Operate Curve
If the function picks up, the logarithmic inverse-time characteristic curve is processed. A time value T
op
is
calculated for every input value exceeding 95 % of the pickup value. An integrator accumulates the value 1/
T
op
. If the accumulated integral reaches the fixed value 1, the stage operates.
The curve used to calculate the time value T
op
is shown in the following figure. The Threshold multi-
plier parameter defines the beginning of the characteristic curve. The Max. time of the curve deter-
mines the initial value of the characteristic curve. The Time dial parameter changes the slope of the charac-
teristic curve. At high currents, the Min. time of the curve parameter indicates the lower time limit.
[dwloginv-300913, 3, en_US]
Figure 7-116
Operate Curve of Logarithmic Inverse-Time Characteristic
The time to operate is calculated with the following formula:
[fomula01-240812-01.tif, 1, en_US]
Where
T
max
Maximum time of the curve (parameter Max. time of the curve)
T
d
Time dial (parameter Time dial)
T
op
Operate time
3I0 Measured zero-sequence current
I
thresh
Threshold value (parameter Threshold)
I
mul
Threshold multiplier (parameter Threshold multiplier)
If the calculated time is less than T
min
(parameter Min. time of the curve), T
min
is used.
Protection and Automation Functions
7.7 Directional Overcurrent Protection, Ground
SIPROTEC 5, High-Voltage Bay Controller, Manual 731
C53000-G5040-C015-9, Edition 11.2017
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