ABB REL670 2.2 IEC - Setting of Zone 1

• 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.
8.13.4.2 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).
8.13.4.3 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.
If the chosen zone 2 reach gives such a value that it will interfere with zone 2 on
adjacent lines, the time delay of zone 2 must be increased by approximately 200 ms
to avoid unwanted operation in cases when the telecommunication for the short
adjacent line at the remote end is down during faults. The zone 2 must not be
reduced below 120% of the protected line section. The whole line must be covered
under all conditions.
1MRK 506 369-UEN B Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 393
Application manual