YOKOGAWA橫河 EB501-10

    在電機(jī)使用中，會(huì)發(fā)現(xiàn)電機(jī)有“漏電”現(xiàn)象產(chǎn)生，有的甚至?xí)a(chǎn)生100V以上的靜電電壓，這樣高的靜電電壓會(huì)讓人有刺痛的感覺(jué)，以致讓人會(huì)誤認(rèn)為電機(jī)“漏電”了，其實(shí)這只是感電。感電的感應(yīng)電流通常比較小，不會(huì)產(chǎn)生嚴(yán)重的后果。

    1.原因

    現(xiàn)代變頻器的控制原理絕大多數(shù)都采用了脈寬調(diào)制(PWM)控制方式，為了**變頻調(diào)速系統(tǒng)的負(fù)載響應(yīng)性及運(yùn)行平穩(wěn)性，同時(shí)為了降低電機(jī)運(yùn)行時(shí)發(fā)出的高頻噪音，調(diào)制波的頻率一般都達(dá)到了4K及以上，特別是中小功率的變頻器，因輸出電流較小，載波頻率可達(dá)10K以上，因此，變頻器輸出的電壓實(shí)際上是一系列寬度不同的脈沖。另外，在一些高性能的電流矢量變頻器中，例如安川G系列變頻器、優(yōu)利康YD系列變頻器、丹佛斯VLT5000系列變頻器等等，在這些變頻器中都接有直流濾波的大電容，使得輸出脈沖的上升下降沿都比較陡。所以，由于電機(jī)線(xiàn)圈與電機(jī)外殼之間有一個(gè)等效電容存在，就在電機(jī)的外殼上感應(yīng)出了一定的電壓。隨著頻率的增加“漏電”越來(lái)越小，低速的時(shí)候“漏電“比較嚴(yán)重但是，感應(yīng)電壓與漏電電壓是不同的，感應(yīng)電壓雖可能比較高，但感應(yīng)電流通常比較小，不會(huì)產(chǎn)生特別嚴(yán)重的后果。而漏電是由于電機(jī)的絕緣受到了損壞，線(xiàn)圈與外殼間的絕緣電阻變得很小，輸出電壓直接通過(guò)這個(gè)變小的絕緣電阻，使電機(jī)外殼帶電，并會(huì)危及人身安全。

    2.措施

    根據(jù)國(guó)家的電氣安裝安全規(guī)程，電動(dòng)機(jī)必須安全可靠接地，在三相四線(xiàn)制供電系統(tǒng)中，零線(xiàn)(N)必須在車(chē)間接入點(diǎn)重復(fù)接地，接地電阻要小于4Ω。

    同樣，在使用變頻器的調(diào)速系統(tǒng)中，電機(jī)的接地是必要的。這不僅能使感應(yīng)電壓有釋放回路，同時(shí)能保護(hù)因電機(jī)的絕緣故障引起的漏電事故，還能減少變頻器對(duì)其它電氣設(shè)備的干擾，使電氣設(shè)備都能安全可靠地運(yùn)行

    宗上所述客戶(hù)這樣檢測(cè)出來(lái)的是感電，而非漏電。（詳細(xì)參數(shù)請(qǐng)參閱國(guó)家電工法手冊(cè)，國(guó)家電氣安裝安全規(guī)程）況且在做CE認(rèn)證時(shí)也不會(huì)用這種方法測(cè)漏電。

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