對于架空輸電(dian)線路(lu)，除了(le)導線電(dian)阻的有(you)功損(sun)(sun)(sun)耗外(wai)，還有(you)電(dian)暈損(sun)(sun)(sun)耗和沿絕緣子漏電(dian)所致的有(you)功損(sun)(sun)(sun)耗；對于電(dian)纜線路(lu)，主要是(shi)介(jie)質損(sun)(sun)(sun)耗。

    一般在架(jia)空線(xian)路(lu)中，由(you)絕緣(yuan)子泄露電流而(er)產(chan)生(sheng)的(de)有功損耗極小，可忽略不記，所以對架(jia)空線(xian)路(lu)主要考慮電暈損耗。

    由(you)于架空(kong)(kong)線(xian)路的(de)絕緣(yuan)介質是(shi)空(kong)(kong)氣(qi)，當導(dao)(dao)線(xian)表面(mian)的(de)電(dian)(dian)(dian)場強(qiang)度超過(guo)空(kong)(kong)氣(qi)的(de)耐壓強(qiang)度時，空(kong)(kong)氣(qi)層就產(chan)生(sheng)游離形成(cheng)(cheng)放電(dian)(dian)(dian)，空(kong)(kong)氣(qi)中帶電(dian)(dian)(dian)離子的(de)移動就構成(cheng)(cheng)電(dian)(dian)(dian)暈(yun)電(dian)(dian)(dian)流。此(ci)刻，我們可(ke)(ke)(ke)以(yi)聽(ting)到"滋(zi)滋(zi)"的(de)放電(dian)(dian)(dian)聲，并可(ke)(ke)(ke)聞到氧(yang)分子被游離后(hou)又結合(he)成(cheng)(cheng)臭氧(yang)（O3）的(de)氣(qi)味，在夜間可(ke)(ke)(ke)見到導(dao)(dao)線(xian)周(zhou)圍發生(sheng)淡藍(lan)色的(de)熒光，這(zhe)種現象稱為"電(dian)(dian)(dian)暈(yun)"。電(dian)(dian)(dian)暈(yun)不但產(chan)生(sheng)有功損耗，而且還(huan)對(dui)無(wu)線(xian)電(dian)(dian)(dian)及(ji)高(gao)頻通訊產(chan)生(sheng)干擾。

    電(dian)暈(yun)的產生主要與輸電(dian)電(dian)壓有(you)關，隨(sui)著電(dian)壓升高，電(dian)暈(yun)常是先從（尖角不(bu)光滑處）電(dian)場強度較(jiao)大的局部開始放電(dian)，叫起始電(dian)暈(yun)。（起始電(dian)暈(yun)臨(lin)界強度為30千伏(fu)/厘(li)米）。隨(sui)后出現可見電(dian)暈(yun)，并擴大到全(quan)部表(biao)面，形成全(quan)面電(dian)暈(yun)。

    為(wei)了減小電暈損耗，特別是減少對(dui)無(wu)線(xian)(xian)(xian)(xian)電和高(gao)頻(pin)通訊的(de)(de)(de)干擾(rao)，應盡量設法(fa)避免電暈的(de)(de)(de)發生。而避免電暈的(de)(de)(de)方法(fa)是，提高(gao)線(xian)(xian)(xian)(xian)路電暈的(de)(de)(de)臨界(jie)電壓(ya)(ya)(ya)，使(shi)其高(gao)于線(xian)(xian)(xian)(xian)路運(yun)行電壓(ya)(ya)(ya)，為(wei)此就必須增大導(dao)線(xian)(xian)(xian)(xian)間(jian)的(de)(de)(de)距(ju)離和導(dao)線(xian)(xian)(xian)(xian)半徑(jing)。但若(ruo)增大線(xian)(xian)(xian)(xian)間(jian)距(ju)離，必定(ding)使(shi)線(xian)(xian)(xian)(xian)路桿塔的(de)(de)(de)建造費用(yong)(yong)增加，而對(dui)臨界(jie)電壓(ya)(ya)(ya)的(de)(de)(de)影(ying)響盛微。因此。增大導(dao)線(xian)(xian)(xian)(xian)半徑(jing)才是提高(gao)臨界(jie)電壓(ya)(ya)(ya)的(de)(de)(de)有效方法(fa)。所以在特高(gao)壓(ya)(ya)(ya)輸電線(xian)(xian)(xian)(xian)路中，采用(yong)(yong)擴徑(jing)導(dao)線(xian)(xian)(xian)(xian)或分(fen)(fen)裂(lie)導(dao)線(xian)(xian)(xian)(xian)（分(fen)(fen)裂(lie)導(dao)線(xian)(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)）。