ABB RELION 670 SERIES Applications Manual page 174

Section 8
Impedance protection
168
Z
I
A
0
Z
B
DOCUMENT11520-IMG7100 V1 EN
Figure 64: Equivalent zero-sequence impedance circuit for the double-circuit line
that operates with one circuit disconnected and grounded at both ends
Here the equivalent zero sequence impedance is equal to Z0-Z0m in parallel with (Z0-
Z0m)/Z0-Z0m+Z0m which is equal to equation 37.
2 2
-
Z Z
0 om
=
Z
E
Z
0
EQUATION2002 V4 EN
The influence on the distance measurement can be a considerable overreach, which must
be considered when calculating the settings. All expressions below are proposed for
practical use. They assume the value of zero sequence, mutual resistance R0m equals to
zero. They consider only the zero-sequence, mutual reactance X0m. Calculate the
equivalent X0E and R0E zero-sequence parameters according to equation
equation 39 for each particular line section and use them for calculating the reach for the
underreaching zone.

X
0
m
R R 1
= ⋅  +
0 E 0
2

R
+
 0
DOCUMENT11520-IMG3502 V2 EN

X
0
X X 1
= ⋅  −
0 E 0
2

R
+
 0
DOCUMENT11520-IMG3503 V2 EN
Z
0 m0
Z m0
Z
0 m0
2


2

X
0 
2

m

2

X
0 
1MRK 506 369-UUS -
I
0
C
99000039.vsd
38
Line distance protection REL670 2.2 ANSI
Application manual
(Equation 37)
and
(Equation 38)
(Equation 39)