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If the short-circuit is located before the capacitor, from the relay location (current transformer) in reverse direc-
tion, the peak displacement of the directional characteristics are shifted to the other direction (Figure 2-57c). A
correct determination of the direction is thus also ensured in this case.
Figure 2-57
Pickup and assignment to the polygons
Using the fault detection modes I, U/I or U/I/ϕ, the impedances that were calculated from the valid loops, are
assigned, after the pick-up, to the zone characteristics set for the distance protection. To avoid unstable signals
at the boundaries of a polygon, the characteristics have a hysteresis of approximately 5 % i.e. as soon as it has
been determined that the fault impedance lies within a polygon, the boundaries are increased by 5 % in all di-
rections. The loop information is also converted to phase-segregated information.
Using the impedance pickup, the calculated loop impedances are also assigned to the zone characteristics set
for the distance protection, but without consideration of an explicit fault detection scheme. The pickup range of
the distance protection is determined from the thresholds of the largest-set polygon taking into consideration
the respective direction. Here the loop information is also converted into phase-segregated indications.
For each zone „pickup" signals are generated and converted to phase information, e.g. „Dis Z1 L1" (internal
message) for zone Z1 and phase L1; this means that each phase and each zone is provided with separate
pickup information; the information is then processed in the zone logic and by additional functions (e.g. telepro-
tection logic, Section 2.7). The loop information is also converted to phase-segregated information. Another
condition for „pickup" of a zone is that the direction matches the direction configured for this zone (refer also to
Section 2.6). Furthermore the distance protection may not be blocked or switched off completely. Figure 2-58
shows these conditions.
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
Directional characteristics for series-compensated lines
Functions
2.5 Distance Protection
151
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