and similar information. Many of the possible variables are mutually dependent. As an example, the initial effective contact resistance between a bolted terminal and an aluminum cable depends on many factors including the length of the contact barrel, the number and type of bolts, the effect of locking washers if used, the relative fit of the terminal on the cable, the conductivity of metals used for the fitting and bolts, the surface finish or treatment of the terminal, the type and method of application of joint compound if used, and the characteristics of the aluminum cable, such as temper, number of strands and length of lay of strands, and surface condition of strands.Similarly, the perforilmance of a bolted terminal in service depends on several factors such as initial contact resistance, load current and type of duty cycles, environment, relative coefficients of expansion of the cable and fittinlgs, inherent elasticity provided in fitting to compensate for creep of fitting and cable, adequacy of sealing of contact areas by joint compounds, and cable characteristics.The problem of the application engineer, presented by Mr. Myers, can be understood and appreciated. It seems, however, from consideration of the factors mentioned that it would be beyond the scope of a paper such as this to attempt to provide the quantitative data sought by Mr. Myers. It was intended rather that the paper would to some extent guide manufacturers and users by calling attention to factot s of importance in the design and application of fittings.In answer to a question, the aluminum bolts to which reference was made would be of 24S-T4 alloy.A number of tests of fittings on aluminum cables have been made with ovei load currents of two to three times the normal current ratings of the cables. Short-circuit tests are planned.Synopsis: The purpose of this paper is to present a brief resume of a rather comprehensive study concerning circuit-breaker operating mechanisms and to describe a new type of mechanism which depenids on a combination of gas and liquid for its energy suipply and transmission medium. The authors believe the new design is a definite improvement from the standpoint of overall cost and reliability, particularly for circuit breakers which now require heavydtity spring or compressed-air operators.
Review of Basic DesignTHE trend toward higher ratings and faster operating speeds in Iiigh-voltage circuit-breaker designs has resulted in a requirement for more powerful operators with increased precision in their control. The result has been an evolutionary trend from manual operation, through various types of mechanisms, including inertia storage schemes and solenoids, to the present spring and compressed-air mechanisms. Each method of operation has distinct advantages and disadvantages which must be weighed in accordance withl the requirements of the trend in circuit-breaker design. For example, manual operation would result in the least maintenance and lowest cost but it was abandoned for reasons of safety, speed, automatic...
