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-US
Figure 224: Voltage inversion in series compensated network due to fault current infeed
Voltage at the B bus (as shown in figure
) 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-US
(Equation 389)
Further development of equation
gives the following expressions:
U
jI
X
I
I
X
X
B
B
LB
A
B
LF
C
=
⋅
+
+
⋅
−
(
)
1
EQUATION1912 V2 EN-US
(Equation 390)
(
)
0
1
=
=
+
+
LB
C
B
LF
A
B
X
X U
X
I
I
EQUATION1913 V1 EN-US
(Equation 391)
Equation
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
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, especially if on one hand the compensated line
is very long with high degree of compensation, and the adjacent lines are, on the other hand,
relatively short.
Extensive system studies are necessary before final decision is made on implementation and
location of series capacitors in network. It requires to correctly estimate their influence on
performances of (especially) existing distance IEDs. It is possible that the costs for number of
protective devices, which should be replaced by more appropriate ones due to the effect of
applied series compensation, influences the future position of series capacitors in power
network.
Possibilities for voltage inversion at remote buses should not be studied for short circuits with
zero fault resistance only. It is necessary to consider cases with higher fault resistances, for
which spark gaps or MOVs on series capacitors will not conduct at all. At the same time this
Section 7
1MRK 505 343-UEN B
Impedance protection
346
Application manual
Содержание Relion 670 series
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