The greatly increased prospective fault MVA at many switching stations, due to the rapid growth of interconnections on many systems during the last 15 years, has necessitated the design of circuit-breakers of larger capacity. This in turn has made desirable improved facilities for technical investigations and for proving the rating of the breakers.The paper discusses the mechanical and electrical factors which affect the design of alternators supplying power for switchgear testing. A review is made of several methods of increasing the output of such alternators, and the merits of each are critically examined.