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Hydroelectric generation is the largest contemporary source of commercially viable renewable energy produced on a large scale. Most of the Australian hydro generating plants are 40 to 60 years old and approaching their ldquohalf liferdquo refurbishment. Uprating of existing generously sized generators is, in most cases, possible and is the easiest and cheapest way of obtaining extra generating capacity without embarking on a costly and uncertain environmental approval process. Full replacement of the stator core is often part of the hydro generator upgrade scope. This is sometimes dictated by the deteriorated state of the original stator core, but more often the benefit is derived from advances in magnetic core steel technology where reductions in core losses permit achievement of required stator assembly temperature rises at an upgraded output, and often result in increased generating plant efficiency. The reduction in core losses may often be a deciding factor when considering feasibility and the possible extent of the hydro generator uprate. In one case with upgrade work on a 50 MVA hydro generator, which included replacement of the stator core, the author has achieved a reduction in core losses from 290 kW down to 160 kW. This resulted in a reduction of stator assembly temperature rise and improved machine efficiency. The two papers on hydro generator stator cores present a synthesis of knowledge derived from the author's many years of experience in refurbishing and upgrading hydro generators.