Functions
6-557SA6 Manual
C53000-G1176-C133-1
The R-reach may be set separately for the phase–phase faults and the phase–earth
faults to achieve a larger fault resistance coverage for earth faults if this is desired.
For the first zone an additional tilt α exists, which may be used to prevent overreach
resulting from angle variance and/or two ended infeed to short-circuits with fault
resistance. For Z1B and the higher zones this tilt does not exist.
Figure 6-29 Polygonal characteristic
Direction
Determination
For each loop an impedance vector is also used to determine the direction of the short-
circuit. Usually similar to the distance calculation, Z
L
is used. However, depending on
the “quality” of the measured values, different computation techniques are used.
Immediately after fault inception, the short circuit voltage is disturbed by transients.
The voltage memorized prior to fault inception is therefore used in this situation. If the
steady-state short-circuit voltage (during a close-in fault) is even too small for direction
determination, an unfaulted voltage is used. This voltage is in theory quadrilateral to
the actual short-circuit voltage for both phase–earth loops as well as for phase–phase
loops (refer to Figure 6-30). This is taken into account when computing the direction
vector by means of a 90°–rotation. In Table 6-9 the allocation of the measured values
to the six fault loops for the determination of the fault direction is shown.
Fo
r
w
ar
d
α
ϕ
R
e
v
e
rs
e
Re
v
e
r
s
e
F
o
r
w
a
r
d
Line Characteristic
Load Area
Load Area
R
X
Z5
Z4
Z2
Z1B
Z3
Z1
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