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The Conowingo Dam (also Conowingo Hydroelectric Plant, Conowingo Hydroelectric Station) is a large hydroelectric dam in the lower Susquehanna River near the town of Conowingo, Maryland. The medium-height, masonry gravity dam is one of the largest non-federal hydroelectric dams in the U.S. The dam sits about from the river mouth at the Chesapeake Bay, south of the Pennsylvania border and northeast of Baltimore, on the border between Cecil and Harford counties. The dam supports a 9,000-acre reservoir, which today covers the original town of Conowingo. During dam construction, the town was moved to its present location about northeast of the dam's eastern end. The rising water also would have covered Conowingo Bridge, the original U.S. Route 1 crossing, so it was demolished in 1928. The Conowingo Reservoir, and the nearby Susquehanna State Park, provide many recreational opportunities. == Construction and hydroelectric power generation == The area, which appears on a 1612 map by John Smith, was originally known as Smyth's Falls. On January 23, 1925, Philadelphia Electric Company awarded the construction contract for the dam to Stone & Webster of Boston,〔(【引用サイトリンク】format=PDF )〕 who did the design. Construction, which started in 1926, was carried out by Arundel Corporation of Maryland. (Abandoned railroad tracks for transporting heavy equipment to the dam site can be seen along the western shore of the river below the dam.) When completed in 1928, it was the second-largest hydroelectric project by power output in the United States after Niagara Falls.〔("A Hydro Plant That Rivals Niagara." ) ''Popular Science Monthly'', November 1930, p. 49.〕 The dam was built with 11 turbine sites, although only seven turbines were initially installed, driving generators each rated for 36 megawatts. A turbine house, on the southwestern end of the dam, encloses these seven units. One additional "house" unit provides 25 Hz power for the dam's electric railroad system (identical to that used by the Pennsylvania Railroad, which had an electrified line (under Norfolk Southern ownership ) running on the eastern shore). In 1978, four higher-capacity turbines were added. Each drives a 65-megawatt generator, increasing the dam's electrical output capacity from 252 to 548 megawatts. The four newer turbines are in the open air section at the northeast end of the power house. The generators produce power at 13,800 volts. This is stepped up to 220,000 volts for transmission, primarily to the Philadelphia area. The dam currently contributes an average of 1.6 billion kilowatt hours annually to the electric grid. Through subsidiaries and mergers, the dam is now operated by the Susquehanna Electric Company, part of Exelon Power Corporation. The current Federal Energy Regulatory Commission license for the dam, which may be renewed, was issued in 1980 and expires on September 1, 2015. The Conowingo Hydroelectric Station would be a primary black start power source if the regional PJM power grid ever had a widespread emergency shutdown (blackout)〔(【引用サイトリンク】title= Exelon Corporation: Conowingo )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Conowingo Dam」の詳細全文を読む スポンサード リンク
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