變(bian)壓(ya)(ya)器(qi)(qi)各個部門(men)有(you)不(bu)同的允(yun)許溫升,不(bu)同的運(yun)行(xing)工況也有(you)不(bu)同的允(yun)許溫升。決定允(yun)許溫升的因素有(you):變(bian)壓(ya)(ya)器(qi)(qi)的運(yun)行(xing)預期(qi)壽命(ming)、變(bian)壓(ya)(ya)器(qi)(qi)的**運(yun)行(xing)、變(bian)壓(ya)(ya)器(qi)(qi)的檢測技術。
繞組(zu)(zu)(zu)(zu)允(yun)(yun)(yun)許(xu)溫(wen)(wen)(wen)升(sheng)(sheng):繞組(zu)(zu)(zu)(zu)的(de)(de)允(yun)(yun)(yun)許(xu)溫(wen)(wen)(wen)升(sheng)(sheng)是指整個(ge)繞組(zu)(zu)(zu)(zu)的(de)(de)平(ping)均(jun)(jun)(jun)溫(wen)(wen)(wen)升(sheng)(sheng),由電阻法(fa)測得,允(yun)(yun)(yun)許(xu)溫(wen)(wen)(wen)升(sheng)(sheng)與絕(jue)(jue)緣(yuan)(yuan)耐熱等級(ji)(ji)(ji)(ji)(ji)有關(guan)。油浸(jin)式(shi)(shi)變(bian)壓(ya)器(qi)屬A級(ji)(ji)(ji)(ji)(ji)絕(jue)(jue)緣(yuan)(yuan),由于傳統的(de)(de)繞組(zu)(zu)(zu)(zu)溫(wen)(wen)(wen)升(sheng)(sheng)測量(liang)(liang)法(fa)為(wei)(wei)(wei)(wei)電阻法(fa),測得的(de)(de)溫(wen)(wen)(wen)升(sheng)(sheng)為(wei)(wei)(wei)(wei)平(ping)均(jun)(jun)(jun)溫(wen)(wen)(wen)升(sheng)(sheng),A級(ji)(ji)(ji)(ji)(ji)絕(jue)(jue)緣(yuan)(yuan)允(yun)(yun)(yun)許(xu)的(de)(de)平(ping)均(jun)(jun)(jun)溫(wen)(wen)(wen)升(sheng)(sheng)為(wei)(wei)(wei)(wei)65K。平(ping)均(jun)(jun)(jun)溫(wen)(wen)(wen)升(sheng)(sheng)與繞組(zu)(zu)(zu)(zu)*熱點溫(wen)(wen)(wen)升(sheng)(sheng)之差假使為(wei)(wei)(wei)(wei)13K。在年平(ping)均(jun)(jun)(jun)溫(wen)(wen)(wen)度為(wei)(wei)(wei)(wei)20℃時,A級(ji)(ji)(ji)(ji)(ji)絕(jue)(jue)緣(yuan)(yuan)繞組(zu)(zu)(zu)(zu)*熱點溫(wen)(wen)(wen)度為(wei)(wei)(wei)(wei)20+65+13=98℃,此時A級(ji)(ji)(ji)(ji)(ji)絕(jue)(jue)緣(yuan)(yuan)具有正常(chang)壽(shou)命(ming)。干式(shi)(shi)變(bian)壓(ya)器(qi)各(ge)種絕(jue)(jue)緣(yuan)(yuan)的(de)(de)允(yun)(yun)(yun)許(xu)平(ping)均(jun)(jun)(jun)溫(wen)(wen)(wen)升(sheng)(sheng):A級(ji)(ji)(ji)(ji)(ji)為(wei)(wei)(wei)(wei)60K,E級(ji)(ji)(ji)(ji)(ji)為(wei)(wei)(wei)(wei)75K,B級(ji)(ji)(ji)(ji)(ji)為(wei)(wei)(wei)(wei)80K,F級(ji)(ji)(ji)(ji)(ji)為(wei)(wei)(wei)(wei)100K,H級(ji)(ji)(ji)(ji)(ji)為(wei)(wei)(wei)(wei)125K,C級(ji)(ji)(ji)(ji)(ji)為(wei)(wei)(wei)(wei)150K。