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If, for example, two single-phase earth faults occur on different lines — these may also be parallel lines —
(Figure 2-5), the protection relays detect the fault type on all four line ends L1-L2-E, i.e. the pickup image cor-
responds to 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. Each of the four devices detects a single-pole internal fault and can thus trip single-pole.
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 ground faults as one double-phase ground fault, with corresponding-
ly 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 ground), provided that single-pole tripping is possible and per-
mitted. This allows a single-pole reclose cycle for this kind of fault. 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. This parameter can only be altered using DIGSI at Addi-
tional Settings. If this possibility 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 2.25.1 Pickup Logic of the Entire Device. The presetting 3pole is
usually used.
Line Sections
The line section parameters 6001 S1: Line angle to 6012 S1: angle K0, 6021 S2: Line angle to
6032 S2: angle K0 and 6041 S3: Line angle to 6052 S3: angle K0 are reserved for the double-
ended fault locator. They are used for parameterization of a line with different sections (overhead line - cable
sections). See Section 2.21 for more details.
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
Multiple fault on a double-circuit line
Multiple fault on a double-circuit line next to a generator
Functions
2.1 General
67
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