ABB REG670 - Page 237

different protection functions, which have their operation based on properties of
measured voltage and current phasors.
Voltage inversion
Figure
110 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
111 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 111). 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 111) 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 (Equation 108)
en06000605.vsd
~
Z<
XS
X
L1
IF
U
U
M
Source
Fault voltage
Pre -fault voltage
X
C
Source voltage
U’
M
With bypassed
capacitor
With inserted
capacitor
F
IEC06000605 V1 EN
Figure 110: Voltage inversion on series compensated line
1MRK 502 071-UEN - Section 8
Impedance protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 231
Application manual