由(you)于我國(guo)社(she)會經(jing)濟的(de)(de)(de)迅速發展，華東、華中和沿(yan)(yan)海地(di)區都出現(xian)用電(dian)(dian)(dian)緊張的(de)(de)(de)情況，對電(dian)(dian)(dian)力系統供(gong)(gong)電(dian)(dian)(dian)數量(liang)(liang)和質(zhi)量(liang)(liang)的(de)(de)(de)要求越(yue)來越(yue)高(gao)(gao)。由(you)于這些(xie)地(di)區能源(yuan)匱乏和對環境保(bao)護(hu)的(de)(de)(de)要求，急(ji)需從外(wai)地(di)大(da)量(liang)(liang)輸(shu)入高(gao)(gao)質(zhi)量(liang)(liang)的(de)(de)(de)電(dian)(dian)(dian)能，而西南地(di)區的(de)(de)(de)川(chuan)、滇等省(sheng)水(shui)(shui)電(dian)(dian)(dian)資源(yuan)蘊(yun)藏豐(feng)富，可(ke)供(gong)(gong)開發的(de)(de)(de)水(shui)(shui)電(dian)(dian)(dian)資源(yuan)占全國(guo)的(de)(de)(de)70％以上(shang)。建設大(da)型(xing)或超大(da)型(xing)水(shui)(shui)電(dian)(dian)(dian)站(zhan)(zhan)，為華東、華中和沿(yan)(yan)海地(di)區提供(gong)(gong)高(gao)(gao)質(zhi)量(liang)(liang)廉價的(de)(de)(de)水(shui)(shui)電(dian)(dian)(dian)，不但能實(shi)(shi)現(xian)全國(guo)電(dian)(dian)(dian)力資源(yuan)優(you)化(hua)配置和實(shi)(shi)現(xian)“西電(dian)(dian)(dian)東送”，還能發揮攔沙(sha)、防洪、改善下(xia)游航運條件等綜合效益。現(xian)以金沙(sha)江上(shang)擬建的(de)(de)(de)巨型(xing)水(shui)(shui)電(dian)(dian)(dian)站(zhan)(zhan)———溪(xi)洛渡水(shui)(shui)電(dian)(dian)(dian)站(zhan)(zhan)為例分(fen)析水(shui)(shui)電(dian)(dian)(dian)站(zhan)(zhan)主變壓器的(de)(de)(de)選擇(ze)。
2 溪洛(luo)渡水電站簡介
溪洛渡水(shui)(shui)電(dian)(dian)站(zhan)是(shi)金沙(sha)江(jiang)下游上的(de)一(yi)座(zuo)巨型水(shui)(shui)電(dian)(dian)站(zhan)，地處四川省雷波縣和云南省永善縣境內，上接白鶴灘(tan)電(dian)(dian)站(zhan)尾水(shui)(shui)，下與向家壩水(shui)(shui)庫(ku)(ku)相(xiang)接。電(dian)(dian)站(zhan)供電(dian)(dian)華(hua)東、華(hua)中，兼顧川、滇(dian)兩省用(yong)電(dian)(dian)需要，是(shi)金沙(sha)江(jiang)“西電(dian)(dian)東送”距(ju)離負荷中心最近的(de)骨干電(dian)(dian)源(yuan)之一(yi)，也是(shi)金沙(sha)江(jiang)上最大(da)的(de)一(yi)座(zuo)水(shui)(shui)電(dian)(dian)站(zhan)。電(dian)(dian)站(zhan)裝(zhuang)機(ji)18臺，單機(ji)容量700 MW，總(zong)裝(zhuang)機(ji)容量達12 600 MW，單機(ji)最大(da)容量855 MVA。年(nian)平均(jun)發電(dian)(dian)量571.2億(yi)(yi)kW·h，年(nian)利用(yong)小時數4 530h，水(shui)(shui)庫(ku)(ku)總(zong)庫(ku)(ku)容126.7億(yi)(yi)m3，調(diao)節庫(ku)(ku)容64．6億(yi)(yi)m3，具有不完全季調(diao)節性能，保證出力3 395 MW。
