變(bian)壓(ya)器(qi)各個(ge)部門有(you)(you)不同的(de)(de)允(yun)許(xu)溫升,不同的(de)(de)運行(xing)工況也有(you)(you)不同的(de)(de)允(yun)許(xu)溫升。決定允(yun)許(xu)溫升的(de)(de)因素有(you)(you):變(bian)壓(ya)器(qi)的(de)(de)運行(xing)預期壽命、變(bian)壓(ya)器(qi)的(de)(de)**運行(xing)、變(bian)壓(ya)器(qi)的(de)(de)檢(jian)測技術。
繞(rao)(rao)(rao)組(zu)(zu)(zu)允許溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng):繞(rao)(rao)(rao)組(zu)(zu)(zu)的(de)允許溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng)是指整個繞(rao)(rao)(rao)組(zu)(zu)(zu)的(de)平(ping)(ping)(ping)均溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng),由(you)電阻法(fa)(fa)測(ce)得,允許溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng)與(yu)絕(jue)(jue)緣(yuan)(yuan)耐熱(re)等級(ji)(ji)有關(guan)。油浸式(shi)(shi)(shi)變(bian)(bian)(bian)壓(ya)(ya)器(qi)屬(shu)A級(ji)(ji)絕(jue)(jue)緣(yuan)(yuan),由(you)于(yu)傳統(tong)的(de)繞(rao)(rao)(rao)組(zu)(zu)(zu)溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng)測(ce)量(liang)法(fa)(fa)為(wei)(wei)(wei)電阻法(fa)(fa),測(ce)得的(de)溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng)為(wei)(wei)(wei)平(ping)(ping)(ping)均溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng),A級(ji)(ji)絕(jue)(jue)緣(yuan)(yuan)允許的(de)平(ping)(ping)(ping)均溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng)為(wei)(wei)(wei)65K。平(ping)(ping)(ping)均溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng)與(yu)繞(rao)(rao)(rao)組(zu)(zu)(zu)*熱(re)點(dian)溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng)之(zhi)差(cha)假使(shi)為(wei)(wei)(wei)13K。在年平(ping)(ping)(ping)均溫(wen)(wen)(wen)度(du)為(wei)(wei)(wei)20℃時(shi),A級(ji)(ji)絕(jue)(jue)緣(yuan)(yuan)繞(rao)(rao)(rao)組(zu)(zu)(zu)*熱(re)點(dian)溫(wen)(wen)(wen)度(du)為(wei)(wei)(wei)20+65+13=98℃,此時(shi)A級(ji)(ji)絕(jue)(jue)緣(yuan)(yuan)具(ju)有正常壽(shou)(shou)命。干式(shi)(shi)(shi)變(bian)(bian)(bian)壓(ya)(ya)器(qi)各種絕(jue)(jue)緣(yuan)(yuan)的(de)允許平(ping)(ping)(ping)均溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng):A級(ji)(ji)為(wei)(wei)(wei)60K,E級(ji)(ji)為(wei)(wei)(wei)75K,B級(ji)(ji)為(wei)(wei)(wei)80K,F級(ji)(ji)為(wei)(wei)(wei)100K,H級(ji)(ji)為(wei)(wei)(wei)125K,C級(ji)(ji)為(wei)(wei)(wei)150K。冬季(ji)繞(rao)(rao)(rao)組(zu)(zu)(zu)溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng)低于(yu)平(ping)(ping)(ping)均溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng),繞(rao)(rao)(rao)組(zu)(zu)(zu)可延長壽(shou)(shou)命,夏(xia)季(ji)的(de)繞(rao)(rao)(rao)組(zu)(zu)(zu)溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng)高于(yu)平(ping)(ping)(ping)均溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)(sheng),繞(rao)(rao)(rao)組(zu)(zu)(zu)要犧牲壽(shou)(shou)命。