什么是功率因數？及提高功率因數方法

來源：金環宇電纜發布日(ri)期：2020-03-28 11:03

什么是功率因數

在(zai)工(gong)業企業中，電(dian)動(dong)機、變(bian)壓器等用電(dian)設備(bei)都具有(you)(you)電(dian)感特(te)性，它們工(gong)作時既要從電(dian)網吸收(shou)有(you)(you)功(gong)(gong)(gong)(gong)(gong)功(gong)(gong)(gong)(gong)(gong)率用于做功(gong)(gong)(gong)(gong)(gong)，還要從電(dian)網吸收(shou)無(wu)功(gong)(gong)(gong)(gong)(gong)功(gong)(gong)(gong)(gong)(gong)率建立磁場。功(gong)(gong)(gong)(gong)(gong)率因(yin)數cosΦ就是反(fan)映總電(dian)功(gong)(gong)(gong)(gong)(gong)率中有(you)(you)功(gong)(gong)(gong)(gong)(gong)功(gong)(gong)(gong)(gong)(gong)率所(suo)占(zhan)的(de)比例(li)大小，即有(you)(you)功(gong)(gong)(gong)(gong)(gong)功(gong)(gong)(gong)(gong)(gong)率與視在(zai)功(gong)(gong)(gong)(gong)(gong)率的(de)比值，是衡(heng)量電(dian)氣設備(bei)效率高低的(de)一個系數。功(gong)(gong)(gong)(gong)(gong)率因(yin)數越(yue)(yue)接近(jin)于1，說(shuo)明其消(xiao)(xiao)耗(hao)(hao)的(de)無(wu)功(gong)(gong)(gong)(gong)(gong)電(dian)量越(yue)(yue)少，電(dian)力有(you)(you)效利(li)(li)用程度(du)越(yue)(yue)高;相反(fan)，功(gong)(gong)(gong)(gong)(gong)率因(yin)數越(yue)(yue)低，則消(xiao)(xiao)耗(hao)(hao)的(de)無(wu)功(gong)(gong)(gong)(gong)(gong)電(dian)量越(yue)(yue)多(duo)，電(dian)力沒有(you)(you)得到充分有(you)(you)效的(de)利(li)(li)用。有(you)(you)功(gong)(gong)(gong)(gong)(gong)功(gong)(gong)(gong)(gong)(gong)率P、無(wu)功(gong)(gong)(gong)(gong)(gong)功(gong)(gong)(gong)(gong)(gong)率Q與視在(zai)功(gong)(gong)(gong)(gong)(gong)率S的(de)關系如下所(suo)示。

由此可知用電設備的有功功率不僅隨電壓與電流的大小變化，而且也隨電壓與電流之間的相位差而變化。當電路中有功功率恒定時，無功需要量越大，其視在功率也就越大，而為滿足用電設備的需要，勢必要增大變壓器及線路的容量。這樣不僅增加了投資，而且增大了設備和線路的損耗，浪費了電力。另外無功功率需要量的增大，還使變壓器及線路的電壓損失增大，劣化電能質量，為此，必須提高功率因數，才能減少無功損耗。相關閱讀：功率因數如何計算?

提高功率因數方法

1)提(ti)高(gao)自(zi)然功率因數

一般來(lai)說，工礦(kuang)企業無功(gong)功(gong)率(lv)中，異步(bu)電(dian)動機(ji)要(yao)(yao)占(zhan)60%以(yi)上，電(dian)力變壓器(qi)要(yao)(yao)占(zhan)20%左右，因(yin)(yin)此，電(dian)力系統(tong)的(de)(de)自然(ran)功(gong)率(lv)因(yin)(yin)數(shu)是(shi)滯后(hou)且(qie)小于1的(de)(de)。要(yao)(yao)想提(ti)(ti)高系統(tong)的(de)(de)功(gong)率(lv)因(yin)(yin)數(shu)，就(jiu)要(yao)(yao)設法改(gai)善異步(bu)電(dian)動機(ji)和電(dian)力變壓器(qi)運行(xing)工況，以(yi)利于提(ti)(ti)高自然(ran)功(gong)率(lv)因(yin)(yin)數(shu)。提(ti)(ti)高自然(ran)功(gong)率(lv)因(yin)(yin)數(shu)的(de)(de)措施主要(yao)(yao)有以(yi)下幾種：

