Voltage distribution on faulty lossless serial compensated line from fault point F to the
bus is linearly dependent on distance from the bus, if there is no capacitor included in
scheme (as shown in figure 204). Voltage V
M
measured at the bus is equal to voltage
drop
D V
L
on the faulty line and lags the current I
F
by 90 electrical degrees.
The situation changes with series capacitor included in circuit between the IED point
and the fault position. The fault current I
F
(see figure
204) is increased due to the series
capacitor, generally decreases total impedance between the sources and the fault. The
reactive voltage drop D
V
L
on X
L1
line impedance leads the current by 90 degrees.
Voltage drop DV
C
on series capacitor lags the fault current by 90 degrees. Note that
line impedance X
L1
could be divided into two parts: one between the IED point and the
capacitor and one between the capacitor and the fault position. The resulting voltage
V
M
in IED point is this way proportional to sum of voltage drops on partial
impedances between the IED point and the fault position F, as presented by
( )
M F L1 C
V I j X X= × -
EQUATION1995-ANSI V1 EN-US (Equation 331)
en06000605_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
ANSI06000605 V1 EN-US
Figure 203: Voltage inversion on series compensated line
Section 8 1MRK 504 163-UUS A
Impedance protection
416 Transformer protection RET670 2.2 ANSI
Application manual
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