Higher cureent-ratinges and improved thermal performance the being sought for existing medium-voltage vacuum circuit-breackers in order to meet market needs. At the same time, it is desired to maintain existing frame sizes and to minimize major edesign changes. Indcreases in current-ratings have an even greater effect o nthe ohmic heat dissipation inside the breaker. The thermal design must account for this increase in heat produced, in order for the breaker to meet various temperature-rise limits imposed by industry standards. To speed up the design cycle of these breakders with the higher current-rating, a thermal analysis has been performed to evaluate several design variations. Aa commercial comutationl package, ICEPAK, was used for the computations. Results from the computational model were validated against actual temperature-rise measurements botained from experiments. The analysis showed the necessity for installing heat sinks on the Vacuum Interupter (VI) stem and the bus extensions, so that the temperature-rise requiremetn of less than 65degC above ambient at any location on the breaker cold be met. Different heat sink designs were separately ananlyzed prior to their incorporation into the system-level ICEPAK model. and appropriate ones chosen on the basis of thermal performance, cost and case of manufacture. Design variations on other system components usch as conductors, buses, VI, and venting were also analyzed. The predicted results provide a basis for the selection of the components to satisfy system constraints.
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