Load cell PFTL101A 0.5KN

Load cell PFTL101A 0.5KN

Load cell PFTL101A 0.5KN

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.