①合(he)理選用異(yi)(yi)(yi)步電動(dong)機(ji)(ji)。異(yi)(yi)(yi)步電動(dong)機(ji)(ji)在(zai)額定負(fu)載(功(gong)(gong)(gong)率(lv))時(shi)(shi)的功(gong)(gong)(gong)率(lv)因(yin)數為(wei)0.85~0.9，而在(zai)空(kong)(kong)載時(shi)(shi)的功(gong)(gong)(gong)率(lv)因(yin)數僅為(wei)0.2~0.3。空(kong)(kong)載或輕載時(shi)(shi)的效率(lv)肯(ken)定也要降低(di)。因(yin)此(ci)，應根據負(fu)荷特牲和(he)運行工(gong)況，合(he)理選擇(ze)異(yi)(yi)(yi)步電動(dong)機(ji)(ji)的容量，使其(qi)在(zai)高(gao)效率(lv)、高(gao)功(gong)(gong)(gong)率(lv)因(yin)數范(fan)圍(wei)內工(gong)作(zuo)。

工礦企(qi)業中(zhong)異步(bu)電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)使用(yong)(yong)數(shu)量(liang)很多(duo)，而且在選擇時(shi)總希望電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)有較大的(de)(de)裕量(liang)，很多(duo)情況下(xia)形(xing)成了 “大馬拉小車” 的(de)(de)現象。這是造成工業企(qi)業功(gong)率因(yin)數(shu)低(di)(di)的(de)(de)重要(yao)原因(yin)之一。可(ke)(ke)以(yi)對負(fu)荷(he)不(bu)足的(de)(de)異步(bu)電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)，用(yong)(yong)鉗形(xing)電(dian)(dian)(dian)(dian)流表測(ce)量(liang)電(dian)(dian)(dian)(dian)流或(huo)利用(yong)(yong)測(ce)繪負(fu)荷(he)曲(qu)線的(de)(de)方(fang)法確定適當(dang)的(de)(de)電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)容(rong)(rong)量(liang)，而后以(yi)小容(rong)(rong)量(liang)電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)代(dai)替之。用(yong)(yong)小容(rong)(rong)量(liang)電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)代(dai)替負(fu)荷(he)不(bu)足的(de)(de)大容(rong)(rong)量(liang)電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)，一般可(ke)(ke)使功(gong)率因(yin)數(shu)提高20%左右;一般電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)負(fu)荷(he)高于70%左右時(shi)可(ke)(ke)以(yi)不(bu)換，當(dang)電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)負(fu)荷(he)低(di)(di)于40%時(shi)，應(ying)對節能(neng)效果進行考核后合理更換。

② 輕負荷(he)(he)電(dian)(dian)動(dong)機(ji)降(jiang)壓(ya)運行(xing)。輕負荷(he)(he)電(dian)(dian)動(dong)機(ji)降(jiang)壓(ya)運行(xing)可以(yi)降(jiang)低其無(wu)功(gong)功(gong)率的(de)需要量(liang)，從而提高了供電(dian)(dian)系統的(de)功(gong)率因數。當然，降(jiang)壓(ya)運行(xing)也使(shi)(shi)電(dian)(dian)動(dong)機(ji)的(de)輸出(chu)轉矩(ju)減小(xiao)，這一(yi)點必須充分考慮(lv)到(dao)。一(yi)般認(ren)為(wei)，電(dian)(dian)動(dong)機(ji)負荷(he)(he)系數在(zai)0.45以(yi)下時。可將正常運行(xing)時為(wei)△接線(xian)的(de)電(dian)(dian)動(dong)機(ji)改為(wei)Y形接線(xian)更為(wei)合(he)理，從而使(shi)(shi)功(gong)率因數及效率都會有所提高。

