Siemens 6MD85, Manual

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This parameter is not available in the basic function. The basic function uses a fixed value of 2 V.
You use the
Min. voltage V0 or V2
parameter to define the minimum zero-sequence voltage or nega-
tive-sequence voltage for the direction determination. The minimum voltage must be set greater than the
maximum operational unbalance plus the voltage-transformer measuring errors.
As the measuring error of the individual voltage transformer is not added up, the critical measuring-error influ-
ence is the unbalance of the primary system.
Siemens recommends observing the operational zero-sequence voltage V0 of the protected object (for
example, the line) via the operational measured values of the device and providing the maximum value with a
certainty of 50 %.
EXAMPLE
Maximum operational measured value of zero-sequence voltage V0 = 0.5 Vsec
Min. voltage V0 or V2
= 1.5 ⋅ 0.5 V = 0.75 Vsec
If you have no information about maximum operational unbalance, Siemens recommends using the default
setting.
Parameter:
Rotation angle of ref. volt.
/
Forward s/-
•
Recommended setting value
(_:2311:102) Rotation angle of ref. volt.
=
-45°
•
Recommended setting value
(_:2311:103) Forward s/-
=
88°
The parameter
Forward s/-
is not available in the basic function. The basic function uses a fixed
value of 88°.
The direction characteristic, that is, the area of the forward and reverse ranges, is set with the
Rotation
angle of ref. volt.
and the
Forward s/-
parameters. The short-circuit angle is typically to
be found in a range from -30° to -60° inductively. Therefore, in most cases, the default setting of -45° can be
retained to position the reference voltage, as it ensures a reliable directional result.
Some example settings for special applications appear below
Table 7-5 . Note that for 1-phase-to-ground faults
(PG faults), the reference voltage is the zero-sequence voltage V0. This results in the following setting for the
rotation angle:
Rotation angle of ref. volt.
= -φk ground-measuring elements (PG faults)
Table 7-5 Example Settings
Application φk Typical Setting
Rotation angle of ref. volt.
60° -60°
30° -30°
Protection and Automation Functions
7.7 Directional Overcurrent Protection, Ground
706 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017