ABB Relion 670 series, Applications Manual

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7.13.4 Setting guidelines
IP14962-1 v1
7.13.4.1 General
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The settings for Distance measuring zones, quadrilateral characteristic (ZMFCPDIS) are done
in primary values. The instrument transformer ratio that has been set for the analog input card
is used to automatically convert the measured secondary input signals to primary values used
in ZMFCPDIS.
The following basics must be considered, depending on application, when doing the setting
calculations:
• Errors introduced by current and voltage instrument transformers, particularly under
transient conditions.
• Inaccuracies in the line zero-sequence impedance data, and their effect on the calculated
value of the earth-return compensation factor.
• The effect of infeed between the IED and the fault location, including the influence of
different Z
0
/Z
1
ratios of the various sources.
• The phase impedance of non transposed lines is not identical for all fault loops. The
difference between the impedances for different phase-to-earth loops can be as large as
5-10% of the total line impedance.
• The effect of a load transfer between the IEDs of the protected fault resistance is
considerable, the effect must be recognized.
• Zero-sequence mutual coupling from parallel lines.
7.13.4.2 Setting of zone 1
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The different errors mentioned earlier usually require a limitation of the underreaching zone
(zone 1) to 75%...90% of the protected line.
In case of parallel lines, consider the influence of the mutual coupling according to section
"Parallel line application with mutual coupling" and select the case(s) that are valid in the
particular application. By proper setting it is possible to compensate for the cases when the
parallel line is in operation, out of service and not earthed and out of service and earthed in
both ends. The setting of the earth-fault reach should be <85% also when the parallel line is
out of service and earthed at both ends (the worst case).
7.13.4.3 Setting of overreaching zone
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The first overreaching zone (zone 2) must detect faults on the whole protected line.
Considering the different errors that might influence the measurement in the same way as for
zone 1, it is necessary to increase the reach of the overreaching zone to at least 120% of the
protected line. The zone 2 reach can be even higher if the fault infeed from adjacent lines at the
remote end is considerably higher than the fault current that comes from behind of the IED
towards the fault.
The setting must not exceed 80% of the following impedances:
• The impedance corresponding to the protected line, plus the first zone reach of the
shortest adjacent line.
• The impedance corresponding to the protected line, plus the impedance of the maximum
number of transformers operating in parallel on the bus at the remote end of the
protected line.
Larger overreach than the mentioned 80% can often be acceptable due to fault current infeed
from other lines. This requires however analysis by means of fault calculations.
1MRK 505 343-UEN B Section 7
Impedance protection
353
Application manual