( )
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 (Equation 368)
( )
0
1
= = +
+
LB
C B LF
A
B
X
X V X
I
I
EQUATION2000-ANSI V1 EN (Equation 369)
Equation 64 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
equation
65 indicates the deepness of the network to which it will feel the influence of
series compensation through the effect of voltage inversion.
It is also obvious that the position of series capacitor on compensated line influences in
great extent the deepness of voltage inversion in adjacent system. Line impedance X
LF
between D bus and the fault becomes equal to zero, if the capacitor is installed near the bus
and the fault appears just behind the capacitor. This may cause the phenomenon of voltage
inversion to be expanded very deep into the adjacent network, especially if on one hand
the compensated line is very long with high degree of compensation, and the adjacent lines
are, on the other hand, relatively short.
Extensive system studies are necessary before final decision is made on implementation
and location of series capacitors in network. It requires to correctly estimate their
influence on performances of (especially) existing distance IEDs. It is possible that the
costs for number of protective devices, which should be replaced by more appropriate
ones due to the effect of applied series compensation, influences the future position of
series capacitors in power network.
Possibilities for voltage inversion at remote buses should not be studied for short circuits
with zero fault resistance only. It is necessary to consider cases with higher fault
resistances, for which spark gaps or MOVs on series capacitors will not conduct at all. At
the same time this kind of investigation must consider also the maximum sensitivity and
possible resistive reach of distance protection devices, which on the other hand simplifies
the problem.
Application of MOVs as non-linear elements for capacitor overvoltage protection makes
simple calculations often impossible. Different kinds of transient or dynamic network
simulations are in such cases unavoidable.
Section 8 1MRK 506 369-UUS -
Impedance protection
412 Line distance protection REL670 2.2 ANSI
Application manual
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