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保(bao)險絲(si)（fuse）也(ye)被稱為(wei)電流(liu)保(bao)險絲(si)，IEC127標準將它定義為(wei)“熔(rong)斷(duan)體（fuse-link）”。其主要是(shi)起過載保(bao)護作(zuo)用。電路(lu)中(zhong)正確安置保(bao)險絲(si)，就會在電流(liu)異常升高到(dao)一定的高度和熱度的時候，自身(shen)熔(rong)斷(duan)切(qie)斷(duan)電流(liu)，保(bao)護了(le)電路(lu)安全運行。
一百多年前由(you)愛(ai)迪(di)生發(fa)(fa)明的保(bao)險絲用于保(bao)護當時昂(ang)貴的白熾(chi)燈，隨著時代(dai)的發(fa)(fa)展，保(bao)險絲保(bao)護電(dian)力設備不受過(guo)電(dian)流過(guo)熱的傷害(hai)，避(bi)免電(dian)子設備因內部故障所(suo)引起的嚴重(zhong)傷害(hai)。
為什么保險絲要電阻率大
保險(xian)(xian)絲(si)由電(dian)(dian)(dian)阻(zu)率比較(jiao)(jiao)熔(rong)點較(jiao)(jiao)低鉛(qian)銻合金制(zhi)導線叫做保險(xian)(xian)絲(si)。 電(dian)(dian)(dian)壓(ya)定電(dian)(dian)(dian)阻(zu)比較(jiao)(jiao)越能(neng)(neng)(neng)檢(jian)測超工作范圍微電(dian)(dian)(dian)流(liu)電(dian)(dian)(dian)阻(zu)需要較(jiao)(jiao)電(dian)(dian)(dian)流(liu)才能(neng)(neng)(neng)熔(rong)斷(duan)能(neng)(neng)(neng)燒毀電(dian)(dian)(dian)器(qi)沒熔(rong)斷(duan)。些原理利用(yong)電(dian)(dian)(dian)流(liu)熱效應(ying)保險(xian)(xian)絲(si)控制(zhi)通(tong)電(dian)(dian)(dian)流(liu)允許電(dian)(dian)(dian)流(liu)通(tong)情況根據(ju)公式(shi)Q=IRT電(dian)(dian)(dian)阻(zu)產更熱量更易熔(rong)斷(duan)安全(quan)起保護作用(yong)，和焦(jiao)耳定律有一(yi)定關系，可生活(huo)中的(de)(de)事(shi)情沒那么簡單，保險(xian)(xian)絲(si)既不能(neng)(neng)(neng)大(da)也不能(neng)(neng)(neng)小(xiao)，過(guo)大(da)容易燒毀家庭中的(de)(de)電(dian)(dian)(dian)線甚至引(yin)起火災，過(guo)小(xiao)則易熔(rong)斷(duan)造成不必(bi)要的(de)(de)麻(ma)煩。
保(bao)(bao)險(xian)(xian)(xian)絲(si)(si)能(neng)直(zhi)接看(kan)(kan)導(dao)(dao)(dao)(dao)線(xian)(xian)道理簡(jian)單額定電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)內候保(bao)(bao)險(xian)(xian)(xian)絲(si)(si)確同導(dao)(dao)(dao)(dao)線(xian)(xian)即便(bian)能(neng)其看(kan)(kan)做(zuo)導(dao)(dao)(dao)(dao)線(xian)(xian)導(dao)(dao)(dao)(dao)線(xian)(xian)橫(heng)截(jie)面積越導(dao)(dao)(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)越保(bao)(bao)險(xian)(xian)(xian)絲(si)(si)則同規(gui)保(bao)(bao)險(xian)(xian)(xian)絲(si)(si)都0.023歐姆電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻且同橫(heng)截(jie)面積導(dao)(dao)(dao)(dao)線(xian)(xian)面前(qian)同電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)保(bao)(bao)險(xian)(xian)(xian)絲(si)(si)溫度高于導(dao)(dao)(dao)(dao)線(xian)(xian)同橫(heng)截(jie)面積同電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)保(bao)(bao)險(xian)(xian)(xian)絲(si)(si)通電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)低于導(dao)(dao)(dao)(dao)線(xian)(xian)忽略電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)情況且電