Siemens 6MD85, Manual

Page: 673 / 1256

Parameter:
Non-directional pickup
•
Recommended setting value
(_:8131:107) Non-directional pickup
=
at volt.< &
mem.empty
This parameter is not visible in the basic stage.
Parameter Value Description
at volt.< & mem.empty
Select this setting if the stage is to pick up in a non-directional manner if the
voltage memory is empty and determining of direction has to be performed
at low voltages (3-phase close-up fault). An empty voltage memory may
exist, for example, if there is a voltage transformer at the line end and the
circuit breaker (CB) trips.
Siemens recommends using the default setting.
no
Select this setting if determining of direction is required under all circum-
stances, that is, even in the event of pickup on a 3-phase close-up fault.
Parameter:
Threshold
•
Default setting
(_:8131:3) Threshold
=
1.50 A
(for the first stage)
The same considerations apply to setting the threshold value as for non-directional overcurrent protection. For
further information, refer to section
7.4.4.2 Application and Setting Notes .
Parameter:
Operate delay
•
Default setting
(_:8131:6) Operate delay
=
0.300 s
(for the 1st stage)
The Operate delay to be set is derived from the time-grading schedule that has been prepared for the system.
Where overcurrent protection is used in emergency mode, shorter time delays might be reasonable (one
grading time above fast tripping), since the emergency mode only operates if the main protection function
fails.
Typical examples of grading times are provided in the chapters
7.6.9 Application Notes for Parallel Lines and
7.6.10 Application Notes for Directional Comparison Protection .
Parameter:
Dropout ratio
•
Recommended setting value
(_:8131:4) Dropout ratio
=
0.95
This parameter is not visible in the basic stage.
The recommended set value of 0.95 is appropriate for most applications.
For high-precision measurements, the setting value of the
Dropout ratio
parameter can be reduced, for
example to 0.98. If you expect heavily fluctuating measurands at the response threshold, you can increase the
setting value of the
Dropout ratio
parameter. This avoids chattering of the tripping stage.
Parameter:
Dropout delay
•
Recommended setting value
(_:8131:101) Dropout delay
=
0 s
This parameter is not visible in the basic stage.
Siemens recommends using this setting value, since the dropout of a protection stage must be performed as
fast as possible.
You can use the
Dropout delay
parameter ≠
0 s
to obtain a uniform dropout behavior if you use it
together with an electromechanical relay. This is required for time grading. The dropout time of the electro-
mechanical relay must be known for this purpose. Subtract the dropout time of your own device (see Tech-
nical Data) and set the result.
Protection and Automation Functions
7.6 Directional Overcurrent Protection, Phases
SIPROTEC 5, High-Voltage Bay Controller, Manual 673
C53000-G5040-C015-9, Edition 11.2017