Mike Krzyzewski is really a famous coach of Dream Team. She has coached north america men's basketball team for some time, that's clinched numerous medals for his country. Following Londonfl jerseys supplyn Olympic was over, Krzyzewski told The Associated Press that this game will be his final one as national coach, a job he's held for seven years. He had left open the possibility of swomen nfl jerseystaying with the team beyond the London Games, when practice on Saturday said these will be his last Olympics.When asked if he was sure, Krzyzewski didn't hesitate before again saying, "yecheap nfl jerseys wholesales," this will be his last game "If we could win it, then it might be three major championships in a row, i always do not know when that has been done because we haven't usually won http://govoriotkrito.bg/libs/nflcn08.htmthe globe championships," Krzyzewski said. "It becomes an enormous thing for the program." Whatever, he's an awesome coach. His achievement are going to be remembered by the country.cheap nfl jerseys
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電力變壓器

2014/8/25 16:36:51      點擊:

電力變壓器是一種靜止的電氣設備,是用來將某一數值的交流電壓(電流)變成頻率相同的另一種或幾種數值不同的電壓(電流)的設備。當一次繞組通以交流電時,就產生交變的磁通,交變的磁通通過鐵芯導磁作用,就在二次繞組中感應出交流電動勢。二次感應電動勢的高低與一二次繞組匝數的多少有關,即電壓大小與匝數成正比。主要作用是傳輸電能,因此,額定容量是它的主要參數。額定容量是一個表現功率的慣用值,它是表征傳輸電能的大小,以kVA或MVA表示,當對變壓器施加額定電壓時,根據它來確定在規定條件下不超過溫升限值的額定電流。較為節能的電力變壓器是非晶合金鐵心配電變壓器,其最大優點是,空載損耗值特低。最終能否確保空載損耗值,是整個設計過程中所要考慮的核心問題。當在產品結構布置時,除要考慮非晶合金鐵心本身不受外力的作用外,同時在計算時還須精確合理選取非晶合金的特性參數。

電力變壓器是發電廠和變電所的主要設備之一。變壓器的作用是多方面的不僅能升高電壓把電能送到用電地區,還能把電壓降低為各級使用電壓,以滿足用電的需要。總之,升壓與降壓都必須由變壓器來完成。在電力系統傳送電能的過程中,必然會產生電壓和功率兩部分損耗,在輸送同一功率時電壓損耗與電壓成反比,功率損耗與電壓的平方成反比。利用變壓器提高電壓,減少了送電損失。
變壓器是由繞在同一鐵芯上的兩個或兩個以上的線圈繞組組成,繞組之間是通過交變磁場而聯系著并按電磁感應原理工作。變壓器安裝位置應考慮便于運行、檢修和運輸,同時應選擇安全可靠的地方。在使用變壓器時必須合理地選用變壓器的額定容量。變壓器空載運行時,需用較大的無功功率。這些無功功率要由供電系統供給。變壓器的容量若選擇過大,不但增加了初投資,而且使變壓器長期處于空載或輕載運行,使空載損耗的比重增大,功率因數降低,網絡損耗增加,這樣運行既不經濟又不合理。變壓器容量選擇過小,會使變壓器長期過負荷,易損壞設備。因此,變壓器的額定容量應根據用電負荷的需要進行選擇,不宜過大或過小。
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