電(dian)(dian)力系(xi)統(tong)三相不平衡(heng)帶來(lai)的(de)危(wei)害(hai)有很多，如(ru)(ru)：增(zeng)加(jia)線路的(de)電(dian)(dian)能損耗(hao)、增(zeng)加(jia)配電(dian)(dian)變壓器的(de)電(dian)(dian)能損耗(hao)、配變出力減少、配變產生(sheng)零序電(dian)(dian)流(liu)、影響用電(dian)(dian)設備(bei)的(de)安全運(yun)行、電(dian)(dian)動機效率降低等。我們如(ru)(ru)何來(lai)改(gai)進電(dian)(dian)力系(xi)統(tong)三相不平衡(heng)呢？

電(dian)力系統三(san)相不(bu)平衡(heng)帶來的危害(hai)：

1、增加線路的(de)電能損耗

在三相四線(xian)制供電(dian)(dian)網絡中，電(dian)(dian)流通過線(xian)路導線(xian)時(shi)，因存在阻抗必將產生電(dian)(dian)能損(sun)(sun)耗(hao)，其損(sun)(sun)耗(hao)與通過電(dian)(dian)流的平方成正(zheng)比。當(dang)低壓電(dian)(dian)網以三相四線(xian)制供電(dian)(dian)時(shi)，由于有單相負載存在，造(zao)成三相負載不平衡在所難(nan)免。當(dang)三相負載不平衡運行(xing)時(shi)，中性線(xian)即有電(dian)(dian)流通過。這(zhe)樣不但相線(xian)有損(sun)(sun)耗(hao)，而(er)且中性線(xian)也(ye)產生損(sun)(sun)耗(hao)，從而(er)增(zeng)加了電(dian)(dian)網線(xian)路的損(sun)(sun)耗(hao)。

2、增加配電變壓器的電能(neng)損耗

配電(dian)(dian)變(bian)(bian)(bian)壓(ya)器是低(di)壓(ya)電(dian)(dian)網(wang)的(de)供電(dian)(dian)主設備(bei)，當(dang)其在三相負載不平衡工況下運行時，將會造(zao)成配變(bian)(bian)(bian)損耗(hao)的(de)增加。因為配變(bian)(bian)(bian)的(de)功(gong)率損耗(hao)是隨負載的(de)不平衡度而變(bian)(bian)(bian)化(hua)的(de)。

3、配變出力減少

配變(bian)設計(ji)時，其繞組結(jie)構是按負載(zai)平(ping)(ping)衡(heng)運(yun)行工況設計(ji)的(de)，其繞組性能基本一(yi)致(zhi)，各(ge)相(xiang)(xiang)(xiang)(xiang)額定(ding)容(rong)量相(xiang)(xiang)(xiang)(xiang)等。配變(bian)的(de)最大允(yun)許出(chu)力要受(shou)到每相(xiang)(xiang)(xiang)(xiang)額定(ding)容(rong)量的(de)限(xian)制。假(jia)(jia)如(ru)當配變(bian)處于三(san)相(xiang)(xiang)(xiang)(xiang)負載(zai)不(bu)平(ping)(ping)衡(heng)工況下(xia)運(yun)行，負載(zai)輕(qing)的(de)一(yi)相(xiang)(xiang)(xiang)(xiang)就有富余容(rong)量，從而(er)使(shi)配變(bian)的(de)出(chu)力減(jian)(jian)少(shao)。其出(chu)力減(jian)(jian)少(shao)程度與三(san)相(xiang)(xiang)(xiang)(xiang)負載(zai)的(de)不(bu)平(ping)(ping)衡(heng)度有關(guan)。三(san)相(xiang)(xiang)(xiang)(xiang)負載(zai)不(bu)平(ping)(ping)衡(heng)越(yue)(yue)大，配變(bian)出(chu)力減(jian)(jian)少(shao)越(yue)(yue)多(duo)。為此，配變(bian)在三(san)相(xiang)(xiang)(xiang)(xiang)負載(zai)不(bu)平(ping)(ping)衡(heng)時運(yun)行，其輸出(chu)的(de)容(rong)量就無(wu)法達到額定(ding)值，其備用容(rong)量亦相(xiang)(xiang)(xiang)(xiang)應減(jian)(jian)少(shao)，過載(zai)能力也降低。假(jia)(jia)如(ru)配變(bian)在過載(zai)工況下(xia)運(yun)行，即極(ji)易引發配變(bian)發熱(re)，嚴重(zhong)時甚至會造成配變(bian)燒損。

