Abstract :
In the 1960´s, the load switch disconnector for Distribution Networks was launched for the first time. Before then, electric utilities had access only to circuit breakers large in size and requiring a lot of maintenance, or simple disconnectors and exchangeable fuses. Therefore the load switch disconnector and the fuse load switch disconnector represented a substantial break through. It opened up for smaller, cheaper substations and switchgears, and made it possible to introduce the open loop system, which reduced outage times when a fault occurred in a cable section. Today the size and price of full range circuit breakers are such that it is possible to use them in Ring Main Units. In combination with modern fault indicators as presented in CIRED in Turin 2005, remarkable improvements in availability can be achieved. The cost for such a Ring Main Unit with circuit breakers is not higher than existing ones with load switch disconnectors.
