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三相異步電機應用
檢查方法
⑴觀(guan)察法(fa)。通過目測繞組端(duan)部及(ji)線(xian)槽內絕緣物觀(guan)察有無損傷(shang)和焦黑(hei)的痕跡,如有就是接地點。
⑵萬(wan)用(yong)表(biao)檢(jian)查(cha)法。用(yong)萬(wan)用(yong)表(biao)低阻檔檢(jian)查(cha),讀(du)數很小,則為接地。
⑶兆(zhao)歐表法。根據不(bu)同(tong)的(de)等(deng)級選用不(bu)同(tong)的(de)兆(zhao)歐表測量每組電(dian)阻的(de)絕緣電(dian)阻,若讀數為(wei)零,則表示該項繞組接地,但(dan)對(dui)電(dian)機絕緣受潮或(huo)因(yin)事故而擊穿,需依據經(jing)驗判定(ding)(ding),一般說來(lai)指針在(zai)“0"處搖擺(bai)不(bu)定(ding)(ding)時,可認為(wei)其具有(you)一定(ding)(ding)的(de)電(dian)阻值。
⑷試燈(deng)法。如果試燈(deng)亮,說(shuo)明(ming)(ming)繞(rao)組接(jie)(jie)地(di),若(ruo)發(fa)現某(mou)處伴有火(huo)(huo)花或冒煙,則該處為繞(rao)組接(jie)(jie)地(di)故障點(dian)。若(ruo)燈(deng)微亮則絕緣有接(jie)(jie)地(di)擊(ji)穿。若(ruo)燈(deng)不亮,但測試棒接(jie)(jie)地(di)時(shi)也出現火(huo)(huo)花,說(shuo)明(ming)(ming)繞(rao)組尚未擊(ji)穿,只是嚴(yan)重受潮。也可用硬木在(zai)外殼的止口(kou)邊(bian)緣輕(qing)敲(qiao),敲(qiao)到某(mou)一處等一滅(mie)一亮時(shi),說(shuo)明(ming)(ming)電流時(shi)通時(shi)斷,則該處就是接(jie)(jie)地(di)點(dian)。
⑸電(dian)(dian)(dian)(dian)流穿燒法(fa)。用一臺調壓變壓器,接(jie)上電(dian)(dian)(dian)(dian)源后(hou),接(jie)地點(dian)很快發熱,絕緣物冒(mao)煙(yan)處即為(wei)接(jie)地點(dian)。應特(te)別(bie)注(zhu)意小(xiao)型電(dian)(dian)(dian)(dian)機不(bu)得超過(guo)額定電(dian)(dian)(dian)(dian)流的(de)兩倍,時間不(bu)超過(guo)半分鐘(zhong);大(da)電(dian)(dian)(dian)(dian)機為(wei)額定電(dian)(dian)(dian)(dian)流的(de)20%-50%或逐步(bu)增大(da)電(dian)(dian)(dian)(dian)流,到接(jie)地點(dian)剛冒(mao)煙(yan)時立即斷電(dian)(dian)(dian)(dian)。
⑹分組(zu)淘(tao)汰法。對于接(jie)地點(dian)在鐵芯心里(li)面(mian)且(qie)燒灼比較厲害,燒損的銅線(xian)與(yu)鐵芯熔在一起。采用的方法是把(ba)接(jie)地的一相繞(rao)組(zu)分成兩半,依此類推,最(zui)后找(zhao)出接(jie)地點(dian)。
此(ci)外,還有高(gao)壓試(shi)驗法(fa)、磁針探索法(fa)、工頻振動法(fa)等,此(ci)處不一(yi)一(yi)介紹。
三相異步電機應用
工作原理
當向(xiang)三(san)相(xiang)定(ding)(ding)子(zi)繞組中(zhong)通入對(dui)(dui)稱的(de)(de)三(san)相(xiang)交(jiao)流(liu)電(dian)時,就產生了(le)一個(ge)以(yi)同(tong)步(bu)轉(zhuan)(zhuan)速n1沿(yan)定(ding)(ding)子(zi)和轉(zhuan)(zhuan)子(zi)內圓空(kong)間作順時針方向(xiang)旋(xuan)轉(zhuan)(zhuan)的(de)(de)旋(xuan)轉(zhuan)(zhuan)磁(ci)(ci)(ci)場(chang)。由于旋(xuan)轉(zhuan)(zhuan)磁(ci)(ci)(ci)場(chang)以(yi)n1轉(zhuan)(zhuan)速旋(xuan)轉(zhuan)(zhuan),轉(zhuan)(zhuan)子(zi)導(dao)體(ti)開(kai)始時是靜止的(de)(de),故轉(zhuan)(zhuan)子(zi)導(dao)體(ti)將切割定(ding)(ding)子(zi)旋(xuan)轉(zhuan)(zhuan)磁(ci)(ci)(ci)場(chang)而產生感(gan)應電(dian)動(dong)(dong)勢(shi)(感(gan)應電(dian)動(dong)(dong)勢(shi)的(de)(de)方向(xiang)用(yong)(yong)右手定(ding)(ding)則判定(ding)(ding))。