Figure 91 presents three typical cases for series capacitor located at line end (case
LOC=0% in figure 89).
• Series capacitor prevails the scheme as long as the line current remains lower or equal
to its protective current level (I £ k
p
· I
NC
). Line apparent impedance is in this case
reduced for the complete reactance of a series capacitor.
• 50% of capacitor reactance appears in series with resistance, which corresponds to
approximately 36% of capacitor reactance when the line current equals two times the
protective current level (I £ 2· k
p
· I
NC
). This information has high importance for
setting of distance protection IED reach in resistive direction, for phase to ground
fault measurement as well as for phase to phase measurement.
• 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
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
L
F
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
Figure 210: Voltage inversion in series compensated network due to fault current
infeed
Voltage at the B bus (as shown in figure 92) 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 (Equation 367)
Further development of equation 63 gives the following expressions:
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 411
Application manual
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