GE 845 Instruction Manual page 257

CHAPTER 4: SETPOINTS
Table 4-39: IEEE CURVE TRIP TIMES (IN SECONDS)
MULTIPLIER CURRENT (I/I
pickup
(TDM)
1.5 2.0
IEEE EXTREMELY INVERSE
0.5 11.341 4.761
1.0 22.682 9.522
2.0 45.363 19.043
4.0 90.727 38.087
6.0 136.090 57.130
8.0 181.454 76.174
10.0 226.817 95.217
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
A time dial multiplier setting allows the selection of a multiple of the base curve shape
(where the time dial multiplier = 1) with the curve shape setting. Unlike the
electromechanical time dial equivalent, operate times are directly proportional to the time
multiplier (TD MULTIPLIER) setting value. For example, all times for a multiplier of 10 are 10
times the multiplier 1 or base curve values. Setting the multiplier to zero results in an
instantaneous response to all current levels above Pickup.
Time Overcurrent time calculations are made with an internal energy capacity memory
variable. When this variable indicates that the energy capacity has reached 100%, a Time
Overcurrent element will operate. If less than 100% energy capacity is accumulated in this
variable and the current falls below the dropout threshold of 97 to 98% of the Pickup value,
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 4-38: IEEE INVERSE TIME CURVE CONSTANTS
IEEE CURVE SHAPE
IEEE Extremely Inverse
IEEE Very Inverse
IEEE Moderately Inverse
)
3.0 4.0
1.823 1.001
3.647 2.002
7.293 4.003
14.587 8.007
21.880 12.010
29.174 16.014
36.467 20.017
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
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
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