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CHAPTER 4: SETPOINTS
Table 4-21: IEEE CURVE TRIP TIMES (IN SECONDS)
MULTIPLIER
CURRENT (I/I
(TDM)
1.5
IEEE EXTREMELY INVERSE
0.5
11.341
1.0
22.682
2.0
45.363
4.0
90.727
6.0
136.090
8.0
181.454
10.0
226.817
IEEE VERY INVERSE
0.5
8.090
1.0
16.179
2.0
32.358
4.0
64.716
6.0
97.074
8.0
129.432
10.0
161.790
IEEE MODERATELY INVERSE
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
the variable must be reduced. Two types of this resetting operation are available:
"Instantaneous" and "Timed". The "Instantaneous" selection is intended for applications
with other relays, such as most static relays, which set the energy capacity directly to zero
when the current falls below the reset threshold. The "Timed" selection can be used where
the relay must coordinate with electromechanical relays.
IEEE CURVES
The IEEE Time Overcurrent curve shapes conform to industry standards and the IEEE
C37.112-1996 curve classifications for extremely, very, and moderately inverse. The IEEE
curves are derived from the formula:
Where:
T = operate time (in seconds)
TDM = Multiplier setting
I = input current
I
= Pickup Current setting
pickup
A, B, p = constants
T
= reset time in seconds (assuming energy capacity is 100% and RESET is
RESET
"Timed")
t
= characteristic constant
r
Table 4-20: IEEE INVERSE TIME CURVE CONSTANTS
IEEE CURVE SHAPE
IEEE Extremely Inverse
IEEE Very Inverse
IEEE Moderately Inverse
)
pickup
2.0
3.0
4.0
4.761
1.823
1.001
9.522
3.647
2.002
19.043
7.293
4.003
38.087
14.587
8.007
57.130
21.880
12.010
76.174
29.174
16.014
95.217
36.467
20.017
3.514
1.471
0.899
7.028
2.942
1.798
14.055
5.885
3.597
28.111
11.769
7.193
42.166
17.654
10.790
56.221
23.538
14.387
70.277
29.423
17.983
A
B
28.2
0.1217
19.61
0.491
0.0515
0.1140
5.0
6.0
7.0
0.648
0.464
0.355
1.297
0.927
0.709
2.593
1.855
1.418
5.187
3.710
2.837
7.780
5.564
4.255
10.374
7.419
5.674
12.967
9.274
7.092
0.654
0.526
0.450
1.308
1.051
0.900
2.616
2.103
1.799
5.232
4.205
3.598
7.849
6.308
5.397
10.465
8.410
7.196
13.081
10.513
8.995
PROTECTION
P
t
r
2.000
29.1
2.000
21.6
0.02000
4.85
8.0
9.0
10.0
0.285
0.237
0.203
0.569
0.474
0.407
1.139
0.948
0.813
2.277
1.897
1.626
3.416
2.845
2.439
4.555
3.794
3.252
5.693
4.742
4.065
0.401
0.368
0.345
0.802
0.736
0.689
1.605
1.472
1.378
3.209
2.945
2.756
4.814
4.417
4.134
6.418
5.889
5.513
8.023
7.361
6.891
4–173
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