擴徑(jing)導線(xian)(xian)線(xian)(xian)膨(peng)脹系(xi)數較好(hao)，電(dian)(dian)(dian)(dian)(dian)暈(yun)損(sun)失小(xiao)，有(you)良好(hao)的(de)散(san)熱性。適(shi)用于高低壓輸電(dian)(dian)(dian)(dian)(dian)線(xian)(xian)中電(dian)(dian)(dian)(dian)(dian)廠及變電(dian)(dian)(dian)(dian)(dian)站配電(dian)(dian)(dian)(dian)(dian)線(xian)(xian)路、母(mu)線(xian)(xian)等。減少電(dian)(dian)(dian)(dian)(dian)暈(yun)損(sun)失，節(jie)約有(you)色金屬。

對于架空(kong)(kong)輸(shu)電線路(lu)，除(chu)了導線電阻(zu)的(de)(de)有(you)(you)功損(sun)(sun)耗(hao)外，還有(you)(you)電暈(yun)損(sun)(sun)耗(hao)和沿絕(jue)緣子漏電所(suo)致的(de)(de)有(you)(you)功損(sun)(sun)耗(hao)；對于電纜線路(lu)，主要是介(jie)質(zhi)損(sun)(sun)耗(hao)。一般在架空(kong)(kong)線路(lu)中，由(you)絕(jue)緣子泄露電流而產生的(de)(de)有(you)(you)功損(sun)(sun)耗(hao)極小，可忽略不記，所(suo)以對架空(kong)(kong)線路(lu)主要考慮電暈(yun)損(sun)(sun)耗(hao)。

由于架空(kong)線(xian)路(lu)的(de)(de)(de)(de)(de)絕緣介(jie)質是(shi)空(kong)氣(qi)(qi)，當導線(xian)表面的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)場強(qiang)度(du)(du)超過空(kong)氣(qi)(qi)的(de)(de)(de)(de)(de)耐壓(ya)(ya)強(qiang)度(du)(du)時(shi)，空(kong)氣(qi)(qi)層(ceng)就(jiu)產(chan)(chan)生(sheng)游(you)離(li)(li)形成(cheng)(cheng)放電(dian)(dian)(dian)(dian)(dian)，空(kong)氣(qi)(qi)中(zhong)帶電(dian)(dian)(dian)(dian)(dian)離(li)(li)子的(de)(de)(de)(de)(de)移動就(jiu)構成(cheng)(cheng)電(dian)(dian)(dian)(dian)(dian)暈(yun)電(dian)(dian)(dian)(dian)(dian)流。此刻(ke)，我們可(ke)(ke)以聽(ting)到(dao)滋滋的(de)(de)(de)(de)(de)放電(dian)(dian)(dian)(dian)(dian)聲，并(bing)可(ke)(ke)聞到(dao)氧(yang)分子被游(you)離(li)(li)后又結合成(cheng)(cheng)臭氧(yang)的(de)(de)(de)(de)(de)氣(qi)(qi)味，在夜間(jian)可(ke)(ke)見到(dao)導線(xian)周圍(wei)發生(sheng)淡(dan)藍色的(de)(de)(de)(de)(de)熒光，這種現(xian)象(xiang)稱為電(dian)(dian)(dian)(dian)(dian)暈(yun)。電(dian)(dian)(dian)(dian)(dian)暈(yun)不但產(chan)(chan)生(sheng)有(you)功損耗(hao)，而且還對(dui)無線(xian)電(dian)(dian)(dian)(dian)(dian)及高(gao)頻通(tong)訊產(chan)(chan)生(sheng)干(gan)擾。電(dian)(dian)(dian)(dian)(dian)暈(yun)的(de)(de)(de)(de)(de)產(chan)(chan)生(sheng)主要與輸電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)有(you)關(guan)，隨(sui)著(zhu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)升高(gao)，電(dian)(dian)(dian)(dian)(dian)暈(yun)常是(shi)先從（尖角不光滑處）電(dian)(dian)(dian)(dian)(dian)場強(qiang)度(du)(du)較大(da)(da)(da)的(de)(de)(de)(de)(de)局部開始(shi)(shi)放電(dian)(dian)(dian)(dian)(dian)，叫起始(shi)(shi)電(dian)(dian)(dian)(dian)(dian)暈(yun)。（起始(shi)(shi)電(dian)(dian)(dian)(dian)(dian)暈(yun)臨界強(qiang)度(du)(du)為30千伏/厘米）。隨(sui)后出現(xian)可(ke)(ke)見電(dian)(dian)(dian)(dian)(dian)暈(yun)，并(bing)擴大(da)(da)(da)到(dao)全部表面，形成(cheng)(cheng)全面電(dian)(dian)(dian)(dian)(dian)暈(yun)。為了減小電(dian)(dian)(dian)(dian)(dian)暈(yun)損耗(hao)，特別是(shi)減少對(dui)無線(xian)電(dian)(dian)(dian)(dian)(dian)和高(gao)頻通(tong)訊的(de)(de)(de)(de)(de)干(gan)擾，應盡(jin)量設法避(bi)免電(dian)(dian)(dian)(dian)(dian)暈(yun)的(de)(de)(de)(de)(de)發生(sheng)。而避(bi)免電(dian)(dian)(dian)(dian)(dian)暈(yun)的(de)(de)(de)(de)(de)方法是(shi)，提高(gao)線(xian)路(lu)電(dian)(dian)(dian)(dian)(dian)暈(yun)的(de)(de)(de)(de)(de)臨界電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，使其高(gao)于線(xian)路(lu)運行(xing)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，為此就(jiu)必須(xu)增大(da)(da)(da)導線(xian)間(jian)的(de)(de)(de)(de)(de)距(ju)離(li)(li)和導線(xian)半徑。但若增大(da)(da)(da)線(xian)間(jian)距(ju)離(li)(li)，必定使線(xian)路(lu)桿塔(ta)的(de)(de)(de)(de)(de)建造費(fei)用增加，而對(dui)臨界電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)的(de)(de)(de)(de)(de)影響盛微。

因此。增大(da)導線(xian)半徑(jing)才是提高(gao)臨界電(dian)壓的(de)有效方法。所以在特高(gao)壓輸(shu)電(dian)線(xian)路中(zhong)，采用(yong)擴(kuo)徑(jing)導線(xian)或分裂導線(xian)（分裂導線(xian)的(de)等(deng)值(zhi)半徑(jing)起了擴(kuo)徑(jing)的(de)作(zuo)用(yong)）。