一般我們的(de)計(ji)算方法是:電動機(ji)(ji)(ji)的(de)額(e)定電流(liu)(a):“電動機(ji)(ji)(ji)的(de)兩倍功(gong)(gong)率”,即“1千(qian)瓦2安培”。通常指功(gong)(gong)率因數約為0.8的(de)常用(yong)380伏(fu)三相異步電動機(ji)(ji)(ji),“千(qian)瓦數翻倍”是電動機(ji)(ji)(ji)的(de)額(e)定電流(liu)。
在相(xiang)應的(de)對應公式(shi):
電動機(ji)額定電流(A)=電動機(ji)容量(kW)數(shu)×2
所(suo)述的(de)速(su)算(suan)口訣(jue)和(he)經驗(yan)公(gong)式的(de)應用(yong)結果全是相同(tong)的(de),所(suo)計算(suan)的(de)額定(ding)電壓(ya)與電機銘牌上的(de)具體交流(liu)電標值十分貼近,合(he)乎好用(yong)規定(ding),比如(ru)每臺Y132S1-2,10kW電機,用(yong)速(su)算(suan)口訣(jue)或經驗(yan)公(gong)式算(suan)是其額定(ding)電壓(ya):10×2=20A。
一般來說,當我選擇電動機保護設備時,我通常選擇電機保護器和斷路器。這里將不詳細描述斷路器。我們將重點關注電機保護器(也叫(jiao)馬(ma)達(da)保(bao)(bao)護(hu)(hu)(hu)器(qi)(qi)(qi))。電(dian)機(ji)(ji)保(bao)(bao)護(hu)(hu)(hu)器(qi)(qi)(qi)有兩種類型(xing):塑料外(wai)殼型(xing)(也稱為(wei)設備型(xing))和框架型(xing)(也稱為(wei)通用型(xing))。380V245kW千(qian)瓦及(ji)以(yi)下 的電(dian)機(ji)(ji)多(duo)采用塑殼電(dian)動機(ji)(ji)保(bao)(bao)護(hu)(hu)(hu)器(qi)(qi)(qi)。電(dian)動機(ji)(ji)保(bao)(bao)護(hu)(hu)(hu)器(qi)(qi)(qi)按(an)用處可(ke)分成維護(hu)(hu)(hu)過壓保(bao)(bao)護(hu)(hu)(hu)器(qi)(qi)(qi)、過流保(bao)(bao)護(hu)(hu)(hu)器(qi)(qi)(qi)、漏電(dian)保(bao)(bao)護(hu)(hu)(hu)開關(guan)、過載保(bao)(bao)護(hu)(hu)(hu)器(qi)(qi)(qi)等維護(hu)(hu)(hu)電(dian)機(ji)(ji)設施。
大多數中小(xiao)型電(dian)(dian)動機采(cai)用輕載(zai)全(quan)壓(ya)或減壓(ya)起動,起動電(dian)(dian)流(liu)一般(ban)為額定電(dian)(dian)流(liu)的5~7倍(bei);電(dian)(dian)源容(rong)量較大,低壓(ya)配電(dian)(dian)主變壓(ya)器1000~400kVA(包括并(bing)列(lie)運(yun)行容(rong)量),系(xi)統阻抗小(xiao),當(dang)發(fa)生(sheng)短(duan)(duan)路故障時,短(duan)(duan)路電(dian)(dian)流(liu)較大;發(fa)生(sheng)短(duan)(duan)路故障時,短(duan)(duan)路電(dian)(dian)流(liu)大;窯(yao)爐和研磨(mo)場所(suo)等工(gong)作(zuo)場所(suo)通風條件差,導致工(gong)作(zuo)環境溫度較高(gao)。因此,與一般(ban)工(gong)業用途相比,電(dian)(dian)動機保護器的斷開能力和熔(rong)體(ti)的額定電(dian)(dian)流(liu)應(ying)適當(dang)增加。
在上(shang)(shang)面的利(li)用(yong)上(shang)(shang)面的計算得出(chu)一臺380V籠(long)(long)型電(dian)動(dong)(dong)機(ji),輕載全壓起(qi)動(dong)(dong)或減壓起(qi)動(dong)(dong),操作頻率較低,適(shi)合(he)于90kW及(ji)以(yi)下的籠(long)(long)型電(dian)動(dong)(dong)機(ji)。使用(yong)的電(dian)動(dong)(dong)機(ji)起(qi)動(dong)(dong)頻繁,或者(zhe)起(qi)動(dong)(dong)時間長,電(dian)流也就會先對應的會大一些,在設(she)置(zhi)電(dian)動(dong)(dong)機(ji)保(bao)(bao)護器(qi)時為確保(bao)(bao)達到(dao)保(bao)(bao)護效果(guo)應包額定(ding)電(dian)流設(she)定(ding)大一些。