Siemens siprotec 7SA6, Manual

Page: 214 / 876

Functions
6-24
7SA6 Manual
C53000-G1176-C156-2
With the setting
with PICKUP
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 with-
in 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
with TRIP
, three-pole coupling of the trip
output (three-pole tripping) only occurs when more than one pole is tripped. 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 dur-
ing 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 ap-
plies 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 net-
work.
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 em-
ployed, it is therefore desirable that each line only trips and recloses single pole. This
is achieved by setting
1155 3pole coupling
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.
Figure 6-13
Multiple fault on a double-circuit line
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 dou-
ble-phase ground fault, with correspondingly high dynamic load on the turbine shaft.
With
1155 3pole coupling
set to
With fault detection
, 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