ABB RELION RET670 - Page 387

distance protection zone is reduced if, due to operating conditions, the equivalent zero
sequence impedance is set according to the conditions when the parallel system is out
of operation and grounded at both ends.
A
B
C
IEC09000255_1_en.vsd
I
0
I
0
Z
0m
Z
0
-
Z
0m
Z
0m
Z
0
-
IEC09000255 V1 EN-US
Figure 182: Equivalent zero-sequence impedance circuit for a double-circuit line
with one circuit disconnected and not grounded
The reduction of the reach is equal to equation
276.
( )
( )
( )
2
1 0
0
1 0
0
1 0
1
2
3
1
1
2 3
2
3
E f
m
U
f
f
Z Z R
Z
K
Z Z Z R
Z Z R
× × + +
= = -
× × + +
× × + +
EQUATION1284 V1 EN-US (Equation 276)
This means that the reach is reduced in reactive and resistive directions. If the real and
imaginary components of the constant A are equal to equation 277 and equation 278.
Re( ) 0 (2 1 0 3 ) 0 ( 0 2 1)A R R R Rf X X X= × × + + × - × + ×
EQUATION1285 V1 EN-US (Equation 277)
0 1 0 1 0 1 0
Im( ) (2 3 ) (2 )A X R R R R X X= × × + + × + × × +
EQUATION1286 V1 EN-US (Equation 278)
The real component of the KU factor is equal to equation
279.
Re
Re
Re Im
K
A X
A A
u
m
( )
= +
( )
⋅
( )




+
( )




1
0
2
2 2
EQUATION1287 V3 EN-US (Equation 279)
The imaginary component of the same factor is equal to equation 280.
1MRK 504 163-UUS A Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 381
Application manual