Siemens SIPROTEC, Руководство пользователя, Страница: 270 / 776

Functions
2.10 Restricted Earth Fault Protection (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
270
Figure 2-137 Tripping characteristic of the restricted earth fault protection in dependence on the phase
displacement between 3
I
0
” and 3
I
0
' at 3
I
0
” = 3
I
0
' (180
o
= external fault)
It is also possible to increase the tripping value proportional to the current sum. In this case the pickup value is
stabilized with the arithmetic sum of all currents, i.e. with
„IrestREF=“
Σ
| I | = | I
L1
| + | I
L2
| + | I
L3
| + | I
4
|.
The slope of the characteristic curve can be adjusted.
Pickup
Normally, a differential protection does not need a „pickup“, since the fault detection and the trip condition are
identical. But the earth fault differential protection, like all protection functions, has a pickup function which is
required for tripping and serves as the starting point for a number of further activities.
As soon as the fundamental component of the differential current reaches approximately 85 % of the pickup
value, pickup is recognized. In this aspect, the differential current is represented by the sum of all in-flowing
currents.
Figure 2-138 Increasing the pickup value