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 89: 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
48.
( )
( )
( )
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 48)
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 49 and equation 50.
Re( ) 0 (2 1 0 3 ) 0 ( 0 2 1)A R R R Rf X X X= × × + + × - × + ×
EQUATION1285 V1 EN-US (Equation 49)
0 1 0 1 0 1 0
Im( ) (2 3 ) (2 )A X R R R R X X= × × + + × + × × +
EQUATION1286 V1 EN-US (Equation 50)
The real component of the KU factor is equal to equation
51.
Re
Re
Re Im
K
A X
A A
u
m
( )
= +
( )
⋅
( )
+
( )
1
0
2
2 2
EQUATION1287 V3 EN-US (Equation 51)
The imaginary component of the same factor is equal to equation 52.
1MRK 502 071-UUS A Section 8
Impedance protection
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062 213
Application manual
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