High Current, High Voltage Bus Design
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The Center for Electromechanics at The University of Texas at Austin (CEM-UT) has developed a high power, multi-megamp bus as part of the 90 mm x 10 m long tactical railgun program. The bus transfers approximately 3,000 MW average or 25,000 MW peak power to accelerate 2.5 to 3.0 ~g projectile packages up to 3 km/s. The original detail design of the bus was reported by Peterson  with a 3.2 MA peak current and 10 kV peak voltage rating published. The chosen design was a flat laminated bus structure which uses interleaved, alternating polarity plates to lower the inductance and magnetic pressure. Powering a railgun with opening switch commutated storage inductors requires that the inductance of the load (i.e. bus and gun), be as low as possible to maximize switching efficiencies [2,3]. Lowering bus inductance requires minimizing the gap between conductors, but opposite polarity current carriers with close proximity can generate magnetic pressures of tens of megapascals. The laminated design reduces both inductance and magnetic loading while providing an efficient and cost effective way to deliver the energy to the railgun. The original bus design was based on known technology and experience dealing with 1 MA peak current bus systems. Shortly after full current testing began on the large bore railgun, it was determined that several areas of the bus were marginally capable of withstanding this severe load. These areas required improvement to allow the bus to consistently operate at full design current and loading. The modified bus design has been demonstrated at a 3.4 MA peak current and a 15-kV standoff. This paper presents experimental observations, diagnosing of problem areas, and successful design of upgrades, all of which are valuable information for future high power bus designs.