YOKOGAWA橫河 EB501-10
在電機使用中,會發現電機有“漏電”現象產生,有的甚至會產生100V以上的靜電電壓,這樣高的靜電電壓會讓人有刺痛的感覺,以致讓人會誤認為電機“漏電”了,其實這只是感電。感電的感應電流通常比較小,不會產生嚴重的后果。
1.原因
現代變頻器的控制原理絕大多數都采用了脈寬調制(PWM)控制方式,為了**變頻調速系統的負載響應性及運行平穩性,同時為了降低電機運行時發出的高頻噪音,調制波的頻率一般都達到了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10K以上,因此,變頻器輸出的電壓實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,由于電機線圈與電機外殼之間有一個等效電容存在,就在電機的外殼上感應出了一定的電壓。隨著頻率的增加“漏電”越來越小,低速的時候“漏電“比較嚴重但是,感應電壓與漏電電壓是不同的,感應電壓雖可能比較高,但感應電流通常比較小,不會產生特別嚴重的后果。而漏電是由于電機的絕緣受到了損壞,線圈與外殼間的絕緣電阻變得很小,輸出電壓直接通過這個變小的絕緣電阻,使電機外殼帶電,并會危及人身安全。
2.措施
根據國家的電氣安裝安全規程,電動機必須安全可靠接地,在三相四線制供電系統中,零線(N)必須在車間接入點重復接地,接地電阻要小于4Ω。
同樣,在使用變頻器的調速系統中,電機的接地是必要的。這不僅能使感應電壓有釋放回路,同時能保護因電機的絕緣故障引起的漏電事故,還能減少變頻器對其它電氣設備的干擾,使電氣設備都能安全可靠地運行
宗上所述客戶這樣檢測出來的是感電,而非漏電。(詳細參數請參閱國家電工法手冊,國家電氣安裝安全規程)況且在做CE認證時也不會用這種方法測漏電。
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