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水泵跳閘故障排除的幾種方法

時(shí)間:2011/11/24閱讀:632
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乾思生物編輯整理:
水泵跳閘故障排除的幾種方法:
水泵跳閘故障的排除方法 
    1:故障現(xiàn)象:某電廠125 mw機(jī)組自投產(chǎn)以來(lái),給水泵偶爾會(huì)發(fā)生一合閘即跳閘的問(wèn)題,并無(wú)任何信號(hào)繼電器掉牌。在排除了開關(guān)機(jī)構(gòu)故障后,按常規(guī)方法檢查電纜、二次回路接線和各繼電器及其定值都正常,再次啟動(dòng)又往往成功。后懷疑是dcs系統(tǒng)軟故障造成的,但改在控制盤上操作,仍會(huì)出現(xiàn)此現(xiàn)象。 
    2:試驗(yàn)查找原因:為查清此現(xiàn)象的原因,觀察開關(guān)合閘過(guò)程中各表計(jì)的變化情況,以確認(rèn)是何原因使水泵跳閘。試驗(yàn)其中電壓表監(jiān)視微機(jī)跳閘回路,毫安表監(jiān)視差動(dòng)繼電器1cj、2cj動(dòng)作情況,電流表監(jiān)視熱工保護(hù)回路。接好表計(jì)后,啟動(dòng)給水泵,經(jīng)過(guò)一段時(shí)間的試驗(yàn),終于有一次一啟動(dòng)就水泵跳閘,同時(shí)觀察到毫安表的指針偏轉(zhuǎn)了一下,其它監(jiān)視表計(jì)沒(méi)有反應(yīng),新?lián)Q上的xjl-0025/31型集成塊式信號(hào)繼電器1xj亦動(dòng)作掉牌,表明是由差動(dòng)保護(hù)動(dòng)作導(dǎo)致水泵跳閘。
    3:根源分析:差動(dòng)保護(hù)動(dòng)作,首先懷疑被保護(hù)設(shè)備內(nèi)部有故障。通過(guò)常規(guī)檢查,給水泵電機(jī)及其電纜正常,差動(dòng)繼電器校驗(yàn)正常,電流互感器極性連接正確。在排除設(shè)備故障和接線錯(cuò)誤的原因后,差動(dòng)保護(hù)在電機(jī)啟動(dòng)過(guò)程中動(dòng)作,表明在這過(guò)程中差動(dòng)回路的差電流超過(guò)差動(dòng)繼電器整定值。正常情況下引起差動(dòng)回路差電流的原因主要有兩點(diǎn):一是電機(jī)首尾兩側(cè)的電流互感器變比誤差不同,存在一個(gè)很小的差電流,這個(gè)差電流小于電機(jī)額定電流id的5%。二是首尾兩側(cè)電流互感器二次負(fù)荷的差別也會(huì)引起其變比的差別,從而存在一個(gè)差電流。在給水泵電機(jī)差動(dòng)保護(hù)回路中的電流互感器負(fù)荷差別只是二次電纜長(zhǎng)度的不同,大約相差50 m,并且在額定電流下,差動(dòng)繼電器的功率消耗不大于3 va,二次負(fù)載并不重。檢查發(fā)現(xiàn)給水泵電機(jī)差動(dòng)保護(hù)用的首尾側(cè)電流互感器型號(hào)均為lmzbj-10,b級(jí)15倍額定電流,變比600/5,容量40 va,完滿足二次負(fù)載的要求。
    以上水泵跳閘的分析是基于正常運(yùn)行的條件下,在電機(jī)啟動(dòng)時(shí),情況又有所不同。電機(jī)啟動(dòng)時(shí)電流很大,首尾兩側(cè)的電流互感器可能飽和,此時(shí)由于各電流互感器磁化特性不一致,二次差電流可能很大。根據(jù)阿城繼電器廠的lcd-12型差動(dòng)繼電器整定說(shuō)明,繼電器的動(dòng)作電流整定值izd=△i1×kk×in/n=0.06×3×356/120=0.534a(式中:△i1—首、尾端電流互感器正常運(yùn)行時(shí)的zui大誤差,0.04~0.06;kk—可靠系數(shù),2~3;in—電機(jī)額定電流;n—電流互感器變比)。應(yīng)整定在1.0a的位置。在使用b級(jí)互感器的情況下,差動(dòng)繼電器動(dòng)作電流整定在1.,制動(dòng)系數(shù)為0.4時(shí),差動(dòng)保護(hù)在電機(jī)啟動(dòng)時(shí)仍偶爾會(huì)動(dòng)作,是由于b級(jí)電流互感器磁化特性飽和點(diǎn)較低,抗飽和能力較低,不能滿足差動(dòng)繼電器的要求。通常要求差動(dòng)保護(hù)回路的電流互感器采用d級(jí),d級(jí)互感器的飽和點(diǎn)高一些,沒(méi)那么容易飽和,可以減小電機(jī)啟動(dòng)時(shí)流過(guò)差動(dòng)回路的差電流。在更換為d級(jí)的電流互感器,同時(shí)把差動(dòng)繼電器動(dòng)作電流整定在1.0a,制動(dòng)系數(shù)為0.4后,再?zèng)]出現(xiàn)過(guò)開關(guān)一合閘即水泵跳閘的故障。 

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