Generator circuit-breakers: maximum availability using progress in self-expansion techniques

Certain special medium voltage switchgear applications sometimes require high ratings, e.g. generator circuit breakers or incomers in large power plant substations most often require a normal rated current at 4000 A or more, with a short circuit capacity of 50 kA and a very high DC component (asymmetry). Rated voltages are generally in the range 7.2, 12 and 17.5 kV. This paper describes a new circuit-breaker design covering these applications. The device takes advantage of the latest developments in modern interrupting techniques and operates using the self-expansion principle. The technical solutions are described (interupting technique, tightness) and their main advantages are explained. Finally, future prospects for this technique and for this kind of switchgear are considered