ABB RELION RET670, Applications Manual

Page: 222 / 1016

without series capacitor. Voltage V
M
in IED point will lag the fault current I
F
in case
when:
L1 C S L1
X X X X
< < +
EQUATION1902 V1 EN-US
(Equation 58)
Where
X
S
is the source impedance behind the IED
The IED point voltage inverses its direction due to presence of series capacitor and its
dimension. It is a common practice to call this phenomenon voltage inversion. Its
consequences on operation of different protections in series compensated networks
depend on their operating principle. The most known effect has voltage inversion on
directional measurement of distance IEDs (see chapter
"Distance protection" for more
details), which must for this reason comprise special measures against this
phenomenon.
There will be no voltage inversion phenomena for reverse faults in system with VTs
located on the bus side of series capacitor. The allocation of VTs to the line side does
not eliminate the phenomenon, because it appears again for faults on the bus side of
IED point.
Current inversion
SEMOD168320-206 v2
Figure 94 presents part of a series compensated line with corresponding equivalent
voltage source. It is generally anticipated that fault current I
F
flows on non-
compensated lines from power source towards the fault F on the protected line. Series
capacitor may change the situation.
Section 8
1MRK 504 163-UUS A
Impedance protection
216 Transformer protection RET670 2.2 ANSI
Application manual