ABB Relion REG670, Applications Manual

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8.3.3.4 Impact of series compensation on protective IED of adjacent lines
Voltage inversion is not characteristic for the buses and IED points closest to the series
compensated line only. It can spread also deeper into the network and this way
influences the selection of protection devices (mostly distance IEDs) on remote ends
of lines adjacent to the series compensated circuit, and sometimes even deeper in the
network.
en06000616.vsd
~
~
F
B
E
B
E
A
Z
SA
U
A
A
Z
LA
I
A
U
D
D
Z
LB
I
B
U
B
Z
SB
Z
LF
I
F
-jX
C
IEC06000616 V1 EN
Figure 119: Voltage inversion in series compensated network due to fault current
infeed
Voltage at the B bus (as shown in figure 119 ) is calculated for the loss-less system
according to the equation below.
U U I jX I I j X X I jX
B D
B
LB
A B
LF C
B
LB
= + ⋅ = +
( )
⋅ −
( )
+ ⋅
EQUATION1911 V2 EN
(Equation 113)
Further development of equation 113 gives the following expressions:
U jI X
I
I
X X
B
B LB
A
B
LF C
= ⋅ + +





 ⋅
−
( )








1
EQUATION1912 V2 EN
(Equation 114)
( )
0
1
= = +
+
LB
C B LF
A
B
X
X U X
I
I
EQUATION1913 V1 EN
(Equation 115)
Equation 114 indicates the fact that the infeed current I
A
increases the apparent value
of capacitive reactance in system: bigger the infeed of fault current, bigger the
apparent series capacitor in a complete series compensated network. It is possible to
say that equation
115 indicates the deepness of the network to which it will feel the
influence of series compensation through the effect of voltage inversion.
It is also obvious that the position of series capacitor on compensated line influences
in great extent the deepness of voltage inversion in adjacent system. Line impedance
X
LF
between D bus and the fault becomes equal to zero, if the capacitor is installed
near the bus and the fault appears just behind the capacitor. This may cause the
phenomenon of voltage inversion to be expanded very deep into the adjacent network,
1MRK 502 071-UEN -
Section 8
Impedance protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 239
Application manual