ABB RELION REX640 Technical Manual page 1120

Section 5
Protection related functions
1114
section length, which differs from zero, to settings Line Len section A, Line Len
section B or Line Len section C in the order section A-> section B-> section C.
The impedance model with one line section is enabled by setting Line Len section A to
differ from zero. In this case, the impedance settings R1 line section A, X1 line section
A, R0 line section A and X0 line section A are used for the fault distance calculation and
for conversion from reactance to physical fault distance. This option should be used
only in the case of a homogeneous line, that is, when the protected feeder consists of
only one conductor type.
The impedance model with two line sections is enabled by setting both Line Len
section A and Line Len section B to 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 and X0 line section B 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 two types of conductors.
The impedance model with three line sections is enabled by setting Line Len section A,
Line Len section B and Line Len section C to 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 on the conversion of fault loop
reactance into physical fault distance is demonstrated in the example shown in
605 with a 10-km-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
1MRS759142 C
Figure
Figure 605.
REX640
Technical Manual