Functions
2.5 Distance Protection
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
134
Parallel line measured value correction (optional)
The mutual coupling between the two lines of a double-circuit configuration is only relevant to the 7SD5 when
it is applied on a double-circuit line and when it is intended to implement parallel line compensation. A prereq-
uisite is that the earth current of the parallel line is connected to the
I
4
measuring input of the device and this
is entered in the configuration settings. In this case, address
1515
Paral.Line Comp
has to be set to
YES
(default setting).
The coupling factors were already set as part of the general protection data (Section 2.1.4.1), as was the reach
of the parallel line compensation.
Double earth faults in effectively earthed systems
The loop selection for double earth faults is set at address
1521
2Ph-E faults
(Phase-to-Phase Earth fault
detection). This parameter can only be altered in DIGSI at
Display Additional Settings
. In most cases,
Block
leading Ø
(blocking of the leading phase, default setting) is favourable because the leading phase-to-earth
loop tends to overreach, especially in conjunction with large earth fault resistance. In certain cases (fault resis-
tance phase-to-phase larger than phase-to-earth) the setting
Block lagging Ø
(blocking of the lagging
phase) may be more favourable. The evaluation of all affected loops with the setting
All loops
allows a
maximum degree of redundancy. It is also possible to evaluate
Ø-Ø loops only
. This ensures the highest
accuracy for 2-phase-to-earth faults. Finally it is possible to declare only the phase-to-earth loops as valid (set-
ting
Ø-E loops only
).
Double earth faults in non-earthed systems
In isolated or resonant-earthed systems it must be guaranteed that the preference for double earth faults in
whole galvanically-connected systems is consistent. The double earth fault preference is set in address
1520
PHASE PREF.2phe
.
7SD5 also enables the user to detect all base points of a multiple earth fault.
PHASE PREF.2phe
=
All loops
means that each earth fault base point is switched off independant of any preference. It can also be combined
with a different preference. For a transformer feeder, for example, any base point can be switched off following
occurrence of a double earth fault, whereas
L1 (L3) ACYCLIC
is consistently valid for the remainder of the
system.
If the earth fault detection threatens to pick up due to fault inception transients following the occurrence of a
single earth fault, the detection can be delayed via parameter
T3I0 1PHAS
(address
1218
). Usually the pre-
setting (0.04 s) is sufficient. For large resonant-earthed systems the time delay should be increased. Set pa-
rameter
T3I0 1PHAS
to
∞
if the earth current threshold can also be exceeded during steady-state conditions.
Then, even with high earth current, no single-phase pickup is possible anymore. Double earth faults are, how-
ever, detected correctly and evaluated according to the preference mode.
Note
When testing a single earth fault by means of a test equipment, it must be made sure that the phase-to-phase
voltages fulfill the symmetry criterion.
