current. Consequently, the result of direction determination is as reliable as possible. Figure 6-56 illustrates
the relationship based on a 1-phase ground fault in phase A. The short-circuit current I
scA
lags the short-circuit
voltage by the short-circuit angle φ
sc
. The reference voltage, in this case V
BC
for measuring element A, is
rotated positively (counterclockwise) by the setting value of the Rotation angle of ref. volt. param-
eter. In the scenario illustrated here, the rotation is +45
o
.
[dwdocp33-070611-01.tif, 2, en_US]
Figure 6-56 Rotation of the Reference Voltage, Phase-Measuring Element
The rotated reference voltage defines the forward and reverse range, as shown in Figure 6-57. The forward
range is calculated as ±88
o
around the rotated reference voltage V
ref,rot
. If the short-circuit current vector is
located in this range, the device decides on the forward direction. In the mirrored range, the device decides on
the backward direction. In the intermediate range, the direction is undetermined.
[dwdocp34-240611-01.tif, 2, en_US]
Figure 6-57 Forward Characteristic of the Directional Function, Phase-Measuring Element
Direction Determination for Test Purposes
If you activate the binary input signal >Test of direction, the direction is determined and indicated even
without the current threshold being exceeded in one of the stages. The direction can be determined as soon
as current and voltage are greater than approx. 7 % of their secondary rated values.
Protection and Automation Functions
6.6 Directional Overcurrent Protection, Phases
SIPROTEC 5, Overcurrent Protection, Manual 435
C53000-G5040-C017-8, Edition 07.2017
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