但也有某些情況，停電吊罩后找不到故障點，為了能確切找到接地點，可(ke)以采用(yong)直(zhi)流(liu)法。將鐵芯片與夾件的連接片打(da)開，在鐵軛兩(liang)側的硅(gui)鋼(gang)片上通6V的(de)直流，然后用直流電(dian)壓(ya)表依次(ci)測量(liang)各級硅鋼片間的(de)電(dian)壓(ya)，當電(dian)壓(ya)等于(yu)零或者表針指示(shi)反向時則可認為該處是故(gu)障接地點。
或者是交流法，將變(bian)壓器低壓繞(rao)組(zu)接入 220～380V交(jiao)流電(dian)壓(ya)，此(ci)時鐵芯片中(zhong)有(you)磁通存(cun)在(zai)。如果(guo)有(you)多點(dian)接(jie)地故障(zhang)時，用毫安(an)表(biao)測量(liang)(liang)會出現電(dian)流。用毫安(an)表(biao)沿鐵軛各級逐(zhu)點(dian)測量(liang)(liang)，當毫安(an)表(biao)中(zhong)電(dian)流為零(ling)時，則該處為故障(zhang)點(dian)。這種(zhong)測電(dian)流法比(bi)測電(dian)壓(ya)法準確、直觀。
若用(yong)上述兩(liang)種方法(fa)，仍查不出故障(zhang)點(dian)，還(huan)可(ke)以使用(yong)鐵(tie)芯(xin)片加(jia)壓(ya)法(fa)。將(jiang)鐵(tie)芯(xin)的正常(chang)接地點(dian)斷開，用(yong)交流試驗裝置給鐵(tie)芯(xin)片加(jia)電(dian)壓(ya)，若故障(zhang)點(dian)接觸不牢固，在升壓(ya)過程中會(hui)聽到(dao)放電(dian)聲，根據放電(dian)火花可(ke)觀察到(dao)故障(zhang)點(dian)。
當試驗(yan)(yan)裝置電(dian)(dian)(dian)流(liu)(liu)增大(da)時(shi)，電(dian)(dian)(dian)壓升不上(shang)去(qu)，沒有放電(dian)(dian)(dian)現象，說明接地故(gu)(gu)障點(dian)(dian)很(hen)穩固，此時(shi)可(ke)采用(yong)電(dian)(dian)(dian)流(liu)(liu)法。將鐵芯片的正常接地點(dian)(dian)斷開，用(yong)電(dian)(dian)(dian)焊(han)機裝置給鐵芯加電(dian)(dian)(dian)流(liu)(liu)。當電(dian)(dian)(dian)流(liu)(liu)逐(zhu)漸增大(da)，且鐵芯故(gu)(gu)障援地點(dian)(dian)電(dian)(dian)(dian)阻大(da)時(shi)，故(gu)(gu)障點(dian)(dian)溫度升高很(hen)快(kuai)，變(bian)壓器油將分解(jie)而(er)冒(mao)煙，從(cong)而(er)可(ke)以觀察(cha)到故(gu)(gu)障點(dian)(dian)部位。故(gu)(gu)障點(dian)(dian)是否消除可(ke)用(yong)鐵芯加壓法驗(yan)(yan)證。
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