A-B 1771-OW16 在熱油噴淋階段,器身絕緣材料中的水分大量蒸發(fā)出來,若真空泵的抽出量小于水蒸氣的蒸發(fā)量,造成Ap
減小,且油箱末采取保溫措施,水蒸氣在溫度較低的油箱頂部凝結(jié)成水球。一部分水球滴在鐵芯柱和繞組端絕
緣上,造成鐵芯生銹,絕緣再次受潮。若抽氣時間過長,箱內(nèi)真空度太篼,噴淋用油不能建立循環(huán),另外容易
造成器身表面絕緣干燥過快,纖維毛細(xì)管萎縮,深層絕緣中的水分就難以擴散與蒸發(fā);同時我們應(yīng)該看到對流
是效率最高的傳熱方式,
當(dāng)真空度提高到一定程度,對流傳熱幾乎不存,靠傳導(dǎo)和輻射傳熱,效益低,當(dāng)真空
度再進(jìn)一步提高,就只能靠輻射傳熱,傳熱效率更低,為此要求箱內(nèi)保持較低的真空度,利用空氣及蒸發(fā)出來
的水蒸氣通過對流和傳導(dǎo)方式對器身傳熱,使得鐵芯和線圈的溫度較快地升高,正確處理好上述幾方面的關(guān)系
,是選取熱油噴淋階段真空度的關(guān)鍵,為此要求熱油噴淋階段對油箱間斷性抽真空,箱內(nèi)真空度不宜太高,確
保噴淋用油能建立循環(huán)(油箱底部-油泵或濾油機油箱頂部-油箱底部)。兼顧上述幾方面的要求,根據(jù)(水分
汽化與真空度關(guān)系曲線)油熱噴淋預(yù)熱階段真空度掌握在。75MPa~0.08MPa之間為佳,此真空度下變壓器器身
中的水分汽化溫度為6(TC~70X:。
在真空階段,熱油噴淋預(yù)熱后的抽真空階段器身的溫度呈下降趨勢,抽真空脫水時不要一口氣將箱內(nèi)真空
度抽到底,真空度維持在一定范圍值內(nèi),此真空度范圍內(nèi)箱內(nèi)還存在適當(dāng)?shù)乃魵,依靠這些水蒸氣進(jìn)行對流
和傳導(dǎo)傳熱,減弱器身溫度呈大輻度下降的趨勢,防止溫度下降過快導(dǎo)致絕緣材料纖維毛細(xì)管萎縮,不利干器
身絕緣材料深層部位的水分向表層遷移。真空階段箱內(nèi)真空度掌握在。2MPa~0.03MPa之間。
在篼真空終干階段,干燥過程通過幾個循環(huán)(油噴加熱-真空-油噴加熱)后,進(jìn)入高真空終干階,持續(xù)長
時間抽真空,箱內(nèi)壓強不斷下降,進(jìn)一步加大絕緣材料內(nèi)外水蒸氣分壓Ap,確保絕緣材料中殘余的水分不斷抽
出。
(3)時間參數(shù)。熱油噴淋階段噴淋用油溫度達(dá)到期95'C后,連續(xù)噴淋時間812h.真空階段抽真空時間一般
掌握在6~8h,如果器身溫度降低到4CTC左右時,即使連續(xù)抽真空的時間不足68h,。
也要停止抽真空。在高真空終干階段抽真空時間一般掌握在12~24h,之后進(jìn)入真空注油階段,注入合格的
變壓器油。
4小結(jié)電力變壓器現(xiàn)場絕緣干燥處理工藝是一項復(fù)雜的系統(tǒng)工作,其干燥質(zhì)量直接影響到整個電力系統(tǒng)供
電的可靠性,充分利用變壓器絕緣系統(tǒng)中存在的兩個動態(tài)平衡過程,科學(xué)合理掌握和控制絕緣干燥進(jìn)程的相關(guān)
參數(shù),是提高變壓器絕緣現(xiàn)場干燥處理效果的關(guān)鍵所在。
用DC-DC級將輸人、輸出隔離,并為DC-AC級提供合適的直流電源。在輸入電壓變化范圍不太大的情況下,DC-
DC級可以采用結(jié)構(gòu)簡單的直流變壓器。為采用雙管正激交錯并聯(lián)的直流變壓器拓?fù)。該電路的兩組開關(guān)管M,
\42和\43,風(fēng)交錯導(dǎo)-通,各自的占空比約為0.5.開關(guān)管M,12導(dǎo)通時,M3,M4關(guān)斷,輸人電壓加在變壓器乃上
,整流二極管U導(dǎo)通,M2關(guān)斷后,續(xù)流二極管E>5,D6續(xù)流,變壓器7\去磁,關(guān)斷。M:,M2關(guān)斷后,M3,%導(dǎo)
通,類似于上述過程m.這種拓?fù)渚哂泻芏鄡?yōu)點。各開關(guān)管的占空比理論上為0.5,占空比固定,整個變壓器副
邊電路占空比為1.輸出濾波器無電感,沒有續(xù)流二極管,結(jié)構(gòu)簡單。U,D,。無二極管反向恢復(fù)產(chǎn)生的尖峰問
題,故輸人和輸出電壓關(guān)系僅僅是變壓器變比,效率高。通過兩個二極管來提供去磁電流回路,實現(xiàn)磁復(fù)位,
去除了復(fù)雜磁復(fù)位電路,且勵磁能量回饋到電源,減小了損耗;而且兩個二極管還起到箝位的作用,使開關(guān)管
的關(guān)斷電壓箝在輸人電壓,電壓應(yīng)力低;該拓?fù)涞拿恳粋橋臂都是由一個二極管和開關(guān)管串聯(lián)構(gòu)成,不存在橋
臂直通的可能,可靠性高。
廈門興銳達(dá)自動化設(shè)備有限公司
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