the feeder is modelled either with one or three line sections with
Table 815: Impedance settings
Parameter
Impedance model with one
section
Impedance model with three
sections
R1 line section A
0.660 Ω/pu
0.236 Ω/pu
X1 line section A
0.341 Ω/pu
0.276 Ω/pu
Line Len section A
10000 pu
4000 pu
R1 line section B
N/A
0.536 Ω/pu
X1 line section B
N/A
0.369 Ω/pu
Line Len section B
0.000 pu
3000 pu
R1 line section C
N/A
1.350 Ω/pu
X1 line section C
N/A
0.398 Ω/pu
Line Len section C
0.000 pu
3000 pu
illustrates the conversion error from measured fault loop reactance into
physical fault distance. The fault location is varied from 1 km to 10 km in 1 km
steps (marked with circles). An error of nearly eight per cent at maximum is created
by the conversion procedure when modeling a non-homogenous line with only one
section. By using impedance model with three line sections, there is no error in the
conversion.
The previous example assumed a short circuit fault and thus, only positive-
sequence impedance settings were used. The results, however, also apply for earth
faults.
Taps or spurs in the feeder
If the protected feeder consists of taps or spurs, the measured fault impedance
corresponds to several physical fault locations (For example, A or B in
). The actual fault location must be identified using additional information, for
example, short circuit current indicators placed on tapping points.
Figure 453: Fault on a distribution line with spurs
1MRS757644 H
Protection related functions
620 series
Technical Manual
851
