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It is obvious that voltage U
M
will lead the fault current I
F
as long as X
L1
> X
C
. This situation
corresponds, from the directionality point of view, to fault conditions on line without series
capacitor. Voltage U
M
in IED point will lag the fault current I
F
in case when:
L1
C
S
L1
X
X
X
X
<
<
+
EQUATION1902 V1 EN-US
(Equation 71)
Where
X
S
is the source impedance behind the IED
The IED point voltage inverses its direction due to presence of series capacitor and its
dimension. It is a common practice to call this phenomenon voltage inversion. Its
consequences on operation of different protections in series compensated networks depend
on their operating principle. The most known effect has voltage inversion on directional
measurement of distance IEDs (see chapter
for more details), which
must for this reason comprise special measures against this phenomenon.
There will be no voltage inversion phenomena for reverse faults in system with VTs located on
the bus side of series capacitor. The allocation of VTs to the line side does not eliminate the
phenomenon, because it appears again for faults on the bus side of IED point.
Current inversion
SEMOD168320-206 v2
Figure
presents part of a series compensated line with corresponding equivalent voltage
source. It is generally anticipated that fault current I
F
flows on non-compensated lines from
power source towards the fault F on the protected line. Series capacitor may change the
situation.
en06000607.vsd
~
Z<
X
S
X
L1
I
F
U
U
M
Source
Fault voltage
Pre -fault voltage
X
C
Source voltage
U’
M
With bypassed
capacitor
With inserted
capacitor
F
IEC06000607 V1 EN-US
Figure 96: Current inversion on series compensated line
The relative phase position of fault current I
F
compared to the source voltage U
S
depends in
general on the character of the resultant reactance between the source and the fault position.
Two possibilities appear:
1
1
0
0
-
+
>
-
+
<
S
C
L
S
C
L
X
X
X
X
X
X
EQUATION1935 V1 EN-US
(Equation 72)
1MRK 505 343-UEN B
Section 7
Impedance protection
165
Application manual
Содержание Relion 670 series
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