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Section 8
Impedance protection
8.13.3.4
384
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.
U
A
Z
SA
E
~
A
Z
LA
A
U
B
Z
E
SB
~
B
Z
LB
B
IEC06000616 V1 EN-US
Figure 208:
Voltage inversion in series compensated network due to fault
current infeed
Voltage at the B bus (as shown in figure 208) is calculated for the loss-less system
according to the equation below.
(
U
=
U
+
I
⋅
jX
=
B
B
D
LB
EQUATION1911 V2 EN-US
Further development of equation
I
U
=
jI
⋅
X
+
1
+
B
B
LB
I
EQUATION1912 V2 EN-US
X
(
)
=
=
X
U
0
LB
C
B
I
+
1
A
I
B
EQUATION1913 V1 EN-US
Equation
367
indicates the fact that the infeed current I
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
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
between D bus and the fault becomes equal to zero, if the
LF
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
U
D
I
A
-jX
C
I
F
Z
LF
I
B
D
en06000616.vsd
)
(
)
I
+
I
⋅
j X
−
X
A
B
LF
C
366
gives the following expressions:
A
(
)
⋅
X
−
X
LF
C
B
+
X
LF
368
indicates the deepness of the network to which it
1MRK 506 369-UEN B
GUID-DA1DBB5B-0AFD-49F4-87C7-0E8AB5006051 v2
F
+
I
⋅
jX
B
LB
increases the apparent
A
Line distance protection REL670 2.2 IEC
Application manual
(Equation 366)
(Equation 367)
(Equation 368)
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