為(wei)什么電(dian)機啟動電(dian)流大(da)、啟動后(hou)電(dian)流又小(xiao)了(le)。

      電(dian)機啟動(dong)時(shi)為什(shen)么它的啟動(dong)電(dian)流會比較大呢(ni)(ni)？而(er)啟動(dong)后正常轉起來(lai)了(le)電(dian)流為什(shen)么又小了(le)呢(ni)(ni)？這里我們有必要從電(dian)機電(dian)機啟動(dong)原(yuan)(yuan)理(li)和電(dian)機旋轉原(yuan)(yuan)理(li)的角度來(lai)理(li)解.

        當(dang)感應(ying)電(dian)動(dong)機(ji)處在停(ting)止狀態時，從電(dian)磁(ci)(ci)(ci)的(de)(de)(de)(de)角(jiao)度看，就像變壓器(qi)，接到(dao)電(dian)源去的(de)(de)(de)(de)定(ding)子(zi)(zi)繞(rao)組相當(dang)于變壓器(qi)的(de)(de)(de)(de)一次(ci)(ci)線(xian)圈，成閉(bi)路(lu)(lu)的(de)(de)(de)(de)轉(zhuan)(zhuan)(zhuan)(zhuan)子(zi)(zi)繞(rao)組相當(dang)于變壓器(qi)被短路(lu)(lu)的(de)(de)(de)(de)二次(ci)(ci)線(xian)圈；定(ding)子(zi)(zi)繞(rao)組和轉(zhuan)(zhuan)(zhuan)(zhuan)子(zi)(zi)繞(rao)組間無電(dian)的(de)(de)(de)(de)的(de)(de)(de)(de)，只有磁(ci)(ci)(ci)的(de)(de)(de)(de)，磁(ci)(ci)(ci)通(tong)(tong)經定(ding)子(zi)(zi)、氣隙、轉(zhuan)(zhuan)(zhuan)(zhuan)子(zi)(zi)鐵(tie)芯成閉(bi)路(lu)(lu)。當(dang)合(he)閘瞬間，轉(zhuan)(zhuan)(zhuan)(zhuan)子(zi)(zi)因慣性還未轉(zhuan)(zhuan)(zhuan)(zhuan)起(qi)來，旋轉(zhuan)(zhuan)(zhuan)(zhuan)磁(ci)(ci)(ci)場以(yi)zui大的(de)(de)(de)(de)切割速(su)度——同步轉(zhuan)(zhuan)(zhuan)(zhuan)速(su)切割轉(zhuan)(zhuan)(zhuan)(zhuan)子(zi)(zi)繞(rao)組，使轉(zhuan)(zhuan)(zhuan)(zhuan)子(zi)(zi)繞(rao)組感應(ying)起(qi)可能達到(dao)的(de)(de)(de)(de)zui高的(de)(de)(de)(de)電(dian)勢(shi)，因而(er)，在轉(zhuan)(zhuan)(zhuan)(zhuan)子(zi)(zi)導體中流(liu)過(guo)很大的(de)(de)(de)(de)電(dian)流(liu)，這個電(dian)流(liu)產(chan)生抵消定(ding)子(zi)(zi)磁(ci)(ci)(ci)場的(de)(de)(de)(de)磁(ci)(ci)(ci)能，就象變壓器(qi)二次(ci)(ci)磁(ci)(ci)(ci)通(tong)(tong)要(yao)抵消一次(ci)(ci)磁(ci)(ci)(ci)通(tong)(tong)的(de)(de)(de)(de)作用(yong)一樣。

       而定子方面為(wei)了(le)維護與該時(shi)電(dian)源電(dian)壓相適應的(de)原有磁(ci)通，遂自動增加電(dian)流。因(yin)為(wei)此時(shi)轉子的(de)電(dian)流很大，故定子電(dian)流也增得(de)很大，甚(shen)至高達額(e)定電(dian)流的(de)4~7倍，這就是啟動電(dian)流大的(de)緣由。

       啟動后(hou)電(dian)流(liu)為什么小(xiao)：隨著電(dian)動機轉(zhuan)速(su)增高，定(ding)子(zi)磁場切割轉(zhuan)子(zi)導(dao)體的(de)(de)(de)速(su)度減(jian)(jian)小(xiao)，轉(zhuan)子(zi)導(dao)體中(zhong)感應電(dian)勢(shi)減(jian)(jian)小(xiao)，轉(zhuan)子(zi)導(dao)體中(zhong)的(de)(de)(de)電(dian)流(liu)也減(jian)(jian)小(xiao)，于是(shi)定(ding)子(zi)電(dian)流(liu)中(zhong)用來(lai)抵消轉(zhuan)子(zi)電(dian)流(liu)所產(chan)生的(de)(de)(de)磁通的(de)(de)(de)影響(xiang)的(de)(de)(de)那部分(fen)電(dian)流(liu)也減(jian)(jian)小(xiao)，所以定(ding)子(zi)電(dian)流(liu)就從大(da)到小(xiao)，直到正常。

三相鼠籠異步電(dian)機(ji)的(de)啟動電(dian)流(liu)(liu)一般(ban)是(shi)4～7倍(bei)，但是(shi)不(bu)是(shi)的(de)。不(bu)過(guo)一般(ban)要求電(dian)機(ji)的(de)起動電(dian)流(liu)(liu)不(bu)能超過(guo)其(qi)額定(ding)電(dian)流(liu)(liu)的(de)2～5倍(bei)。電(dian)機(ji)功率超過(guo)30kw的(de)電(dian)動機(ji)不(bu)適合頻(pin)繁啟動，因為(wei)30kw以上電(dian)機(ji)啟動電(dian)流(liu)(liu)一般(ban)為(wei)額定(ding)電(dian)流(liu)(liu)的(de)6－7倍(bei)，頻(pin)繁啟動會增加電(dian)機(ji)溫升，造成燒毀電(dian)機(ji)的(de)可能。

一般交(jiao)流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)是(shi)(shi)異步電(dian)(dian)(dian)(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)，它的直接啟(qi)動(dong)(dong)(dong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)約是(shi)(shi)額定電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的4-7倍，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)機(ji)(ji)小，則是(shi)(shi)7倍，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)機(ji)(ji)大(da)，則是(shi)(shi)5-4倍。因為(wei)交(jiao)流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)有阻(zu)(zu)抗(kang)，不像直流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)只有電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)，所以啟(qi)動(dong)(dong)(dong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)不可能有十幾倍。對于同一臺電(dian)(dian)(dian)(dian)(dian)(dian)(dian)機(ji)(ji)來說，不管(guan)重載(zai)輕載(zai)，它的啟(qi)動(dong)(dong)(dong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)是(shi)(shi)一樣的。僅僅在用儀(yi)表(biao)測(ce)量時(shi)看起來有點不一樣。因為(wei)輕載(zai)時(shi)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)機(ji)(ji)啟(qi)動(dong)(dong)(dong)較快，當(dang)儀(yi)表(biao)指針還未升到zui大(da)時(shi)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)機(ji)(ji)已起來了，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)開始(shi)下降，因此看上去電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)較小。而當(dang)重載(zai)時(shi)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)機(ji)(ji)啟(qi)動(dong)(dong)(dong)慢(man)，儀(yi)表(biao)基本能跟上電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的變(bian)化，看起來電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)較大(da)。實(shi)際是(shi)(shi)一樣的。