對于架(jia)空輸電線路，除了導(dao)線電阻的有(you)功損耗外，還(huan)有(you)電暈損耗和沿絕緣子漏(lou)電所(suo)致的有(you)功損耗；對于電纜(lan)線路，主要是介質(zhi)損耗。

    一般在架(jia)(jia)空(kong)線(xian)路(lu)中(zhong)，由絕緣(yuan)子泄露(lu)電流而產(chan)生的有功損(sun)耗極小，可忽(hu)略不記，所以對架(jia)(jia)空(kong)線(xian)路(lu)主要考慮電暈損(sun)耗。

    由于(yu)架空線(xian)路的(de)絕緣介質是空氣，當導線(xian)表面的(de)電(dian)(dian)(dian)(dian)場(chang)強度超過空氣的(de)耐壓強度時，空氣層就(jiu)產生游離(li)形(xing)成(cheng)放電(dian)(dian)(dian)(dian)，空氣中帶電(dian)(dian)(dian)(dian)離(li)子的(de)移動就(jiu)構(gou)成(cheng)電(dian)(dian)(dian)(dian)暈(yun)電(dian)(dian)(dian)(dian)流。此(ci)刻，我們可以聽到(dao)(dao)"滋(zi)(zi)滋(zi)(zi)"的(de)放電(dian)(dian)(dian)(dian)聲，并可聞(wen)到(dao)(dao)氧(yang)分子被游離(li)后又結合成(cheng)臭氧(yang)（O3）的(de)氣味，在夜間(jian)可見到(dao)(dao)導線(xian)周圍發生淡藍色的(de)熒光，這種現象稱為"電(dian)(dian)(dian)(dian)暈(yun)"。電(dian)(dian)(dian)(dian)暈(yun)不但產生有(you)功(gong)損耗，而且還對無線(xian)電(dian)(dian)(dian)(dian)及(ji)高(gao)頻通訊產生干擾。

    電(dian)暈的產生主要與(yu)輸電(dian)電(dian)壓有關，隨著電(dian)壓升高(gao)，電(dian)暈常是先從（尖(jian)角不光滑處）電(dian)場(chang)強度較(jiao)大的局部開始放電(dian)，叫起始電(dian)暈。（起始電(dian)暈臨(lin)界強度為(wei)30千伏/厘米(mi)）。隨后(hou)出現可見電(dian)暈，并擴大到全(quan)部表面，形成(cheng)全(quan)面電(dian)暈。

    為了減小電(dian)(dian)暈損(sun)耗，特(te)別是(shi)(shi)減少對無線(xian)(xian)(xian)電(dian)(dian)和高(gao)頻(pin)通訊的(de)(de)(de)干擾，應盡量(liang)設法(fa)避免電(dian)(dian)暈的(de)(de)(de)發生。而避免電(dian)(dian)暈的(de)(de)(de)方法(fa)是(shi)(shi)，提高(gao)線(xian)(xian)(xian)路(lu)電(dian)(dian)暈的(de)(de)(de)臨(lin)界電(dian)(dian)壓(ya)，使(shi)其高(gao)于線(xian)(xian)(xian)路(lu)運行(xing)電(dian)(dian)壓(ya)，為此就必須增(zeng)大導(dao)(dao)線(xian)(xian)(xian)間的(de)(de)(de)距離(li)和導(dao)(dao)線(xian)(xian)(xian)半徑(jing)。但(dan)若增(zeng)大線(xian)(xian)(xian)間距離(li)，必定使(shi)線(xian)(xian)(xian)路(lu)桿(gan)塔的(de)(de)(de)建造(zao)費用(yong)(yong)增(zeng)加，而對臨(lin)界電(dian)(dian)壓(ya)的(de)(de)(de)影響盛微。因此。增(zeng)大導(dao)(dao)線(xian)(xian)(xian)半徑(jing)才是(shi)(shi)提高(gao)臨(lin)界電(dian)(dian)壓(ya)的(de)(de)(de)有效方法(fa)。所以在特(te)高(gao)壓(ya)輸(shu)電(dian)(dian)線(xian)(xian)(xian)路(lu)中，采用(yong)(yong)擴徑(jing)導(dao)(dao)線(xian)(xian)(xian)或分裂導(dao)(dao)線(xian)(xian)(xian)（分裂導(dao)(dao)線(xian)(xian)(xian)的(de)(de)(de)等值半徑(jing)起了擴徑(jing)的(de)(de)(de)作用(yong)(yong)）。