Siemens 6MD85, Manual

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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 threshold 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 graphic. The curve is composed of 2
sections with different slops. 7 parameters are used to define the logarithmic inverse time with knee-point
characteristic curve. The parameter
Max. time of the curve
determines the initial time value of the
characteristic curve, and relates to the 3I0
Threshold
value. The transition point is defined by parameter
Knee-point current
and parameter
Knee-point time
. The parameter
Min. time of the curve
indicates the lower time limit, and parameter
Current at Min. time
determines the current value at
Min. time of the curve
. The parameter
Time dial
servers as a time factor to the operate time.
[dwloinkn-300913, 3, en_US]
Figure 7-118 Operate Curve of the Logarithmic Inverse Time with Knee-Point Characteristic (In the Example
of
Threshold
=
0.004 A
)
Application and Setting Notes
Apart from the operate curve, this type of stage is almost identical to the Inverse-time overcurrent protec-
tion – advanced stage (see chapter
7.7.6.1 Description ). The only difference is that the dynamic settings
change functionality is not available.
This section only discusses the nature of the operate curve. For further functionality, refer to chapter
7.7.6.2 Application and Setting Notes .
Parameter:
Threshold
•
Default setting
(_:3) Threshold
=
1.20 A
You can use the
Threshold
parameter to define the pickup value of the stage corresponding to the specific
application.
7.7.8.2
Protection and Automation Functions
7.7 Directional Overcurrent Protection, Ground
SIPROTEC 5, High-Voltage Bay Controller, Manual 737
C53000-G5040-C015-9, Edition 11.2017