目前測(ce)(ce)量(liang)直流(liu)電(dian)(dian)(dian)阻(zu)(zu)的(de)(de)方(fang)法(fa)(fa)有電(dian)(dian)(dian)橋(qiao)法(fa)(fa)和電(dian)(dian)(dian)壓(ya)降法(fa)(fa)兩種(zhong)。電(dian)(dian)(dian)橋(qiao)法(fa)(fa)是(shi)用(yong)單(dan)臂電(dian)(dian)(dian)橋(qiao)或(huo)雙臂電(dian)(dian)(dian)橋(qiao)進行測(ce)(ce)量(liang)，這種(zhong)方(fang)法(fa)(fa)可以(yi)直接(jie)讀取(qu)數(shu)據，準確度較(jiao)高，但設備價格較(jiao)貴。電(dian)(dian)(dian)壓(ya)降法(fa)(fa)是(shi)對(dui)每相(xiang)(xiang)繞組進行直流(liu)電(dian)(dian)(dian)阻(zu)(zu)的(de)(de)測(ce)(ce)量(liang)，然(ran)后(hou)利用(yong)測(ce)(ce)量(liang)數(shu)據，計算得(de)出(chu)線(xian)圈(quan)的(de)(de)直流(liu)電(dian)(dian)(dian)阻(zu)(zu)。在不具備電(dian)(dian)(dian)橋(qiao)的(de)(de)地方(fang)，一般采用(yong)這種(zhong)測(ce)(ce)量(liang)方(fang)法(fa)(fa)。這種(zhong)方(fang)法(fa)(fa)的(de)(de)主(zhu)要缺點是(shi)需要較(jiao)長的(de)(de)時間才能測(ce)(ce)到(dao)(dao)(dao)準確值(zhi)。因(yin)為(wei)每相(xiang)(xiang)繞組可以(yi)等效成電(dian)(dian)(dian)阻(zu)(zu)和電(dian)(dian)(dian)感的(de)(de)串聯(lian)電(dian)(dian)(dian)路，在接(jie)通電(dian)(dian)(dian)源(yuan)后(hou)，電(dian)(dian)(dian)感中電(dian)(dian)(dian)流(liu)從(cong)零逐(zhu)漸(jian)增加(jia)，達到(dao)(dao)(dao)一穩定數(shu)值(zhi)，電(dian)(dian)(dian)感兩端(duan)電(dian)(dian)(dian)壓(ya)則從(cong)零忽然(ran)增加(jia)到(dao)(dao)(dao)電(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)壓(ya)，然(ran)后(hou)逐(zhu)漸(jian)下降到(dao)(dao)(dao)穩態值(zhi)，需要一個(ge)過(guo)渡(du)過(guo)程，過(guo)程的(de)(de)長短(duan)取(qu)決于電(dian)(dian)(dian)路的(de)(de)時間常數(shu)t=L/R。

由于(yu)變(bian)壓器鐵(tie)心(xin)的(de)(de)磁導(dao)率(lv)(lv)很高(gao)，L值(zhi)大(da)大(da)增加，而(er)線圈的(de)(de)直流(liu)電(dian)阻數(shu)值(zhi)又很小，因此時(shi)間常(chang)數(shu)t值(zhi)很大(da)。一般(ban)來說(shuo)，大(da)約經(jing)過時(shi)間T=3～5倍(bei)時(shi)間常(chang)數(shu)，電(dian)流(liu)才能達到穩態值(zhi)，即需要幾十分(fen)鐘(zhong)甚至(zhi)更長時(shi)間，才能測(ce)出(chu)直流(liu)電(dian)阻的(de)(de)準確值(zhi)。這無疑不符合(he)當今快(kuai)節奏(zou)、率(lv)(lv)的(de)(de)工(gong)作(zuo)方式互(hu)感(gan)器綜合(he)特性測(ce)試(shi)儀(yi)可(ke)以完成的(de)(de)試(shi)驗(yan)(yan)包括：CT伏安(an)特性試(shi)驗(yan)(yan)、PT伏安(an)特性試(shi)驗(yan)(yan)，CT變(bian)比性試(shi)驗(yan)(yan)和PT變(bian)比性試(shi)驗(yan)(yan)，自動(dong)計算CT的(de)(de)任意點誤差曲線等(deng)結果(guo)參數(shu)。。

