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

8.3.3.2 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).
8.3.3.3 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 higher if the fault infeed from
adjacent lines at remote end is 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.
If any of the above gives a zone 2 reach less than 120%, the time delay of zone 2 must be
increased by approximately 200ms to avoid unwanted operation in cases when the
telecommunication for the short adjacent line at 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.
If a fault occurs at point F see figure
121, the IED at point A senses the impedance:
Section 8 1MRK 506 369-UUS -
Impedance protection
242 Line distance protection REL670 2.2 ANSI
Application manual