Clearance of Short-Circuits With Delayed Current Zeros in the Itaipu 550 kV-Substation

The results of Kema-tests with short-circuit currents with delayed zeros carried out on a Siemens SF6 circuit-breaker have been transferred into a digital computer program and applied upon the conditions in the Itaipu 550 kV-substation for various cases of faults near the generators. The most critical condition occurs when the generators have been operating in the underexited state followed by a three-phase non-simultaneous fault at the entrance of a line. Theoretically there might be only one line in service and 5 generators feeding through one breaker. The circuit-braker under investigation will even clear this fault without necessitating any tripping delay.