Distance Protection - ABB RELION 670 SERIES Applications Manual

Section 8
Impedance protection
8.1.2.11
194
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
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 steady-state network simulations
are in such cases unavoidable.

Distance protection

Distance protection due to its basic characteristics, is the most used protection principle on
series compensated and adjacent lines worldwide. It has at the same time caused a lot of
challenges to protection society, especially when it comes to directional measurement and
transient overreach.
Distance IED in fact does not measure impedance or quotient between line current and
voltage. Quantity 1= Operating quantity - Restraing quantity Quantity 2= Polarizing
quantity. Typically Operating quantity is the replica impedance drop. Restraining quantity
is the system voltage Polarizing quantity shapes the characteristics in different way and is
not discussed here.
Distance IEDs comprise in their replica impedance only the replicas of line inductance
and resistance, but they do not comprise any replica of series capacitor on the protected
line and its protection circuits (spark gap and or MOV). This way they form wrong picture
of the protected line and all "solutions" related to distance protection of series
1MRK 506 369-UUS -
Line distance protection REL670 2.2 ANSI
Application manual
LF