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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