Voltage and current inversion
SEMOD168320-168 v2
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
SEMOD168320-171 v2
Figure
79 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 80 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
80). Voltage U
M
measured at the bus is
equal to voltage drop D U
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
80) is increased due to
the series capacitor, generally decreases total impedance between the sources and
the fault. The reactive voltage drop D U
L
on X
L1
line impedance leads the current
by 90 degrees. Voltage drop DU
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 U
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
( )
1
= × -
M F L C
U I j X X
EQUATION1901 V1 EN-US (Equation 49)
Section 8 1MRK 506 369-UEN B
Impedance protection
170 Line distance protection REL670 2.2 IEC
Application manual
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