In some applications it might be necessary to consider the enlarging factor due to
fault current infeed from adjacent lines in the reverse direction to obtain certain
sensitivity.
8.1.3.5
Series compensated and adjacent lines
SEMOD168247-142 v2
Directional control
SEMOD168247-145 v2
The directional function (ZDSRDIR) which is able to cope with the condition at
voltage reversal, shall be used in all IEDs with conventional distance protection
(ZMCPDIS,ZMCAPDIS). This function is necessary in the protection on
compensated lines as well as all non-compensated lines connected to this busbar
(adjacent lines). All protections that can be exposed to voltage reversal must have
the special directional function, including the protections on busbar where the
voltage can be reversed by series compensated lines not terminated to this busbar.
The directional function is controlled by faulty phase criteria. These criteria must
identify all forward and reverse faults that can cause voltage reversal. Setting of the
corresponding reach of the impedance measuring elements is separate for reactive
and resistive reach and independent of each other for phase-to-earth and for phase-
to-phase measurement.
It is also necessary to consider the minimum load impedance limiting conditions:
Setting of zone 1
SEMOD168247-150 v3
A voltage reversal can cause an artificial internal fault (voltage zero) on faulty line
as well as on the adjacent lines. This artificial fault always have a resistive
component, this is however small and can mostly not be used to prevent tripping of
a healthy adjacent line.
An independent tripping zone 1 facing a bus which can be exposed to voltage
reversal have to be set with reduced reach with respect to this false fault. When the
fault can move and pass the bus, the zone 1 in this station must be blocked.
Protection further out in the net must be set with respect to this apparent fault as the
protection at the bus.
Different settings of the reach for the zone (ZMCPDIS) characteristic in forward
and reverse direction makes it possible to optimize the settings in order to
maximize dependability and security for independent zone1.
Due to the sub-harmonic oscillation swinging caused by the series capacitor at fault
conditions the reach of the under-reaching zone 1 must be further reduced. Zone 1
can only be set with a percentage reach to the artificial fault according to the curve
in
Section 8
1MRK 506 369-UEN B
Impedance protection
192
Line distance protection REL670 2.2 IEC
Application manual
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