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ix ABSTRACTThe purpose of this study was to develop an assessment of the national utility system's needs for electric transmission during the period 1995-2020 that could be met by fbture reducedcost HVDC systems. The assessment was to include an economic evaluation of HVDC as a means for meeting those needs as well as a comparison w i t h competing technologies such as ac transmission with and without Flexible AC Transmission System (FACTS) controllers. The role of force commutated dc converters was to be assumed where appropriate.The assessment begins by identifjrlng the general needs for transmission in the U. S . in the context of a future deregulated power industry. The possible roles for direct current transmission are then postulated in terms of representative scenarios. A few of the scenarios are ill-ed with the help of actual U. S. system examples. Non-traditional applications as well as traditional applications such as long lines and asynchronous interconnections are discussed. The classid "break-even distance" concept for comparing HVDC and ac lines is used to assess the selected scenarios. The impact of reduced-cost converters is reflected in terms of the break-even distance.This report presents a comprehensive review of the functional benefits of HVDC transmission and updated cost data for both ac and dc system components. It also provides some provocative thoughts on how direct current transmission might be applied to better utilize and expand our nation's increasingly stressed transmission assets. X EXECUTIVE SUMMARY & CONCLUSIONS IntroductionThis project continues an effort that was started in 1992 wherein industry experts, including HVDC system suppliers, explored the concept of reducing converter station costs by about 50 % [Clark 1993; ORNL, 19931. The statement of work requested an assessment of the nation's transmission needs €or the period 1995-2020 and how cost-reduced HVDC might help in hlfilling those needs. The goal of this Task was to assess whether HVDC could be costeffective compared with ac transmission ifthe targeted 50 % reduction in converter costs was achieved in the fiiture. The determination of how the cost reduction can be accomplished is not covered herein. That question is the subject of parallel investigations [Project 20001 that includes the development of advanced converters exploiting the benefits of forced commutation. Project MethodologyThe project began with a critical review of the functional needs for transmission in the United States for the subject period. To the extent possible, the anticipated changes in the industry leading to open access and competition were considered as the bctional needs were identified. Recent reports by the North American Reliability Council (NERC) and specific utilities were reviewed to recognize their current plans for transmission upgrades between now and the year 2004. While there are 10,000 miles of new transmission scheduled for that time period, most of the individual projects are short lines (200 miles or less) and all of them, in...

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