變壓(ya)(ya)器各個(ge)部(bu)門(men)有不同(tong)的(de)(de)(de)允許(xu)溫(wen)升(sheng),不同(tong)的(de)(de)(de)運行(xing)(xing)工況也有不同(tong)的(de)(de)(de)允許(xu)溫(wen)升(sheng)。決定允許(xu)溫(wen)升(sheng)的(de)(de)(de)因素有:變壓(ya)(ya)器的(de)(de)(de)運行(xing)(xing)預期(qi)壽命、變壓(ya)(ya)器的(de)(de)(de)**運行(xing)(xing)、變壓(ya)(ya)器的(de)(de)(de)檢測技(ji)術。
繞組(zu)(zu)(zu)(zu)允(yun)(yun)許(xu)(xu)溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng):繞組(zu)(zu)(zu)(zu)的(de)允(yun)(yun)許(xu)(xu)溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)是指整個繞組(zu)(zu)(zu)(zu)的(de)平均(jun)(jun)溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng),由電(dian)阻法測得(de)(de),允(yun)(yun)許(xu)(xu)溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)與絕緣(yuan)耐熱等(deng)級(ji)(ji)(ji)(ji)有關。油(you)浸(jin)(jin)式(shi)變壓(ya)器(qi)(qi)屬A級(ji)(ji)(ji)(ji)絕緣(yuan),由于(yu)(yu)傳統的(de)繞組(zu)(zu)(zu)(zu)溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)測量法為(wei)(wei)(wei)(wei)(wei)電(dian)阻法,測得(de)(de)的(de)溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)為(wei)(wei)(wei)(wei)(wei)平均(jun)(jun)溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng),A級(ji)(ji)(ji)(ji)絕緣(yuan)允(yun)(yun)許(xu)(xu)的(de)平均(jun)(jun)溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)為(wei)(wei)(wei)(wei)(wei)65K。平均(jun)(jun)溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)與繞組(zu)(zu)(zu)(zu)*熱點溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)之差假使為(wei)(wei)(wei)(wei)(wei)13K。在年平均(jun)(jun)溫(wen)(wen)(wen)(wen)(wen)度為(wei)(wei)(wei)(wei)(wei)20℃時,A級(ji)(ji)(ji)(ji)絕緣(yuan)繞組(zu)(zu)(zu)(zu)*熱點溫(wen)(wen)(wen)(wen)(wen)度為(wei)(wei)(wei)(wei)(wei)20+65+13=98℃,此時A級(ji)(ji)(ji)(ji)絕緣(yuan)具有正常(chang)壽(shou)(shou)命(ming)。干式(shi)變壓(ya)器(qi)(qi)各種(zhong)絕緣(yuan)的(de)允(yun)(yun)許(xu)(xu)平均(jun)(jun)溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng):A級(ji)(ji)(ji)(ji)為(wei)(wei)(wei)(wei)(wei)60K,E級(ji)(ji)(ji)(ji)為(wei)(wei)(wei)(wei)(wei)75K,B級(ji)(ji)(ji)(ji)為(wei)(wei)(wei)(wei)(wei)80K,F級(ji)(ji)(ji)(ji)為(wei)(wei)(wei)(wei)(wei)100K,H級(ji)(ji)(ji)(ji)為(wei)(wei)(wei)(wei)(wei)125K,C級(ji)(ji)(ji)(ji)為(wei)(wei)(wei)(wei)(wei)150K。