ABB RELION RET670 Applications Manual page 422

Section 8
Impedance protection
416
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
drop D V
on the faulty line and lags the current I
L
The situation changes with series capacitor included in circuit between the IED point
and the fault position. The fault current I
capacitor, generally decreases total impedance between the sources and the fault. The
reactive voltage drop D V
Voltage drop DV
on series capacitor lags the fault current by 90 degrees. Note that
C
line impedance X could be divided into two parts: one between the IED point and the
L1
capacitor and one between the capacitor and the fault position. The resulting voltage
V in IED point is this way proportional to sum of voltage drops on partial
M
impedances between the IED point and the fault position F, as presented by
( )
= × -
V I j X X
M F L1 C
EQUATION1995-ANSI V1 EN-US
With bypassed
Source voltage
Source
X
S
~
I
F
ANSI06000605 V1 EN-US
Figure 203: Voltage inversion on series compensated line
measured at the bus is equal to voltage
M
(see figure 204) is increased due to the series
F
on X line impedance leads the current by 90 degrees.
L L1
With inserted
capacitor capacitor
V'
M
V
M
V
X
L1
X
F
X
C
21
en06000605_ansi.vsd
1MRK 504 163-UUS A
by 90 electrical degrees.
F
Pre -fault voltage
Fault voltage
Transformer protection RET670 2.2 ANSI
Application manual
(Equation 331)