對于架空輸電線路，除(chu)了導線電阻的(de)有(you)(you)功損耗外，還有(you)(you)電暈損耗和沿(yan)絕緣子漏電所致(zhi)的(de)有(you)(you)功損耗；對于電纜線路，主(zhu)要是介(jie)質損耗。

    一(yi)般在架空線路中，由絕(jue)緣子(zi)泄(xie)露電流而(er)產(chan)生(sheng)的有功損耗(hao)極小，可忽略不記，所(suo)以(yi)對(dui)架空線路主要考慮電暈損耗(hao)。

    由于架(jia)空線(xian)(xian)(xian)路的(de)絕(jue)緣介質是空氣(qi)，當導線(xian)(xian)(xian)表面的(de)電(dian)場(chang)強度(du)超過空氣(qi)的(de)耐壓強度(du)時，空氣(qi)層就產(chan)生游離形(xing)成放電(dian)，空氣(qi)中帶(dai)電(dian)離子(zi)的(de)移動就構(gou)成電(dian)暈電(dian)流。此刻，我們可以聽(ting)到"滋滋"的(de)放電(dian)聲，并可聞到氧(yang)分子(zi)被游離后又結(jie)合成臭(chou)氧(yang)（O3）的(de)氣(qi)味，在夜間可見到導線(xian)(xian)(xian)周圍發生淡藍色的(de)熒光(guang)，這種現象稱為"電(dian)暈"。電(dian)暈不但產(chan)生有功損耗，而且(qie)還對無線(xian)(xian)(xian)電(dian)及高頻通訊產(chan)生干擾。

    電(dian)(dian)(dian)暈(yun)的產生主要與輸電(dian)(dian)(dian)電(dian)(dian)(dian)壓有(you)關，隨著電(dian)(dian)(dian)壓升高(gao)，電(dian)(dian)(dian)暈(yun)常是先從(cong)（尖角不光(guang)滑(hua)處）電(dian)(dian)(dian)場(chang)強度較大(da)的局部開始放(fang)電(dian)(dian)(dian)，叫起始電(dian)(dian)(dian)暈(yun)。（起始電(dian)(dian)(dian)暈(yun)臨界強度為30千伏/厘米）。隨后出現可見(jian)電(dian)(dian)(dian)暈(yun)，并擴(kuo)大(da)到全(quan)部表面，形成全(quan)面電(dian)(dian)(dian)暈(yun)。

    為(wei)了(le)減小電(dian)(dian)(dian)暈損(sun)耗(hao)，特別是減少對無線(xian)(xian)電(dian)(dian)(dian)和高(gao)(gao)頻(pin)通訊的(de)(de)(de)(de)干擾，應盡量設法避(bi)免(mian)電(dian)(dian)(dian)暈的(de)(de)(de)(de)發生。而避(bi)免(mian)電(dian)(dian)(dian)暈的(de)(de)(de)(de)方(fang)法是，提高(gao)(gao)線(xian)(xian)路(lu)電(dian)(dian)(dian)暈的(de)(de)(de)(de)臨(lin)界(jie)電(dian)(dian)(dian)壓(ya)(ya)，使其高(gao)(gao)于(yu)線(xian)(xian)路(lu)運行電(dian)(dian)(dian)壓(ya)(ya)，為(wei)此(ci)就必須增大導(dao)(dao)(dao)(dao)線(xian)(xian)間(jian)的(de)(de)(de)(de)距離和導(dao)(dao)(dao)(dao)線(xian)(xian)半徑。但若增大線(xian)(xian)間(jian)距離，必定使線(xian)(xian)路(lu)桿塔的(de)(de)(de)(de)建造費用(yong)增加，而對臨(lin)界(jie)電(dian)(dian)(dian)壓(ya)(ya)的(de)(de)(de)(de)影響盛微。因(yin)此(ci)。增大導(dao)(dao)(dao)(dao)線(xian)(xian)半徑才是提高(gao)(gao)臨(lin)界(jie)電(dian)(dian)(dian)壓(ya)(ya)的(de)(de)(de)(de)有效方(fang)法。所(suo)以在特高(gao)(gao)壓(ya)(ya)輸電(dian)(dian)(dian)線(xian)(xian)路(lu)中，采用(yong)擴徑導(dao)(dao)(dao)(dao)線(xian)(xian)或分裂(lie)導(dao)(dao)(dao)(dao)線(xian)(xian)（分裂(lie)導(dao)(dao)(dao)(dao)線(xian)(xian)的(de)(de)(de)(de)等值半徑起(qi)了(le)擴徑的(de)(de)(de)(de)作(zuo)用(yong)）。