變壓(ya)(ya)器（Transformer）是(shi)利用電(dian)(dian)(dian)磁(ci)(ci)(ci)感應的原理來改變交(jiao)流電(dian)(dian)(dian)壓(ya)(ya)的裝置，主(zhu)(zhu)要(yao)構件是(shi)初級線(xian)(xian)圈、次級線(xian)(xian)圈和(he)鐵心（磁(ci)(ci)(ci)芯(xin)(xin)）。它的主(zhu)(zhu)要(yao)功能有電(dian)(dian)(dian)壓(ya)(ya)變換、電(dian)(dian)(dian)流變換、阻抗變換、隔離、穩壓(ya)(ya)（磁(ci)(ci)(ci)飽和(he)變壓(ya)(ya)器）等。當初級線(xian)(xian)圈中(zhong)通有交(jiao)流電(dian)(dian)(dian)流時，鐵芯(xin)(xin)（或(huo)磁(ci)(ci)(ci)芯(xin)(xin)）中(zhong)便(bian)產(chan)生(sheng)交(jiao)流磁(ci)(ci)(ci)通，使次級線(xian)(xian)圈中(zhong)感應出電(dian)(dian)(dian)壓(ya)(ya)（或(huo)電(dian)(dian)(dian)流）。

變(bian)壓器(qi)一般裝設以(yi)下保(bao)(bao)(bao)(bao)護(hu)(hu)：1.防(fang)御(yu)變(bian)壓器(qi)油(you)箱(xiang)內部(bu)故障和(he)(he)油(you)面(mian)降低的(de)瓦(wa)斯保(bao)(bao)(bao)(bao)護(hu)(hu)。2.防(fang)御(yu)變(bian)壓器(qi)繞(rao)組和(he)(he)引線的(de)多相(xiang)短路、中(zhong)性點直接接地(di)(di)電(dian)(dian)網側繞(rao)組和(he)(he)引線的(de)接地(di)(di)短路以(yi)及繞(rao)組匝間短路的(de)縱差動(dong)保(bao)(bao)(bao)(bao)護(hu)(hu)或電(dian)(dian)流(liu)(liu)速斷保(bao)(bao)(bao)(bao)護(hu)(hu)。3.防(fang)御(yu)外部(bu)相(xiang)間短路并作瓦(wa)斯保(bao)(bao)(bao)(bao)護(hu)(hu)和(he)(he)縱差動(dong)保(bao)(bao)(bao)(bao)護(hu)(hu)或電(dian)(dian)流(liu)(liu)速斷保(bao)(bao)(bao)(bao)護(hu)(hu)后備(bei)的(de)過(guo)電(dian)(dian)流(liu)(liu)保(bao)(bao)(bao)(bao)護(hu)(hu)。 4.防(fang)御(yu)中(zhong)性點直接接地(di)(di)電(dian)(dian)網中(zhong)外部(bu)接地(di)(di)短路的(de)零序電(dian)(dian)流(liu)(liu)保(bao)(bao)(bao)(bao)護(hu)(hu)，防(fang)御(yu)對(dui)稱過(guo)負(fu)荷的(de)過(guo)負(fu)荷保(bao)(bao)(bao)(bao)護(hu)(hu)。