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CHAPTER 4: SETPOINTS
Table 4-27: IAC CURVE TRIP TIMES (IN SECONDS)
MULTIPLIER
CURRENT (I/I
(TDM)
1.5
IAC EXTREMELY INVERSE
0.5
1.699
1.0
3.398
2.0
6.796
4.0
13.591
6.0
20.387
8.0
27.183
10.0
33.979
IAC VERY INVERSE
0.5
1.451
1.0
2.901
2.0
5.802
4.0
11.605
6.0
17.407
8.0
23.209
10.0
29.012
IAC INVERSE
0.5
0.578
1.0
1.155
2.0
2.310
4.0
4.621
6.0
6.931
8.0
9.242
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
IAC CURVES
The curves for the General Electric type IAC relay family are derived from the formula:
Where:
T = operate time (in seconds)
TDM = Multiplier setting
I = input current
I
= Pickup Current setting
pickup
A to E = constants
t
= characteristic constant
r
T
= reset time in seconds (assuming energy capacity is 100% and RESET is
RESET
"Timed")
Table 4-26: GE TYPE IAC INVERSE TIME CURVE CONSTANTS
IAC CURVE SHAPE
A
IAC Extremely Inverse 0.0040
IAC Very Inverse
0.0900
IAC Inverse
0.2078
IAC Short Inverse
0.0428
)
pickup
2.0
3.0
4.0
0.749
0.303
0.178
1.498
0.606
0.356
2.997
1.212
0.711
5.993
2.423
1.422
8.990
3.635
2.133
11.987
4.846
2.844
14.983
6.058
3.555
0.656
0.269
0.172
1.312
0.537
0.343
2.624
1.075
0.687
5.248
2.150
1.374
7.872
3.225
2.061
10.497
4.299
2.747
13.121
5.374
3.434
0.375
0.266
0.221
0.749
0.532
0.443
1.499
1.064
0.885
2.997
2.128
1.770
4.496
3.192
2.656
5.995
4.256
3.541
B
C
0.6379
0.6200
0.7965
0.1000
0.8630
0.8000
0.0609
0.6200
5.0
6.0
7.0
0.123
0.093
0.074
0.246
0.186
0.149
0.491
0.372
0.298
0.983
0.744
0.595
1.474
1.115
0.893
1.966
1.487
1.191
2.457
1.859
1.488
0.133
0.113
0.101
0.266
0.227
0.202
0.533
0.453
0.405
1.065
0.906
0.810
1.598
1.359
1.215
2.131
1.813
1.620
2.663
2.266
2.025
0.196
0.180
0.618
0.392
0.360
0.337
0.784
0.719
0.674
1.569
1.439
1.348
2.353
2.158
2.022
3.138
2.878
2.695
PROTECTION
D
E
t
r
1.7872
0.2461
6.008
-1.2885
7.9586
4.678
-0.4180
0.1947
0.990
-0.0010
0.0221
0.222
8.0
9.0
10.0
0.062
0.053
0.046
0.124
0.106
0.093
0.248
0.212
0.185
0.495
0.424
0.370
0.743
0.636
0.556
0.991
0.848
0.741
1.239
1.060
0.926
0.093
0.087
0.083
0.186
0.174
0.165
0.372
0.349
0.331
0.745
0.698
0.662
1.117
1.046
0.992
1.490
1.395
1.323
1.862
1.744
1.654
0.160
0.154
0.148
0.320
0.307
0.297
0.640
0.614
0.594
1.280
1.229
1.188
1.921
1.843
1.781
2.561
2.457
2.375
4–177
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