軸電流 — 變頻電機軸承系統中的“隱患”！

      軸(zhou)(zhou)電(dian)(dian)流(liu)(liu)的產生(sheng)緣于軸(zhou)(zhou)電(dian)(dian)壓和閉合回(hui)路，多出現在高(gao)壓電(dian)(dian)機(ji)(ji)和變(bian)(bian)頻電(dian)(dian)機(ji)(ji)的使用中，是變(bian)(bian)頻電(dian)(dian)機(ji)(ji)、大(da)型變(bian)(bian)頻電(dian)(dian)機(ji)(ji)、高(gao)壓電(dian)(dian)機(ji)(ji)的一(yi)大(da)質(zhi)量(liang)殺手(shou)，并且軸(zhou)(zhou)電(dian)(dian)流(liu)(liu)會對電(dian)(dian)機(ji)(ji)軸(zhou)(zhou)承系(xi)統(tong)造成極(ji)大(da)的傷害，可以說軸(zhou)(zhou)電(dian)(dian)流(liu)(liu)是變(bian)(bian)頻電(dian)(dian)機(ji)(ji)軸(zhou)(zhou)承系(xi)統(tong)中的“黑客”！

      變(bian)(bian)(bian)頻(pin)(pin)電(dian)(dian)機(ji)(ji)實際上是一種，由變(bian)(bian)(bian)頻(pin)(pin)器供電(dian)(dian)的籠(long)(long)型變(bian)(bian)(bian)頻(pin)(pin)異步(bu)電(dian)(dian)動機(ji)(ji)，其(qi)結構(gou)設計(ji)參(can)數，機(ji)(ji)座號和尺寸均可參(can)照通用的籠(long)(long)型異步(bu)電(dian)(dian)動機(ji)(ji)，但是由于變(bian)(bian)(bian)頻(pin)(pin)電(dian)(dian)機(ji)(ji)在(zai)各種不同的頻(pin)(pin)率(lv)下運行，所以(yi)軸(zhou)電(dian)(dian)流多出現在(zai)此類變(bian)(bian)(bian)頻(pin)(pin)電(dian)(dian)機(ji)(ji)使用中。就從(cong)以(yi)下幾個方(fang)面闡述變(bian)(bian)(bian)頻(pin)(pin)電(dian)(dian)機(ji)(ji)軸(zhou)電(dian)(dian)流對電(dian)(dian)機(ji)(ji)軸(zhou)承的影(ying)響(xiang)以(yi)及(ji)防范措施。

1、軸(zhou)承電流的種類(lei)及產生的原因(yin)。

低頻軸(zhou)(zhou)承電(dian)(dian)(dian)(dian)流(liu)(liu)：電(dian)(dian)(dian)(dian)動機磁(ci)(ci)(ci)路(lu)不(bu)(bu)對稱(cheng)會產(chan)生(sheng)(sheng)低頻軸(zhou)(zhou)電(dian)(dian)(dian)(dian)流(liu)(liu)，這(zhe)種現象在容量大于(yu)400KW的(de)電(dian)(dian)(dian)(dian)動機中(zhong)常見(jian)，這(zhe)是(shi)因為(wei)，不(bu)(bu)對稱(cheng)的(de)磁(ci)(ci)(ci)路(lu)會在磁(ci)(ci)(ci)軛中(zhong)產(chan)生(sheng)(sheng)環形交流(liu)(liu)磁(ci)(ci)(ci)通（環狀磁(ci)(ci)(ci)通）從而由(you)電(dian)(dian)(dian)(dian)動機轉軸(zhou)(zhou)、軸(zhou)(zhou)承、端蓋和(he)電(dian)(dian)(dian)(dian)動機定子(zi)機座(zuo)組成的(de)導電(dian)(dian)(dian)(dian)性回(hui)路(lu)中(zhong)產(chan)生(sheng)(sheng)交流(liu)(liu)感應電(dian)(dian)(dian)(dian)壓，當此感應電(dian)(dian)(dian)(dian)壓破(po)壞(huai)了軸(zhou)(zhou)承潤滑劑的(de)絕緣能(neng)力后，電(dian)(dian)(dian)(dian)流(liu)(liu)就會流(liu)(liu)過包括電(dian)(dian)(dian)(dian)動機前(qian)后軸(zhou)(zhou)承在內的(de)這(zhe)個(ge)回(hui)路(lu)。

