Table 715: 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 419 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 ground 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 420). The actual fault
location must be identified using additional information, for example, short circuit current
indicators placed on tapping points.
1MAC059074-MB A Section 5
Protection related functions
615 series ANSI 821
Technical Manual
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