Siemens siprotec 7SD5 User Manual page 67

This parameter is valid for all protection functions of 7SD5 which are capable of single-
pole tripping. The default setting is with TRIP.
The difference is noticeable when multiple faults occur, which means faults that occur
at nearly the same time at different places in the system.
If, for example, two single-phase ground faults occur on different lines — these may
also be parallel lines — (Figure 2-5), the protective relays of all four line ends detect a
fault L1-L2-E, i.e. the pickup image is consistent with a two-phase earth fault. If single
pole tripping and reclosure is employed, it is therefore desirable that each line only
trips and recloses single pole. This is possible with setting 1155 3pole coupling =
with TRIP. In this manner each of the four relays at the four line ends recognizes
that single pole tripping for the fault on the respective line is required.
Figure 2-5
In some cases, however, three-pole tripping would be preferable for this fault scenario,
for example in the event that the double-circuit line is located in the vicinity of a large
generator unit (Figure 2-6). This is because the generator considers the two single-
phase to earth faults as one double-phase earth fault, with correspondingly high
dynamic load on the turbine shaft. With the setting 1155 3pole coupling = with
PICKUP, the two lines are switched off three-pole, since each device picks up as with
L1-L2-E, i.e. as with a multi-phase fault.
Figure 2-6
Address 1156 Trip2phFlt determines that the short-circuit protection functions
perform only a single-pole trip in case of isolated two-phase faults (clear of earth), pro-
vided that single-pole tripping is possible and permitted. This allows a single-pole au-
tomatic reclosure cycle for this kind of fault. Thereby you can specify whether the
leading phase (1pole leading Ø), or the lagging phase 1pole lagging Ø) is
tripped. The parameter is only available in versions with single-pole and three-pole
tripping. It can only be altered with DIGSI
ity is to be used, you have to bear in mind that the phase selection should be the same
throughout the entire network and that it must be the same at all ends of one line. More
information on the functions is also contained in Section 2.23.1 Pickup Logic for the
Entire Device. Usually the presetting 3pole is used here.
7SD5 Manual
C53000-G1176-C169-1
Multiple fault on a double-circuit line
Multiple fault on a double-circuit line next to a generator
®
under Additional Settings. If this possibil-
2.1 General
67