ABB REG670 Applications Manual page 230

Section 8
Impedance protection
224
-
Z Z
I 0 0m
A
0
-
Z
Z
0
B 0m
IEC09000252 V1 EN
Figure 102: Equivalent zero sequence impedance circuit for the double-circuit
line that operates with one circuit disconnected and earthed at both
ends
Here the equivalent zero-sequence impedance is equal to Z
Z )/Z -Z +Z which is equal to equation 48.
0m 0 0m 0m
2 2
-
Z Z
0 om
=
Z
E
Z
0
EQUATION2002 V4 EN
The influence on the distance measurement will be a considerable overreach, which
must be considered when calculating the settings. It is recommended to use a separate
setting group for this operation condition since it will reduce the reach considerably
when the line is in operation.
All expressions below are proposed for practical use. They assume the value of zero
sequence, mutual resistance R
mutual reactance X . Calculate the equivalent X
0m
parameters according to equation
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
= ⋅  1 −
X X
0 E 0

2
+
R

0
DOCUMENT11520-IMG3503 V2 EN
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Z
0m
I
0
C
IEC09000252_1_en.vsd
equals to zero. They consider only the zero sequence,
0m
49 and equation
2


2 
X

0
2

m


2
X

0
1MRK 502 071-UEN -
-Z m in parallel with (Z
0 0
and R zero sequence
0E 0E
50 for each particular line section
Application manual
-
0
(Equation 94)
(Equation 95)
(Equation 96)