ABB RELION RET670 - Page 208

Z Z0
0 m
Z Z0
0
m
Z0
m
A
B
C
99000040.vsd
I
0
I
0
IEC99000040 V1 EN-US
Figure 77: 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
45.
( )
( )
( )
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 45)
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 46 and equation 47.
Re( ) 0 (2 1 0 3 ) 0 ( 0 2 1)A R R R Rf X X X= × × + + × - × + ×
EQUATION1285 V1 EN-US (Equation 46)
0 1 0 1 0 1 0
Im( ) (2 3 ) (2 )A X R R R R X X= × × + + × + × × +
EQUATION1286 V1 EN-US (Equation 47)
The real component of the KU factor is equal to equation 48.
Re
Re
Re Im
K
A X
A A
u
m
( )
= +
( )
⋅
( )




+
( )




1
0
2
2 2
EQUATION1287 V3 EN-US (Equation 48)
The imaginary component of the same factor is equal to equation 49.
Section 8 1MRK 504 163-UUS A
Impedance protection
202 Transformer protection RET670 2.2 ANSI
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