冬季(ji)繞組(zu)(zu)(zu)(zu)溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)低于(yu)(yu)平均(jun)(jun)溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng),繞組(zu)(zu)(zu)(zu)可延長壽(shou)(shou)命(ming),夏季(ji)的(de)繞組(zu)(zu)(zu)(zu)溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng)高于(yu)(yu)平均(jun)(jun)溫(wen)(wen)(wen)(wen)(wen)升(sheng)(sheng)(sheng)(sheng),繞組(zu)(zu)(zu)(zu)要犧(xi)(xi)牲壽(shou)(shou)命(ming)。如超品牌容量也要犧(xi)(xi)牲壽(shou)(shou)命(ming),但超品牌容量運行(xing)時,油(you)浸(jin)(jin)式(shi)變壓(ya)器(qi)(qi)A級(ji)(ji)(ji)(ji)絕緣(yuan)繞組(zu)(zu)(zu)(zu)*熱點溫(wen)(wen)(wen)(wen)(wen)度不能超過(guo)(guo)140℃,即使犧(xi)(xi)牲的(de)壽(shou)(shou)命(ming)不多,也不允(yun)(yun)許(xu)(xu)超過(guo)(guo)140℃,因超過(guo)(guo)140℃時油(you)要分解(jie)出(chu)氣體(ti)而影響絕緣(yuan)強度。所(suo)以油(you)浸(jin)(jin)式(shi)變壓(ya)器(qi)(qi)A級(ji)(ji)(ji)(ji)絕緣(yuan)的(de)*熱點溫(wen)(wen)(wen)(wen)(wen)度不能超過(guo)(guo)140℃是從變壓(ya)器(qi)(qi)**運行(xing)出(chu)發的(de)。
大(da)容(rong)(rong)量(liang)變壓器有時(shi)有幾種冷(leng)卻(que)(que)方(fang)(fang)式(shi),例如ONAN/ONAF,變壓器額(e)定(ding)容(rong)(rong)量(liang)一般是指ONAF下的允許(xu)值(zhi),當風扇失去電源后,冷(leng)卻(que)(que)效率下降(jiang),如仍按ONAF冷(leng)卻(que)(que)方(fang)(fang)式(shi)下容(rong)(rong)量(liang)運行時(shi),繞組平均(jun)溫升必將升高,故ONAN冷(leng)卻(que)(que)方(fang)(fang)式(shi)下必須降(jiang)低容(rong)(rong)量(liang)運行,使繞組平均(jun)溫升不(bu)超過65K。
另外,雙繞(rao)(rao)(rao)組(zu)或(huo)(huo)三(san)繞(rao)(rao)(rao)組(zu)變(bian)壓器中,二個或(huo)(huo)三(san)個繞(rao)(rao)(rao)組(zu)應同(tong)時達(da)(da)相(xiang)同(tong)的(de)溫(wen)(wen)(wen)升(sheng),當一個繞(rao)(rao)(rao)組(zu)達(da)(da)65K平均溫(wen)(wen)(wen)升(sheng)時另一個或(huo)(huo)二個繞(rao)(rao)(rao)組(zu)低于(yu)65K,則這(zhe)樣的(de)設計(ji)是(shi)不經濟的(de)。油浸式(shi)變(bian)壓器還應使油面(mian)頂層(ceng)與幾個繞(rao)(rao)(rao)組(zu)平均溫(wen)(wen)(wen)升(sheng)同(tong)時達(da)(da)允許溫(wen)(wen)(wen)升(sheng)是(shi)較為(wei)(wei)經濟的(de)。即油面(mian)頂層(ceng)溫(wen)(wen)(wen)升(sheng)達(da)(da)55K,繞(rao)(rao)(rao)組(zu)平均溫(wen)(wen)(wen)升(sheng)達(da)(da)65K為(wei)(wei)經濟的(de)方案(an)。在(zai)(zai)設計(ji)階段,就合理選取每一繞(rao)(rao)(rao)組(zu)的(de)電流密度,在(zai)(zai)保持負載(zai)損耗不超過標準值時使各個繞(rao)(rao)(rao)組(zu)的(de)溫(wen)(wen)(wen)升(sheng)接近(jin)65K,同(tong)時油面(mian)頂層(ceng)也達(da)(da)55K。但是(shi),這(zhe)對強油循環(huan)的(de)變(bian)壓器是(shi)難以達(da)(da)到的(de)。因強油風(feng)冷(leng)(leng)式(shi)變(bian)壓器的(de)油頂層(ceng)溫(wen)(wen)(wen)升(sheng)一般為(wei)(wei)40K,強油水冷(leng)(leng)式(shi)變(bian)壓器的(de)油頂層(ceng)溫(wen)(wen)(wen)升(sheng)一般為(wei)(wei)35K。
