Mechanical Features of New Frame-Mounted Outdoor Oil Circuit Breakers [includes discussion]

Science and technology of circuit breaker design are continuously improving. It would seem desirable if this continuous process of improvement could be incorporated in equipment as it is developed. Modern production methods and consideration of users´ personnel training and stocking problems prompt the desire to keep equipment as nearly standard as possible for reasonable periods of time and to refrain from changing designs from day to day. This is especially true of large equipment such as the intermediate-voltage outdoor oil circuit breaker. It is better periodically to redesign the equipment completely and incorporate all of the latest technological advancements at one time. The intermediate-voltage frame-mounted outdoor oil circuit breakers identified as type FZO-15-1000 through FZO-69-2500 (rated 14.4 kv to 69 kv, 600 amperes and 1,200 amperes) described in this paper (Fig. 1) have recently undergone such a major redesign. The introduction of the new American Standards Association-National Electrical Manufacturers Association (NEMA) standard bushings for this class breaker made it desirable to redesign a considerable portion of the circuit breaker. A reduced-size PNEU-DRAULIC (Allis-Chalmers trademark) operator was designed for application to this class of breaker. A new mechanically trip-free operating mechanism has been developed which is adaptable to pneumohydraulic, pneumatic, or solenoid operation. Therefore, it was decided that this was an opportune time to redesign this line of circuit breakers completely.