電站地(di)處高山(shan)峽谷(gu)，河床狹窄。根據(ju)樞(shu)紐布置(zhi)和地(di)形條(tiao)件，電站設左(zuo)、右兩個(ge)地(di)下廠房，各布置(zhi)9 臺機組。主廠房、主變壓(ya)(ya)器室和尾水調壓(ya)(ya)室相互平行，呈三洞式布置(zhi)。發電機引(yin)出(chu)回路選用(yong)全聯式離相封(feng)閉母線(xian)與(yu)主變低壓(ya)(ya)端子相連，主變壓(ya)(ya)器的500kV出(chu)線(xian)采用(yong)超高壓(ya)(ya)擠包絕緣(yuan)電纜通過垂直豎井引(yin)至地(di)面(mian)開關(guan)站。
3 運(yun)輸條(tiao)件
超大(da)型水(shui)(shui)電(dian)(dian)(dian)(dian)(dian)站(zhan)(zhan)(zhan)(zhan)(zhan)(zhan)機(ji)電(dian)(dian)(dian)(dian)(dian)設(she)備(bei)重大(da)件(jian)(jian)包括：水(shui)(shui)輪(lun)機(ji)轉(zhuan)輪(lun)、主(zhu)變壓器(qi)、橋(qiao)機(ji)主(zhu)梁(liang)、主(zhu)軸、轉(zhuan)子中心體、轉(zhuan)子支架(jia)扇形(xing)(xing)體、上機(ji)架(jia)中心體和(he)下機(ji)架(jia)中心體、定子機(ji)座以及(ji)水(shui)(shui)輪(lun)機(ji)頂蓋、座環等，而主(zhu)變壓器(qi)是運(yun)(yun)輸(shu)(shu)的一(yi)個重要環節。超大(da)型水(shui)(shui)電(dian)(dian)(dian)(dian)(dian)站(zhan)(zhan)(zhan)(zhan)(zhan)(zhan)一(yi)般(ban)地處偏僻的高山(shan)峽谷(gu)區，地形(xing)(xing)條件(jian)(jian)復雜，交通(tong)(tong)運(yun)(yun)輸(shu)(shu)設(she)施(shi)和(he)條件(jian)(jian)惡劣，因(yin)此機(ji)電(dian)(dian)(dian)(dian)(dian)設(she)備(bei)重大(da)件(jian)(jian)運(yun)(yun)輸(shu)(shu)方案是電(dian)(dian)(dian)(dian)(dian)站(zhan)(zhan)(zhan)(zhan)(zhan)(zhan)設(she)計初期重要的研究課題之一(yi)。主(zhu)變壓器(qi)一(yi)般(ban)可通(tong)(tong)過(guo)(guo)(guo)水(shui)(shui)運(yun)(yun)運(yun)(yun)至電(dian)(dian)(dian)(dian)(dian)站(zhan)(zhan)(zhan)(zhan)(zhan)(zhan)附近(jin)碼(ma)頭(tou)，上岸后(hou)經(jing)電(dian)(dian)(dian)(dian)(dian)站(zhan)(zhan)(zhan)(zhan)(zhan)(zhan)專(zhuan)(zhuan)(zhuan)用(yong)公路運(yun)(yun)抵工地；或者通(tong)(tong)過(guo)(guo)(guo)鐵路和(he)專(zhuan)(zhuan)(zhuan)用(yong)鐵路運(yun)(yun)至電(dian)(dian)(dian)(dian)(dian)站(zhan)(zhan)(zhan)(zhan)(zhan)(zhan)附近(jin)車(che)站(zhan)(zhan)(zhan)(zhan)(zhan)(zhan)（運(yun)(yun)輸(shu)(shu)尺(chi)寸應控(kong)制在二級超限內）后(hou)，再通(tong)(tong)過(guo)(guo)(guo)電(dian)(dian)(dian)(dian)(dian)站(zhan)(zhan)(zhan)(zhan)(zhan)(zhan)專(zhuan)(zhuan)(zhuan)用(yong)公路運(yun)(yun)至工地。