2.5 Distance Protection
127
7SD5 Manual
C53000-G1176-C169-1
ferred setting in the case of other distance protection relays in the power system
working with this start timing. Where grading of the delay times is especially important,
for instance if the fault location shifts from zone Z3 to zone Z2, the setting on Zone
Pickup should be chosen.
Angle of Inclination
of the Tripping
Charac teristics
The shape of the tripping characteristic is among other factors influenced by the incli-
nation angle Distance Angle (address 1540). Details about the tripping character-
istics can be found in Section 2.5.2 and 2.5.3). Usually, the line angle is set here, i.e.
the same value as in address 1105 Line Angle (Section 2.1.4.1). Irrespective of the
line angle it is, however, possible to select a different inclination angle of the tripping
characteristic.
Parallel Line Mea-
sured Value Correc-
tion (optional)
The mutual coupling between the two lines of a double-circuit configuration is only rel-
evant to the 7SD5 when it is applied on a double-circuit line and when it is intended to
implement parallel line compensation. A prerequisite 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 in address 1521 2Ph-E faults
(Phase-Phase-Earth fault detection). This parameter can only be altered with DIGSI
®
under Additional Settings. In most cases, Block leading Ø (blocking of the
leading phase, default setting) is favourable because the leading phase-earth loop
tends to overreach, especially in conjunction with large earth fault resistance. In
certain cases (fault resistance phase-phase larger than phase-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 as loop Ø-Ø loops only. This ensures
the most accuracy for two phase-to-earth faults. Ultimately it is possible to declare the
phase-to-earth loops as valid (setting 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 enables the user to detect all base points of a multiple earth fault. PHASE
PREF.2phe = All loops means that each earth fault point on a protected line is
switched off independent from the 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 consis-
tently valid for the remainder of the system.
If the earth fault detection threatens to pick up due to fault inception transients follow-
ing the occurrence of a single earth fault, the detection can be delayed via parameter
T3I0 1PHAS (address 1218). Usually the presetting (0.04 s) is sufficient. For large
resonant-earthed systems the time delay should be increased. Set parameter 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 any-
more. Double earth faults are, however, detected correctly and evaluated according to
the preference mode.
If a double earth fault occurs right after a single earth fault, it is detected and evaluated
according to the preference scheme. The already existing earth fault is detected by
www . ElectricalPartManuals . com
To Next Page
Loading...
Need help?
General