Recently, the issue of auxiliary system performance during bus transfers has received attention in the nuclear industry due to the interest of the USNRC [Ref. 6]. However, these same issues are equally applicable to any generating station, be it nuclear, fossil steam, combustion turbine, or combined cycle. In the past fossil stations had the benefit of the high inertias of the fan loads to help maintain the bus voltage and frequency during the bus dead time to allow the use of a fast transfer scheme. When these fans are fed from adjustable-speed drives or are isolated from the remainder of the loads by being placed on separate higher voltage buses, this advantage is eliminated. The trend towards combined cycle plants where the loads are all low inertia loads, such as pumps, also makes the issue of bus transfer schemes important for fossil plants as well.
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