Development of high-voltage air-break circuit-breakers with insulated-steel-plate arc chutes

The paper reports research and development done over the past ten years to investigate the principles of operation of a.c. air-break circuit-breakers for voltages up to 15kV and breaking capacities up to 500 MVA. Much of the research data on contacts, arc runners, the behaviour and control of arcs in arc chutes and arc extinction is of a fundamental nature and suitable for general application. High-speed photography played an important part in obtaining the data. The arc chute that was finally developed is of the insulated-steel-plate type, but no blow-out coil is used. The research has been applied to the design and manufacture of air-break circuit-breakers with British ratings up to 250 MVA at 3.3 kV, and up to 500 MVA at 6.6kV, 11 kV and 15kV, and American ratings up to 750 MVA. Details of the performance of the circuit-breakers and the effect of the system characteristics are given. Development is continuing to higher voltages and ratings.