ABB RELION 670 Series Applications Manual page 344

Section 7
Impedance protection
X1Fw is set to (XLine-XC · K) · p/100.
•
X1Rv can be set to the same value as X1Fw
•
K equals side infeed factor at next busbar.
•
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 earth- 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-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.
Reverse zone
The reverse zone that is normally used in the communication schemes for functions like fault
current reversal logic, weak-in-feed logic or issuing carrier send in blocking scheme must
detect all faults in the reverse direction which is detected in the opposite IED by the
overreaching zone 2. The maximum reach for the protection in the opposite IED can be
achieved with the series capacitor in operation.
The reactive reach can be set according to the following formula: X1=1.3·(X1
Settings of the resistive reaches are according to the minimum load impedance:
338
When the calculation of
permanently blocked.
X1Fw gives a negative value the zone 1 must be
1MRK 504 152-UEN B
GUID-5F350226-4C8C-400E-93B3-7975CF1456B9 v1
GUID-F3704F5E-5604-470D-829F-C4594329ABFB v2
GUID-BDDB2E91-3E37-4F78-99C2-8A9C3E3B275B v2
-0.5(X1 -X ))
2Rem L C
Application manual