由于架(jia)空(kong)線(xian)路的(de)絕緣介質(zhi)是空(kong)氣(qi)(qi)，當(dang)導線(xian)表面的(de)電(dian)(dian)(dian)(dian)(dian)場(chang)強(qiang)度(du)超過空(kong)氣(qi)(qi)的(de)耐壓強(qiang)度(du)時(shi)，空(kong)氣(qi)(qi)層就產生游離(li)形成(cheng)放電(dian)(dian)(dian)(dian)(dian)，空(kong)氣(qi)(qi)中帶電(dian)(dian)(dian)(dian)(dian)離(li)子的(de)移動就構成(cheng)電(dian)(dian)(dian)(dian)(dian)暈電(dian)(dian)(dian)(dian)(dian)流。此(ci)刻，我們可以聽到(dao)"滋(zi)滋(zi)"的(de)放電(dian)(dian)(dian)(dian)(dian)聲，并可聞到(dao)氧分子被游離(li)后又結(jie)合成(cheng)臭氧（O3）的(de)氣(qi)(qi)味，在夜間可見到(dao)導線(xian)周圍發生淡藍色的(de)熒光，這(zhe)種現象(xiang)稱(cheng)為"電(dian)(dian)(dian)(dian)(dian)暈"。電(dian)(dian)(dian)(dian)(dian)暈不(bu)但(dan)產生有功損耗，而且還對無線(xian)電(dian)(dian)(dian)(dian)(dian)及(ji)高頻通訊產生干擾(rao)。

為(wei)了(le)減(jian)小電(dian)(dian)暈損耗，特(te)別是(shi)減(jian)少對無線(xian)電(dian)(dian)和高(gao)頻通(tong)訊的(de)(de)干(gan)擾，應(ying)盡量設(she)法(fa)避免電(dian)(dian)暈的(de)(de)發生。而(er)避免電(dian)(dian)暈的(de)(de)方法(fa)是(shi)，提高(gao)線(xian)路(lu)電(dian)(dian)暈的(de)(de)臨(lin)界電(dian)(dian)壓(ya)，使其高(gao)于(yu)線(xian)路(lu)運(yun)行電(dian)(dian)壓(ya)，為(wei)此就(jiu)必須增(zeng)(zeng)(zeng)大(da)(da)導(dao)(dao)線(xian)間(jian)的(de)(de)距離和導(dao)(dao)線(xian)半徑(jing)(jing)。但若增(zeng)(zeng)(zeng)大(da)(da)線(xian)間(jian)距離，必定(ding)使線(xian)路(lu)桿塔的(de)(de)建造費用(yong)增(zeng)(zeng)(zeng)加，而(er)對臨(lin)界電(dian)(dian)壓(ya)的(de)(de)影響盛微(wei)。因此。增(zeng)(zeng)(zeng)大(da)(da)導(dao)(dao)線(xian)半徑(jing)(jing)才是(shi)提高(gao)臨(lin)界電(dian)(dian)壓(ya)的(de)(de)有(you)效方法(fa)。所以在特(te)高(gao)壓(ya)輸電(dian)(dian)線(xian)路(lu)中(zhong)，采用(yong)擴徑(jing)(jing)導(dao)(dao)線(xian)或分(fen)裂(lie)導(dao)(dao)線(xian)（分(fen)裂(lie)導(dao)(dao)線(xian)的(de)(de)等值(zhi)半徑(jing)(jing)起了(le)擴徑(jing)(jing)的(de)(de)作用(yong)）。