ABB REL670 2.2 IEC - Page 163

Z Z
0 m0
Z Z
0 m0
Z
m0
A
B
C
99000039.vsd
I
0
I
0
DOCUMENT11520-IMG7100 V1 EN-US
Figure 62: 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 Z0-Z0m in parallel with
(Z0-Z0m)/Z0-Z0m+Z0m which is equal to equation
34.
2 2
0
0
om
E
Z Z
Z
Z
-
=
EQUATION2002 V4 EN-US (Equation 34)
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
35 and equation 36 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 35)
X X
X
R X
E
m
0 0
0
2
0
2
0
2
1= ⋅ −
+








DOCUMENT11520-IMG3503 V2 EN-US (Equation 36)
1MRK 506 369-UEN B Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 157
Application manual