2 Functions
56
7SA522 Manual
C53000-G1176-C155-3
fault L1–L2–E, i.e. the pickup image is consistent with a two-phase 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 possible with setting SROH
FRXSOLQJ = ZLWK75,3. 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 2-5 Multiple fault on a double-circuit line
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 ground faults as one double-phase ground fault, with correspondingly high
dynamic load on the turbine shaft. With the setting SROHFRXSOLQJ = ZLWK
3,&.83, the two lines are switched off three-pole, since each device detects L1-L2-E
on pickup , i.e. a multi-phase fault.
Figure 2-6 Multiple fault on a double-circuit line next to a generator
Address 7ULSSK)OW 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 permitted. This allows a single-pole
automatic reclosure cycle for this kind of fault. Thereby you can specify whether the
leading phase (SROHOHDGLQJ), or the lagging phase SROHODJJLQJ) is
tripped. The parameter is only available in versions with single-pole and three-pole
tripping. This setting is only possible via DIGSI
®
at Additional Settings. If this possi-
bility 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 this functions is also contained in Subsection 2.20.1 Pickup
Logic for the Entire Device. Usually the presetting SROH is used here.
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