ABB RELION RET670, Applications Manual

Page: 307 / 1016

When the parallel line is out of service and grounded at both ends on the bus bar side
of the line CT so that zero sequence current can flow on the parallel line, the equivalent
zero sequence circuit of the parallel lines will be according to figure
143 .
Z Z
0 m0
Z Z
0 m0
Zm0
A
B
C
99000039.vsd
I
0
I
0
DOCUMENT11520-IMG7100 V1 EN-US
Figure 144: 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
165 .
2 2
0
0
om
E
Z Z
Z
Z
-
=
EQUATION2002 V4 EN-US
(Equation 165)
The influence on the distance measurement will be a considerable overreach, which
must be considered when calculating the settings. It is a recommendation to use a
separate setting group for this operation condition since it will reduce the reach
considerable when the line is in operation. 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
166 and
equation 167 for each particular line section and use them for calculating the reach for
the underreaching zone.
R R
X
R X
E
m
0 0
0
2
0
2
0
2
1
= ⋅ +
+








DOCUMENT11520-IMG3502 V2 EN-US
(Equation 166)
X X
X
R X
E
m
0 0
0
2
0
2
0
2
1
= ⋅ −
+








DOCUMENT11520-IMG3503 V2 EN-US
(Equation 167)
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 301
Application manual