When the calculation of XFw gives a negative value the zone 1 must be
permanently blocked.
For protection on non compensated lines facing series capacitor on next line. The setting
is thus:
• X1 is set to (XLine-XC · K) · p/100.
• K equals side infeed factor at next busbar.
When the calculation of XFw gives a negative value the zone 1 must be
permanently blocked.
Fault resistance
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 ground- fault measurement as well
as, for phase-to-phase measurement.
Overreaching zone 2
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-
ground faults is the same. The X1Fw, for all lines affected by the series capacito, are set
to:
• X1 >= 1,5 · XLine
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 209
Application manual
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