ABB RELION RET670, Applications Manual

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• Series capacitor becomes nearly completely bridged by MOV when the line
current becomes higher than 10-times the protective current level (I
£
10· k
p
· I
NC
).
8.13.3.4 Impact of series compensation on protective IED of adjacent lines
GUID-DA1DBB5B-0AFD-49F4-87C7-0E8AB5006051 v2
Voltage inversion is not characteristic for the buses and IED points closest to the series
compensated line only. It can spread also deeper into the network and this way
influences the selection of protection devices (mostly distance IEDs) on remote ends of
lines adjacent to the series compensated circuit, and sometimes even deeper in the
network.
en06000616_ansi.vsd
~
~
Z
LF
Z
LA
Z
LB
E
A
E
B
V
A
V
B
V
D
I
B
I
A
I
F
-jX
C
F
A
B
D
Z
SA
Z
SB
ANSI06000616 V1 EN-US
Figure 212: Voltage inversion in series compensated network due to fault current
infeed
Voltage at the B bus (as shown in figure 212 ) is calculated for the loss-less system
according to the equation below.
( ) ( )
= + × = + × - + ×
B D B LB A B LF C B LB
V V I jX I I j X X I jX
EQUATION1998-ANSI V1 EN-US
(Equation 336)
Further development of equation 336 gives the following expressions:
( )
1
= × + + × -
é ù
æ ö
ê ç ÷ ú
è ø ë û
A
B B LB LF C
B
I
V jI X X X
I
EQUATION1999-ANSI V1 EN-US
(Equation 337)
( )
0
1
= = +
+
LB
C B LF
A
B
X
X V X
I
I
EQUATION2000-ANSI V1 EN-US
(Equation 338)
Equation 337 indicates the fact that the infeed current I
A
increases the apparent value
of capacitive reactance in system: bigger the infeed of fault current, bigger the apparent
series capacitor in a complete series compensated network. It is possible to say that
Section 8
1MRK 504 163-UUS A
Impedance protection
424 Transformer protection RET670 2.2 ANSI
Application manual