2、高頻軸電流

高(gao)頻(pin)(pin)軸電(dian)(dian)(dian)流產生(sheng)(sheng)的(de)原因：工頻(pin)(pin)三(san)相(xiang)正(zheng)弦(xian)(xian)電(dian)(dian)(dian)源電(dian)(dian)(dian)壓(ya)是(shi)(shi)平(ping)衡對稱的(de)，因此(ci)，其中(zhong)(zhong)性點(dian)電(dian)(dian)(dian)壓(ya)為零(ling)，可是(shi)(shi)變頻(pin)(pin)器的(de)輸出電(dian)(dian)(dian)壓(ya)是(shi)(shi)通(tong)過 PWM脈寬調制(zhi)產生(sheng)(sheng)的(de)，既通(tong)過逆(ni)變器將直流電(dian)(dian)(dian)壓(ya)轉(zhuan)變成三(san)相(xiang)正(zheng)弦(xian)(xian)交流電(dian)(dian)(dian)壓(ya)雖然其基頻(pin)(pin)分量是(shi)(shi)對稱平(ping)衡的(de)，但(dan)由于在逆(ni)變單元(yuan)中(zhong)(zhong)二(er)極(ji)管(guan)的(de)開(kai)斷不(bu)可能絕對同步，故可產生(sheng)(sheng)不(bu)對稱的(de)高(gao)次諧波(bo)，導致(zhi)零(ling)序電(dian)(dian)(dian)壓(ya)分量增(zeng)大，即中(zhong)(zhong)性點(dian)電(dian)(dian)(dian)壓(ya)不(bu)為零(ling)。標準(zhun)中(zhong)(zhong)將此(ci)零(ling)序電(dian)(dian)(dian)壓(ya)定義為共模電(dian)(dian)(dian)壓(ya)，此(ci)電(dian)(dian)(dian)壓(ya)可以在負載電(dian)(dian)(dian)動機繞(rao)組中(zhong)(zhong)的(de)中(zhong)(zhong)性點(dian)處(chu)測得，其頻(pin)(pin)率(lv)與逆(ni)變單元(yuan)中(zhong)(zhong)二(er)極(ji)管(guan)的(de)開(kai)斷頻(pin)(pin)率(lv)相(xiang)同，其幅值(zhi)與直流母線電(dian)(dian)(dian)壓(ya)成正(zheng)比。標準(zhun)規定由共模電(dian)(dian)(dian)壓(ya)產生(sheng)(sheng)的(de)軸電(dian)(dian)(dian)流叫高(gao)頻(pin)(pin)軸電(dian)(dian)(dian)流。

高頻軸電(dian)流(liu)的種類：

1、在共(gong)模電壓(ya)作(zuo)用下，由沿定(ding)子軛循環的(de)高頻磁通產生高頻感(gan)應(ying)電壓(ya)，當此(ci)感(gan)應(ying)電壓(ya)高到夠破壞(huai)軸承潤(run)滑劑的(de)絕緣時(shi)，所產生的(de)沿軸承、軸和定(ding)子機座連成的(de)回路中流動(dong)的(de)循環電流。

2、在共模電壓(ya)作用下，在電動機(ji)機(ji)座和變頻(pin)器機(ji)架(jia)之間會出現超(chao)過(guo)100V的(de)電壓(ya)降，泄漏到定子(zi)機(ji)座中(zhong)的(de)電流(liu)(liu)(liu)通過(guo)金屬聯軸(zhou)器與從動機(ji)械設(she)備回流(liu)(liu)(liu)到變頻(pin)器中(zhong)，所形成的(de)軸(zhou)接地電流(liu)(liu)(liu)。

3、在高頻共模電(dian)(dian)壓(ya)作用(yong)下，電(dian)(dian)動機(ji)內的各種雜散電(dian)(dian)容形(xing)成的阻(zu)抗(kang)變小，從(cong)而為電(dian)(dian)流(liu)(liu)流(liu)(liu)通提供低阻(zu)抗(kang)路徑，故當電(dian)(dian)機(ji)內部的電(dian)(dian)容放(fang)電(dian)(dian)時，就會產生高頻的軸承電(dian)(dian)流(liu)(liu)。該電(dian)(dian)流(liu)(liu)通過變頻器的接地導體和電(dian)(dian)容返回電(dian)(dian)源(yuan)。

