開關柜是在電力系統進行發電、輸電、配電和電能轉換的過程中，進行開合、控制和保護用電設備。還應保證設備長期、安全、可靠無故障地運行，在系統發生各種故障或不正常工作的情況下對供電設備和電動機實行保護，因此保護環節是所有電氣控制系統不可缺少的組成部分。開關柜控(kong)制系統中常用(yong)的保(bao)護環節(jie)有短路保(bao)護、過載保(bao)護、過電(dian)流(liu)保(bao)護、失壓和欠壓保(bao)護等。

1.短路保護

電(dian)動機、電(dian)器以及導線(xian)的絕(jue)緣損(sun)壞或線(xian)路(lu)發生故(gu)障時(shi)，都可能造成(cheng)短(duan)路(lu)事故(gu)。很大的短(duan)路(lu)電(dian)流和電(dian)動力可能使電(dian)器設備損(sun)壞。因此要求一(yi)旦發生短(duan)路(lu)故(gu)障時(shi)，控制線(xian)路(lu)能迅(xun)速切除電(dian)源。常用的短(duan)路(lu)保護元件有熔斷(duan)器和低壓(ya)斷(duan)路(lu)器，電(dian)動機短(duan)路(lu)保護的元件可按(an)下述要求裝設：

1）在中性點直接(jie)接(jie)地的系統中，應(ying)在每(mei)相(xiang)上裝設。

2）在(zai)(zai)中性點不接(jie)地的系統(tong)中，以熔斷(duan)器(qi)作(zuo)保(bao)護時(shi)，應在(zai)(zai)每相(xiang)上(shang)裝(zhuang)設(she)(she)；用低壓斷(duan)路器(qi)作(zuo)保(bao)護時(shi)，應在(zai)(zai)不少于兩相(xiang)上(shang)裝(zhuang)設(she)(she)。

2.過載保護

電(dian)動機長(chang)期超載(zai)(zai)運(yun)行(xing)，繞組溫升將超過其允許(xu)值，造成絕緣材料老化，壽(shou)命減小(xiao)，嚴(yan)重(zhong)時會(hui)使電(dian)動機損(sun)壞，過載(zai)(zai)電(dian)流(liu)(liu)越大(da)，達到允許(xu)溫升的(de)時間就越短。常用的(de)過載(zai)(zai)保護(hu)元件(jian)是(shi)熱繼電(dian)器(qi)，對(dui)大(da)功率的(de)重(zhong)要電(dian)動機，應(ying)采用反時限性的(de)過電(dian)流(liu)(liu)繼電(dian)器(qi)。

由于熱(re)(re)慣性(xing)的(de)原因，熱(re)(re)繼電(dian)器不(bu)會受電(dian)動機短(duan)時過(guo)(guo)載(zai)沖擊電(dian)流或短(duan)路電(dian)流的(de)影響(xiang)而瞬(shun)時動作(zuo)，所以(yi)在使(shi)用熱(re)(re)繼電(dian)器作(zuo)過(guo)(guo)載(zai)保(bao)(bao)護(hu)(hu)時，還必須(xu)設有(you)短(duan)路保(bao)(bao)護(hu)(hu)，并且選作(zuo)短(duan)路保(bao)(bao)護(hu)(hu)的(de)熔斷器熔體的(de)額(e)定電(dian)流不(bu)應超(chao)過(guo)(guo)4倍熱(re)(re)繼電(dian)器發熱(re)(re)元(yuan)件(jian)的(de)額(e)定電(dian)流。由于過(guo)(guo)載(zai)保(bao)(bao)護(hu)(hu)特性(xing)與(yu)過(guo)(guo)電(dian)流保(bao)(bao)護(hu)(hu)特性(xing)不(bu)同，故不(bu)能用過(guo)(guo)電(dian)流保(bao)(bao)護(hu)(hu)方(fang)式來進行過(guo)(guo)載(zai)保(bao)(bao)護(hu)(hu)。

3.過電流保護

過電(dian)流(liu)保護(hu)廣泛用于(yu)直流(liu)電(dian)動(dong)機或繞線式(shi)異(yi)步電(dian)動(dong)機。對于(yu)三相(xiang)籠型異(yi)步電(dian)動(dong)機，由于(yu)其短(duan)時(shi)過電(dian)流(liu)不會產生(sheng)嚴重后果，故可不設置(zhi)過電(dian)流(liu)保護(hu)。

過電(dian)流(liu)保護往往是(shi)由于不正確(que)的(de)啟(qi)動(dong)和過大(da)的(de)負載引起的(de)，一(yi)般(ban)比短路(lu)電(dian)流(liu)要(yao)小(xiao)，在(zai)電(dian)動(dong)機運(yun)行中(zhong)產生過電(dian)流(liu)比發(fa)生短路(lu)的(de)可(ke)能性更大(da)，尤其(qi)是(shi)在(zai)頻繁正反(fan)轉(zhuan)啟(qi)動(dong)的(de)重復短時工作(zuo)制(zhi)電(dian)動(dong)機中(zhong)更是(shi)如此。

必須強調指出，短路、過電(dian)流(liu)(liu)、過載保(bao)(bao)護雖(sui)然都是電(dian)流(liu)(liu)保(bao)(bao)護，但由(you)于故障電(dian)流(liu)(liu)、動作值以(yi)及保(bao)(bao)護特性、保(bao)(bao)護要求以(yi)及使用元件的不(bu)同，它(ta)們之間是不(bu)能相互取代的。