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)僅保(bao)(bao)險(xian)(xian)(xian)絲(si)(si)耐限電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)2.3%才保(bao)(bao)險(xian)(xian)(xian)絲(si)(si)同等于導(dao)(dao)(dao)(dao)線(xian)(xian)看(kan)(kan)待例額定電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)12v1A保(bao)(bao)險(xian)(xian)(xian)絲(si)(si)放380V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)且電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)僅20毫安保(bao)(bao)險(xian)(xian)(xian)絲(si)(si)相于導(dao)(dao)(dao)(dao)線(xian)(xian)類推保(bao)(bao)險(xian)(xian)(xian)絲(si)(si)并聯燈泡：電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)低于保(bao)(bao)險(xian)(xian)(xian)絲(si)(si)額定電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)燈泡僅微弱電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)（類似短路(lu)）電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)超保(bao)(bao)險(xian)(xian)(xian)絲(si)(si)額定電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)燈泡亮保(bao)(bao)險(xian)(xian)(xian)絲(si)(si)燒斷。
保險絲有阻值嗎？
保險絲(si)有(you)電(dian)阻值，其實就連(lian)導(dao)線也有(you)電(dian)阻，只是(shi)導(dao)線的電(dian)阻很小(xiao)（導(dao)體的性質），在一般(ban)的電(dian)路(lu)計(ji)算中，我(wo)們(men)通常(chang)不(bu)計(ji)，但保險絲(si)的電(dian)阻明顯要(yao)比等長導(dao)線的電(dian)阻要(yao)大，這(zhe)樣它(ta)才(cai)能起到保護電(dian)路(lu)的作用。
保險絲上標有“5A 250V”，說明深圳保險絲允許通過的最大電流為5A，稱為額定電流；允許通過的最大電壓250V，稱為額定電壓。如果電流或電壓超過額定值，保險絲就會熔斷，使電路斷路，從而保護了用電器（如果沒保險絲，用電器可能被燒壞）。
保險絲(si)熔斷和原理是焦(jiao)耳定(ding)律(lv)(lv)。焦(jiao)耳定(ding)律(lv)(lv)：電流通(tong)過導體產生(sheng)的(de)熱量(liang)跟電流的(de)平(ping)方成正比，跟導體的(de)電阻成正比，跟通(tong)電的(de)時(shi)間(jian)成正比。焦(jiao)耳定(ding)律(lv)(lv)數(shu)學(xue)表達(da)式(shi)：Q=I2Rt，導出(chu)公(gong)式(shi)有Q=UIt和Q=U22/R×t。保險絲(si)中電流所(suo)做的(de)功全部產生(sheng)熱量(liang)，即電能全部轉化(hua)為內能，這時(shi)有Q=W。所(suo)以(yi)，當I或U大(da)于額定(ding)值后(hou)，Q就變大(da)，使(shi)保險絲(si)不能及時(shi)散熱而過熱，最終(zhong)熔斷。
一般情況，當電(dian)(dian)(dian)路電(dian)(dian)(dian)流(liu)或(huo)(huo)電(dian)(dian)(dian)壓超過額(e)(e)定(ding)值(zhi)時，保險(xian)絲(si)不(bu)會馬上熔斷，因為保險(xian)絲(si)都(dou)允(yun)(yun)許通過更(geng)大點的電(dian)(dian)(dian)流(liu)或(huo)(huo)電(dian)(dian)(dian)壓值(zhi)，允(yun)(yun)許短(duan)期的超額(e)(e)工作狀(zhuang)態。也就是(shi)說，如果你(ni)發現了(le)電(dian)(dian)(dian)路電(dian)(dian)(dian)流(liu)或(huo)(huo)電(dian)(dian)(dian)壓不(bu)正常，你(ni)還有(you)糾錯的機會，但對(dui)于事故性的失誤(wu)（如干線(xian)(xian)短(duan)路），可(ke)能保險(xian)沒來得及絲(si)熔斷就使(shi)電(dian)(dian)(dian)線(xian)(xian)著火了(le)，只能事先注(zhu)意防范，沒有(you)后悔的機會了(le)。
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