非柔性直流輸電系統中，兩端換流站都配有大量的交流濾波器，其作用主要為補償無功功率和濾除諧波。以某±800kV換流站為例，其直流輸電容量為5000MVA，站內配有15組交流濾波器，每組交流濾波器主要由電力電容器組成。

常見故障(zhang)為本(ben)體發熱、本(ben)體漏(lou)油以(yi)及內部放(fang)電(dian)擊(ji)穿。本(ben)文就電(dian)力(li)電(dian)容(rong)器內部放(fang)電(dian)典(dian)型故障(zhang)進行分析。

一、電力電容器內部結構

交流(liu)濾(lv)(lv)波器一(yi)(yi)般由高壓塔(ta)(ta)和低壓塔(ta)(ta)兩(liang)座電(dian)(dian)容(rong)(rong)器塔(ta)(ta)構(gou)成，每(mei)座塔(ta)(ta)由一(yi)(yi)定數量的(de)電(dian)(dian)力電(dian)(dian)容(rong)(rong)器串并聯組成（因(yin)設計要(yao)求，采(cai)用不同的(de)連接方式）。如(ru)下圖1所示，該換流(liu)站內交流(liu)濾(lv)(lv)波器高壓塔(ta)(ta)稱為上橋(qiao)臂(bei)，分為左(zuo)右兩(liang)個臂(bei)（現(xian)場(chang)稱為A臂(bei)與B臂(bei)），每(mei)個臂(bei)由40只電(dian)(dian)容(rong)(rong)器單(dan)元（單(dan)只電(dian)(dian)力電(dian)(dian)容(rong)(rong)器），通過每(mei)兩(liang)只并聯后再(zai)逐(zhu)對串聯組成。

圖1  交流濾(lv)波器電(dian)容(rong)器塔結構

單(dan)(dan)只電(dian)(dian)(dian)(dian)(dian)力電(dian)(dian)(dian)(dian)(dian)容器(qi)內(nei)部結(jie)構如下(xia)圖(tu)2所示，單(dan)(dan)只電(dian)(dian)(dian)(dian)(dian)容器(qi)由5個(ge)(ge)(ge)電(dian)(dian)(dian)(dian)(dian)容串(chuan)聯(lian)段(duan)組(zu)成(cheng)(cheng)，每(mei)個(ge)(ge)(ge)串(chuan)聯(lian)段(duan)由19個(ge)(ge)(ge)電(dian)(dian)(dian)(dian)(dian)容元(yuan)(yuan)(yuan)件(jian)單(dan)(dan)元(yuan)(yuan)(yuan)并(bing)聯(lian)組(zu)成(cheng)(cheng)。其中，每(mei)個(ge)(ge)(ge)電(dian)(dian)(dian)(dian)(dian)容串(chuan)聯(lian)段(duan)有(you)一個(ge)(ge)(ge)并(bing)聯(lian)電(dian)(dian)(dian)(dian)(dian)阻R1，整個(ge)(ge)(ge)電(dian)(dian)(dian)(dian)(dian)容有(you)一個(ge)(ge)(ge)并(bing)聯(lian)電(dian)(dian)(dian)(dian)(dian)阻R2，起到內(nei)部故障(zhang)放電(dian)(dian)(dian)(dian)(dian)保護作用；并(bing)且，每(mei)個(ge)(ge)(ge)電(dian)(dian)(dian)(dian)(dian)容元(yuan)(yuan)(yuan)件(jian)單(dan)(dan)元(yuan)(yuan)(yuan)都單(dan)(dan)獨串(chuan)聯(lian)一個(ge)(ge)(ge)內(nei)熔(rong)絲(si)，該內(nei)熔(rong)絲(si)作用非常(chang)大，在電(dian)(dian)(dian)(dian)(dian)容元(yuan)(yuan)(yuan)件(jian)單(dan)(dan)元(yuan)(yuan)(yuan)單(dan)(dan)個(ge)(ge)(ge)被過(guo)電(dian)(dian)(dian)(dian)(dian)壓(ya)等其它因素擊穿時，對(dui)應的內(nei)熔(rong)絲(si)會同步熔(rong)斷，將故障(zhang)電(dian)(dian)(dian)(dian)(dian)容元(yuan)(yuan)(yuan)件(jian)單(dan)(dan)元(yuan)(yuan)(yuan)進行隔離，防止電(dian)(dian)(dian)(dian)(dian)容器(qi)內(nei)部故障(zhang)持續(xu)擴大。

圖2  電力電容器內(nei)部結構

二、電力電容器內部故障對繼電保護的動作影響

圖(tu)1中所(suo)示(shi)的T2電(dian)(dian)流(liu)(liu)互(hu)(hu)感器，為不平(ping)衡電(dian)(dian)流(liu)(liu)互(hu)(hu)感器，理想情況時(shi)流(liu)(liu)過T2的電(dian)(dian)流(liu)(liu)為零，當電(dian)(dian)容(rong)器內部單(dan)個元(yuan)件故障擊穿時(shi)，會導致(zhi)該只(zhi)電(dian)(dian)容(rong)器電(dian)(dian)容(rong)值(zhi)發生變化，從而使(shi)電(dian)(dian)容(rong)塔的橋(qiao)臂電(dian)(dian)容(rong)值(zhi)出(chu)現變化，當橋(qiao)臂值(zhi)不一致(zhi)時(shi)，會有不平(ping)衡電(dian)(dian)流(liu)(liu)流(liu)(liu)過T2電(dian)(dian)流(liu)(liu)互(hu)(hu)感器，該電(dian)(dian)流(liu)(liu)達到一定值(zhi)時(shi)，保護裝置(zhi)會出(chu)現告警與跳閘出(chu)口動(dong)作(zuo)，該換流(liu)(liu)站(zhan)保護整定的定值(zhi)如下圖(tu)3所(suo)示(shi)。

