Siemens SIPROTEC 4 7UT6 Series Manual page 131

[erddiff-ausloesekennlinie-020926-rei, 1, en_GB]
Figure 2-62
It was assumed in the above examples that the currents 3Ι
faults which is only true for the primary measured quantities. Current transformer saturation may cause phase
shifting between the fundamental waves of the secondary currents which reduces the restraint quantity. If the
phase displacement φ(3Ι
method of direction determination by use of the vectorial sum and difference comparison.
[erddiff-stabgroesse-020926-rei, 1, en_GB]
Figure 2-63
The restraint quantity can be influenced by means of a factor k. This factor has a certain relationship to the
limit angle φ
Limit
This limit angle determines for which phase displacement between 3Ι
grows to ∞, i.e. no pickup occurs. In7UT6x is equal to 4.
The restraint quantity Ι
tripping effect quantity Ι
SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016
Tripping characteristic of the restricted earth fault protection depending on the earth current
ratio 3Ι "/3Ι ' (both currents in phase + or counter-phase –); Ι
0 0
current
"; 3Ι ') = 90° then the restraint quantity is zero. This corresponds to the conventional
0 0
Phasor diagram of the restraint quantity during internal fault
.
in the first example above is quadrupled once more; it becomes thus 8 times the
stab
.
Trip
2.3 Restricted Earth Fault Protection
≥ Einstellwert; Ι
REF
" and 3Ι ' are in counter-phase for external earth
0 0
" and 3Ι ' the pickup value for 3Ι
0 0
Functions
= tripping
Trip
" = 3Ι '
0 0
131