冬季繞組(zu)(zu)(zu)(zu)溫(wen)(wen)(wen)升(sheng)(sheng)低于平(ping)均(jun)(jun)(jun)溫(wen)(wen)(wen)升(sheng)(sheng),繞組(zu)(zu)(zu)(zu)可延(yan)長(chang)壽(shou)命(ming),夏(xia)季的(de)(de)繞組(zu)(zu)(zu)(zu)溫(wen)(wen)(wen)升(sheng)(sheng)高于平(ping)均(jun)(jun)(jun)溫(wen)(wen)(wen)升(sheng)(sheng),繞組(zu)(zu)(zu)(zu)要(yao)犧(xi)牲壽(shou)命(ming)。如超(chao)品牌(pai)容量(liang)(liang)也(ye)要(yao)犧(xi)牲壽(shou)命(ming),但超(chao)品牌(pai)容量(liang)(liang)運行時,油浸(jin)式(shi)(shi)變(bian)壓(ya)器(qi)A級(ji)(ji)(ji)(ji)(ji)絕(jue)(jue)緣(yuan)(yuan)繞組(zu)(zu)(zu)(zu)*熱點溫(wen)(wen)(wen)度不(bu)(bu)能(neng)超(chao)過140℃,即使犧(xi)牲的(de)(de)壽(shou)命(ming)不(bu)(bu)多,也(ye)不(bu)(bu)允(yun)(yun)(yun)許(xu)超(chao)過140℃,因超(chao)過140℃時油要(yao)分解出(chu)氣體而影(ying)響(xiang)絕(jue)(jue)緣(yuan)(yuan)強度。所以油浸(jin)式(shi)(shi)變(bian)壓(ya)器(qi)A級(ji)(ji)(ji)(ji)(ji)絕(jue)(jue)緣(yuan)(yuan)的(de)(de)*熱點溫(wen)(wen)(wen)度不(bu)(bu)能(neng)超(chao)過140℃是從變(bian)壓(ya)器(qi)**運行出(chu)發的(de)(de)。
大容(rong)(rong)量(liang)變(bian)壓器有時有幾種冷(leng)卻方式(shi),例如ONAN/ONAF,變(bian)壓器額定容(rong)(rong)量(liang)一般是指(zhi)ONAF下(xia)(xia)(xia)的允許值,當(dang)風扇失去(qu)電源后,冷(leng)卻效率下(xia)(xia)(xia)降,如仍按ONAF冷(leng)卻方式(shi)下(xia)(xia)(xia)容(rong)(rong)量(liang)運行時,繞組平均溫(wen)升必將升高,故ONAN冷(leng)卻方式(shi)下(xia)(xia)(xia)必須(xu)降低(di)容(rong)(rong)量(liang)運行,使繞組平均溫(wen)升不(bu)超過65K。
另外,雙繞(rao)(rao)(rao)組(zu)(zu)(zu)(zu)或(huo)三繞(rao)(rao)(rao)組(zu)(zu)(zu)(zu)變壓(ya)(ya)器(qi)(qi)中,二(er)個或(huo)三個繞(rao)(rao)(rao)組(zu)(zu)(zu)(zu)應同(tong)時(shi)(shi)(shi)(shi)達(da)相同(tong)的(de)溫升(sheng)(sheng),當一(yi)(yi)個繞(rao)(rao)(rao)組(zu)(zu)(zu)(zu)達(da)65K平(ping)均(jun)(jun)溫升(sheng)(sheng)時(shi)(shi)(shi)(shi)另一(yi)(yi)個或(huo)二(er)個繞(rao)(rao)(rao)組(zu)(zu)(zu)(zu)低于65K,則這樣的(de)設(she)計(ji)是不經(jing)濟(ji)的(de)。