ABB RELION REX640 Technical Manual page 1212

Protection related functions
physical fault distance conversion done in the protection relay, especially in cases
where the line impedance non-homogeneity is severe. Each section is enabled by
entering a section length, which differs from zero, to settings
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
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
section A and Line Len section B to differ from zero. In this case the impedance
settings
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
A , Line Len section B and Line Len section C to differ from zero. In this case, the
impedance settings
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
Figure 692
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
1212
R1 line section A , X1 line section A , R0 line section A , X0 line section A , R1
R1 line section A , X1 line section A , R0 line section A , X0 line
with a 10-km-long feeder with three line types. The total line impedance
1MRS759142 F
Line Len section A ,
Line Len section
Line Len
Line Len section
Figure 692
.
REX640
Technical Manual