Developments in microprocessor controlled sectionalisers

In the past, overhead lines have been protected by the use of fuses. However fuses, being open to the elements, need regular maintenance and, when a fuse has operated, a field visit for replacement. A further disadvantage of fuses is that they cannot detect low levels of earth fault current. The authors describe how the versatility of the microprocessor controlled relay has been exploited to modify its operation from that of a recloser control relay to that of a sectionaliser control relay. The relay has the following features: remote operation, including remote closure for switches equipped with a closing coil; earth fault capability; and dead line detection down to 10% of setting