如超(chao)品牌容量(liang)也要犧牲壽(shou)(shou)命,但超(chao)品牌容量(liang)運行時(shi),油浸式(shi)(shi)(shi)變(bian)(bian)(bian)壓(ya)(ya)器(qi)A級(ji)(ji)絕(jue)(jue)緣(yuan)(yuan)繞(rao)(rao)(rao)組(zu)(zu)(zu)*熱(re)點(dian)溫(wen)(wen)(wen)度(du)不(bu)能超(chao)過140℃,即使(shi)犧牲的(de)壽(shou)(shou)命不(bu)多,也不(bu)允許超(chao)過140℃,因超(chao)過140℃時(shi)油要分解出氣(qi)體而影響(xiang)絕(jue)(jue)緣(yuan)(yuan)強度(du)。所(suo)以油浸式(shi)(shi)(shi)變(bian)(bian)(bian)壓(ya)(ya)器(qi)A級(ji)(ji)絕(jue)(jue)緣(yuan)(yuan)的(de)*熱(re)點(dian)溫(wen)(wen)(wen)度(du)不(bu)能超(chao)過140℃是從變(bian)(bian)(bian)壓(ya)(ya)器(qi)**運行出發(fa)的(de)。
大容(rong)量變(bian)壓器有時(shi)有幾(ji)種冷卻(que)(que)方式(shi),例如(ru)ONAN/ONAF,變(bian)壓器額定容(rong)量一般是指ONAF下(xia)(xia)(xia)的允許值,當風扇失去電源后,冷卻(que)(que)效率下(xia)(xia)(xia)降,如(ru)仍按ONAF冷卻(que)(que)方式(shi)下(xia)(xia)(xia)容(rong)量運行(xing)時(shi),繞組(zu)(zu)平均溫升(sheng)必將升(sheng)高(gao),故(gu)ONAN冷卻(que)(que)方式(shi)下(xia)(xia)(xia)必須降低容(rong)量運行(xing),使(shi)繞組(zu)(zu)平均溫升(sheng)不超過65K。
另外(wai),雙繞(rao)(rao)(rao)組(zu)(zu)或三繞(rao)(rao)(rao)組(zu)(zu)變(bian)(bian)壓(ya)器(qi)中,二(er)個(ge)(ge)或三個(ge)(ge)繞(rao)(rao)(rao)組(zu)(zu)應同時達相同的(de)溫(wen)(wen)(wen)升(sheng)(sheng)(sheng),當一個(ge)(ge)繞(rao)(rao)(rao)組(zu)(zu)達65K平(ping)均溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)時另一個(ge)(ge)或二(er)個(ge)(ge)繞(rao)(rao)(rao)組(zu)(zu)低于65K,則這樣的(de)設(she)計是不(bu)經濟(ji)的(de)。油浸式(shi)變(bian)(bian)壓(ya)器(qi)還應使(shi)油面(mian)(mian)頂層(ceng)與幾個(ge)(ge)繞(rao)(rao)(rao)組(zu)(zu)平(ping)均溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)同時達允(yun)許溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)是較為(wei)(wei)經濟(ji)的(de)。即(ji)油面(mian)(mian)頂層(ceng)溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)達55K,繞(rao)(rao)(rao)組(zu)(zu)平(ping)均溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)達65K為(wei)(wei)經濟(ji)的(de)方案。在設(she)計階段,就合理選取(qu)每一繞(rao)(rao)(rao)組(zu)(zu)的(de)電流密度,在保持負載損耗不(bu)超過標(biao)準(zhun)值時使(shi)各個(ge)(ge)繞(rao)(rao)(rao)組(zu)(zu)的(de)溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)接近65K,同時油面(mian)(mian)頂層(ceng)也(ye)達55K。但是,這對強(qiang)油循環的(de)變(bian)(bian)壓(ya)器(qi)是難以達到的(de)。因強(qiang)油風冷(leng)式(shi)變(bian)(bian)壓(ya)器(qi)的(de)油頂層(ceng)溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)一般為(wei)(wei)40K,強(qiang)油水(shui)冷(leng)式(shi)變(bian)(bian)壓(ya)器(qi)的(de)油頂層(ceng)溫(wen)(wen)(wen)升(sheng)(sheng)(sheng)一般為(wei)(wei)35K。
