In
Figure 257
the feeder is modelled either with one or three line sections with
parameters given in
Table 537
.
Table 537: 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
Figure 257
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
Figure
258
). The actual fault location must be identified using additional information, for
example, short circuit current indicators placed on tapping points.
Figure 258: Fault on a distribution line with spurs
Protection related functions
1MRS758755 C
512 REC615 & RER615
Technical Manual
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