Siemens siprotec 7SA6 User Manual page 239

Characteristics of
the Directional
Measurement
7SA6 Manual
C53000-G1176-C133-1
A non-directional zone has no directional characteristic. The entire tripping area
applies here.
"non-directional"
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) also applies to "
Figure 6-31 Directional characteristic in the R–X–diagram
The theoretical steady-state directional characteristic shown in Figure 6-31 applies to
faulted loop voltages. In the case of quadrature voltages or memorized voltage, the
position of the directional characteristic is dependant on both the source impedance
as well as the load transferred across the line prior to fault inception.
Figure 6-32 shows the directional characteristic using quadrature or memorized
voltage as well as taking the source impedance into account (no load transfer). As
these voltages are equal to the corresponding generator e.m.f. E and they do not
change after fault inception, the directional characteristic is shifted in the impedance
diagram by the source impedance Z
(Figure 6-32a), the short-circuit is located in the forward direction, and the source
impedance in the reverse direction. For all fault locations, right up to the device
location (current transformers), a definite "forward" decision is made (Figure 6-32b). If
the current direction is reversed, the position of the directional characteristic changes
abruptly (Figure 6-32c). The current flowing via the measuring point (current
transformer) is now reversed I
When load is transferred across the line, the directional characteristic may additionally
be rotated by the load angle.
jX
*
)
"forward"
"reverse"
"
= E /I . In the case of a fault located at F
S1 1 1
, and is determined by the source impedance Z
2
*
"non-directional" )
Functions
R
1
+ Z .
S2 L
6-57