Siemens siprotec 7SA6 User Manual page 205

7SA6 Manual
C53000-G1176-C133-1
relevant with one- and three-pole tripping and therefore only available in this version.
Additional information can be found in Section 6.20.3 fault detection logic of the
device.
With the setting ZLWK 3,&.83 every pickup in more than one phase leads to three-
pole coupling of the trip outputs, even if only a single-phase earth fault is situated
within the tripping area, and further faults only affect the higher zones, or are located
in the reverse direction. Even if a single-phase trip command has already been issued,
each further fault detection will lead to three-pole coupling of the trip outputs.
If, on the other hand, this address is set to ZLWK 75,3, three-pole coupling of the trip
output (three-pole tripping) only occurs when more than one pole is trip ped. Therefore
if a single-phase fault is located within the zone of tripping, and a further arbitrary fault
is outside the tripping zone, single-phase tripping is possible. Even a further fault
during the single-pole tripping will only cause three-pole coupling if it is located within
the tripping zone.
This parameter is only available in the single- and three-pole tripping version. It
applies to all protection functions of the 7SA6, which can trip single-pole.
The difference made by this parameter becomes apparent when multiple faults are
cleared, i.e. faults occurring almost simultaneously at different locations in the
network.
If, as shown in the example (Figure 6-13), two single phase to ground faults occur on
different lines – in this example parallel lines – the protection relays on the two faulted
lines, at all four line ends, pick up. In this example, all four relays detect a L1-L2-E
fault, in other words a two phase to ground fault. However, each individual line is only
subjected to a single phase to ground fault. If single pole tripping and reclosure is
employed, it is therefore desirable that each line only trips and recloses single pole.
This is achieved by setting  SROH FRXSOLQJ to with TRIP . In this manner
each of the four relays at the four line ends recognises that single pole tripping for the
fault on the respective line is required.
Multiple fault on a double-circuit line
Figure 6-13
In some cases, however, a three-pole trip would be preferable for this fault scenario,
e.g. if the double-circuit line is located next to a large generator unit (Figure 6-14). This
is because the generator considers the two single-phase to ground faults as one
double-phase ground fault, with correspondingly high dynamic load on the turbine
shaft. With  SROH FRXSOLQJ set to :LWK IDXOW GHWHFWLRQ, 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.
L1–E
L2–E
Functions
6-23