油(you)(you)(you)浸式(shi)變壓(ya)(ya)器(qi)(qi)還應使(shi)油(you)(you)(you)面頂層(ceng)(ceng)與幾個繞(rao)(rao)(rao)組(zu)(zu)(zu)(zu)平(ping)均(jun)(jun)溫升(sheng)(sheng)同(tong)時(shi)(shi)(shi)(shi)達(da)允許溫升(sheng)(sheng)是較為經(jing)濟(ji)的(de)。即(ji)油(you)(you)(you)面頂層(ceng)(ceng)溫升(sheng)(sheng)達(da)55K,繞(rao)(rao)(rao)組(zu)(zu)(zu)(zu)平(ping)均(jun)(jun)溫升(sheng)(sheng)達(da)65K為經(jing)濟(ji)的(de)方案。在設(she)計(ji)階段,就(jiu)合理選取每一(yi)(yi)繞(rao)(rao)(rao)組(zu)(zu)(zu)(zu)的(de)電流密度,在保持負載損(sun)耗(hao)不超過標準值時(shi)(shi)(shi)(shi)使(shi)各個繞(rao)(rao)(rao)組(zu)(zu)(zu)(zu)的(de)溫升(sheng)(sheng)接近65K,同(tong)時(shi)(shi)(shi)(shi)油(you)(you)(you)面頂層(ceng)(ceng)也(ye)達(da)55K。但是,這對強(qiang)油(you)(you)(you)循環的(de)變壓(ya)(ya)器(qi)(qi)是難以達(da)到的(de)。因強(qiang)油(you)(you)(you)風冷(leng)式(shi)變壓(ya)(ya)器(qi)(qi)的(de)油(you)(you)(you)頂層(ceng)(ceng)溫升(sheng)(sheng)一(yi)(yi)般為40K,強(qiang)油(you)(you)(you)水冷(leng)式(shi)變壓(ya)(ya)器(qi)(qi)的(de)油(you)(you)(you)頂層(ceng)(ceng)溫升(sheng)(sheng)一(yi)(yi)般為35K。
實(shi)際上,油(you)(you)面(mian)頂層溫(wen)(wen)(wen)(wen)升(sheng)與繞組(zu)平均(jun)溫(wen)(wen)(wen)(wen)升(sheng)很(hen)難同時(shi)到達極限允許值,因(yin)此,一(yi)般(ban)不能根(gen)據(ju)油(you)(you)面(mian)頂層溫(wen)(wen)(wen)(wen)升(sheng)來判(pan)斷(duan)繞組(zu)平均(jun)溫(wen)(wen)(wen)(wen)升(sheng)。這(zhe)也是大(da)容量變(bian)壓(ya)器(qi)既裝(zhuang)油(you)(you)面(mian)溫(wen)(wen)(wen)(wen)度(du)指(zhi)(zhi)示儀與繞組(zu)熱點溫(wen)(wen)(wen)(wen)度(du)指(zhi)(zhi)示儀的原因(yin)。如(ru)單裝(zhuang)油(you)(you)面(mian)溫(wen)(wen)(wen)(wen)度(du)指(zhi)(zhi)示儀時(shi),有時(shi)較難判(pan)斷(duan)繞組(zu)平均(jun)溫(wen)(wen)(wen)(wen)升(sheng)。尤(you)其強(qiang)油(you)(you)循環冷卻(que)變(bian)壓(ya)器(qi)。
在(zai)分析變(bian)壓(ya)器溫升時(shi)還要注意冷卻介質的溫度(du):
一般風(feng)冷(leng)式變(bian)壓器(qi)的(de)冷(leng)卻介(jie)質(zhi)為(wei)(wei)空氣,水冷(leng)變(bian)壓器(qi)冷(leng)卻介(jie)質(zhi)為(wei)(wei)水。