這兩種情況均需(xu)經(jing)過(guo)(guo)(guo)詳細周密的經(jing)濟技術比較后(hou)，才能(neng)最終確定電(dian)(dian)(dian)(dian)(dian)站(zhan)(zhan)(zhan)(zhan)(zhan)(zhan)機(ji)電(dian)(dian)(dian)(dian)(dian)設(she)備(bei)重大(da)件(jian)(jian)的運(yun)(yun)輸(shu)(shu)方案。溪洛渡水(shui)(shui)電(dian)(dian)(dian)(dian)(dian)站(zhan)(zhan)(zhan)(zhan)(zhan)(zhan)主(zhu)變壓器(qi)單相運(yun)(yun)輸(shu)(shu)尺(chi)寸約5．0m×4．0m×4．0m，運(yun)(yun)輸(shu)(shu)重量約178t，共54相，運(yun)(yun)輸(shu)(shu)任(ren)務(wu)繁重，經(jing)專(zhuan)(zhuan)(zhuan)題研究后(hou)提出先通(tong)(tong)過(guo)(guo)(guo)專(zhuan)(zhuan)(zhuan)用(yong)鐵路運(yun)(yun)至電(dian)(dian)(dian)(dian)(dian)站(zhan)(zhan)(zhan)(zhan)(zhan)(zhan)附近(jin)車(che)站(zhan)(zhan)(zhan)(zhan)(zhan)(zhan)，再通(tong)(tong)過(guo)(guo)(guo)電(dian)(dian)(dian)(dian)(dian)站(zhan)(zhan)(zhan)(zhan)(zhan)(zhan)專(zhuan)(zhuan)(zhuan)用(yong)公路運(yun)(yun)至電(dian)(dian)(dian)(dian)(dian)站(zhan)(zhan)(zhan)(zhan)(zhan)(zhan)工地。
4 主變(bian)壓器主要(yao)參數和中(zhong)性點接地方(fang)式
4．1 額定值
隨著發(fa)電(dian)(dian)設(she)(she)備的(de)設(she)(she)計和制造技術的(de)發(fa)展(zhan)，發(fa)電(dian)(dian)機(ji)(ji)(ji)組單機(ji)(ji)(ji)容量(liang)越(yue)來越(yue)大(da)，已建(jian)(jian)二灘水(shui)(shui)電(dian)(dian)站(zhan)單機(ji)(ji)(ji)容量(liang)為550 MW，在建(jian)(jian)三峽、龍灘和小灣水(shui)(shui)電(dian)(dian)站(zhan)單機(ji)(ji)(ji)容量(liang)均(jun)為700 MW，擬(ni)建(jian)(jian)的(de)溪(xi)洛(luo)渡水(shui)(shui)電(dian)(dian)站(zhan)單機(ji)(ji)(ji)容量(liang)也為700 MW，并(bing)且發(fa)電(dian)(dian)設(she)(she)備的(de)單機(ji)(ji)(ji)容量(liang)還(huan)有(you)增大(da)的(de)趨勢。考慮到許多電(dian)(dian)站(zhan)的(de)發(fa)電(dian)(dian)機(ji)(ji)(ji)均(jun)有(you)設(she)(she)置(zhi)最大(da)容量(liang)的(de)要(yao)求，因此(ci)需(xu)要(yao)有(you)相(xiang)應的(de)大(da)型(xing)變(bian)壓器設(she)(she)計和制造技術相(xiang)匹配。根據溪(xi)洛(luo)渡水(shui)(shui)電(dian)(dian)站(zhan)的(de)具體條(tiao)件，選(xuan)擇的(de)主(zhu)變(bian)壓器的(de)主(zhu)要(yao)技術參數(shu)如下：
