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
"Distance protection" 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
Figure
83 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_ansi.vsd
~
21
XS
X
L1
IF
v
V
M
Source
Fault voltage
Pre -fault voltage
X
C
Source voltage
V’
M
With bypassed
capacitor
With inserted
capacitor
F
X
ANSI06000607 V1 EN
Figure 203: Current inversion on series compensated line
The relative phase position of fault current I
F
compared to the source voltage V
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
(Equation 364)
The first case corresponds also to conditions on non compensated lines and in cases, when
the capacitor is bypassed either by spark gap or by the bypass switch, as shown in phasor
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 405
Application manual
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