Siemens siprotec 7SA522 User Manual page 196

Functions
Characteristics of
the Directional
Measurement
6-48
A non-directional zone has no directional characteristic. The entire tripping region ap-
plies here.
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Figure 6-27 Directional characteristic in the R–X–diagram
The theoretical steady-state directional characteristic shown in Figure 6-27 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 6-28 shows the directional characteristic using quadrature or memorized volt-
age 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
28a), 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 6-28b). If the current direc-
tion is reversed, the position of the directional characteristic changes abruptly (Figure
6-28c). The current flowing via the measuring point (current transformer) is now re-
versed I , and is determined by the source impedance Z
2
ferred across the line, the directional characteristic may additionally be rotated by the
load angle.
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„forward"
„reverse"
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= E /I . In the case of a fault located at F
S1 1 1
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+ Z . When load is trans-
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7SA522 Manual
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