Developing a Superspeed Trip-Free Reclosing Circuit-Breaker Mechanism [includes discussion]

Circuit-breaker engineers are challenged by the demands for ever-increasing interrupting capacities of power circuit breakers, increases required as load growth and nation-wide system interconnections are planned. Within the past 10 years the maximum interrupting ratings of high-voltage circuit breakers has tripled and the ceiling is not yet in sight. These high interrupting capacities represent substantial increases in the duty imposed on the operating mechanism, for the magnetic forces alone imposed on the contacts of a circuit breaker multiply as the squares of the short-circuit current. Modern operating requirements which add to the duty of the circuit-breaker operating mechanism are the requirements for circuit clearing in 3 cycles and repetitive reclosing in intervals as fast as 15 cycles. These necessitate the control of accelerating and decelerating forces considered extreme a few years ago. With these new demands for operating requirements is a matching development in circuit breakers. This paper describes the development and design of a new operating mechanism offered to meet the advanced specifications of high-voltage circuit breakers. As specified, this mechanism is required to control the circuit-breaker contacts for circuit clearing in 3 cycles. Successive reclosing operations are to be completed in intervals as short as 15 cycles without intentional time delay. The operating mechanism continues to be mechanically trip-free during any operation and is suitable for application to the largest tank-type circuit breakers now listed in the standards. The methods used for satisfying these requirements are described.