The zero-sequence voltage V0 is generally the reference value for the real axis and is identical to the G0 axis.
The axis of symmetry of the direction-characteristic curve coincides with the B0 (reactive) axis for this
example. For the direction determination, the component of the admittance perpendicular to the set direc-
tion-characteristic curve (= axis of symmetry) is decisive G0dir (=Y0dir). In this example, this is the active
component G0active of the admittance Y0. The conductance G0dir. (here = G0active) is calculated and
compared with the setting value Polarized G0/B0 threshold. If the conductance G0dir. exceeds the
positive setting value, the direction is forward. If the conductance G0dir. exceeds the negative setting value,
the direction is backward. In the range in between, the direction is undetermined.
With the α1 reduction dir. area and α2 reduction dir. area parameters, you can limit the
forward and backward ranges as shown in Figure 6-138. With this, the direction determination is secured in
case of high currents in the direction of the axis of symmetry.
The symmetry axis can be turned via a correction angle (φ correction parameter) in a range of ±45.
Through this, it is possible, for example, to attain the greatest sensitivity in grounded systems in the resistive-
inductive range with a -45° turn. In the case of electric machines in busbar connection on the isolated system,
the greatest sensitivity in the resistive-capacitive range can be attained with a turn of +45° (see following
figure).
[DwY0meas-171012-01, 1, en_US]
Figure 6-138
Turning the Direction-Characteristic Curves with G0 Measurement with Angle Correction
If you set the Dir. measuring method parameter to B0 and the φ correction parameter to 0, the axis
of symmetry of the direction-characteristic curve coincides with the G0 and V0 axes. Since the component of
the admittance Y0 perpendicular to the direction-characteristic curve (= axis of symmetry) is decisive (B0dir.
(=Y0dir.)), here, the susceptance B0 (reactive) is used in the direction determination. If the susceptance B0dir.
(B0reactive) exceeds the negative setting value Polarized G0/B0 threshold, the direction is forward. If
the susceptance B0dir. exceeds the positive setting value, the direction is backward. In the range in between,
the direction is undetermined.
This direction measurement thus is appropriate for the determination of ground-fault direction in isolated
systems.
Protection and Automation Functions
6.15 Sensitive Ground-Fault Detection
594 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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