ABB RELION 620 Series Technical Manual page 859

1MRS757644 F
620 series
Technical Manual
The non-homogeneity of feeder impedance can be illustrated by drawing the protected
feeder in RX-diagram (in the impedance plane), as shown in
GUID-AEA0E874-C871-4C90-82ED-3AFE41D28145 V2 EN
Figure 442: Example impedance diagram of an electrically non-homogeneous
feeder (left), and the resulting error in fault distance if the measured
fault loop reactance is converted into physical fault distance by using
only one line section parameters (right).
In Figure 442 the feeder is modelled either with one or three line sections with
parameters given in Table
Table 815: Impedance settings
Parameter
R1 line section A
X1 line section A
Line Len section A
R1 line section B
X1 line section B
Line Len section B
R1 line section C
X1 line section C
Line Len section C
Figure 442 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.
Protection related functions
815.
Impedance model with one
section
0.660 Ω/pu
0.341 Ω/pu
10000 pu
N/A
N/A
0.000 pu
N/A
N/A
0.000 pu
Section 5
Figure 442.
Impedance model with three
sections
0.236 Ω/pu
0.276 Ω/pu
4000 pu
0.536 Ω/pu
0.369 Ω/pu
3000 pu
1.350 Ω/pu
0.398 Ω/pu
3000 pu
853