變壓器組件由鐵芯（或(huo)磁(ci)芯）和線(xian)圈(quan)(quan)組成，線(xian)圈(quan)(quan)有兩個或(huo)兩個以上的繞(rao)組，其中(zhong)接電源的繞(rao)組叫初級線(xian)圈(quan)(quan)，其余的繞(rao)組叫次(ci)級線(xian)圈(quan)(quan)。它可以變換交流(liu)電壓(ya)、電流(liu)和阻抗。簡單的鐵心(xin)變壓(ya)器由一個軟磁(ci)材料做(zuo)成的鐵心(xin)及套在(zai)鐵心(xin)上的兩個匝數不等的線(xian)圈(quan)(quan)構成。

　　鐵(tie)(tie)(tie)(tie)心(xin)的(de)(de)(de)(de)作用是加強兩(liang)個(ge)線(xian)(xian)(xian)(xian)圈(quan)(quan)間(jian)的(de)(de)(de)(de)磁(ci)耦合。為(wei)了減少鐵(tie)(tie)(tie)(tie)內渦流(liu)和磁(ci)滯損耗，鐵(tie)(tie)(tie)(tie)心(xin)由(you)涂漆(qi)的(de)(de)(de)(de)硅鋼片(pian)疊壓(ya)(ya)(ya)而成;兩(liang)個(ge)線(xian)(xian)(xian)(xian)圈(quan)(quan)之間(jian)沒有電(dian)(dian)的(de)(de)(de)(de)聯(lian)系，線(xian)(xian)(xian)(xian)圈(quan)(quan)由(you)絕緣銅(tong)線(xian)(xian)(xian)(xian)（或鋁(lv)線(xian)(xian)(xian)(xian)）繞(rao)成。一個(ge)線(xian)(xian)(xian)(xian)圈(quan)(quan)接(jie)(jie)交流(liu)電(dian)(dian)源稱為(wei)初級(ji)線(xian)(xian)(xian)(xian)圈(quan)(quan)（或原(yuan)線(xian)(xian)(xian)(xian)圈(quan)(quan)），另一個(ge)線(xian)(xian)(xian)(xian)圈(quan)(quan)接(jie)(jie)用電(dian)(dian)器(qi)(qi)(qi)稱為(wei)次級(ji)線(xian)(xian)(xian)(xian)圈(quan)(quan)（或副(fu)線(xian)(xian)(xian)(xian)圈(quan)(quan)）。實際的(de)(de)(de)(de)變(bian)壓(ya)(ya)(ya)器(qi)(qi)(qi)是很(hen)復雜的(de)(de)(de)(de)，不可避(bi)免(mian)地存在銅(tong)損（線(xian)(xian)(xian)(xian)圈(quan)(quan)電(dian)(dian)阻發熱）、鐵(tie)(tie)(tie)(tie)損（鐵(tie)(tie)(tie)(tie)心(xin)發熱）和漏磁(ci)（經空氣閉合的(de)(de)(de)(de)磁(ci)感應線(xian)(xian)(xian)(xian)）等，為(wei)了簡化討論(lun)這里只(zhi)介紹理想(xiang)變(bian)壓(ya)(ya)(ya)器(qi)(qi)(qi)。理想(xiang)變(bian)壓(ya)(ya)(ya)器(qi)(qi)(qi)成立的(de)(de)(de)(de)條件(jian)是：忽略漏磁(ci)通，忽略原(yuan)、副(fu)線(xian)(xian)(xian)(xian)圈(quan)(quan)的(de)(de)(de)(de)電(dian)(dian)阻，忽略鐵(tie)(tie)(tie)(tie)心(xin)的(de)(de)(de)(de)損耗，忽略空載(zai)電(dian)(dian)流(liu)（副(fu)線(xian)(xian)(xian)(xian)圈(quan)(quan)開路原(yuan)線(xian)(xian)(xian)(xian)圈(quan)(quan)線(xian)(xian)(xian)(xian)圈(quan)(quan)中的(de)(de)(de)(de)電(dian)(dian)流(liu)）。例如電(dian)(dian)力(li)變(bian)壓(ya)(ya)(ya)器(qi)(qi)(qi)在滿載(zai)運行時（副(fu)線(xian)(xian)(xian)(xian)圈(quan)(quan)輸出額定功率）即接(jie)(jie)近理想(xiang)變(bian)壓(ya)(ya)(ya)器(qi)(qi)(qi)情況(kuang)。

　　變(bian)(bian)壓(ya)器(qi)組(zu)件(jian)是(shi)利用(yong)(yong)電(dian)(dian)磁(ci)(ci)感(gan)應(ying)原(yuan)(yuan)理(li)(li)制成的(de)(de)(de)靜止用(yong)(yong)電(dian)(dian)器(qi)。當變(bian)(bian)壓(ya)器(qi)的(de)(de)(de)原(yuan)(yuan)線(xian)(xian)(xian)圈(quan)(quan)(quan)接在交流電(dian)(dian)源(yuan)上(shang)時(shi)，鐵心中便(bian)產生交變(bian)(bian)磁(ci)(ci)通(tong)，交變(bian)(bian)磁(ci)(ci)通(tong)用(yong)(yong)φ表(biao)示(shi)。原(yuan)(yuan)、副(fu)線(xian)(xian)(xian)圈(quan)(quan)(quan)中的(de)(de)(de)φ是(shi)相同的(de)(de)(de)，φ也是(shi)簡諧函數，表(biao)為φ=φmsinωt。由(you)法拉第電(dian)(dian)磁(ci)(ci)感(gan)應(ying)定律可知，原(yuan)(yuan)、副(fu)線(xian)(xian)(xian)圈(quan)(quan)(quan)中的(de)(de)(de)感(gan)應(ying)電(dian)(dian)動勢(shi)為e1=-N1dφ/dt、e2=-N2dφ/dt。式中N1、N2為原(yuan)(yuan)、副(fu)線(xian)(xian)(xian)圈(quan)(quan)(quan)的(de)(de)(de)匝數。由(you)圖可知U1=-e1，U2=e2（原(yuan)(yuan)線(xian)(xian)(xian)圈(quan)(quan)(quan)物(wu)理(li)(li)量用(yong)(yong)下角標(biao)1表(biao)示(shi)，副(fu)線(xian)(xian)(xian)圈(quan)(quan)(quan)物(wu)理(li)(li)量用(yong)(yong)下角標(biao)2表(biao)示(shi)），其(qi)復有(you)效值(zhi)為U1=-E1=jN1ωΦ、U2=E2=-jN2ωΦ，令k=N1/N2，稱(cheng)變(bian)(bian)壓(ya)器(qi)的(de)(de)(de)變(bian)(bian)比(bi)(bi)。由(you)上(shang)式可得U1/ U2=-N1/N2=-k，即變(bian)(bian)壓(ya)器(qi)原(yuan)(yuan)、副(fu)線(xian)(xian)(xian)圈(quan)(quan)(quan)電(dian)(dian)壓(ya)有(you)效值(zhi)之(zhi)比(bi)(bi)，等(deng)于(yu)其(qi)匝數比(bi)(bi)而且(qie)原(yuan)(yuan)、副(fu)線(xian)(xian)(xian)圈(quan)(quan)(quan)電(dian)(dian)壓(ya)的(de)(de)(de)位相差為π。