Functions
6-40 7SA522 Manual
C53000-G1176-C119-2
breaker. The setting 3LFNXS implies that the non-delayed tripping following line ener-
gization is activated for all recognized faults in any zone (i.e. with general fault detec-
tion of the distance protection).
Load Area On long heavily loaded lines, the risk of encroachment of the load impedance into the
tripping characteristic of the distance protection may exist. To exclude the risk of un-
wanted fault detection by the distance protection during heavy load flow, a load trap-
ezoid characteristic may be set for tripping characteristics with a large R-reach, which
excludes such unwanted fault detection by overload. This load area is considered in
the description of the tripping characteristics (refer to Figure 6-25, Sub-section 6.2.3.1,
and Figure 6-31, Sub-section 6.2.4.1).
The R–value 5ORDG( (address ) and 5ORDG (address )
must be set somewhat (approx. 10 %) smaller than the minimum load impedance
which may occur. The minimum load impedance results when the maximum load cur-
rent and minimum operating voltage exist.
Calculation example:
110 kV overhead line 150 mm
2
with the following data:
maximum transferrable load
P
max
= 100 MVA corresponding to
I
max
=525A
minimum operating voltage
U
min
=0.9U
N
current transformer 600 A/5 A
voltage transformer 110 kV/0.1 kV
The resulting minimum load impedance is therefore:
When applying the settings with a personal computer and DIGSI
®
4 these values may
be entered as primary values. The conversion to secondary values is
when applying a security margin of 10 % the following is set:
primary: 5ORDG( = Ω or
secondary: 5ORDG( = Ω.
R
Load prim
U
min
3
I
L max
⋅
-------------------------
0.9 110 kV
⋅
3525A
⋅
--------------------------
108.87
Ω== =
R
Load sec
N
CT
N
VT
----------
R
Load prim
⋅
600 A/5 A
110kV/0.1kV
--------------------------------------
108.87
Ω⋅
11.88
Ω
== =
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