③電(dian)力(li)變(bian)(bian)(bian)(bian)壓(ya)(ya)(ya)器(qi)的合(he)理運行(xing)。電(dian)力(li)變(bian)(bian)(bian)(bian)壓(ya)(ya)(ya)器(qi)不(bu)(bu)宜輕載運行(xing)，因為變(bian)(bian)(bian)(bian)壓(ya)(ya)(ya)器(qi)一(yi)次(ci)側的功率因數(shu)(shu)不(bu)(bu)僅與(yu)負荷(he)(he)的功率因數(shu)(shu)有(you)關，而且與(yu)負荷(he)(he)率有(you)關。若變(bian)(bian)(bian)(bian)壓(ya)(ya)(ya)器(qi)滿載運行(xing)時(shi)(shi)，一(yi)次(ci)側的功率因數(shu)(shu)僅比二次(ci)側低(di)3%~5%;若變(bian)(bian)(bian)(bian)壓(ya)(ya)(ya)器(qi)輕載運行(xing)，當負荷(he)(he)率小于0.6時(shi)(shi)，一(yi)次(ci)側的功率因數(shu)(shu)將(jiang)顯著(zhu)下降(jiang)，可(ke)達11%~18%。所以，電(dian)力(li)變(bian)(bian)(bian)(bian)壓(ya)(ya)(ya)器(qi)在負荷(he)(he)率0.6以上運行(xing)時(shi)(shi)才較為經(jing)濟(ji)，一(yi)般在75%~80%比較合(he)適。為了充分(fen)利用設備(bei)和(he)提高功率因數(shu)(shu)，電(dian)力(li)變(bian)(bian)(bian)(bian)壓(ya)(ya)(ya)器(qi)不(bu)(bu)作輕載運行(xing)。變(bian)(bian)(bian)(bian)壓(ya)(ya)(ya)器(qi)負荷(he)(he)率小于30%時(shi)(shi)，應更換容(rong)量較小的變(bian)(bian)(bian)(bian)壓(ya)(ya)(ya)器(qi)。

④ 合理(li)(li)安排(pai)和調(diao)整工藝流程。合理(li)(li)安排(pai)和調(diao)整工藝流程，以改變電動機設備的(de)運(yun)行狀況，限制電焊機和機床(chuang)電動機的(de)空載(zai)運(yun)轉，即采用空載(zai)自動延(yan)時斷電裝置。

⑤ 異(yi)步(bu)(bu)(bu)電(dian)(dian)動(dong)(dong)機(ji)同(tong)(tong)步(bu)(bu)(bu)化運行(xing)。對于(yu)負(fu)荷率不(bu)大于(yu)0.7及最大負(fu)荷不(bu)大干90%的繞(rao)(rao)(rao)線式異(yi)步(bu)(bu)(bu)電(dian)(dian)動(dong)(dong)機(ji)，必(bi)要時使其同(tong)(tong)步(bu)(bu)(bu)化運行(xing)，即當繞(rao)(rao)(rao)線式異(yi)步(bu)(bu)(bu)電(dian)(dian)動(dong)(dong)機(ji)在啟動(dong)(dong)完畢后，向轉(zhuan)子(zi)三相繞(rao)(rao)(rao)組(zu)輸入(ru)直流(liu)勵磁(ci)，即產生(sheng)轉(zhuan)矩把異(yi)步(bu)(bu)(bu)電(dian)(dian)動(dong)(dong)機(ji)轉(zhuan)入(ru)同(tong)(tong)步(bu)(bu)(bu)運行(xing)，其運行(xing)狀態(tai)與同(tong)(tong)步(bu)(bu)(bu)電(dian)(dian)動(dong)(dong)機(ji)相似，在勵磁(ci)過剩的情(qing)況(kuang)下，電(dian)(dian)動(dong)(dong)機(ji)可向電(dian)(dian)網輸送(song)無功功率，從而達到(dao)提高(gao)功率因(yin)數的目的。

2)提高(gao)功(gong)率(lv)因數的補(bu)償法

所(suo)謂補償(chang)法，就是采(cai)(cai)用(yong)(yong)無功(gong)(gong)功(gong)(gong)率(lv)(lv)的(de)設備(bei)來補償(chang)用(yong)(yong)電(dian)沒備(bei)所(suo)需的(de)無功(gong)(gong)功(gong)(gong)率(lv)(lv)，以提高功(gong)(gong)率(lv)(lv)因數(shu)。采(cai)(cai)用(yong)(yong)補償(chang)法，無疑需要增添補償(chang)設備(bei)。所(suo)以從整體來看，應首(shou)先采(cai)(cai)用(yong)(yong)提高自(zi)然(ran)功(gong)(gong)率(lv)(lv)因數(shu)的(de)方(fang)法，但當功(gong)(gong)率(lv)(lv)因數(shu)達不到(dao)供電(dian)部門或設計(ji)規(gui)范要求時，則(ze)需采(cai)(cai)用(yong)(yong)專門的(de)補償(chang)設備(bei)進行補償(chang)。常用(yong)(yong)的(de)補償(chang)無功(gong)(gong)功(gong)(gong)率(lv)(lv)方(fang)法有：采(cai)(cai)用(yong)(yong)并聯(lian)電(dian)容器，選用(yong)(yong)同步電(dian)動機，采(cai)(cai)用(yong)(yong)同步調(diao)相機等。

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