Applications of digital differential protection

It has long been recognised that differential protection can provide unit protection for two ended and multiple ended feeders without the problems associated with other forms of protection. However, the need for continuous metallic pilots between line ends was often a insurmountable disadvantage of earlier generations of differential relays. The principle was revitalised in the mid 1980s with the launch of the first digital current differential relays. These eliminated pilot wires by using wideband digital channels for communication. The increasing availability of wideband channels has resulted in a steady growth in the application of digital differential relays. This paper describes developments in the relays themselves which have helped this growth by making the relays suitable for more diverse applications