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Protection and Automation Functions
6.7 Directional Overcurrent Protection, Ground
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 section +/-
•
Recommended setting value (_:2311:102) Rotation angle of ref. volt.= -45°
•
Recommended setting value (_:2311:103) Forward section +/- = 88°
The parameter Forward section +/- 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 section +/- 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
(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 6-6
Application
446
Example Settings
Table
6-6. Note that for 1-phase-to-ground faults
φk Typical
Setting
Rotation angle of ref. volt.
60°
-60°
30°
-30°
SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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