實際(ji)上,油(you)(you)(you)面(mian)(mian)頂層(ceng)溫(wen)(wen)(wen)(wen)升(sheng)與(yu)繞(rao)(rao)組平(ping)均(jun)(jun)溫(wen)(wen)(wen)(wen)升(sheng)很難(nan)同時(shi)到(dao)達極限允許值,因此,一般(ban)不能根據油(you)(you)(you)面(mian)(mian)頂層(ceng)溫(wen)(wen)(wen)(wen)升(sheng)來判(pan)斷繞(rao)(rao)組平(ping)均(jun)(jun)溫(wen)(wen)(wen)(wen)升(sheng)。這也是大(da)容量變(bian)壓器既(ji)裝油(you)(you)(you)面(mian)(mian)溫(wen)(wen)(wen)(wen)度指(zhi)(zhi)示儀(yi)與(yu)繞(rao)(rao)組熱點溫(wen)(wen)(wen)(wen)度指(zhi)(zhi)示儀(yi)的(de)原因。如單裝油(you)(you)(you)面(mian)(mian)溫(wen)(wen)(wen)(wen)度指(zhi)(zhi)示儀(yi)時(shi),有時(shi)較難(nan)判(pan)斷繞(rao)(rao)組平(ping)均(jun)(jun)溫(wen)(wen)(wen)(wen)升(sheng)。尤其強(qiang)油(you)(you)(you)循環冷卻變(bian)壓器。
在分析變壓器溫升時還要注意冷(leng)卻介質的溫度:
一(yi)般風(feng)冷(leng)式變壓(ya)器的冷(leng)卻介(jie)(jie)質為(wei)空氣,水冷(leng)變壓(ya)器冷(leng)卻介(jie)(jie)質為(wei)水。
當裝有(you)封(feng)閉(bi)母(mu)線(xian)時(shi),低壓套管(guan)(guan)在(zai)封(feng)閉(bi)母(mu)線(xian)內的介質雖為(wei)空(kong)氣,但溫度(du)為(wei)80℃。所以(yi)當低壓套管(guan)(guan)用(yong)于敞開式時(shi)與用(yong)于封(feng)閉(bi)母(mu)線(xian)內時(shi)有(you)不同的允許溫度(du)。一般,用(yong)于封(feng)閉(bi)母(mu)線(xian)內的套管(guan)(guan)要(yao)降低額(e)定(ding)電流,因封(feng)閉(bi)母(mu)線(xian)內空(kong)氣溫度(du)較高。
由(you)此可知(zhi),引線、套管、有載(zai)分(fen)接開(kai)關(guan)或無(wu)載(zai)分(fen)接開(kai)關(guan)的(de)(de)(de)(de)允(yun)許溫升決定(ding)(ding)于(yu)其周圍介質的(de)(de)(de)(de)溫升。變壓器又具有一定(ding)(ding)的(de)(de)(de)(de)超(chao)品(pin)牌運行的(de)(de)(de)(de)能(neng)力,帶電組件也應具有相同的(de)(de)(de)(de)能(neng)力,既有一定(ding)(ding)的(de)(de)(de)(de)壽命,又不影(ying)響**運行。
前面分析的油面頂層溫(wen)升(sheng)與(yu)繞組平(ping)均溫(wen)升(sheng)是指穩態(tai)下的溫(wen)升(sheng)。有(you)時(shi),在運行中常有(you)瞬時(shi)負(fu)載的變化,如突(tu)然接(jie)入(ru)較大負(fu)載,突(tu)然甩負(fu)載,此時(shi)還應(ying)注意溫(wen)度變化的時(shi)間(jian)常數。
油的時(shi)間常(chang)數(shu)較(jiao)大(da),就是負載變(bian)化(hua)后(hou),油面溫(wen)度(du)(du)在(zai)較(jiao)長(chang)時(shi)間后(hou)才能(neng)達(da)穩(wen)定溫(wen)升值,而繞(rao)(rao)組的時(shi)間常(chang)數(shu)較(jiao)小,繞(rao)(rao)組平均(jun)溫(wen)度(du)(du)能(neng)較(jiao)快地隨著負載的變(bian)化(hua)而變(bian)化(hua)。
當負載增加時(shi)(shi)(shi),不能認為油面溫(wen)度(du)沒有變(bian)化,而繞(rao)組溫(wen)度(du)也(ye)沒有變(bian)化。油的時(shi)(shi)(shi)間(jian)常數較(jiao)大,油面溫(wen)度(du)上升(sheng)較(jiao)慢,繞(rao)組時(shi)(shi)(shi)間(jian)常數較(jiao)小(xiao),繞(rao)組溫(wen)度(du)上升(sheng)較(jiao)快。如(ru)有繞(rao)組溫(wen)度(du)指(zhi)示(shi)儀,這(zhe)個指(zhi)示(shi)儀也(ye)應有較(jiao)好的響(xiang)應時(shi)(shi)(shi)間(jian),時(shi)(shi)(shi)間(jian)常數也(ye)要很(hen)小(xiao)。
