對于排擠輸電線路,除導線電阻(zu)的(de)有功消(xiao)耗(hao)外(wai),還有電暈消(xiao)耗(hao)和沿盡緣子漏電而至的(de)有功消(xiao)耗(hao);
對于電纜線路(lu),主要是介質消(xiao)(xiao)耗(hao),一(yi)般在排(pai)擠線路(lu)中(zhong),由盡緣子泄露電流而發生的(de)有功(gong)消(xiao)(xiao)耗(hao)極小,可疏忽不記,所以對排(pai)擠線路(lu)主要斟(zhen)酌電暈消(xiao)(xiao)耗(hao)。
由于架空線(xian)路的(de)絕(jue)緣介質是空氣(qi),當導線(xian)表面的(de)電(dian)場強度超過空氣(qi)的(de)耐(nai)壓強度時,空氣(qi)層(ceng)就產(chan)生游離形成放(fang)電(dian),空氣(qi)中帶電(dian)離子的(de)移動就構成電(dian)暈電(dian)流。此刻(ke),我(wo)們可以聽到(dao)"滋滋"的(de)放(fang)電(dian)聲,并(bing)可聞到(dao)氧分子被(bei)游離后又結合成臭(chou)氧(O3)的(de)氣(qi)味,在(zai)夜間可見到(dao)導線(xian)周(zhou)圍發生淡藍色的(de)熒光,這種現(xian)象稱為"電(dian)暈"。電(dian)暈不(bu)但產(chan)生有功損耗,而且還對無線(xian)電(dian)及高頻通訊產(chan)生干擾(rao)。
電(dian)暈(yun)(yun)的產(chan)生(sheng)主(zhu)要與(yu)輸電(dian)電(dian)壓有關,隨(sui)著電(dian)壓升高,電(dian)暈(yun)(yun)常是先從(尖角不光滑(hua)處)電(dian)場強度(du)較大的局部(bu)開始放電(dian),叫(jiao)起始電(dian)暈(yun)(yun)。(起始電(dian)暈(yun)(yun)臨界強度(du)為30千伏/厘米)。隨(sui)后出(chu)現(xian)可見電(dian)暈(yun)(yun),并擴大到全(quan)(quan)部(bu)表(biao)面(mian),形(xing)成全(quan)(quan)面(mian)電(dian)暈(yun)(yun)。
一(yi)般(ban)在架空線路中(zhong),由絕緣子泄(xie)露(lu)電流而(er)產生的有(you)功損(sun)耗極小(xiao),可忽略不記,所以對架空線路主要考慮(lv)電暈損(sun)耗。
為了(le)減(jian)小電(dian)(dian)暈(yun)損耗,特別是減(jian)少對無(wu)線(xian)(xian)(xian)電(dian)(dian)和(he)高頻通(tong)訊的(de)(de)(de)干擾,應盡量設法避(bi)(bi)免(mian)電(dian)(dian)暈(yun)的(de)(de)(de)發生。而避(bi)(bi)免(mian)電(dian)(dian)暈(yun)的(de)(de)(de)方法是,提(ti)高線(xian)(xian)(xian)路(lu)電(dian)(dian)暈(yun)的(de)(de)(de)臨界電(dian)(dian)壓(ya)(ya),使(shi)其高于線(xian)(xian)(xian)路(lu)運行電(dian)(dian)壓(ya)(ya),為此就必須增(zeng)大導(dao)(dao)線(xian)(xian)(xian)間(jian)的(de)(de)(de)距(ju)離和(he)導(dao)(dao)線(xian)(xian)(xian)半(ban)(ban)徑。但若(ruo)增(zeng)大線(xian)(xian)(xian)間(jian)距(ju)離,必定使(shi)線(xian)(xian)(xian)路(lu)桿(gan)塔的(de)(de)(de)建造費用(yong)增(zeng)加,而對臨界電(dian)(dian)壓(ya)(ya)的(de)(de)(de)影響甚微。因此。增(zeng)大導(dao)(dao)線(xian)(xian)(xian)半(ban)(ban)徑才是提(ti)高臨界電(dian)(dian)壓(ya)(ya)的(de)(de)(de)有(you)效方法。所以在特高壓(ya)(ya)輸電(dian)(dian)線(xian)(xian)(xian)路(lu)中,采(cai)用(yong)擴徑導(dao)(dao)線(xian)(xian)(xian)或分裂導(dao)(dao)線(xian)(xian)(xian)(分裂導(dao)(dao)線(xian)(xian)(xian)的(de)(de)(de)等值半(ban)(ban)徑起了(le)擴徑的(de)(de)(de)作(zuo)用(yong))。