[dwcosphi-171012-01.tif, 3, en_US]
Figure 6-127 Direction-Characteristic Curve with Cos φ Measurement
The zero-sequence voltage V0 is basically the reference value for the real axis. The axis of symmetry of the
direction-characteristic curve coincides with the 3I0reactive axis for this example. For the direction determina-
tion, basically the portion of the current vertical to the set direction-characteristic curve (= axis of symmetry) is
decisive (3I0 dir.). In this example, this is the active portion 3l0active of the current 3l0. The current 3l0dir.
(here = 3I0active) is calculated and compared with the setting value Min.polar.3I0> for dir.det.. If
the current 3I0 dir. exceeds the positive setting value, the direction is forward. If the current 3I0 dir. 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 the figure. 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 rotation of +45°.
Protection and Automation Functions
6.15 Sensitive Ground-Fault Detection
SIPROTEC 5, Overcurrent Protection, Manual 571
C53000-G5040-C017-8, Edition 07.2017
To Next Page
Loading...
