CHAPTER 4: SETPOINTS PROTECTION
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL 4–173
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
= Pickup Current setting
A, B, p = constants
T
RESET
= reset time in seconds (assuming energy capacity is 100% and RESET is
“Timed”)
t
r
= characteristic constant
Table 4-20: IEEE INVERSE TIME CURVE CONSTANTS
Table 4-21: IEEE CURVE TRIP TIMES (IN SECONDS)
IEEE CURVE SHAPE A B P t
r
IEEE Extremely Inverse 28.2 0.1217 2.000 29.1
IEEE Very Inverse 19.61 0.491 2.000 21.6
IEEE Moderately Inverse 0.0515 0.1140 0.02000 4.85
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
IEEE EXTREMELY INVERSE
0.5 11.341 4.761 1.823 1.001 0.648 0.464 0.355 0.285 0.237 0.203
1.0 22.682 9.522 3.647 2.002 1.297 0.927 0.709 0.569 0.474 0.407
2.0 45.363 19.043 7.293 4.003 2.593 1.855 1.418 1.139 0.948 0.813
4.0 90.727 38.087 14.587 8.007 5.187 3.710 2.837 2.277 1.897 1.626
6.0 136.090 57.130 21.880 12.010 7.780 5.564 4.255 3.416 2.845 2.439
8.0 181.454 76.174 29.174 16.014 10.374 7.419 5.674 4.555 3.794 3.252
10.0 226.817 95.217 36.467 20.017 12.967 9.274 7.092 5.693 4.742 4.065
IEEE VERY INVERSE
0.5 8.090 3.514 1.471 0.899 0.654 0.526 0.450 0.401 0.368 0.345
1.0 16.179 7.028 2.942 1.798 1.308 1.051 0.900 0.802 0.736 0.689
2.0 32.358 14.055 5.885 3.597 2.616 2.103 1.799 1.605 1.472 1.378
4.0 64.716 28.111 11.769 7.193 5.232 4.205 3.598 3.209 2.945 2.756
6.0 97.074 42.166 17.654 10.790 7.849 6.308 5.397 4.814 4.417 4.134
8.0 129.432 56.221 23.538 14.387 10.465 8.410 7.196 6.418 5.889 5.513
10.0 161.790 70.277 29.423 17.983 13.081 10.513 8.995 8.023 7.361 6.891
IEEE MODERATELY INVERSE
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