額定容量：855 MVA；額定電壓：高壓525kV，低壓20kV；接(jie)線組別：YN，d11；阻抗電壓：15％～17％；絕緣(yuan)水平：見表(biao)1。
4．2 中性點接地方式(shi)
根據(ju)水電(dian)站升(sheng)壓(ya)(ya)變壓(ya)(ya)器(qi)(qi)中(zhong)(zhong)性(xing)(xing)點接地方(fang)式及(ji)其(qi)實踐(jian)經驗，在電(dian)力系統中(zhong)(zhong)運行(xing)變壓(ya)(ya)器(qi)(qi)的(de)中(zhong)(zhong)性(xing)(xing)點接地方(fang)式，將直接影響(xiang)電(dian)力系統的(de)內(nei)部過(guo)電(dian)壓(ya)(ya)水平、電(dian)氣設備的(de)絕緣強度、系統的(de)穩定(ding)(ding)、繼電(dian)保護(hu)、開(kai)關遮斷容量、對通信線路干(gan)擾、變壓(ya)(ya)器(qi)(qi)中(zhong)(zhong)性(xing)(xing)點過(guo)電(dian)壓(ya)(ya)保護(hu)方(fang)式、變壓(ya)(ya)器(qi)(qi)中(zhong)(zhong)性(xing)(xing)點絕緣水平以(yi)及(ji)變壓(ya)(ya)器(qi)(qi)制造等。因此，變壓(ya)(ya)器(qi)(qi)中(zhong)(zhong)性(xing)(xing)點的(de)接地方(fang)式應根據(ju)諸方(fang)面的(de)影響(xiang)因素進行(xing)綜合的(de)技術經濟分析和(he)比(bi)較(jiao)后加以(yi)確定(ding)(ding)。
現階段我國超高壓(ya)(ya)(ya)電壓(ya)(ya)(ya)等級為500kV，對500kV變(bian)壓(ya)(ya)(ya)器(qi)(qi)(qi)中性點(dian)接地方(fang)式有(you)兩種不(bu)(bu)同觀(guan)點(dian)：一種沿用220kV系統所采(cai)用的(de)(de)(de)(de)(de)部(bu)分(fen)變(bian)壓(ya)(ya)(ya)器(qi)(qi)(qi)中性點(dian)接地的(de)(de)(de)(de)(de)方(fang)式，這樣可采(cai)用簡單可靠的(de)(de)(de)(de)(de)零序(xu)電流繼(ji)電保護，斷路(lu)器(qi)(qi)(qi)遮斷容量不(bu)(bu)受單相(xiang)短路(lu)電流的(de)(de)(de)(de)(de)限(xian)制，同時單相(xiang)接地對通信線(xian)路(lu)的(de)(de)(de)(de)(de)干(gan)擾也較小；另一種為500kV變(bian)壓(ya)(ya)(ya)器(qi)(qi)(qi)全部(bu)采(cai)用中性點(dian)直接接地，變(bian)壓(ya)(ya)(ya)器(qi)(qi)(qi)中性點(dian)絕緣(yuan)水平(ping)最低，便于變(bian)壓(ya)(ya)(ya)器(qi)(qi)(qi)制造，變(bian)壓(ya)(ya)(ya)器(qi)(qi)(qi)中性點(dian)不(bu)(bu)會失(shi)地，也不(bu)(bu)會產(chan)(chan)生不(bu)(bu)接地的(de)(de)(de)(de)(de)孤(gu)立系統。但兩者均不(bu)(bu)能有(you)效(xiao)地解決單相(xiang)短路(lu)電流在(zai)變(bian)壓(ya)(ya)(ya)器(qi)(qi)(qi)中性點(dian)產(chan)(chan)生的(de)(de)(de)(de)(de)過電壓(ya)(ya)(ya)問題，都存(cun)在(zai)明顯的(de)(de)(de)(de)(de)局限(xian)性。