由于轉(zhuan)(zhuan)子(zi)導(dao)體(ti)兩端被短路環短接,在(zai)感(gan)應電(dian)動(dong)(dong)勢(shi)的(de)(de)作用(yong)(yong)下,轉(zhuan)(zhuan)子(zi)導(dao)體(ti)中(zhong)將產生與(yu)感(gan)應電(dian)動(dong)(dong)勢(shi)方向(xiang)基(ji)本一致的(de)(de)感(gan)生電(dian)流(liu)。轉(zhuan)(zhuan)子(zi)的(de)(de)載流(liu)導(dao)體(ti)在(zai)定(ding)(ding)子(zi)磁(ci)(ci)(ci)場(chang)中(zhong)受到電(dian)磁(ci)(ci)(ci)力(li)的(de)(de)作用(yong)(yong)(力(li)的(de)(de)方向(xiang)用(yong)(yong)左手定(ding)(ding)則判定(ding)(ding))。電(dian)磁(ci)(ci)(ci)力(li)對(dui)(dui)轉(zhuan)(zhuan)子(zi)軸產生電(dian)磁(ci)(ci)(ci)轉(zhuan)(zhuan)矩,驅(qu)動(dong)(dong)轉(zhuan)(zhuan)子(zi)沿(yan)著旋(xuan)轉(zhuan)(zhuan)磁(ci)(ci)(ci)場(chang)方向(xiang)旋(xuan)轉(zhuan)(zhuan)。
通過上(shang)述分析可以總結(jie)出電(dian)動(dong)(dong)機(ji)(ji)(ji)工作(zuo)原理為:當電(dian)動(dong)(dong)機(ji)(ji)(ji)的三(san)相(xiang)定子(zi)繞(rao)(rao)組(zu)(zu)(各相(xiang)差120度電(dian)角(jiao)度),通入三(san)相(xiang)對稱(cheng)交流(liu)電(dian)后,將產生一(yi)個旋(xuan)轉(zhuan)(zhuan)(zhuan)(zhuan)(zhuan)磁(ci)(ci)場(chang),該旋(xuan)轉(zhuan)(zhuan)(zhuan)(zhuan)(zhuan)磁(ci)(ci)場(chang)切割轉(zhuan)(zhuan)(zhuan)(zhuan)(zhuan)子(zi)繞(rao)(rao)組(zu)(zu),從而在(zai)轉(zhuan)(zhuan)(zhuan)(zhuan)(zhuan)子(zi)繞(rao)(rao)組(zu)(zu)中產生感應電(dian)流(liu)(轉(zhuan)(zhuan)(zhuan)(zhuan)(zhuan)子(zi)繞(rao)(rao)組(zu)(zu)是閉(bi)合(he)通路),載流(liu)的轉(zhuan)(zhuan)(zhuan)(zhuan)(zhuan)子(zi)導(dao)體在(zai)定子(zi)旋(xuan)轉(zhuan)(zhuan)(zhuan)(zhuan)(zhuan)磁(ci)(ci)場(chang)作(zuo)用下(xia)將產生電(dian)磁(ci)(ci)力,從而在(zai)電(dian)機(ji)(ji)(ji)轉(zhuan)(zhuan)(zhuan)(zhuan)(zhuan)軸上(shang)形(xing)成(cheng)電(dian)磁(ci)(ci)轉(zhuan)(zhuan)(zhuan)(zhuan)(zhuan)矩,驅(qu)動(dong)(dong)電(dian)動(dong)(dong)機(ji)(ji)(ji)旋(xuan)轉(zhuan)(zhuan)(zhuan)(zhuan)(zhuan),并(bing)且電(dian)機(ji)(ji)(ji)旋(xuan)轉(zhuan)(zhuan)(zhuan)(zhuan)(zhuan)方向(xiang)與旋(xuan)轉(zhuan)(zhuan)(zhuan)(zhuan)(zhuan)磁(ci)(ci)場(chang)方向(xiang)相(xiang)同。
基本結構
三(san)相(xiang)異(yi)步(bu)電動(dong)機(ji)(ji)由固(gu)定(ding)(ding)的定(ding)(ding)子(zi)和旋轉(zhuan)(zhuan)的轉(zhuan)(zhuan)子(zi)兩個基(ji)本部(bu)分組(zu)成,轉(zhuan)(zhuan)子(zi)裝在(zai)定(ding)(ding)子(zi)內(nei)腔(qiang)里,借助軸承被(bei)支(zhi)撐(cheng)在(zai)兩個端蓋上。為(wei)了保證轉(zhuan)(zhuan)子(zi)能(neng)在(zai)定(ding)(ding)子(zi)內(nei)自由轉(zhuan)(zhuan)動(dong),定(ding)(ding)子(zi)和轉(zhuan)(zhuan)子(zi)之間必須有(you)(you)一間隙,稱為(wei)氣隙。電動(dong)機(ji)(ji)的氣隙是(shi)一個非常重要的參數,其大(da)小及對稱性等對電動(dong)機(ji)(ji)的性能(neng)有(you)(you)很大(da)影(ying)響。圖2所示為(wei)三(san)相(xiang)籠型異(yi)步(bu)電動(dong)機(ji)(ji)的組(zu)成部(bu)件。
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