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The ability to transmit larger amounts of electric power over longer distances increases with the transmission voltage. Historically, this relationship--in conjunction with its associated economies of scale--provided the basic impetus for the technological drive to utilize increasingly higher voltages for the transmission of electric power: from "high voltage" (HV) transmission at 100, 138, 161, and 230 kV to "extra-high voltage" (EHV) transmission at 345, 400, 500, and 765 kV. For the past several years, research has been under way--in this country and abroad--to bring about transmission of electric power at "ultra-high voltage" (UHV), i.e., voltage in the range of 1000 to 1600 kV. This paper reviews the present status of UHV transmission research and development and discusses current prospects for the introduction of UHV technology in the commercial transmission of electric power.