Determination of Direction
When determining the sensitive ground fault direction it is not the current value that is crucial, but the part of
the current which is perpendicular to a settable directional characteristic (axis of symmetry). As a prerequisite
for determining the direction, the displacement voltage V
part influencing the direction (active or reactive component).
The following figure illustrates an example using a complex vector diagram in which the displacement voltage
V
is the reference magnitude of the real axis. The active part 3I0
0
to the displacement voltage V
suitable for ground fault direction in grounded systems where quantity 3I
limit lines are perpendicular to axis 3I0
Figure 2-77
The directional limit lines may be rotated by a correction angle (address PHI CORRECTION) up to ± 45°. There-
fore, in grounded systems it is possible e.g. to increase sensitivity in the resistive-inductive range with a rotation
of –45°, or in case of electric machines in busbar connection in the resistive-capacitive range with a rotation of
+45° (see the following Figure). Furthermore the directional limit lines may be rotated by 90° to determine
ground faults and their direction in grounded systems.
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
and compared with setting value RELEASE DIRECT.. The example is therefore
0
.
real
Directional characteristic for cos–ϕ–measurement
2.12 Ground Fault Protection 64, 67N(s), 50N(s), 51N(s)
must be exceeded as well as a configurable current
0
of current 3I
is calculated with reference
real
0
· cos ϕ is relevant. The directional
0
Functions
221