Abstract :
THE air-blast principle of circuit interruption is a recent introduction to the United States, although interrupting devices utilizing compressed air have been available in Europe for a number of years. The service performance of European breakers has been satisfactory, but inherent limitations prevented adoption in this country where large values of fault current and high rates of rise of recovery voltage are the rule rather than the exception. Exhaustive tests on forms of available air breakers heretofore available have shown that approximately 40,000 amperes represents the maximum current that can be safely interrupted at generator voltage, and then only under conditions of moderate rate of rise of recovery voltage. This fact alone made it essential, if air breakers were to be utilized, to develop an entirely different type, since applications in this country have commonly required oil breakers with interrupting ratings up to 60,000 amperes at 15 kv. Even this value of current does not represent the maximum requirement, since an increasingly strong demand exists for ratings at least up to 100,000 amperes at 15 kv or 2,500,000 kva.