實際上,油(you)(you)面(mian)頂層(ceng)溫(wen)(wen)(wen)(wen)升(sheng)與(yu)繞組(zu)平(ping)均(jun)(jun)溫(wen)(wen)(wen)(wen)升(sheng)很(hen)難(nan)(nan)同(tong)時到達極限(xian)允許值(zhi),因此,一般不能根據油(you)(you)面(mian)頂層(ceng)溫(wen)(wen)(wen)(wen)升(sheng)來判(pan)斷繞組(zu)平(ping)均(jun)(jun)溫(wen)(wen)(wen)(wen)升(sheng)。這也是大(da)容量變壓器既(ji)裝(zhuang)油(you)(you)面(mian)溫(wen)(wen)(wen)(wen)度指示儀(yi)與(yu)繞組(zu)熱點溫(wen)(wen)(wen)(wen)度指示儀(yi)的原因。如(ru)單裝(zhuang)油(you)(you)面(mian)溫(wen)(wen)(wen)(wen)度指示儀(yi)時,有時較難(nan)(nan)判(pan)斷繞組(zu)平(ping)均(jun)(jun)溫(wen)(wen)(wen)(wen)升(sheng)。尤(you)其強油(you)(you)循環(huan)冷卻(que)變壓器。
在分析變壓器溫升(sheng)時(shi)還要注意冷卻介質的溫度:
一般風冷(leng)式變壓(ya)器的冷(leng)卻(que)介質為空氣,水冷(leng)變壓(ya)器冷(leng)卻(que)介質為水。
當(dang)裝有封閉母(mu)(mu)線時,低(di)(di)壓套管(guan)在封閉母(mu)(mu)線內(nei)的(de)介質(zhi)雖為空(kong)氣,但溫度為80℃。所以(yi)當(dang)低(di)(di)壓套管(guan)用于(yu)敞開式時與用于(yu)封閉母(mu)(mu)線內(nei)時有不同的(de)允許(xu)溫度。一般,用于(yu)封閉母(mu)(mu)線內(nei)的(de)套管(guan)要降低(di)(di)額(e)定電流,因封閉母(mu)(mu)線內(nei)空(kong)氣溫度較高。
由此(ci)可(ke)知,引(yin)線、套管、有載(zai)分(fen)接(jie)開關(guan)或無載(zai)分(fen)接(jie)開關(guan)的(de)允許(xu)溫(wen)升決定于(yu)其周圍介質的(de)溫(wen)升。變壓(ya)器(qi)又具(ju)有一(yi)定的(de)超品牌運行的(de)能力(li),帶電組件也(ye)應具(ju)有相(xiang)同的(de)能力(li),既(ji)有一(yi)定的(de)壽命,又不影響(xiang)**運行。
前面分析的(de)油面頂(ding)層溫(wen)升(sheng)與繞(rao)組(zu)平均溫(wen)升(sheng)是指穩態下的(de)溫(wen)升(sheng)。有時(shi)(shi),在運行中常有瞬時(shi)(shi)負載(zai)的(de)變化(hua),如(ru)突然接入較大(da)負載(zai),突然甩負載(zai),此時(shi)(shi)還應注意溫(wen)度變化(hua)的(de)時(shi)(shi)間常數。
油的時間(jian)(jian)常(chang)數較大,就是(shi)負載(zai)變化后,油面溫度(du)在較長時間(jian)(jian)后才能達穩定溫升值,而(er)繞組(zu)的時間(jian)(jian)常(chang)數較小(xiao),繞組(zu)平均(jun)溫度(du)能較快地隨著負載(zai)的變化而(er)變化。
當(dang)負(fu)載(zai)增加(jia)時,不能認為油(you)面溫(wen)(wen)度(du)(du)沒有變化(hua),而繞組(zu)溫(wen)(wen)度(du)(du)也(ye)(ye)沒有變化(hua)。油(you)的時間常數較(jiao)(jiao)(jiao)大(da),油(you)面溫(wen)(wen)度(du)(du)上(shang)升較(jiao)(jiao)(jiao)慢(man),繞組(zu)時間常數較(jiao)(jiao)(jiao)小(xiao),繞組(zu)溫(wen)(wen)度(du)(du)上(shang)升較(jiao)(jiao)(jiao)快。如(ru)有繞組(zu)溫(wen)(wen)度(du)(du)指示(shi)儀(yi),這個(ge)指示(shi)儀(yi)也(ye)(ye)應有較(jiao)(jiao)(jiao)好的響應時間,時間常數也(ye)(ye)要很小(xiao)。
