Abstract :
The paper reviews some of the factors influencing air-blast circuit-breaker design, more especially in the range 110¿264 kV and 1500¿5000 MVA. The influence of air-pressure range on excess breaking capacity at normal pressure, and methods of achieving economy in air consumption, are described. Limitations and advantages of multi-break interruption are discussed with reference to constructional, voltage grading, and air-flow problems. Design limits of shunts for voltage control and the advantages of non-linear resistors for this purpose are given. Methods of short-circuit testing are examined, and the severity of test-plant restriking rate, both for tests made on complete and subdivided breakers, is compared with that for actual systems. The performance of a double-break 3500-MVA 132-kV circuit breaker incorporating parallel air flow and non-linear resistor voltage control is presented in graphical form, showing the effect of voltage, current and restriking rate in terms of air pressure, and the behaviour of n.l.r. (non-linear resistor) shunting. The facilities offered by air-blast breakers for high-speed reclosure and service maintenance are outlined, and also the manner in which these requirements are executed in the designs referred to in the paper. Finally, conclusions are drawn as regards design, test, and future possibilities, based on the combined effect of the factors discussed.
