Siemens siprotec 7SA6, Manual

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Functions
6-58
7SA6 Manual
C53000-G1176-C156-2
A non-directional zone has no directional characteristic. The entire tripping area ap-
plies here.
Figure 6-31 Directional characteristic in the R–X–diagram
Characteristics of
the Directional
Measurement 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 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
S1
= E
1
/ I
1
. In the case of a fault located at F
1
(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 direc-
tion is reversed, the position of the directional characteristic changes abruptly (Figure
6-32c). The current flowing via the measuring point (current transformer) is now re-
versed
I
2
, and is determined by the source impedance Z
S2
+ Z
L
. When load is trans-
ferred across the line, the directional characteristic may additionally be rotated by the
load angle.
“forward”
“reverse”
R
jX
“non-directional”
*
)
“non-directional”
*
)
*
) also applies to “
Non-Directional
”
ca. 30
°
c
a
.
2
2
°