當裝有(you)封(feng)(feng)閉(bi)母線(xian)時,低壓套(tao)管在封(feng)(feng)閉(bi)母線(xian)內的介質雖為空氣,但溫度為80℃。所(suo)以當低壓套(tao)管用(yong)于敞開式時與用(yong)于封(feng)(feng)閉(bi)母線(xian)內時有(you)不同的允許(xu)溫度。一般,用(yong)于封(feng)(feng)閉(bi)母線(xian)內的套(tao)管要降(jiang)低額定電流,因(yin)封(feng)(feng)閉(bi)母線(xian)內空氣溫度較(jiao)高(gao)。
由(you)此可(ke)知,引線、套管、有(you)(you)載(zai)分(fen)接(jie)開(kai)關或無載(zai)分(fen)接(jie)開(kai)關的允許溫升決定于其周圍介質的溫升。變壓器(qi)又具有(you)(you)一定的超品牌運行(xing)的能力,帶電組(zu)件也應具有(you)(you)相同的能力,既(ji)有(you)(you)一定的壽命,又不(bu)影(ying)響**運行(xing)。
前面(mian)分(fen)析的(de)油(you)面(mian)頂層溫(wen)升(sheng)與繞組平均溫(wen)升(sheng)是(shi)指穩態下(xia)的(de)溫(wen)升(sheng)。有時(shi),在運行(xing)中常有瞬時(shi)負(fu)載的(de)變(bian)化,如(ru)突然接入較大負(fu)載,突然甩負(fu)載,此時(shi)還應(ying)注意溫(wen)度變(bian)化的(de)時(shi)間常數。
油的(de)時(shi)間(jian)常數(shu)較(jiao)大(da),就是(shi)負載變化后,油面溫(wen)度在較(jiao)長時(shi)間(jian)后才能達穩定溫(wen)升(sheng)值,而(er)繞組(zu)的(de)時(shi)間(jian)常數(shu)較(jiao)小,繞組(zu)平均溫(wen)度能較(jiao)快(kuai)地隨著負載的(de)變化而(er)變化。
當負載(zai)增加時(shi)(shi),不能認為油(you)面溫(wen)度沒有(you)變(bian)化(hua),而繞組(zu)溫(wen)度也沒有(you)變(bian)化(hua)。油(you)的(de)時(shi)(shi)間(jian)常數較(jiao)(jiao)(jiao)大,油(you)面溫(wen)度上(shang)升較(jiao)(jiao)(jiao)慢,繞組(zu)時(shi)(shi)間(jian)常數較(jiao)(jiao)(jiao)小(xiao),繞組(zu)溫(wen)度上(shang)升較(jiao)(jiao)(jiao)快。如有(you)繞組(zu)溫(wen)度指示(shi)(shi)儀,這(zhe)個指示(shi)(shi)儀也應(ying)(ying)有(you)較(jiao)(jiao)(jiao)好的(de)響(xiang)應(ying)(ying)時(shi)(shi)間(jian),時(shi)(shi)間(jian)常數也要(yao)很(hen)小(xiao)。
要控制(zhi)ONAF風扇啟動就(jiu)不(bu)能靠油面溫度(du)指示(shi)儀,只能由繞組溫度(du)指示(shi)儀實現,或由套管(guan)電流互感器(qi)來(lai)控制(zhi)。
在(zai)變壓器中(zhong),有(you)時(shi)漏磁產生的損耗密度(du)太大時(shi),會產生局(ju)(ju)部過熱。大電流引線附近的箱壁,大電流套(tao)管引出(chu)處(chu)箱蓋等處(chu),有(you)時(shi)會有(you)局(ju)(ju)部過熱。引起油分解出(chu)氣體的局(ju)(ju)部過溫度(du)是不允許的,這會引起可(ke)靠性的下降。這就(jiu)要采(cai)取措施(shi)改變漏磁的途(tu)徑,采(cai)取隔磁措施(shi)或在(zai)漏磁集(ji)中(zhong)處(chu)用(yong)不導磁材料。
