4–158
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
PROTECTION
CHAPTER 4: SETPOINTS
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
= Pickup Current setting
A to E = constants
t
r
= characteristic constant
T
RESET
= reset time in seconds (assuming energy capacity is 100% and RESET is
“Timed”)
Table 4-30: GE TYPE IAC INVERSE TIME CURVE CONSTANTS
Table 4-31: IAC CURVE TRIP TIMES (IN SECONDS)
IAC CURVE SHAPE
A
B
C
D
E
t
r
IAC Extremely Inverse 0.0040
0.6379
0.6200
1.7872
0.2461
6.008
IAC Very Inverse
0.0900
0.7965
0.1000
-1.2885
7.9586
4.678
IAC Inverse
0.2078
0.8630
0.8000
-0.4180
0.1947
0.990
IAC Short Inverse
0.0428
0.0609
0.6200
-0.0010
0.0221
0.222
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
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
0.618
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
Summary of Contents for 845
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Page 526: ...6 22 845 TRANSFORMER PROTECTION SYSTEM INSTRUCTION MANUAL FLEXELEMENTS CHAPTER 6 METERING ...