①三芯電纜一芯或兩芯接地。
②二相芯線間短路。
③三相芯線完全短路。
④一相芯線斷線或多相斷線。
      對于直接短路或斷線故障用萬用表可直接測量判斷，對于非直接短路和接地故障，用兆歐表搖測芯線間絕緣電阻或芯線對地絕緣電阻，根據其阻值可判定故障類型。
      故障類型確定后，查找故障點并不是一件容易的事情，下面根據筆者的經驗，介紹幾種查找故障點的方法，供參考。

二、電纜故障點的查找方法

1、測聲(sheng)(sheng)(sheng)(sheng)(sheng)法(fa)：所謂測聲(sheng)(sheng)(sheng)(sheng)(sheng)法(fa)就是(shi)根據(ju)故(gu)障(zhang)電(dian)(dian)(dian)(dian)(dian)(dian)纜(lan)(lan)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)聲(sheng)(sheng)(sheng)(sheng)(sheng)音(yin)進行查找，該方法(fa)對(dui)于(yu)高壓(ya)電(dian)(dian)(dian)(dian)(dian)(dian)纜(lan)(lan)芯線(xian)對(dui)絕(jue)緣(yuan)(yuan)層(ceng)閃絡放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)較為有(you)效。此方法(fa)所用設備為直(zhi)流耐壓(ya)試驗機。電(dian)(dian)(dian)(dian)(dian)(dian)路接線(xian)如(ru)圖(tu)1所示(shi)，其(qi)中SYB為高壓(ya)試驗變壓(ya)器，C為高壓(ya)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器，ZL為高壓(ya)整流硅堆，R為限流電(dian)(dian)(dian)(dian)(dian)(dian)阻，Q為放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)球間(jian)(jian)隙，L為電(dian)(dian)(dian)(dian)(dian)(dian)纜(lan)(lan)芯線(xian)。當電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器C充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)到(dao)一定電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)值時，球間(jian)(jian)隙對(dui)電(dian)(dian)(dian)(dian)(dian)(dian)纜(lan)(lan)故(gu)障(zhang)芯線(xian)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)，在(zai)(zai)故(gu)障(zhang)處電(dian)(dian)(dian)(dian)(dian)(dian)纜(lan)(lan)芯線(xian)對(dui)絕(jue)緣(yuan)(yuan)層(ceng)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)產生“滋、滋”的(de)火花放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)聲(sheng)(sheng)(sheng)(sheng)(sheng)，對(dui)于(yu)明敷設電(dian)(dian)(dian)(dian)(dian)(dian)纜(lan)(lan)憑聽覺可直(zhi)接查找，若為地(di)埋電(dian)(dian)(dian)(dian)(dian)(dian)纜(lan)(lan)，則(ze)首先(xian)要確定并標明電(dian)(dian)(dian)(dian)(dian)(dian)纜(lan)(lan)走(zou)向，再(zai)在(zai)(zai)雜噪聲(sheng)(sheng)(sheng)(sheng)(sheng)音(yin)最小的(de)時候，借助(zhu)耳聾助(zhu)聽器或醫用聽診器等(deng)音(yin)頻放(fang)(fang)大設備進行查找。查找時，將拾音(yin)器貼近地(di)面，沿電(dian)(dian)(dian)(dian)(dian)(dian)纜(lan)(lan)走(zou)向慢慢移動，當聽到(dao)“滋、滋 ”放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)聲(sheng)(sheng)(sheng)(sheng)(sheng)最大時，該處即為故(gu)障(zhang)點。使(shi)用該方法(fa)一定要注(zhu)意安全，在(zai)(zai)試驗設備端和電(dian)(dian)(dian)(dian)(dian)(dian)纜(lan)(lan)末端應設專人(ren)監(jian)視。
2、電橋法：電橋法就是用雙臂電橋測出電纜芯線的直流電阻值，再準確測量電纜實際長度，按照電纜長度與電阻的正比例關系，計算出故障點。該方法對于電纜芯線間直接短路或短路點接觸電阻小于1Ω的故障，判斷誤差一般不大于3m，對于故障點接觸電阻大于1Ω的故障，可采用加高電壓燒穿的方法使電阻降至1Ω以下，再按此方法測量。
       首先測出芯線a與b之間的電阻R1，則R1=2Rx+R，其中Rx為a相或b相至故障點的一相電阻值，R為短接點的接觸電阻。再就電纜的另一端測出a′與b′芯線間的直流電阻值R2，則R2=2R(L-X)+R,式中R(L-X)為a′相或b′相芯線至故障點的一相電阻值，測完R1與R2后，再按圖3所示電路將b′與c′短接，測出b、c兩相芯線間的直流電阻值，則該阻值的1/2為每相芯線的電阻值，用RL表示，RL=Rx+R(L-X)，由此可得出故障點的接觸電阻值：R=R1+R2-2RL，因此，故障點兩側芯線的電阻值可用下式表示：Rx=(R1-R)/2，R(L-X)=(R2-R)/2。Rx、R(L-X)、RL三個數值確定后，按比例公式即可求出故障點距電纜端頭的距離X或(L-X)：X=(RX/RL)L，(L-X)=(R(L-X)/RL)L，式中L為電纜的總長度。采用電橋法時應保證測量精度，電橋連接線要盡量短，線徑要足夠大，與電纜芯線連接要采用壓接或焊接，計算過程中小數位數要全部保留。
3、電容電流測定法：
      電纜在運行中，芯線之間、芯線對地都存在電容，該電容是均勻分布的，電容量與電纜長度呈線性比例關系，電容電流測定法就是根據這一原理進行測定的，對于電纜芯線斷線故障的測定非常準確。測量電路如圖4所示，使用設備為1～2kVA單相調壓器一臺，0～30V、0.5級交流電壓表一只，0～100mA、0.5級交流毫安表一只。

