護層是電(dian)(dian)(dian)(dian)纜(lan)外層的(de)保護部分。根(gen)據電(dian)(dian)(dian)(dian)纜(lan)的(de)用途以及(ji)使用環境(jing)和絕緣(yuan)(yuan)的(de)不同(tong)，護層有許(xu)多不同(tong)型式和結構，它們所起的(de)作用也(ye)不盡相同(tong)。扇(shan)形芯(xin)的(de)中(zhong)(zhong)央導線(xian)(xian)(xian)必須位于扇(shan)形芯(xin)的(de)中(zhong)(zhong)心線(xian)(xian)(xian)上，否則，當線(xian)(xian)(xian)芯(xin)彎(wan)曲時，位于中(zhong)(zhong)心線(xian)(xian)(xian)上部導線(xian)(xian)(xian)將(jiang)被拉伸，而下部的(de)將(jiang)受壓縮而可能(neng)擠出，電(dian)(dian)(dian)(dian)力電(dian)(dian)(dian)(dian)纜(lan)廠家排名(ming)，這(zhe)將(jiang)引起扇(shan)形破(po)壞而損傷絕緣(yuan)(yuan)。電(dian)(dian)(dian)(dian)力電(dian)(dian)(dian)(dian)纜(lan)主要有導體直流電(dian)(dian)(dian)(dian)阻、絕緣(yuan)(yuan)電(dian)(dian)(dian)(dian)阻、成(cheng)品電(dian)(dian)(dian)(dian)壓試(shi)驗及(ji)絕緣(yuan)(yuan)線(xian)(xian)(xian)芯(xin)間電(dian)(dian)(dian)(dian)壓試(shi)驗，每(mei)項都很(hen)重要，導體電(dian)(dian)(dian)(dian)阻直接反映了電(dian)(dian)(dian)(dian)纜(lan)的(de)電(dian)(dian)(dian)(dian)傳輸性能(neng)，直接影(ying)響電(dian)(dian)(dian)(dian)纜(lan)在通電(dian)(dian)(dian)(dian)運行(xing)中(zhong)(zhong)的(de)溫度、壽命、電(dian)(dian)(dian)(dian)壓降、以及(ji)運行(xing)安全。

引(yin)起電(dian)纜(lan)導(dao)體(ti)本身(shen)(shen)發熱，引(yin)起包覆導(dao)體(ti)的(de)(de)(de)絕(jue)(jue)(jue)緣老化開裂，造成(cheng)供(gong)電(dian)線(xian)路(lu)漏(lou)電(dian)、短路(lu)，甚(shen)至造成(cheng)火(huo)災(zai)，危及人身(shen)(shen)、財產的(de)(de)(de)安全。標準(zhun)對(dui)不(bu)同規(gui)格電(dian)纜(lan)的(de)(de)(de)導(dao)體(ti)直(zhi)流電(dian)阻值(zhi)均有(you)嚴格的(de)(de)(de)規(gui)定，不(bu)得大于標準(zhun)規(gui)定的(de)(de)(de)值(zhi)。成(cheng)品電(dian)壓(ya)試驗及絕(jue)(jue)(jue)緣線(xian)芯間電(dian)壓(ya)試驗不(bu)光要求電(dian)纜(lan)有(you)足夠(gou)的(de)(de)(de)絕(jue)(jue)(jue)緣能(neng)力，還要求絕(jue)(jue)(jue)緣或(huo)護套材料均勻無雜(za)質、厚(hou)度足夠(gou)均勻，表面不(bu)能(neng)有(you)看不(bu)見的(de)(de)(de)、等，否則(ze)就(jiu)會(hui)造成(cheng)耐壓(ya)試驗時局(ju)部(bu)擊穿(chuan)。絕(jue)(jue)(jue)緣是將絕(jue)(jue)(jue)緣材料按其耐受電(dian)壓(ya)程度的(de)(de)(de)要求，以不(bu)同的(de)(de)(de)厚(hou)度包復在(zai)導(dao)體(ti)外(wai)面而(er)成(cheng)，起著使帶電(dian)體(ti)與其他(ta)部(bu)分隔絕(jue)(jue)(jue)的(de)(de)(de)作用。

電(dian)力電(dian)纜(lan)主要考(kao)查(cha)導(dao)體的(de)(de)(de)材質和截面(mian)積，若導(dao)體的(de)(de)(de)材質不好或截面(mian)積嚴重不足，就會造成導(dao)體直流電(dian)阻(zu)嚴重超標，這種電(dian)纜(lan)鋪設在(zai)線路中(zhong)就會增加(jia)電(dian)流在(zai)線路上(shang)(shang)通過時(shi)的(de)(de)(de)損耗(hao)。圓形(xing)導(dao)電(dian)線芯(xin)(xin)，其絞合排列(lie)一(yi)般(ban)(ban)采用“正規絞合”的(de)(de)(de)形(xing)式，絞合原則是，中(zhong)心(xin)一(yi)般(ban)(ban)為一(yi)根單線，第(di)二層(ceng)為六(liu)根單線，以(yi)后(hou)每層(ceng)比內(nei)層(ceng)多六(liu)根，單線采用相同(tong)的(de)(de)(de)線徑。扇形(xing)芯(xin)(xin)的(de)(de)(de)中(zhong)央導(dao)線必須位于扇形(xing)芯(xin)(xin)的(de)(de)(de)中(zhong)心(xin)線上(shang)(shang)，否則，當(dang)線芯(xin)(xin)彎(wan)曲(qu)時(shi)，位于中(zhong)心(xin)線上(shang)(shang)部導(dao)線將被拉伸(shen)，而下部的(de)(de)(de)將受壓縮而可能(neng)擠(ji)出，這將引起(qi)扇形(xing)破壞而損傷(shang)絕緣。