Introduction: At present the interconnected 11kV and 6.6kV networks are protected through the use traditional unit based schemes. However a subset of these networks utilise bidirectional overcurrent and earth fault relays at remote primary substations.

Protection theory shows that it is impossible to achieve true time-based discrimination in a solidly interconnected ring network. In practice, experience shows that suitable grading can be achieved, with limitations (such as the use of relatively high time multipliers, and limited deployment around the ring resulting in large protection zones).

Objectives: The aim of this project is to investigate and develop a radio-based directional blocking scheme for use on interconnected ring-type 11kV and 6.6kV networks in the SP-M licence area.