Siemens siprotec 7SD5 User Manual page 140

2 Functions
Figure 2-43
Since each zone can be set to Forward, Reverse or Non-Directional, different
(centrically mirrored) directional characteristics are available for Forward and
Reverse. A non-directional zone has no directional characteristic. The entire tripping
region applies here.
Characteristics of The theoretical steady-state directional characteristic shown in Figure 2-43 applies to
the Directional faulted loop voltages. In the case of quadrature voltages or memorized voltage, the
Measurement position of the directional characteristic is dependent on both the source impedance
as well as the load transferred across the line prior to fault inception.
Figure 2-44 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 voltage E and they do not
change after fault inception, the directional characteristic is shifted in the impedance
diagram by the source impedance Z
the short-circuit location is in the forward direction and the source impedance is in the
reverse direction. For all fault locations, right up to the device location (current trans-
formers), a definite Forward decision is made (Figure 2-44b). If the current direction
is reversed, the position of the directional characteristic changes abruptly (Figure 2-
44c). A reversed current I
which is determined by the source impedance Z
across the line, the directional characteristic may additionally be rotated by the load
angle.
140
Directional characteristic in the R-X-diagram
= E
S1
now flows via the measuring location (current transformer)
2
/I . For the fault location F
1 1
+ Z . When load is transferred
S2 L
C53000-G1176-C169-1
(Figure 2-44a)
1
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