對于架空輸電線路，除了導線電阻的有功損耗外，還有電暈損耗和沿絕緣子漏電所致的有功損耗；對于電纜線路，主要是介質損耗。

 ;   一般(ban)在架空(kong)(kong)線(xian)(xian)路中，由絕緣子泄露電流而產(chan)生的有功損(sun)耗極小(xiao)，可(ke)忽略不記，所以對架空(kong)(kong)線(xian)(xian)路主要(yao)考慮電暈損(sun)耗。

    由(you)于架空(kong)線路的(de)絕(jue)緣介質是空(kong)氣(qi)(qi)(qi)，當導(dao)線表面的(de)電(dian)(dian)場強度(du)(du)超過空(kong)氣(qi)(qi)(qi)的(de)耐壓強度(du)(du)時，空(kong)氣(qi)(qi)(qi)層就產(chan)生游離(li)(li)形成放(fang)(fang)電(dian)(dian)，空(kong)氣(qi)(qi)(qi)中帶電(dian)(dian)離(li)(li)子(zi)的(de)移動就構成電(dian)(dian)暈(yun)電(dian)(dian)流。此刻，我們可以(yi)聽到"滋滋"的(de)放(fang)(fang)電(dian)(dian)聲，并(bing)可聞到氧分(fen)子(zi)被游離(li)(li)后(hou)又(you)結合成臭氧（O3）的(de)氣(qi)(qi)(qi)味，在(zai)夜間可見(jian)到導(dao)線周圍發生淡藍色的(de)熒光(guang)，這種現象稱為"電(dian)(dian)暈(yun)"。電(dian)(dian)暈(yun)不但產(chan)生有(you)功(gong)損耗，而且還對無線電(dian)(dian)及高頻通訊產(chan)生干擾(rao)。

    電(dian)(dian)暈的(de)(de)產(chan)生主(zhu)要與輸(shu)電(dian)(dian)電(dian)(dian)壓(ya)有關(guan)，隨著電(dian)(dian)壓(ya)升高，電(dian)(dian)暈常是先從（尖角不光滑處）電(dian)(dian)場強度較大的(de)(de)局部開(kai)始放電(dian)(dian)，叫起(qi)始電(dian)(dian)暈。（起(qi)始電(dian)(dian)暈臨界強度為30千伏/厘(li)米）。隨后出現可見電(dian)(dian)暈，并擴大到(dao)全部表(biao)面(mian)，形成全面(mian)電(dian)(dian)暈。

    為(wei)了(le)(le)減小(xiao)電(dian)(dian)(dian)(dian)(dian)暈損(sun)耗，特(te)別是(shi)減少對無線(xian)(xian)(xian)(xian)電(dian)(dian)(dian)(dian)(dian)和高(gao)頻通訊的(de)(de)干擾(rao)，應(ying)盡量(liang)設法(fa)避(bi)免電(dian)(dian)(dian)(dian)(dian)暈的(de)(de)發(fa)生。而避(bi)免電(dian)(dian)(dian)(dian)(dian)暈的(de)(de)方法(fa)是(shi)，提高(gao)線(xian)(xian)(xian)(xian)路(lu)電(dian)(dian)(dian)(dian)(dian)暈的(de)(de)臨(lin)界(jie)(jie)(jie)電(dian)(dian)(dian)(dian)(dian)壓，使(shi)其(qi)高(gao)于線(xian)(xian)(xian)(xian)路(lu)運(yun)行(xing)電(dian)(dian)(dian)(dian)(dian)壓，為(wei)此就(jiu)必須增(zeng)大導(dao)(dao)線(xian)(xian)(xian)(xian)間(jian)的(de)(de)距(ju)離和導(dao)(dao)線(xian)(xian)(xian)(xian)半(ban)徑。但(dan)若增(zeng)大線(xian)(xian)(xian)(xian)間(jian)距(ju)離，必定使(shi)線(xian)(xian)(xian)(xian)路(lu)桿塔的(de)(de)建造費(fei)用增(zeng)加，而對臨(lin)界(jie)(jie)(jie)電(dian)(dian)(dian)(dian)(dian)壓的(de)(de)影(ying)響盛微。因此。增(zeng)大導(dao)(dao)線(xian)(xian)(xian)(xian)半(ban)徑才是(shi)提高(gao)臨(lin)界(jie)(jie)(jie)電(dian)(dian)(dian)(dian)(dian)壓的(de)(de)有效方法(fa)。所以在特(te)高(gao)壓輸電(dian)(dian)(dian)(dian)(dian)線(xian)(xian)(xian)(xian)路(lu)中，采用擴徑導(dao)(dao)線(xian)(xian)(xian)(xian)或分裂(lie)(lie)導(dao)(dao)線(xian)(xian)(xian)(xian)（分裂(lie)(lie)導(dao)(dao)線(xian)(xian)(xian)(xian)的(de)(de)等值半(ban)徑起了(le)(le)擴徑的(de)(de)作用）。