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. Using the new Reyrolle Protection GAC sectionaliser control relay, described by the authors, in conjunction with an SF₆ filled switch, it is possible to provide a sectionaliser with the following features: remote operation, including remote closure for switches equipped with a closing coil; earth fault capability, down to 0.5% of rating, and dead line detection down to 10% of setting