Siemens 6MD85, Manual

Page: 704 / 1256

into account, the reference voltage V0 can be rotated through an adjustable angle (parameter
Rotation
angle of ref. volt.
). This moves the vector of the rotated reference voltage close to the vector of the
short-circuit current -3I0. Consequently, the result of direction determination is as reliable as possible.
Figure 7-107 illustrates the relationship based on a 1-phase-to-ground fault in phase A. The fault current has a
phase displacement of 180° to the fault current IscA and lags the fault voltage by the fault angle φsc. The
reference voltage V0 is rotated by φrot which is -45°.
[dwroreze-300913, 2, en_US]
Figure 7-107 Rotation of the Reference Voltage, Directional Overcurrent Protection, Ground Function with
Zero-Sequence Values
The rotated reference voltage V
ref, rot
and the parameter
Forward s/-
define the forward and
reverse ranges, see Figure 7-108 . The forward range is calculated as ± Δφ° around the rotated reference
voltage V
ref, rot
. Δφ is set with the parameter
Forward s/-
. If the short-circuit current vector -3I0
is located in this range, the device decides on the forward direction. In the mirrored range, the device decides
on the reverse direction. In the intermediate range, the direction is undetermined.
Protection and Automation Functions
7.7 Directional Overcurrent Protection, Ground
704 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017