變(bian)壓器(qi)在運(yun)行(xing)(xing)中(zhong),不(bu)可避(bi)免地會有短路(lu)(lu),變(bian)壓器(qi)短路(lu)(lu)時(shi)將流過短路(lu)(lu)電流,此時(shi),變(bian)壓器(qi)迅速(su)發(fa)熱(re),由于短路(lu)(lu)電流很大,變(bian)壓器(qi)等(deng)于在絕熱(re)條件(jian)下運(yun)行(xing)(xing)而不(bu)考慮(lv)散熱(re)。
A級(ji)絕緣銅導線繞組在短路時的允(yun)許溫度為(wei)250℃。
為保持這(zhe)一溫度不超過,要(yao)在設計中計算短路電流下許用電流密度,使在允許的持續(xu)時間(jian)時銅導線不超過250℃。
銅導線(xian)的(de)機械應(ying)力(li)(li)允許(xu)(xu)(xu)值與(yu)溫(wen)度(du)有關,銅導線(xian)的(de)工作(zuo)溫(wen)度(du)超(chao)過(guo),允許(xu)(xu)(xu)應(ying)力(li)(li)降低(di)。所以(yi)在(zai)引伸率為0.2%時允許(xu)(xu)(xu)應(ying)力(li)(li)應(ying)是250℃下(xia)的(de)許(xu)(xu)(xu)用值。
研究變壓器允許溫(wen)升(sheng)時,還有幾(ji)點(dian)要引起注意:
(1)有載調壓變壓器中(zhong)有載分接開(kai)關內的過度電阻(zu)器,應(ying)使(shi)有載分接開(kai)關在連續操作(zuo)下,電阻(zu)器對油溫升(sheng)不超過350K。
(2)做溫升試(shi)驗時,外(wai)部的熱不要倒(dao)流入變壓器,如短接引(yin)線電流密(mi)度太大就屬這種情況的例子(zi)。
(3)可在繞組內埋設傳感器靠光(guang)導纖維引出以測繞組熱(re)點(dian)溫度,這樣,更能(neng)(neng)測出變壓器的超品牌(pai)運(yun)行能(neng)(neng)力(li)。
(4)高(gao)海拔處運(yun)行的(de)變壓(ya)器(qi),應注(zhu)意高(gao)海拔處的(de)散(san)熱困難(nan),但(dan)同時高(gao)海拔處的(de)周圍環(huan)境溫度(du)會下降(jiang),二者有時可(ke)補償(chang)。
(5)干(gan)式變(bian)壓器的鐵(tie)心(xin)溫(wen)度(du)會影響靠鐵(tie)心(xin)柱繞(rao)組的溫(wen)升。
(6)散熱器(qi)內(nei)不能有(you)剩氣沒有(you)放(fang)出,散熱器(qi)上(shang)必須要有(you)放(fang)氣塞(sai),在溫升試驗前先放(fang)氣。
(7)散(san)熱器的散(san)熱中(zhong)心(xin)比發熱中(zhong)心(xin)要高為(wei)好。
(8)箱蓋下不能有死油區。
(9)散(san)熱(re)器或冷(leng)卻器進入(ru)油箱中(zhong)油,要能(neng)流入(ru)繞(rao)組,不能(neng)在繞(rao)組外空間短路流通。
(10)溫升(sheng)試(shi)驗用(yong)(yong)機組要有(you)足夠容量(liang),必要時(shi)可用(yong)(yong)電容器補償。溫升(sheng)試(shi)驗前后油中含氣色(se)譜分(fen)析是檢(jian)測(ce)有(you)無過熱的檢(jian)測(ce)手段,但溫升(sheng)試(shi)驗時(shi)間(jian)要足夠長(chang)。也可用(yong)(yong)液相色(se)譜分(fen)析檢(jian)測(ce)糠醛含量(liang)來判斷有(you)無低溫過熱。
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