The limit angle is φ
Limit
= 100°. This means, no tripping is possible anymore for a phase displacement
φ(3Ι
0
"; 3Ι
0
') ≥ 100°
Figure 2-64 shows the tripping characteristics of the restricted earth fault protection dependent of the phase
displacement between 3
Ι
0
" and 3Ι
0
', for a constant infeed ratio |3Ι
0
"| = |3Ι
0
'|.
[erddiff-ausloesekennlinie-phasenw-020926-rei, 1, en_GB]
Figure 2-64 Tripping characteristic of the restricted earth fault protection depending on the phase
displacement between 3Ι
0
” and 3Ι
0
' bei 3Ι
0
” = 3Ι
0
' (180
o
= external fault)
It is possible to increase the tripping value in the tripping area proportional to the arithmetic sum of all
currents, i.e. with the sum of the magnitudes
IrestREF=
or
IrestRE2=
Σ | Ι | = | Ι
L1
| + | Ι
L2
| + | Ι
L3
| + | Ι
Z
|
(Figure 2-65). The slope of this restraint characteristic can be set.
Pickup
Normally, a differential protection does not need a “pickup”, since the condition for a fault detection is iden-
tical to the trip condition. As with all protective functions the earth fault differential protection has a pickup
that displays a precondition for tripping and defines the fault inception instant for a number or further activi-
ties.
As soon as the fundamental wave of the differential current exceeds 85 % of the pickup value, fault detection
is indicated. In this aspect, the differential current is represented by the sum of all in-flowing currents.
[erddiff-ansprechwerterh-020926-rei, 1, en_GB]
Figure 2-65 Increasing the Pickup Value
Functions
2.3 Restricted Earth Fault Protection
132 SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016
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