為了(le)限制(zhi)單(dan)相短路(lu)電(dian)(dian)(dian)流，宜(yi)采用變(bian)(bian)壓(ya)(ya)(ya)器中(zhong)(zhong)性(xing)點經(jing)小電(dian)(dian)(dian)抗(kang)(kang)器的(de)接(jie)(jie)地(di)(di)方(fang)式，只(zhi)要小電(dian)(dian)(dian)抗(kang)(kang)器選擇適(shi)當(dang)就(jiu)可以(yi)起到(dao)變(bian)(bian)壓(ya)(ya)(ya)器中(zhong)(zhong)性(xing)點部(bu)分(fen)接(jie)(jie)地(di)(di)的(de)作用。經(jing)計算(suan)分(fen)析，經(jing)小電(dian)(dian)(dian)抗(kang)(kang)器接(jie)(jie)地(di)(di)的(de)變(bian)(bian)壓(ya)(ya)(ya)器中(zhong)(zhong)性(xing)點的(de)過(guo)(guo)電(dian)(dian)(dian)壓(ya)(ya)(ya)比不接(jie)(jie)地(di)(di)變(bian)(bian)壓(ya)(ya)(ya)器中(zhong)(zhong)性(xing)點的(de)過(guo)(guo)電(dian)(dian)(dian)壓(ya)(ya)(ya)低得(de)多，不會產生危害性(xing)很大(da)的(de)諧振過(guo)(guo)電(dian)(dian)(dian)壓(ya)(ya)(ya)和(he)(he)弧光接(jie)(jie)地(di)(di)過(guo)(guo)電(dian)(dian)(dian)壓(ya)(ya)(ya)，不易產生 失步(bu)過(guo)(guo)電(dian)(dian)(dian)壓(ya)(ya)(ya)。500kV變(bian)(bian)壓(ya)(ya)(ya)器中(zhong)(zhong)性(xing)點經(jing)小電(dian)(dian)(dian)抗(kang)(kang)器接(jie)(jie)地(di)(di)已投入(ru)工程(cheng)應(ying)用，如(ru)葛洲壩(ba)水(shui)電(dian)(dian)(dian)站(zhan)大(da)江電(dian)(dian)(dian)廠500kV工程(cheng)、隔河巖(yan)水(shui)電(dian)(dian)(dian)站(zhan)和(he)(he)巖(yan)灘水(shui)電(dian)(dian)(dian)站(zhan)500kV工程(cheng)，分(fen)別于20世紀80年代末期和(he)(he)90年代初期投運，運行(xing)正(zheng)常，收(shou)到(dao)了(le)良好的(de)效(xiao)果(guo)。
通過以上技術分析可見，超大型水電(dian)站(zhan)500kV主變壓(ya)器(qi)(qi)中(zhong)性(xing)點(dian)(dian)接地方式，一般采用(yong)(yong)經小(xiao)電(dian)抗器(qi)(qi)接地方式，且變壓(ya)器(qi)(qi)中(zhong)性(xing)點(dian)(dian)采用(yong)(yong)避雷器(qi)(qi)保護，并(bing)應根據工程具體情(qing)況選用(yong)(yong)適當(dang)的(de)中(zhong)性(xing)點(dian)(dian)小(xiao)電(dian)抗器(qi)(qi)。經過論證，溪(xi)洛(luo)渡水電(dian)站(zhan)的(de)主變壓(ya)器(qi)(qi)中(zhong)性(xing)點(dian)(dian)采用(yong)(yong)小(xiao)電(dian)抗器(qi)(qi)的(de)接地方式。
5 主變壓器型式
