ABB REL670 2.2 IEC, Applications Manual

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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.
8.13.3.5 Distance protection
GUID-B8441469-8B23-494F-9BA8-D6A88DB2DC38 v2
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 - Restrain 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 compensated and adjacent lines are concentrated on finding
some parallel ways, which may help eliminating the basic reason for wrong
measurement. The most known of them are decrease of the reach due to presence
of series capacitor, which apparently decreases the line reactance, and introduction
of permanent memory voltage in directional measurement.
Series compensated and adjacent lines are often the more important links in a
transmission networks and delayed fault clearance is undesirable. This makes it
necessary to install distance protection in combination with telecommunication.
The most common is distance protection in Permissive Overreaching Transfer Trip
mode (POTT).
1MRK 506 369-UEN B
Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 385
Application manual