要控制(zhi)ONAF風扇啟動就不能靠油(you)面(mian)溫(wen)度指示儀(yi),只(zhi)能由(you)繞組溫(wen)度指示儀(yi)實現,或由(you)套管電流互(hu)感(gan)器來控制(zhi)。
在變(bian)(bian)壓器中(zhong),有時漏(lou)(lou)(lou)磁產生的(de)(de)(de)損(sun)耗密(mi)度(du)太大(da)時,會(hui)產生局部過熱。大(da)電(dian)流(liu)引(yin)線附近的(de)(de)(de)箱壁,大(da)電(dian)流(liu)套管引(yin)出(chu)處箱蓋等處,有時會(hui)有局部過熱。引(yin)起油(you)分解出(chu)氣體的(de)(de)(de)局部過溫度(du)是(shi)不(bu)(bu)允許的(de)(de)(de),這會(hui)引(yin)起可靠性的(de)(de)(de)下降。這就要采取措施(shi)改(gai)變(bian)(bian)漏(lou)(lou)(lou)磁的(de)(de)(de)途徑,采取隔磁措施(shi)或在漏(lou)(lou)(lou)磁集中(zhong)處用不(bu)(bu)導磁材料(liao)。
變(bian)(bian)壓(ya)(ya)器在運行(xing)中,不(bu)可避(bi)免地會有短(duan)(duan)路(lu),變(bian)(bian)壓(ya)(ya)器短(duan)(duan)路(lu)時將流過短(duan)(duan)路(lu)電流,此時,變(bian)(bian)壓(ya)(ya)器迅(xun)速發熱,由于短(duan)(duan)路(lu)電流很大,變(bian)(bian)壓(ya)(ya)器等于在絕熱條(tiao)件下(xia)運行(xing)而不(bu)考慮散熱。
A級絕緣銅導線繞組在短路時的允許溫度為250℃。
為保持這(zhe)一溫度不超過,要在設計(ji)中計(ji)算短路電(dian)流下(xia)許用電(dian)流密度,使在允許的持續時間時銅(tong)導線不超過250℃。
銅導(dao)線(xian)的機械應力(li)允許(xu)值與溫度有關,銅導(dao)線(xian)的工(gong)作(zuo)溫度超過,允許(xu)應力(li)降低。所(suo)以在引(yin)伸率為0.2%時允許(xu)應力(li)應是250℃下的許(xu)用值。
研究變(bian)壓器(qi)允(yun)許溫升時(shi),還有幾點(dian)要引起注意:
(1)有載(zai)(zai)調壓變(bian)壓器中有載(zai)(zai)分(fen)接開關(guan)內的過度電阻器,應使有載(zai)(zai)分(fen)接開關(guan)在(zai)連續操作(zuo)下(xia),電阻器對油溫升不(bu)超過350K。
(2)做溫升(sheng)試(shi)驗(yan)時(shi),外(wai)部的(de)熱(re)不要倒流入變壓(ya)器,如(ru)短接引線(xian)電流密度太大就屬這種情況的(de)例子(zi)。
(3)可(ke)在繞(rao)(rao)組(zu)(zu)內埋設傳感器靠光導纖維引出(chu)以測繞(rao)(rao)組(zu)(zu)熱(re)點(dian)溫度,這樣,更能(neng)(neng)測出(chu)變壓器的(de)超品牌運行能(neng)(neng)力。
(4)高海拔處運(yun)行的(de)變壓器(qi),應注(zhu)意高海拔處的(de)散熱(re)困難(nan),但(dan)同時(shi)(shi)高海拔處的(de)周圍環境(jing)溫(wen)度會下降(jiang),二者有時(shi)(shi)可補償。
(5)干式變壓(ya)器的鐵心溫(wen)度(du)會影(ying)響靠鐵心柱繞組(zu)的溫(wen)升。
(6)散(san)熱器(qi)(qi)內不能有(you)剩(sheng)氣(qi)(qi)沒有(you)放出,散(san)熱器(qi)(qi)上必須要有(you)放氣(qi)(qi)塞,在溫升試驗前先放氣(qi)(qi)。
(7)散熱器的散熱中(zhong)心(xin)比發熱中(zhong)心(xin)要(yao)高為好。
(8)箱蓋下不能有(you)死油區(qu)。
(9)散(san)熱器或冷卻器進入油(you)(you)箱(xiang)中油(you)(you),要能(neng)流入繞組,不能(neng)在繞組外空間短路流通。
(10)溫升試驗用(yong)(yong)機(ji)組(zu)要有(you)足(zu)夠容(rong)量(liang),必要時可用(yong)(yong)電容(rong)器補償。溫升試驗前后油中含(han)氣色(se)譜(pu)分(fen)析是檢測有(you)無過熱的檢測手(shou)段,但(dan)溫升試驗時間要足(zu)夠長。也可用(yong)(yong)液相色(se)譜(pu)分(fen)析檢測糠醛(quan)含(han)量(liang)來判(pan)斷有(you)無低溫過熱。
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