremely, very, and moderately inverse. The ANSI curves
are derived from the following formulae:
Where:
T = operate time (in seconds)
TDM = Multiplier setting
I = input current
I
pickup
= Pickup Current setting
A to E = constants
T
RESET
= reset time in seconds (assuming energy capacity is 100% and RESET is
“Timed”)
t
r
= characteristic constant
Table 4-24: ANSI INVERSE TIME CURVE CONSTANTS
Table 4-25: ANSI CURVE TRIP TIMES (IN SECONDS)
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
MULTIPLIER
(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
ANSI CURVE SHAPE A B C D E t
r
ANSI Extremely Inverse 0.0399 0.2294 0.5000 3.0094 0.7222 5.67
ANSI Very Inverse 0.0615 0.7989 0.3400 -0.2840 4.0505 3.88
ANSI Normally Inverse 0.0274 2.2614 0.3000 -4.1899 9.1272 5.95
ANSI Moderately Inverse 0.1735 0.6791 0.8000 -0.0800 0.1271 1.08
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
ANSI EXTREMELY INVERSE
0.5 2.000 0.872 0.330 0.184 0.124 0.093 0.075 0.063 0.055 0.049
1.0 4.001 1.744 0.659 0.368 0.247 0.185 0.149 0.126 0.110 0.098
2.0 8.002 3.489 1.319 0.736 0.495 0.371 0.298 0.251 0.219 0.196
4.0 16.004 6.977 2.638 1.472 0.990 0.742 0.596 0.503 0.439 0.393
6.0 24.005 10.466 3.956 2.208 1.484 1.113 0.894 0.754 0.658 0.589
8.0 32.007 13.955 5.275 2.944 1.979 1.483 1.192 1.006 0.878 0.786
10.0 40.009 17.443 6.594 3.680 2.474 1.854 1.491 1.257 1.097 0.982
ANSI VERY INVERSE
0.5 1.567 0.663 0.268 0.171 0.130 0.108 0.094 0.085 0.078 0.073
1.0 3.134 1.325 0.537 0.341 0.260 0.216 0.189 0.170 0.156 0.146
2.0 6.268 2.650 1.074 0.682 0.520 0.432 0.378 0.340 0.312 0.291
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