目(mu)前測(ce)(ce)量直(zhi)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)阻的方法(fa)有電(dian)(dian)(dian)(dian)(dian)橋(qiao)法(fa)和(he)(he)電(dian)(dian)(dian)(dian)(dian)壓(ya)降(jiang)法(fa)兩(liang)種。電(dian)(dian)(dian)(dian)(dian)橋(qiao)法(fa)是(shi)用單臂電(dian)(dian)(dian)(dian)(dian)橋(qiao)或雙臂電(dian)(dian)(dian)(dian)(dian)橋(qiao)進(jin)行測(ce)(ce)量，這(zhe)(zhe)種方法(fa)可以(yi)直(zhi)接讀取(qu)數據(ju)，準確度較高，但設備價格較貴。電(dian)(dian)(dian)(dian)(dian)壓(ya)降(jiang)法(fa)是(shi)對每(mei)相繞(rao)組(zu)進(jin)行直(zhi)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)阻的測(ce)(ce)量，然后(hou)利用測(ce)(ce)量數據(ju)，計算得出線圈的直(zhi)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)阻。在不具備電(dian)(dian)(dian)(dian)(dian)橋(qiao)的地(di)方，一般采用這(zhe)(zhe)種測(ce)(ce)量方法(fa)。這(zhe)(zhe)種方法(fa)的主要(yao)(yao)缺點是(shi)需要(yao)(yao)較長(chang)(chang)的時間(jian)(jian)才能測(ce)(ce)到(dao)準確值。因為每(mei)相繞(rao)組(zu)可以(yi)等(deng)效成電(dian)(dian)(dian)(dian)(dian)阻和(he)(he)電(dian)(dian)(dian)(dian)(dian)感的串聯(lian)電(dian)(dian)(dian)(dian)(dian)路，在接通電(dian)(dian)(dian)(dian)(dian)源(yuan)后(hou)，電(dian)(dian)(dian)(dian)(dian)感中電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)從零(ling)逐(zhu)(zhu)漸(jian)增加(jia)，達到(dao)一穩定數值，電(dian)(dian)(dian)(dian)(dian)感兩(liang)端電(dian)(dian)(dian)(dian)(dian)壓(ya)則從零(ling)忽然增加(jia)到(dao)電(dian)(dian)(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)(dian)(dian)壓(ya)，然后(hou)逐(zhu)(zhu)漸(jian)下降(jiang)到(dao)穩態值，需要(yao)(yao)一個過(guo)(guo)渡過(guo)(guo)程，過(guo)(guo)程的長(chang)(chang)短取(qu)決于電(dian)(dian)(dian)(dian)(dian)路的時間(jian)(jian)常數t=L/R。

由于(yu)變壓器鐵心的(de)(de)(de)磁導(dao)率很高，L值(zhi)大(da)(da)大(da)(da)增加，而線(xian)圈的(de)(de)(de)直(zhi)流(liu)電阻數(shu)值(zhi)又很小(xiao)，因此時(shi)間(jian)常數(shu)t值(zhi)很大(da)(da)。一般來(lai)說，大(da)(da)約經過時(shi)間(jian)T=3～5倍時(shi)間(jian)常數(shu)，電流(liu)才能(neng)達(da)到穩(wen)態值(zhi)，即(ji)需要幾十分鐘(zhong)甚至更(geng)長(chang)時(shi)間(jian)，才能(neng)測出直(zhi)流(liu)電阻的(de)(de)(de)準確值(zhi)。這無(wu)疑不(bu)符合(he)當今快節奏(zou)、率的(de)(de)(de)工作方式互(hu)感器綜合(he)特(te)性(xing)測試儀可(ke)以完成的(de)(de)(de)試驗(yan)包括：CT伏(fu)(fu)安特(te)性(xing)試驗(yan)、PT伏(fu)(fu)安特(te)性(xing)試驗(yan)，CT變比(bi)性(xing)試驗(yan)和PT變比(bi)性(xing)試驗(yan)，自動(dong)計算CT的(de)(de)(de)任(ren)意點誤差曲線(xian)等結果參數(shu)。。