軸電流的危害

      流(liu)入軸(zhou)承(cheng)(cheng)中的(de)電(dian)(dian)(dian)流(liu)變化快，其變化速率取決于(yu)軸(zhou)承(cheng)(cheng)的(de)工(gong)藝(yi)，當軸(zhou)承(cheng)(cheng)的(de)滾(gun)珠(zhu)被潤滑(hua)劑(ji)完全(quan)浸沒不(bu)導電(dian)(dian)(dian)時(shi)(shi)，此時(shi)(shi)存(cun)在的(de)軸(zhou)承(cheng)(cheng)電(dian)(dian)(dian)容處于(yu)靜電(dian)(dian)(dian)充電(dian)(dian)(dian)狀(zhuang)態，如(ru)果靜電(dian)(dian)(dian)充電(dian)(dian)(dian)的(de)電(dian)(dian)(dian)壓超出軸(zhou)承(cheng)(cheng)潤滑(hua)劑(ji)的(de)絕緣(yuan)(yuan)性(xing)能(neng)，就將(jiang)破(po)(po)壞軸(zhou)承(cheng)(cheng)潤滑(hua)劑(ji)形成的(de)油膜(mo)，此外電(dian)(dian)(dian)動機磁路不(bu)對稱產生(sheng)的(de)感應電(dian)(dian)(dian)壓也(ye)能(neng)破(po)(po)壞軸(zhou)承(cheng)(cheng)潤滑(hua)劑(ji)的(de)絕緣(yuan)(yuan)性(xing)能(neng)進(jin)而形成較大(da)的(de)軸(zhou)承(cheng)(cheng)電(dian)(dian)(dian)流(liu)，當軸(zhou)承(cheng)(cheng)電(dian)(dian)(dian)流(liu)的(de)密(mi)度(du)超過1.5A/mm后，軸(zhou)電(dian)(dian)(dian)流(liu)局部放(fang)(fang)電(dian)(dian)(dian)能(neng)量釋放(fang)(fang)產生(sheng)的(de)高溫，可以融化軸(zhou)承(cheng)(cheng)內(nei)圈、外圈或滾(gun)珠(zhu)上許(xu)多 微(wei)小區域，并(bing)形成凹槽(cao)，從而產生(sheng)噪聲、振動，若不(bu)能(neng)及(ji)時(shi)(shi)發現處理將(jiang)導致軸(zhou)承(cheng)(cheng)失效(xiao)，對生(sheng)產帶(dai)來極大(da)影(ying)響

      要(yao)解(jie)決的(de)規(gui)避軸(zhou)(zhou)電流問(wen)(wen)題，目前常(chang)用(yong)的(de)方法是，在(zai)變頻(pin)電機的(de)設計環(huan)節(jie)、制造過程都必須采取必要(yao)的(de)措(cuo)(cuo)施(shi)(shi)，比如(ru)在(zai)端蓋、軸(zhou)(zhou)承(cheng)(cheng)套上增加必要(yao)的(de)絕緣(yuan)措(cuo)(cuo)施(shi)(shi)，對于小規(gui)格產(chan)(chan)品(pin)可(ke)以(yi)(yi)采用(yong)絕緣(yuan)軸(zhou)(zhou)承(cheng)(cheng)，也可(ke)以(yi)(yi)在(zai)使(shi)用(yong)環(huan)節(jie)增加絕緣(yuan)措(cuo)(cuo)施(shi)(shi)。從使(shi)用(yong)的(de)角(jiao)度分析，在(zai)零部件上采取斷路措(cuo)(cuo)施(shi)(shi)是一勞永逸的(de)措(cuo)(cuo)施(shi)(shi)，可(ke)以(yi)(yi)避免(mian)在(zai)變頻(pin)電機的(de)維護保(bao)養(yang)周期內軸(zhou)(zhou)承(cheng)(cheng)系統(tong)產(chan)(chan)生其他保(bao)養(yang)問(wen)(wen)題。

 

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