• X1Rvcan be set to the same value as X1Fw
• K equals side infeed factor at next busbar.
When the calculation of X1Fwgives a negative value the zone 1
must be permanently blocked.
Fault resistance
GUID-5F350226-4C8C-400E-93B3-7975CF1456B9 v1
The resistive reach is, for all affected applications, restricted by the set reactive
reach and the load impedance and same conditions apply as for a non-compensated
network.
However, special notice has to be taken during settings calculations due to the ZnO
because 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. This information has high importance
for setting of distance protection IED reach in resistive direction, for phase to
earth- fault measurement as well as, for phase-to-phase measurement.
Overreaching zone 2
GUID-F3704F5E-5604-470D-829F-C4594329ABFB v2
In series compensated network where independent tripping zones will have reduced
reach due to the negative reactance in the capacitor and the sub-harmonic swinging
the tripping will to a high degree be achieved by the communication scheme.
With the reduced reach of the under-reaching zones not providing effective
protection for all faults along the length of the line, it becomes essential to provide
over-reaching schemes like permissive overreach transfer trip (POTT) or blocking
scheme can be used.
Thus it is of great importance that the zone 2 can detect faults on the whole line
both with the series capacitor in operation and when the capacitor is bridged (short
circuited). It is supposed also in this case that the reactive reach for phase-to-phase
and for phase-to-earth faults is the same. The X1Fw, for all lines affected by the
series capacitor, are set to:
• X1 >= 1,5 · XLine
The safety factor of 1.5 appears due to speed requirements and possible under
reaching caused by the sub harmonic oscillations.
The increased reach related to the one used in non compensated system is
recommended for all protections in the vicinity of series capacitors to compensate
for delay in the operation caused by the sub harmonic swinging.
Settings of the resistive reaches are limited according to the minimum load
impedance.
Section 8 1MRK 506 369-UEN B
Impedance protection
398 Line distance protection REL670 2.2 IEC
Application manual
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