Setting Of Zone 1 - ABB REG670 Applications Manual

Section 8
Impedance protection
8.3.4.2
8.3.4.3
248
• 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.

Setting of zone 1

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"
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).
Setting of overreaching zone
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.
The requirement that the zone 2 shall not reach more than 80% of the shortest adjacent
line at remote end is highlighted in the example below.
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
1MRK 502 071-UEN -
and select the case(s) that are
Application manual