2、三(san)相繞組同時加壓法測量直流電阻

用(yong)電(dian)(dian)壓降法測量直流(liu)電(dian)(dian)阻需要很長的(de)(de)(de)(de)時(shi)(shi)(shi)間(jian)才能(neng)獲得準確值(zhi)，主(zhu)要由(you)于線圈中(zhong)(zhong)通(tong)(tong)入(ru)的(de)(de)(de)(de)電(dian)(dian)流(liu)在(zai)(zai)(zai)變化(hua)過(guo)(guo)程(cheng)中(zhong)(zhong)，在(zai)(zai)(zai)高導(dao)磁率的(de)(de)(de)(de)鐵(tie)心(xin)中(zhong)(zhong)產生磁通(tong)(tong)，致使(shi)L增(zeng)(zeng)大(da)。若使(shi)磁通(tong)(tong)減(jian)少，也(ye)就降低了L值(zhi)，則電(dian)(dian)流(liu)變化(hua)的(de)(de)(de)(de)時(shi)(shi)(shi)間(jian)(取決于時(shi)(shi)(shi)間(jian)常數(shu))便減(jian)小。在(zai)(zai)(zai)變壓器的(de)(de)(de)(de)三相(xiang)(xiang)繞組(zu)同時(shi)(shi)(shi)加電(dian)(dian)壓，同時(shi)(shi)(shi)測量每相(xiang)(xiang)的(de)(de)(de)(de)直流(liu)電(dian)(dian)阻，可(ke)以(yi)達到此目的(de)(de)(de)(de)。三相(xiang)(xiang)繞組(zu)同時(shi)(shi)(shi)加電(dian)(dian)壓時(shi)(shi)(shi)，在(zai)(zai)(zai)每相(xiang)(xiang)繞組(zu)中(zhong)(zhong)通(tong)(tong)入(ru)的(de)(de)(de)(de)電(dian)(dian)流(liu)從零開始增(zeng)(zeng)加，由(you)右手螺(luo)旋(xuan)定(ding)則可(ke)知，三相(xiang)(xiang)電(dian)(dian)流(liu)在(zai)(zai)(zai)每個鐵(tie)心(xin)柱(zhu)中(zhong)(zhong)產生的(de)(de)(de)(de)磁通(tong)(tong)方向不同，它們的(de)(de)(de)(de)作(zuo)用(yong)相(xiang)(xiang)互(hu)抵消(xiao)，結果是使(shi)鐵(tie)心(xin)中(zhong)(zhong)的(de)(de)(de)(de)合成(cheng)磁通(tong)(tong)近似為(wei)(wei)零。這(zhe)使(shi)電(dian)(dian)感值(zhi)L大(da)為(wei)(wei)減(jian)小，因(yin)此時(shi)(shi)(shi)間(jian)常數(shu)τ也(ye)就降為(wei)(wei)低，測試時(shi)(shi)(shi)電(dian)(dian)流(liu)變化(hua)的(de)(de)(de)(de)過(guo)(guo)渡過(guo)(guo)程(cheng)大(da)為(wei)(wei)縮(suo)短，短時(shi)(shi)(shi)間(jian)內便能(neng)獲得穩(wen)定(ding)的(de)(de)(de)(de)電(dian)(dian)流(liu)值(zhi)，進而求出繞組(zu)的(de)(de)(de)(de)直流(liu)電(dian)(dian)阻值(zhi)。

3、結論

三相繞組同(tong)時(shi)(shi)加(jia)電(dian)壓(ya)(ya)測(ce)量(liang)變壓(ya)(ya)器的(de)(de)直流電(dian)阻(zu)，是根據楞次定律，使(shi)各相電(dian)流所產生的(de)(de)磁通在(zai)鐵心(xin)中(zhong)相互抵消，合成磁通為零，從而減小電(dian)感(gan)L值，使(shi)電(dian)路的(de)(de)時(shi)(shi)間常(chang)數減小，即減少了測(ce)量(liang)直流電(dian)阻(zu)的(de)(de)時(shi)(shi)間，提高(gao)了工作(zuo)效率。在(zai)測(ce)量(liang)時(shi)(shi)，還應考慮繞組電(dian)阻(zu)的(de)(de)大小受(shou)溫度(du)影響(xiang)的(de)(de)因素和直流電(dian)阻(zu)的(de)(de)不(bu)平衡率等問(wen)題。