ABB Distributed Control System PFSK162

ABB Distributed Control System PFSK162

ABB Distributed Control System PFSK162

The first overreaching zone (normally zone2) must detect faults on the whole protected line. Considering the different errors that might influence the measurement in the same way as for zone1, it is necessary to increase the reach of the overreaching zone to at least 120% of the protected line. The zone2 reach can be even higher if the fault infeed from adjacent lines at remote end are considerable higher than the fault current at the IED location.

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.
• If the requirements in the bullet—listed paragraphs above gives a zone2 reach less than 120%, the time delay of zone2 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 zone2 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 with a simple example below.