4、配變產生零序電(dian)流

配(pei)變在(zai)三相(xiang)負載不(bu)(bu)平衡工況下運行，將(jiang)產(chan)生零(ling)(ling)序(xu)(xu)電(dian)(dian)流(liu)，該(gai)電(dian)(dian)流(liu)將(jiang)隨(sui)三相(xiang)負載不(bu)(bu)平衡的(de)(de)程度而(er)變化，不(bu)(bu)平衡度越(yue)大，則(ze)(ze)零(ling)(ling)序(xu)(xu)電(dian)(dian)流(liu)也越(yue)大。運行中的(de)(de)配(pei)變若(ruo)存在(zai)零(ling)(ling)序(xu)(xu)電(dian)(dian)流(liu)，則(ze)(ze)其鐵芯中將(jiang)產(chan)生零(ling)(ling)序(xu)(xu)磁通。(高(gao)壓側(ce)沒(mei)有零(ling)(ling)序(xu)(xu)電(dian)(dian)流(liu))這(zhe)迫使(shi)零(ling)(ling)序(xu)(xu)磁通只能以油箱壁及(ji)鋼(gang)構(gou)(gou)件(jian)作為通道通過(guo)(guo)(guo)，而(er)鋼(gang)構(gou)(gou)件(jian)的(de)(de)導磁率較低(di)，零(ling)(ling)序(xu)(xu)電(dian)(dian)流(liu)通過(guo)(guo)(guo)鋼(gang)構(gou)(gou)件(jian)時(shi)，即要產(chan)生磁滯和渦流(liu)損耗(hao)，從而(er)使(shi)配(pei)變的(de)(de)鋼(gang)構(gou)(gou)件(jian)局部溫度升(sheng)高(gao)發熱(re)。配(pei)變的(de)(de)繞組絕緣因過(guo)(guo)(guo)熱(re)而(er)加快(kuai)老化，導致設備壽(shou)命(ming)降低(di)。同時(shi)，零(ling)(ling)序(xu)(xu)電(dian)(dian)流(liu)的(de)(de)存也會增加配(pei)變的(de)(de)損耗(hao)。

