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CHAPTER 6: SETPOINTS
339 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
electromechanical units. With this setpoint, the energy capacity variable is
decremented according to the following equation.
where: T
= reset time in seconds; E = energy capacity reached (per unit); M = curve
RESET
multiplier; CR = characteristic constant (5 for ANSI, IAC, Definite Time, and FlexCurves™; 8
for IEC curves)
ANSI Curves
The ANSI time overcurrent curve shapes conform to industry standards and the ANSI
C37.90 curve classifications for extremely, very, normally, and moderately inverse. The
ANSI curves are derived from the following formula:
where:T = trip time (seconds); M = multiplier value; I = input current; I
setpoint; A, B, C, D, E = constants
Table 6-3: ANSI Curve Constants
ANSI Curve Shape
ANSI Extremely Inverse
ANSI Very Inverse
ANSI Normally Inverse
ANSI Moderately Inverse
Table 6-4: ANSI Curve Trip Times (in seconds)
Multiplier (TDM)
Current (I/Ipickup)
1.5
ANSI Extremely Inverse
0.5
2.000
1.0
4.001
2.0
8.002
4.0
16.004 6.977
6.0
24.005 10.466 3.956
8.0
32.007 13.955 5.275
10.0
40.009 17.443 6.594
ANSI Very Inverse
0.5
1.567
1.0
3.134
2.0
6.268
4.0
12.537 5.301
6.0
18.805 7.951
8.0
25.073 10.602 4.295
10.0
31.341 13.252 5.369
ANSI Normally Inverse
0.5
2.142
1.0
4.284
2.0
8.568
4.0
17.137 7.062
6.0
25.705 10.594 4.524
A
B
0.0399
0.2294
0.0615
0.7989
0.0274
2.2614
0.1735
0.6791
2.0
3.0
4.0
5.0
0.872
0.330
0.184
0.124
1.744
0.659
0.368
0.247
3.489
1.319
0.736
0.495
2.638
1.472
0.990
2.208
1.484
2.944
1.979
3.680
2.474
0.663
0.268
0.171
0.130
1.325
0.537
0.341
0.260
2.650
1.074
0.682
0.520
2.148
1.365
1.040
3.221
2.047
1.559
2.730
2.079
3.412
2.599
0.883
0.377
0.256
0.203
1.766
0.754
0.513
0.407
3.531
1.508
1.025
0.814
3.016
2.051
1.627
3.076
2.441
S3 PROTECTION
= pickup current
pu
C
D
E
0.5000
3.0094
0.7222
0.3400
–0.2840
4.0505
0.3000
–4.1899
9.1272
0.8000
–0.0800
0.1271
6.0
7.0
8.0
9.0
0.093
0.075
0.063
0.055
0.185
0.149
0.126
0.110
0.371
0.298
0.251
0.219
0.742
0.596
0.503
0.439
1.113
0.894
0.754
0.658
1.483
1.192
1.006
0.878
1.854
1.491
1.257
1.097
0.108
0.094
0.085
0.078
0.216
0.189
0.170
0.156
0.432
0.378
0.340
0.312
0.864
0.755
0.680
0.625
1.297
1.133
1.020
0.937
1.729
1.510
1.360
1.250
2.161
1.888
1.700
1.562
0.172
0.151
0.135
0.123
0.344
0.302
0.270
0.246
0.689
0.604
0.541
0.492
1.378
1.208
1.082
0.983
2.067
1.812
1.622
1.475
Eq. 17
10.0
0.049
0.098
0.196
0.393
0.589
0.786
0.982
0.073
0.146
0.291
0.583
0.874
1.165
1.457
0.113
0.226
0.452
0.904
1.356
6–67
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