4.失電壓保護

電(dian)(dian)(dian)(dian)動機正常工作時，如(ru)果電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)壓(ya)因某種原(yuan)因消失，那么在電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)壓(ya)恢復時，如(ru)果電(dian)(dian)(dian)(dian)動機自(zi)行(xing)(xing)啟動，將可能使生產設備損壞，也可能造成(cheng)人身(shen)事故(gu)。此外，對供(gong)電(dian)(dian)(dian)(dian)系統的(de)電(dian)(dian)(dian)(dian)網，同時有許多(duo)電(dian)(dian)(dian)(dian)動機及其他用電(dian)(dian)(dian)(dian)設備自(zi)行(xing)(xing)啟動也會引(yin)起不允許的(de)過電(dian)(dian)(dian)(dian)流及瞬間網絡電(dian)(dian)(dian)(dian)壓(ya)下降。為防止(zhi)電(dian)(dian)(dian)(dian)壓(ya)恢復時電(dian)(dian)(dian)(dian)動機自(zi)行(xing)(xing)啟動或電(dian)(dian)(dian)(dian)氣元件自(zi)行(xing)(xing)投(tou)入工作而(er)設置的(de)保護稱為失電(dian)(dian)(dian)(dian)壓(ya)保護。

采(cai)用接觸器(qi)(qi)(qi)(qi)和按鈕(niu)控(kong)制(zhi)的(de)啟(qi)動(dong)(dong)、停止控(kong)制(zhi)環(huan)節就具有(you)失(shi)電壓(ya)保護功能(neng)(neng)。因為當(dang)電源(yuan)電壓(ya)消失(shi)時(shi)，接觸器(qi)(qi)(qi)(qi)會(hui)自(zi)動(dong)(dong)釋放而切(qie)斷(duan)電動(dong)(dong)機電源(yuan)；電源(yuan)電壓(ya)恢復(fu)時(shi)，由于接觸器(qi)(qi)(qi)(qi)自(zi)鎖(suo)觸點已斷(duan)開，不會(hui)自(zi)行啟(qi)動(dong)(dong)。如(ru)果用不能(neng)(neng)復(fu)位的(de)手動(dong)(dong)開關、主令控(kong)制(zhi)器(qi)(qi)(qi)(qi)來控(kong)制(zhi)接觸器(qi)(qi)(qi)(qi)，必須采(cai)用專(zhuan)門的(de)零(ling)電壓(ya)繼(ji)電器(qi)(qi)(qi)(qi)。工作過程中(zhong)一旦(dan)失(shi)電壓(ya)，零(ling)電壓(ya)繼(ji)電器(qi)(qi)(qi)(qi)就釋放，其自(zi)鎖(suo)電路斷(duan)開，電源(yuan)電壓(ya)恢復(fu)時(shi)，不會(hui)自(zi)行啟(qi)動(dong)(dong)。

5.欠電壓保護

當電(dian)(dian)(dian)(dian)動(dong)(dong)機(ji)正常運(yun)行時，電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)壓(ya)(ya)過分地降低將引(yin)起(qi)一些電(dian)(dian)(dian)(dian)器釋放，造成控制線(xian)路工(gong)作不正常，甚至產生事故(gu)。當電(dian)(dian)(dian)(dian)網電(dian)(dian)(dian)(dian)壓(ya)(ya)過低時，如(ru)果電(dian)(dian)(dian)(dian)動(dong)(dong)機(ji)負載不變，則會造成電(dian)(dian)(dian)(dian)動(dong)(dong)機(ji)電(dian)(dian)(dian)(dian)流(liu)增(zeng)大，引(yin)起(qi)電(dian)(dian)(dian)(dian)動(dong)(dong)機(ji)發熱，嚴重時甚至燒(shao)壞(huai)電(dian)(dian)(dian)(dian)動(dong)(dong)機(ji)。此(ci)外，電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)壓(ya)(ya)過低還會引(yin)起(qi)電(dian)(dian)(dian)(dian)動(dong)(dong)機(ji)轉速(su)下(xia)降，甚至停轉。因此(ci)，在(zai)電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)壓(ya)(ya)降到(dao)允許值以下(xia)時，需要(yao)采(cai)用保護(hu)(hu)措(cuo)施，及時切斷電(dian)(dian)(dian)(dian)源，這(zhe)就是(shi)欠電(dian)(dian)(dian)(dian)壓(ya)(ya)保護(hu)(hu)。通(tong)常是(shi)采(cai)用欠電(dian)(dian)(dian)(dian)壓(ya)(ya)繼(ji)電(dian)(dian)(dian)(dian)器來實現。

上圖為電動機常(chang)用保(bao)護的接線，圖中各(ge)電器元件所起的保(bao)護作用分別為：

短(duan)路(lu)保護——熔斷器(qi)FU；

過載保護——熱繼電器(qi)FR；

過流保(bao)護——過電(dian)(dian)流繼電(dian)(dian)器KI1、KI2；

失電壓保護——中間繼電器KA；

欠電(dian)壓(ya)保護——欠電(dian)壓(ya)繼(ji)電(dian)器(qi)KV；

連(lian)鎖(suo)保護——通過(guo)KM1和KM2互鎖(suo)點實現。

以(yi)上就是得潤電氣(qi)的(de)(de)小編(bian)給大家(jia)分享的(de)(de)電氣(qi)知識，希望可以(yi)電氣(qi)的(de)(de)朋(peng)友們有所(suo)幫助哈！

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