要控制ONAF風扇啟(qi)動就不(bu)能(neng)靠油面溫(wen)度(du)指(zhi)示(shi)儀,只能(neng)由(you)繞組溫(wen)度(du)指(zhi)示(shi)儀實現,或由(you)套管電流(liu)互感器來(lai)控制。
在(zai)變壓器中,有時(shi)(shi)漏(lou)磁(ci)(ci)產生(sheng)的(de)損耗密度太大(da)(da)時(shi)(shi),會產生(sheng)局(ju)部過(guo)熱。大(da)(da)電(dian)(dian)流引線(xian)附近(jin)的(de)箱壁,大(da)(da)電(dian)(dian)流套管引出(chu)處(chu)箱蓋等處(chu),有時(shi)(shi)會有局(ju)部過(guo)熱。引起(qi)油分解出(chu)氣體的(de)局(ju)部過(guo)溫(wen)度是(shi)不(bu)允許的(de),這(zhe)會引起(qi)可靠性的(de)下(xia)降。這(zhe)就(jiu)要采取措施改變漏(lou)磁(ci)(ci)的(de)途徑,采取隔磁(ci)(ci)措施或在(zai)漏(lou)磁(ci)(ci)集中處(chu)用不(bu)導(dao)磁(ci)(ci)材料。
變(bian)(bian)壓器(qi)(qi)在運行中,不(bu)可避(bi)免地會有(you)短(duan)(duan)路(lu)(lu),變(bian)(bian)壓器(qi)(qi)短(duan)(duan)路(lu)(lu)時(shi)將流(liu)過短(duan)(duan)路(lu)(lu)電流(liu),此時(shi),變(bian)(bian)壓器(qi)(qi)迅速發(fa)熱(re),由于短(duan)(duan)路(lu)(lu)電流(liu)很大,變(bian)(bian)壓器(qi)(qi)等于在絕熱(re)條件(jian)下運行而不(bu)考慮散熱(re)。
A級絕(jue)緣銅導線繞組(zu)在(zai)短(duan)路時的允(yun)許溫(wen)度為250℃。
為保持這一(yi)溫度不(bu)超(chao)過,要在設計(ji)中(zhong)計(ji)算短(duan)路電(dian)流下(xia)許用(yong)電(dian)流密度,使在允許的(de)持續(xu)時間時銅導(dao)線不(bu)超(chao)過250℃。
銅(tong)導線(xian)的(de)機械應力(li)允許(xu)值(zhi)與(yu)溫度有關,銅(tong)導線(xian)的(de)工作溫度超過,允許(xu)應力(li)降(jiang)低。所以在引伸率為(wei)0.2%時允許(xu)應力(li)應是250℃下(xia)的(de)許(xu)用值(zhi)。
研(yan)究變壓器允(yun)許溫升時,還有幾點要引(yin)起注意(yi):
(1)有載(zai)調壓變(bian)壓器(qi)中有載(zai)分(fen)(fen)接開關(guan)內的過度(du)電阻器(qi),應使有載(zai)分(fen)(fen)接開關(guan)在連續操作下,電阻器(qi)對油溫升不(bu)超過350K。
(2)做溫升試(shi)驗(yan)時,外部的熱不(bu)要倒流入變壓器,如短(duan)接引線電流密度太大就屬這種(zhong)情況的例子。
(3)可在繞組內埋設傳感器靠(kao)光導(dao)纖維引(yin)出(chu)以測繞組熱點溫度,這樣(yang),更能測出(chu)變(bian)壓(ya)器的超品牌運行(xing)能力。
(4)高(gao)海(hai)拔處(chu)運行的(de)變壓器,應注意高(gao)海(hai)拔處(chu)的(de)散熱困(kun)難,但同時高(gao)海(hai)拔處(chu)的(de)周圍環境溫(wen)度(du)會下降,二者有時可(ke)補償。
(5)干(gan)式變(bian)壓器的鐵(tie)心(xin)溫度會影響靠鐵(tie)心(xin)柱繞組(zu)的溫升(sheng)。
(6)散熱器內不能有剩氣(qi)沒有放(fang)出(chu),散熱器上必須要有放(fang)氣(qi)塞,在(zai)溫升試驗(yan)前先放(fang)氣(qi)。
(7)散熱(re)器的(de)散熱(re)中心(xin)比發熱(re)中心(xin)要高(gao)為好。
(8)箱蓋下不能有死油區。
(9)散(san)熱(re)器(qi)或冷卻(que)器(qi)進入(ru)油箱中油,要能流(liu)(liu)入(ru)繞組,不能在繞組外(wai)空間短路流(liu)(liu)通。
(10)溫(wen)升(sheng)試驗(yan)用(yong)(yong)機組要有足夠容(rong)量(liang),必要時可用(yong)(yong)電容(rong)器補償。溫(wen)升(sheng)試驗(yan)前后油中含氣(qi)色譜分(fen)析(xi)是(shi)檢測(ce)有無過熱的檢測(ce)手段,但溫(wen)升(sheng)試驗(yan)時間要足夠長。也可用(yong)(yong)液相色譜分(fen)析(xi)檢測(ce)糠醛含量(liang)來判斷有無低溫(wen)過熱。
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