2、三相繞組同時加壓法測量(liang)直(zhi)流(liu)電阻(zu)

用電(dian)(dian)(dian)壓降法(fa)測量直流(liu)電(dian)(dian)(dian)阻需要(yao)很長的(de)時(shi)(shi)間(jian)才能獲(huo)得準確(que)值，主要(yao)由于(yu)線圈(quan)中(zhong)(zhong)通入的(de)電(dian)(dian)(dian)流(liu)在(zai)(zai)變化過(guo)程(cheng)中(zhong)(zhong)，在(zai)(zai)高導(dao)磁(ci)率的(de)鐵(tie)心(xin)(xin)中(zhong)(zhong)產生磁(ci)通，致使L增(zeng)大。若(ruo)使磁(ci)通減少(shao)，也(ye)就降低了L值，則(ze)電(dian)(dian)(dian)流(liu)變化的(de)時(shi)(shi)間(jian)(取決于(yu)時(shi)(shi)間(jian)常數)便(bian)減小。在(zai)(zai)變壓器的(de)三(san)相(xiang)繞(rao)組(zu)同時(shi)(shi)加(jia)電(dian)(dian)(dian)壓，同時(shi)(shi)測量每相(xiang)的(de)直流(liu)電(dian)(dian)(dian)阻，可(ke)以達到此(ci)目的(de)。三(san)相(xiang)繞(rao)組(zu)同時(shi)(shi)加(jia)電(dian)(dian)(dian)壓時(shi)(shi)，在(zai)(zai)每相(xiang)繞(rao)組(zu)中(zhong)(zhong)通入的(de)電(dian)(dian)(dian)流(liu)從零(ling)開始增(zeng)加(jia)，由右手螺旋定則(ze)可(ke)知，三(san)相(xiang)電(dian)(dian)(dian)流(liu)在(zai)(zai)每個(ge)鐵(tie)心(xin)(xin)柱(zhu)中(zhong)(zhong)產生的(de)磁(ci)通方向不同，它們的(de)作(zuo)用相(xiang)互抵消，結(jie)果(guo)是(shi)使鐵(tie)心(xin)(xin)中(zhong)(zhong)的(de)合(he)成磁(ci)通近(jin)似(si)為零(ling)。這使電(dian)(dian)(dian)感值L大為減小，因此(ci)時(shi)(shi)間(jian)常數τ也(ye)就降為低，測試時(shi)(shi)電(dian)(dian)(dian)流(liu)變化的(de)過(guo)渡過(guo)程(cheng)大為縮短，短時(shi)(shi)間(jian)內便(bian)能獲(huo)得穩定的(de)電(dian)(dian)(dian)流(liu)值，進(jin)而(er)求出繞(rao)組(zu)的(de)直流(liu)電(dian)(dian)(dian)阻值。

3、結論

三相繞組(zu)(zu)同時(shi)加電(dian)(dian)壓測量(liang)(liang)變壓器的(de)直流電(dian)(dian)阻，是根(gen)據楞(leng)次定律，使各相電(dian)(dian)流所(suo)產生的(de)磁(ci)通(tong)在鐵心中相互抵(di)消，合成(cheng)磁(ci)通(tong)為零，從而減小(xiao)電(dian)(dian)感L值，使電(dian)(dian)路(lu)的(de)時(shi)間常數減小(xiao)，即(ji)減少(shao)了測量(liang)(liang)直流電(dian)(dian)阻的(de)時(shi)間，提(ti)高(gao)了工作效率。在測量(liang)(liang)時(shi)，還(huan)應考(kao)慮繞組(zu)(zu)電(dian)(dian)阻的(de)大小(xiao)受溫(wen)度影響的(de)因素和直流電(dian)(dian)阻的(de)不平衡率等(deng)問題。