對于架空(kong)輸(shu)電(dian)(dian)線(xian)路(lu)，除了導(dao)線(xian)電(dian)(dian)阻的有功損(sun)(sun)耗外，還有電(dian)(dian)暈損(sun)(sun)耗和沿(yan)絕(jue)緣子(zi)漏電(dian)(dian)所致的有功損(sun)(sun)耗；對于電(dian)(dian)纜線(xian)路(lu)，主要是介(jie)質損(sun)(sun)耗。

    一般在架(jia)空(kong)線(xian)路(lu)中，由絕緣(yuan)子泄露電流而(er)產生的有(you)功損(sun)耗極小，可(ke)忽略不記，所以對架(jia)空(kong)線(xian)路(lu)主要考(kao)慮(lv)電暈損(sun)耗。

    由于架空線路的(de)絕緣介質是(shi)空氣，當導(dao)線表面的(de)電(dian)(dian)場強度(du)超過空氣的(de)耐壓強度(du)時，空氣層就(jiu)產生(sheng)(sheng)(sheng)游離形成(cheng)放電(dian)(dian)，空氣中帶(dai)電(dian)(dian)離子(zi)的(de)移動就(jiu)構成(cheng)電(dian)(dian)暈(yun)電(dian)(dian)流(liu)。此刻，我們可(ke)(ke)以聽到"滋滋"的(de)放電(dian)(dian)聲，并可(ke)(ke)聞到氧分子(zi)被游離后又結合(he)成(cheng)臭氧（O3）的(de)氣味，在(zai)夜(ye)間可(ke)(ke)見到導(dao)線周(zhou)圍發(fa)生(sheng)(sheng)(sheng)淡藍色的(de)熒光，這(zhe)種現象稱(cheng)為(wei)"電(dian)(dian)暈(yun)"。電(dian)(dian)暈(yun)不但產生(sheng)(sheng)(sheng)有功損耗(hao)，而且還對(dui)無(wu)線電(dian)(dian)及(ji)高頻通訊產生(sheng)(sheng)(sheng)干擾(rao)。

    電(dian)暈(yun)(yun)(yun)(yun)(yun)的產生主要與輸電(dian)電(dian)壓(ya)有(you)關，隨著電(dian)壓(ya)升高，電(dian)暈(yun)(yun)(yun)(yun)(yun)常是先從（尖(jian)角不光滑(hua)處）電(dian)場強(qiang)度較大(da)的局部開始放電(dian)，叫起(qi)始電(dian)暈(yun)(yun)(yun)(yun)(yun)。（起(qi)始電(dian)暈(yun)(yun)(yun)(yun)(yun)臨界(jie)強(qiang)度為30千伏(fu)/厘米）。隨后出現可見(jian)電(dian)暈(yun)(yun)(yun)(yun)(yun)，并擴大(da)到全部表(biao)面(mian)，形成全面(mian)電(dian)暈(yun)(yun)(yun)(yun)(yun)。

    為(wei)了減小電(dian)(dian)(dian)(dian)暈(yun)損耗(hao)，特(te)別是(shi)減少對無(wu)線(xian)(xian)(xian)電(dian)(dian)(dian)(dian)和(he)高(gao)(gao)(gao)頻通訊(xun)的(de)(de)(de)干擾(rao)，應盡量設法(fa)避免電(dian)(dian)(dian)(dian)暈(yun)的(de)(de)(de)發(fa)生。而避免電(dian)(dian)(dian)(dian)暈(yun)的(de)(de)(de)方法(fa)是(shi)，提高(gao)(gao)(gao)線(xian)(xian)(xian)路電(dian)(dian)(dian)(dian)暈(yun)的(de)(de)(de)臨(lin)界(jie)電(dian)(dian)(dian)(dian)壓(ya)，使(shi)其高(gao)(gao)(gao)于線(xian)(xian)(xian)路運行電(dian)(dian)(dian)(dian)壓(ya)，為(wei)此就必須增(zeng)(zeng)(zeng)大(da)導(dao)線(xian)(xian)(xian)間(jian)的(de)(de)(de)距(ju)離和(he)導(dao)線(xian)(xian)(xian)半徑。但若(ruo)增(zeng)(zeng)(zeng)大(da)線(xian)(xian)(xian)間(jian)距(ju)離，必定使(shi)線(xian)(xian)(xian)路桿塔的(de)(de)(de)建(jian)造費用(yong)增(zeng)(zeng)(zeng)加，而對臨(lin)界(jie)電(dian)(dian)(dian)(dian)壓(ya)的(de)(de)(de)影(ying)響盛微。因此。增(zeng)(zeng)(zeng)大(da)導(dao)線(xian)(xian)(xian)半徑才是(shi)提高(gao)(gao)(gao)臨(lin)界(jie)電(dian)(dian)(dian)(dian)壓(ya)的(de)(de)(de)有(you)效方法(fa)。所以在特(te)高(gao)(gao)(gao)壓(ya)輸電(dian)(dian)(dian)(dian)線(xian)(xian)(xian)路中，采用(yong)擴徑導(dao)線(xian)(xian)(xian)或(huo)分裂導(dao)線(xian)(xian)(xian)（分裂導(dao)線(xian)(xian)(xian)的(de)(de)(de)等(deng)值半徑起(qi)了擴徑的(de)(de)(de)作(zuo)用(yong)）。