case of a non-homogeneous line when the protected feeder consists of two types of
conductors.
Impedance model with three line sections is enabled by setting Line Len section A, Line
Len section B and Line Len section C all differ from zero. In this case the impedance
settings R1 line section A, X1 line section A, R0 line section A, X0 line section A, R1 line
section B, X1 line section B, R0 line section B, X0 line section B, R1 line section C, X1 line
section C, R0 line section C and X0 line section C are used for the fault distance calculation
and for conversion from reactance to physical fault distance. This option should be used
in the case of a non-homogeneous line when the protected feeder consists of more than two
types of conductors.
The effect of line impedance non-homogeneity in the conversion of fault loop reactance
into physical fault distance is demonstrated in example shown in
Figure 419 with 10
kilometer long feeder with three line types. The total line impedance for the 10 km line is
R1 = 6.602 Ω (0.660 Ω/km) and X1 = 3.405 Ω (0.341 Ω/km), consisting of the following
sections and impedance values.
• 4 km of PAS 150 (R1 = 0.236 Ω/km, X1 = 0.276 Ω/km)
• 3 km of Al/Fe 54/9 Raven (R1 = 0.536 Ω/km, X1 = 0.369 Ω/km)
• 3 km of Al/Fe 21/4 Swan (R1 = 1.350 Ω/km, X1 = 0.398 Ω/km)
The non-homogeneity of feeder impedance can be illustrated by drawing the protected
feeder in RX-diagram (in the impedance plane), as shown in
Figure 419.
GUID-AEA0E874-C871-4C90-82ED-3AFE41D28145 V2 EN
Figure 419: 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 419 the feeder is modelled either with one or three line sections with parameters
given in Table 715.
Section 5 1MAC059074-MB A
Protection related functions
820 615 series ANSI
Technical Manual
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