什(shen)么是發(fa)電機勵磁系統 

　　供給同步

發電機

勵(li)(li)磁(ci)電(dian)流的(de)電(dian)源及其附屬設備統(tong)(tong)(tong)稱為勵(li)(li)磁(ci)系統(tong)(tong)(tong)。它(ta)一(yi)般由(you)勵(li)(li)磁(ci)功(gong)率(lv)單元(yuan)和勵(li)(li)磁(ci)調(diao)節(jie)(jie)器(qi)兩(liang)個主要部分(fen)組(zu)成(cheng)。勵(li)(li)磁(ci)功(gong)率(lv)單元(yuan)向同步(bu)(bu)發電(dian)機(ji)轉子提供勵(li)(li)磁(ci)電(dian)流；而勵(li)(li)磁(ci)調(diao)節(jie)(jie)器(qi)則(ze)(ze)根據(ju)輸入信(xin)號和給定(ding)的(de)調(diao)節(jie)(jie)準則(ze)(ze)控制勵(li)(li)磁(ci)功(gong)率(lv)單元(yuan)的(de)輸出。勵(li)(li)磁(ci)系統(tong)(tong)(tong)的(de)自動勵(li)(li)磁(ci)調(diao)節(jie)(jie)器(qi)對(dui)提高電(dian)力系統(tong)(tong)(tong)并聯機(ji)組(zu)的(de)穩(wen)定(ding)性具有相當大的(de)作(zuo)用。尤其是現代(dai)電(dian)力系統(tong)(tong)(tong)的(de)發展導致機(ji)組(zu)穩(wen)定(ding)極(ji)限降低(di)的(de)趨勢，也促使(shi)勵(li)(li)磁(ci)技(ji)術不斷發展。同步(bu)(bu)發電(dian)機(ji)的(de)勵(li)(li)磁(ci)系統(tong)(tong)(tong)主要由(you)功(gong)率(lv)單元(yuan)和調(diao)節(jie)(jie)器(qi)（裝(zhuang)置）兩(liang)大部分(fen)組(zu)成(cheng)。 

　　勵磁變的作用 

　　勵(li)磁(ci)(ci)變(bian)(bian)繞組的(de)(de)(de)聯接組別，通(tong)(tong)常(chang)為Y，yo，對于(yu)副(fu)方電(dian)(dian)(dian)(dian)(dian)流(liu)大(da)的(de)(de)(de)情況下，采用(yong)(yong)Y，dll組別。勵(li)磁(ci)(ci)變(bian)(bian)就設計和(he)結(jie)構(gou)來說，與普通(tong)(tong)配電(dian)(dian)(dian)(dian)(dian)變(bian)(bian)壓(ya)器(qi)(qi)一樣，短(duan)路電(dian)(dian)(dian)(dian)(dian)壓(ya)4％－8％。考慮(lv)到勵(li)磁(ci)(ci)變(bian)(bian)必(bi)須可靠(kao)，強勵(li)時要(yao)有(you)一定的(de)(de)(de)過載(zai)能力，且勵(li)磁(ci)(ci)電(dian)(dian)(dian)(dian)(dian)源一般不(bu)設計備用(yong)(yong)電(dian)(dian)(dian)(dian)(dian)源，因此宜選(xuan)用(yong)(yong)維護簡單、過載(zai)能力強的(de)(de)(de)干(gan)(gan)式變(bian)(bian)壓(ya)器(qi)(qi)。從目前(qian)國內干(gan)(gan)式變(bian)(bian)壓(ya)器(qi)(qi)制造工(gong)藝水平來說，已能生產容(rong)量達(da)16000kVA、電(dian)(dian)(dian)(dian)(dian)壓(ya)等(deng)級35KV的(de)(de)(de)干(gan)(gan)式變(bian)(bian)壓(ya)器(qi)(qi)，以滿足大(da)型機組的(de)(de)(de)需(xu)要(yao)。若從降低勵(li)磁(ci)(ci)系統造價來說，采用(yong)(yong)油浸(jin)變(bian)(bian)壓(ya)器(qi)(qi)也是(shi)可行的(de)(de)(de)。當勵(li)磁(ci)(ci)變(bian)(bian)壓(ya)器(qi)(qi)安裝在戶外時，由(you)變(bian)(bian)壓(ya)器(qi)(qi)副(fu)方到整流(liu)橋之(zhi)間的(de)(de)(de)饋線，由(you)于(yu)有(you)電(dian)(dian)(dian)(dian)(dian)抗壓(ya)降，不(bu)宜太(tai)長，特別是(shi)在勵(li)磁(ci)(ci)電(dian)(dian)(dian)(dian)(dian)流(liu)很大(da)的(de)(de)(de)情況下，這一點(dian)必(bi)須考慮(lv)。還有(you)不(bu)宜用(yong)(yong)單芯鎧裝電(dian)(dian)(dian)(dian)(dian)纜，而應選(xuan)用(yong)(yong)橡皮電(dian)(dian)(dian)(dian)(dian)纜。因為單芯鎧裝電(dian)(dian)(dian)(dian)(dian)纜通(tong)(tong)以交流(liu)電(dian)(dian)(dian)(dian)(dian)時，在鋼甲中需(xu)要(yao)感應較高的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)以及不(bu)能忽略的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)，并對通(tong)(tong)信電(dian)(dian)(dian)(dian)(dian)纜造成干(gan)(gan)擾。 

　　三相勵磁變的選擇計(ji)算如下(xia)； 

　　計算變壓器的變比和容量用到以下參數：(鴨河口電(dian)廠實際值) 

　　發電(dian)機額定勵磁(ci)電(dian)流Ifn＝4469A 

　　發(fa)電機額定勵磁電壓Ufn＝364V 

　　強勵倍數Kc＝2 

　　可控硅最(zui)小控制角αmin＝10。 

　　變壓器漏抗Xk一(yi)般取4％一(yi)8％ 

　　饋電回(hui)路電壓降之和∑△U：一般為2—4V 

　　按照可控(kong)硅全控(kong)橋整流(liu)計算方(fang)法計算勵磁變低壓(ya)側Us： 

　　1.35UsCOSαmin=KcUfn+3KcIfnXk/π+∑△U 

　　由(you)于在初設時Xk無法(fa)確認，∑△U也為估(gu)計值，因此可以把回路(lu)中總的電(dian)壓損失估(gu)計為15％。 

　　由COSαmin≈COS0。=1 

　　則(ze)：上式可(ke)變(bian)為Us＝KcUfn／(85％×1.35)＝2×364／(85％×1.35)＝634．4V 

　　實際取勵磁變(bian)副邊(bian)電壓Us＝650V 

　　發(fa)電機(ji)出口(kou)電壓為(wei)22000V，所以(yi)勵磁(ci)變變比為(wei)22000V／650V。 

　　勵磁(ci)變壓器也可以由直流側電流折算(suan)，取裕度系數(shu)為(wei)1.15，則(ze)副(fu)邊(bian)電流為(wei)： 

　　Is＝1.15×0.816×Ifn＝1.15×0.816×4469＝4193.7A 

　　實際取勵(li)磁變副邊電流Is＝4393.3A 

　　由Is、Us可以計(ji)算出勵磁變(bian)容量(liang)： 

　　S＝√-3IsUs＝√-3×634.4×4193.7＝4608kVA 

　　實際(ji)變壓(ya)器容(rong)量(liang)S＝4950kVA，留有一定的容(rong)量(liang)。