Study of Stresses of Circuit-breakers: Combined Statistical Method

Circuit-breakers are one of the most important equipment in power systems. They serve as interrupting devices which interrupt the operating and short-circuit currents. In the past, electrical stresses of circuit-breakers are determined mainly by operating currents, short-circuit currents and switching operation. In addition, the number of faults on overhead lines which circuit-breakers have to be interrupted is taken into account but considered separately from the electrical stresses. The aim of this study is to combine and investigate electrical stresses of circuit-breakers as a function of fault frequency and fault severity. The combination of fault density and fault severity of circuit-breakers are carried out by statistical method. Number of faults, short-circuit currents and length of transmission lines in 123 kV, 245 kV and 420 kV were collected from the utility during 10-year operation