【測量(liang)步驟】

①首先在電纜首端分別測出每相芯線的電容電流(應保持施加電壓相等)Ia、Ib、Ic的數值。

②在電纜的末端再測量每相芯線的電容電流Ia′、Ib′、Ic′的數值，以核對完好芯線與斷線芯線的電容之比，初步可判斷出斷線距離近似點。③根據電容量計算公式C=1/2πfU可知，在電壓U、頻率f不變時C與I成正比。因為工頻電壓的f(頻率)不變，測量時只要保證施加電壓不變，電容電流之比即為電容量之比。設電纜全長為L，芯線斷線點距離為X，則Ia/Ic=L/X，X=(Ic/Ia)L。
      測量過程中，只要保證電壓不變，電流表讀數準確，電纜總長度測量精確，其測定誤差比較小。
4、零電位法：零電位法也就是電位比較法，它適應于長度較短的電纜芯線對地故障，應用此方法測量簡便精確，不需要精密儀器和復雜計算，其接線如圖5所示，測量原理如下：將電纜故障芯線與等長的比較導線并聯，在兩端加電壓E時，相當于在兩個并聯的均勻電阻絲兩端接了電源，此時，一條電阻絲上的任何一點和另一條電阻絲上的對應點之間的電位差必然為零。反之，電位差為零的兩點必然是對應點。因為微伏表的負極接地，與電纜故障點等電位，所以，當微伏表的正極在比較導線上移動至指示值為零時的點與故障點等電位，即故障點的對應點。
【測量(liang)步(bu)驟】①先在(zai)b和c相芯線(xian)上(shang)接(jie)上(shang)電池E，再(zai)在(zai)地(di)面上(shang)敷設一根(gen)與(yu)故(gu)障電纜(lan)長度相等的比較(jiao)導線(xian)S，該導線(xian)要用(yong)裸銅線(xian)或裸鋁(lv)線(xian)，其(qi)截面應相等，不能有中(zhong)間接(jie)頭。

②將微伏表的負極接地，正極接一根較長的軟導線，導線另一端要求在敷設的比較導線上滑動時能充分接觸。
③合上閘刀開關K，將軟導線的端頭在比較導線上滑動，當微伏表指示為零時的位置即為電纜故障點的位置。