ABB Relion 670 series - Setting of Overreaching Zone; Setting of Zone 1

• 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 ground-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-ground loops can be as
large as 5-10% of the total line impedance.
• The effect from load transfer together with fault resistance may be considerable in
some extreme cases.
• Zero sequence mutual coupling from parallel lines.
8.9.3.2 Setting of zone 1
The different errors mentioned earlier usually require a limitation of the underreaching
zone (normally 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 grounded and out of service and
grounded in both ends. The setting of ground-fault reach should be selected to be <95%
also when parallel line is out of service and grounded at both ends (worst case).
8.9.3.3 Setting of overreaching zone
The first overreaching zone (normally 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 longer if the fault infeed from
adjacent lines at remote end are considerable higher than the fault current at the IED
location.
The setting shall generally 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.
Section 8 1MRK 506 369-UUS -
Impedance protection
326 Line distance protection REL670 2.2 ANSI
Application manual