根據溪洛渡水(shui)電站(zhan)的(de)具體條件，主變壓器型式考慮了四種可能的(de)方案，即三(san)相(xiang)、單相(xiang)、組(zu)合式三(san)相(xiang)和(he)現(xian)場組(zu)裝(zhuang)三(san)相(xiang)變壓器。
5．1 三相變(bian)壓器
三(san)相變壓(ya)(ya)(ya)器在(zai)設計制造及運(yun)行管理(li)上具有一定的優點，但運(yun)輸(shu)重量(liang)巨大，超過了鐵(tie)路和公路的運(yun)輸(shu)極限，且(qie)運(yun)輸(shu)費用(yong)昂貴。溪洛渡水電站主變壓(ya)(ya)(ya)器若采用(yong)三(san)相變壓(ya)(ya)(ya)器方案，運(yun)輸(shu)重量(liang)將達(da)到480t，無論是鐵(tie)路運(yun)輸(shu)或(huo)公路運(yun)輸(shu)均不能實現，故不宜采用(yong)。
5．2 單相變(bian)壓器組(zu)方案
單(dan)相變壓器組方(fang)案由(you)三臺普(pu)通單(dan)相變壓器組合成三相變壓器，具(ju)有(you)設(she)計制(zhi)造經驗成熟、運(yun)輸重量及(ji)運(yun)輸尺寸(cun)小、占用安(an)裝布置場地(di)大和安(an)裝時(shi)間短的(de)特點。
5．3 組合三相變壓器方(fang)案
經研究分析，由三(san)臺(tai)(tai)特殊(shu)單(dan)相(xiang)變(bian)壓(ya)器(qi)組(zu)合(he)的(de)(de)(de)三(san)相(xiang)變(bian)壓(ya)器(qi)方案設計及制(zhi)造(zao)經驗成(cheng)(cheng)熟，應(ying)用(yong)(yong)較(jiao)廣。特殊(shu)單(dan)相(xiang)變(bian)壓(ya)器(qi)的(de)(de)(de)結(jie)構(gou)與普通單(dan)相(xiang)變(bian)壓(ya)器(qi)基本相(xiang)同(tong)，一(yi)種組(zu)合(he)方式(shi)是三(san)臺(tai)(tai)單(dan)相(xiang)變(bian)壓(ya)器(qi)分別裝(zhuang)在各自(zi)的(de)(de)(de)下節(jie)油(you)箱中，在運到(dao)安(an)(an)裝(zhuang)地(di)點前用(yong)(yong)副箱蓋各自(zi)密封，到(dao)達(da)使(shi)用(yong)(yong)現(xian)場后換上共(gong)(gong)用(yong)(yong)箱蓋使(shi)三(san)臺(tai)(tai)單(dan)相(xiang)變(bian)壓(ya)器(qi)連成(cheng)(cheng)一(yi)體，形(xing)成(cheng)(cheng)三(san)相(xiang)變(bian)壓(ya)器(qi)；另一(yi)種組(zu)合(he)方式(shi)采用(yong)(yong)單(dan)獨的(de)(de)(de)油(you)箱，僅(jin)用(yong)(yong)引(yin)線管道將(jiang)三(san)臺(tai)(tai)連成(cheng)(cheng)一(yi)體，此(ci)種變(bian)壓(ya)器(qi)相(xiang)當于(yu)將(jiang)三(san)臺(tai)(tai)獨立的(de)(de)(de)單(dan)相(xiang)變(bian)壓(ya)器(qi)的(de)(de)(de)油(you)路連接在一(yi)起。目前國內已基本不采用(yong)(yong)第一(yi)種方式(shi)（共(gong)(gong)用(yong)(yong)箱蓋），而采用(yong)(yong)第二種組(zu)合(he)方式(shi)。這種方式(shi)運輸重量小、運輸尺(chi)寸小、布置安(an)(an)裝(zhuang)占地(di)面積小、安(an)(an)裝(zhuang)時間(jian)較(jiao)短。
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