變壓器組件由鐵芯（或磁芯）和線圈組成，線圈有兩個或兩個以上的繞組，其中接電源的繞組叫初級線圈，其余的繞組叫次級線圈。它可以變換交流電壓、電流和阻抗。簡單的鐵心變壓器由一個軟磁材料做成的鐵心及套在鐵心上的兩個匝數不等的線圈構成。

鐵(tie)心的作用(yong)是加強兩(liang)個(ge)線(xian)(xian)(xian)圈(quan)(quan)(quan)間(jian)的磁(ci)耦(ou)合(he)。為(wei)了減少(shao)鐵(tie)內渦流和(he)磁(ci)滯損(sun)耗(hao)，鐵(tie)心由(you)涂(tu)漆(qi)的硅鋼(gang)片(pian)疊壓(ya)(ya)而成(cheng);兩(liang)個(ge)線(xian)(xian)(xian)圈(quan)(quan)(quan)之間(jian)沒(mei)有電(dian)(dian)的聯系，線(xian)(xian)(xian)圈(quan)(quan)(quan)由(you)絕(jue)緣(yuan)銅(tong)線(xian)(xian)(xian)（或(huo)鋁線(xian)(xian)(xian)）繞成(cheng)。一(yi)個(ge)線(xian)(xian)(xian)圈(quan)(quan)(quan)接(jie)交流電(dian)(dian)源稱為(wei)初(chu)級線(xian)(xian)(xian)圈(quan)(quan)(quan)（或(huo)原(yuan)線(xian)(xian)(xian)圈(quan)(quan)(quan)），另一(yi)個(ge)線(xian)(xian)(xian)圈(quan)(quan)(quan)接(jie)用(yong)電(dian)(dian)器(qi)稱為(wei)次級線(xian)(xian)(xian)圈(quan)(quan)(quan)（或(huo)副線(xian)(xian)(xian)圈(quan)(quan)(quan)）。實際的變壓(ya)(ya)器(qi)是很復雜的，不可避免(mian)地存在銅(tong)損(sun)（線(xian)(xian)(xian)圈(quan)(quan)(quan)電(dian)(dian)阻發熱(re)）、鐵(tie)損(sun)（鐵(tie)心發熱(re)）和(he)漏磁(ci)（經空氣閉(bi)合(he)的磁(ci)感應(ying)線(xian)(xian)(xian)）等，為(wei)了簡化討(tao)論這(zhe)里只介紹理想(xiang)變壓(ya)(ya)器(qi)。理想(xiang)變壓(ya)(ya)器(qi)成(cheng)立的條(tiao)件是：忽略漏磁(ci)通(tong)，忽略原(yuan)、副線(xian)(xian)(xian)圈(quan)(quan)(quan)的電(dian)(dian)阻，忽略鐵(tie)心的損(sun)耗(hao)，忽略空載(zai)電(dian)(dian)流（副線(xian)(xian)(xian)圈(quan)(quan)(quan)開路原(yuan)線(xian)(xian)(xian)圈(quan)(quan)(quan)線(xian)(xian)(xian)圈(quan)(quan)(quan)中的電(dian)(dian)流）。例如(ru)電(dian)(dian)力變壓(ya)(ya)器(qi)在滿載(zai)運行時（副線(xian)(xian)(xian)圈(quan)(quan)(quan)輸出額(e)定功率）即接(jie)近(jin)理想(xiang)變壓(ya)(ya)器(qi)情況。

變壓器組件是利用電磁感應原理制成的靜止用電器。當變壓器的原線圈接在交流電源上時，鐵心中便產生交變磁通，交變磁通用φ表示。原、副線圈中的φ是相同的，φ也是簡諧函數，表為φ=φmsinωt。由法拉第電磁感應定律可知，原、副線圈中的感應電動勢為e1=-N1dφ/dt、e2=-N2dφ/dt。式中N1、N2為原、副線圈的匝數。由圖可知U1=-e1，U2=e2（原線圈物理量用下角標1表示，副線圈物理量用下角標2表示），其復有效值為U1=-E1=jN1ωΦ、U2=E2=-jN2ωΦ，令k=N1/N2，稱變壓器的變比。由上式可得U1/ U2=-N1/N2=-k，即變壓器原、副線圈電壓有效值之比，等于其匝數比而且原、副線圈電壓的位相差為π。

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