8.13.3.3 Voltage and current inversion
Series capacitors influence the magnitude and the direction of fault currents in series
compensated networks. They consequently influence phase angles of voltages measured
in different points of series compensated networks and this performances of different
protection functions, which have their operation based on properties of measured voltage
and current phasors.
Voltage inversion
Figure
81 presents a part of series compensated line with reactance X
L1
between the IED
point and the fault in point F of series compensated line. The voltage measurement is
supposed to be on the bus side, so that series capacitor appears between the IED point and
fault on the protected line. Figure
82 presents the corresponding phasor diagrams for the
cases with bypassed and fully inserted series capacitor.
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
82). 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 82) 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
(Equation 362)
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 403
Application manual
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