Siemens siprotec 7SD5 User Manual page 142

2 Functions
always smaller than the series reactance — does not cause the apparent direction re-
versal (Figure 2-46b).
If the short-circuit is located before the capacitor, from the relay location (current trans-
former) in reverse direction, the zeniths of the directional characteristics are shifted to
the other direction (Figure 2-46c). A correct determination of the direction is thus also
ensured in this case.
Figure 2-46
Pickup and Assign- Using the fault detection modes I, U/I or U/I/ϕ, the impedances that were calculated
ment to the Poly- from the valid loops, are assigned, after the pickup, to the zone characteristics set for
gons 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 de-
termined that the fault impedance lies within a polygon, the boundaries are increased
by 5 % in all directions. 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 a query 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 faulted phase indication.
„Pickup" signals are generated for each zone and converted into phase information,
e.g. „Dis. L1L1" (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. teleprotection logic,
Section 2.7). The loop information is also converted to phase segregated information.
Further conditions for „pickup" of a zone are that the direction corresponds to the set
direction for the zone, and that the zone is not blocked by the power swing blocking
(refer to Section 2.6). Furthermore the distance protection may not be blocked or
switched off completely. Figure 2-47 shows these conditions.
142
Determination of direction in case of series-compensated lines
7SD5 Manual
C53000-G1176-C169-1