5、影響用電設(she)備的安全(quan)運行

配變是根據三相負載平衡運行工況設計的，其每相繞組的電阻、漏抗和激磁阻抗基本一致。當配變在三相負載平衡時運行，其三相電流基本相等，配變內部每相壓降也基本相同，則配變輸出的三相電壓也是平衡的。假如配變在三相負載不平衡時運行，其各相輸出電流就不相等，其配變內部三相壓降就不相等，這必將導致配變輸出電壓三相不平衡。
同時，配變在三(san)相(xiang)負(fu)載(zai)不平衡(heng)(heng)時運行(xing)(xing)，三(san)相(xiang)輸出電(dian)(dian)(dian)(dian)流(liu)不一樣(yang)，而(er)中(zhong)性(xing)線(xian)就會有電(dian)(dian)(dian)(dian)流(liu)通過。因而(er)使(shi)中(zhong)性(xing)線(xian)產(chan)生(sheng)阻抗壓(ya)(ya)降(jiang)(jiang)，從而(er)導致(zhi)中(zhong)性(xing)點漂移，致(zhi)使(shi)各相(xiang)相(xiang)電(dian)(dian)(dian)(dian)壓(ya)(ya)發生(sheng)變化(hua)。負(fu)載(zai)重(zhong)的(de)一相(xiang)電(dian)(dian)(dian)(dian)壓(ya)(ya)降(jiang)(jiang)低，而(er)負(fu)載(zai)輕(qing)的(de)一相(xiang)電(dian)(dian)(dian)(dian)壓(ya)(ya)升(sheng)高。在電(dian)(dian)(dian)(dian)壓(ya)(ya)不平衡(heng)(heng)狀況(kuang)下供電(dian)(dian)(dian)(dian)，即容易(yi)造成電(dian)(dian)(dian)(dian)壓(ya)(ya)高的(de)一相(xiang)接(jie)帶(dai)的(de)用(yong)戶(hu)用(yong)電(dian)(dian)(dian)(dian)設(she)備(bei)燒(shao)壞(huai)，而(er)電(dian)(dian)(dian)(dian)壓(ya)(ya)低的(de)一相(xiang)接(jie)帶(dai)的(de)用(yong)戶(hu)用(yong)電(dian)(dian)(dian)(dian)設(she)備(bei)則可能無法(fa)使(shi)用(yong)。所以三(san)相(xiang)負(fu)載(zai)不平衡(heng)(heng)運行(xing)(xing)時，將(jiang)嚴重(zhong)危及用(yong)電(dian)(dian)(dian)(dian)設(she)備(bei)的(de)安全運行(xing)(xing)。

6、電動機效率降(jiang)低

配變在三(san)相負(fu)(fu)(fu)載不(bu)(bu)(bu)平(ping)衡工況下運(yun)(yun)行(xing)(xing)，將引起(qi)輸(shu)(shu)出(chu)電(dian)(dian)壓三(san)相不(bu)(bu)(bu)平(ping)衡。由于(yu)不(bu)(bu)(bu)平(ping)衡電(dian)(dian)壓存在著正序(xu)(xu)、負(fu)(fu)(fu)序(xu)(xu)、零序(xu)(xu)三(san)個電(dian)(dian)壓分(fen)量，當這種(zhong)不(bu)(bu)(bu)平(ping)衡的(de)電(dian)(dian)壓輸(shu)(shu)入電(dian)(dian)動(dong)(dong)(dong)(dong)機后，負(fu)(fu)(fu)序(xu)(xu)電(dian)(dian)壓產生旋(xuan)轉磁(ci)(ci)場(chang)與(yu)正序(xu)(xu)電(dian)(dian)壓產生的(de)旋(xuan)轉磁(ci)(ci)場(chang)相反(fan)，起(qi)到制動(dong)(dong)(dong)(dong)作用。但由于(yu)正序(xu)(xu)磁(ci)(ci)場(chang)比負(fu)(fu)(fu)序(xu)(xu)磁(ci)(ci)場(chang)要強得多，電(dian)(dian)動(dong)(dong)(dong)(dong)機仍按正序(xu)(xu)磁(ci)(ci)場(chang)方向轉動(dong)(dong)(dong)(dong)。而(er)由于(yu)負(fu)(fu)(fu)序(xu)(xu)磁(ci)(ci)場(chang)的(de)制動(dong)(dong)(dong)(dong)作用，必(bi)將引起(qi)電(dian)(dian)動(dong)(dong)(dong)(dong)機輸(shu)(shu)出(chu)功率減少，從而(er)導致電(dian)(dian)動(dong)(dong)(dong)(dong)機效率降低(di)。同時，電(dian)(dian)動(dong)(dong)(dong)(dong)機的(de)溫升和無功損耗，也將隨三(san)相電(dian)(dian)壓的(de)不(bu)(bu)(bu)平(ping)衡度而(er)增大。所(suo)以電(dian)(dian)動(dong)(dong)(dong)(dong)機在三(san)相電(dian)(dian)壓不(bu)(bu)(bu)平(ping)衡狀況下運(yun)(yun)行(xing)(xing)，是非常不(bu)(bu)(bu)經濟和不(bu)(bu)(bu)安全的(de)。