4,370,000-Kva Short-Circuit Tests on Grand Coulee 230-Kv Bus

The unusually large concentration of generating capacity Coulee Dam makes possible short-circuit power on the 230-kv bus considerably in excess of the rupturing capacity of circuit breakers now available at that voltage. Methods of sectionalizing the bus and segregating the transmission lines to limit the maximum short circuit to less than 3,500,000 kva are described in this paper. A group of fault tests on one of the 230-kv 3-cycle 3,500,000-kva steel tank oil circuit breakers was made with a maximum of six generators connected. Three-phase faults close to the breaker rating and single phase-to-ground short-circuit currents equivalent to 4,370,-000-kva 3-phase were cleared with no apparent effort by the breaker. These are believed to be the heaviest short circuits ever interrupted on any power system in the world.