圖3  電容器不平衡電流保護整(zheng)定(ding)值

可見，如果(guo)一個電容器(qi)內部電容單元(yuan)元(yuan)件(jian)有(you)1至2個擊穿，且熔絲(si)即時熔斷，對整(zheng)個保護系統是(shi)沒有(you)影(ying)響的。

三、典型故障

該換流(liu)站交流(liu)濾波器(qi)(qi)電(dian)(dian)容(rong)(rong)器(qi)(qi)頻(pin)繁出現(xian)不平衡電(dian)(dian)流(liu)保護直接出口跳閘(zha)，每次現(xian)場檢查均發現(xian)有(you)1只(zhi)電(dian)(dian)容(rong)(rong)器(qi)(qi)的電(dian)(dian)容(rong)(rong)值(zhi)變(bian)化(hua)特(te)別(bie)大，后續經過電(dian)(dian)容(rong)(rong)器(qi)(qi)解(jie)體分析，發現(xian)了跳閘(zha)的根本原(yuan)因為該電(dian)(dian)容(rong)(rong)器(qi)(qi)內(nei)部的電(dian)(dian)容(rong)(rong)元(yuan)件(jian)被擊穿時(shi)，熔(rong)絲未及時(shi)熔(rong)斷，導致整個串(chuan)聯(lian)段（19個串(chuan)聯(lian)電(dian)(dian)容(rong)(rong)元(yuan)件(jian)）短路，如下圖4所示。

圖(tu)4  電容器(qi)解剖(pou)情況

故障電容器比額(e)定(ding)值(zhi)偏大了約25%，理論(lun)分析為5個(ge)(ge)(ge)串聯(lian)段變成了4個(ge)(ge)(ge)串聯(lian)段；現場解(jie)剖也(ye)證實了這一(yi)點(dian)，內部存在一(yi)個(ge)(ge)(ge)串聯(lian)段短路(lu)，且(qie)短路(lu)的串聯(lian)段中存在兩個(ge)(ge)(ge)相(xiang)鄰電容器元件擊(ji)穿(chuan)(chuan)，擊(ji)穿(chuan)(chuan)點(dian)均在元件表(biao)面，僅(jin)一(yi)個(ge)(ge)(ge)擊(ji)穿(chuan)(chuan)電容器元件熔(rong)絲熔(rong)斷(duan)，另一(yi)擊(ji)穿(chuan)(chuan)電容器元件熔(rong)絲未(wei)熔(rong)斷(duan)，未(wei)熔(rong)斷(duan)的熔(rong)絲導(dao)致(zhi)整個(ge)(ge)(ge)串聯(lian)段短路(lu)。

四、原因分析與總結

該換流站交流濾(lv)波器跳閘時(shi)刻(ke)(ke)故障錄波如下圖5所示，跳閘時(shi)刻(ke)(ke)，T2不平(ping)衡(heng)電流突然出現兩次高頻的(de)大不平(ping)衡(heng)電流，可知兩次異(yi)常的(de)高頻不平(ping)衡(heng)電流由電容器單元內同一串聯段的(de)兩個(ge)相鄰(lin)電容元件連續(xu)擊穿(chuan)引起。第一次擊穿(chuan)時(shi)，持(chi)續(xu)時(shi)間(jian)約2ms，熔(rong)(rong)(rong)絲熔(rong)(rong)(rong)斷(duan)；第二次擊穿(chuan)時(shi)，持(chi)續(xu)時(shi)間(jian)約4ms，熔(rong)(rong)(rong)絲未熔(rong)(rong)(rong)斷(duan)，保護出口(kou)跳閘。

圖5  跳閘時刻故障錄(lu)波(bo)

電(dian)(dian)(dian)容(rong)(rong)內部單個元(yuan)件表面擊(ji)穿時會產生電(dian)(dian)(dian)弧，由于電(dian)(dian)(dian)弧溫度高，引(yin)起相鄰電(dian)(dian)(dian)容(rong)(rong)器(qi)(qi)元(yuan)件因(yin)燒灼而擊(ji)穿，雖第一(yi)次發(fa)生擊(ji)穿的電(dian)(dian)(dian)容(rong)(rong)器(qi)(qi)元(yuan)件熔(rong)(rong)絲(si)已熔(rong)(rong)斷(duan)，但依據內熔(rong)(rong)絲(si)設計參(can)數(shu)和故障時刻(ke)錄波曲線，殘(can)余放(fang)電(dian)(dian)(dian)能量不(bu)足(zu)以熔(rong)(rong)斷(duan)另一(yi)擊(ji)穿電(dian)(dian)(dian)容(rong)(rong)器(qi)(qi)元(yuan)件熔(rong)(rong)絲(si)，導致其所在串聯段短(duan)路，使(shi)整體(ti)容(rong)(rong)值陡增約25%，引(yin)起電(dian)(dian)(dian)容(rong)(rong)器(qi)(qi)組(zu)不(bu)平衡(heng)電(dian)(dian)(dian)流突增而發(fa)生跳閘事故。后續(xu)電(dian)(dian)(dian)力電(dian)(dian)(dian)容(rong)(rong)器(qi)(qi)制造(zao)方(fang)，需(xu)多(duo)方(fang)面考(kao)慮(lv)內熔(rong)(rong)絲(si)的熔(rong)(rong)斷(duan)基(ji)理(li)，合理(li)設計參(can)數(shu)，保證電(dian)(dian)(dian)容(rong)(rong)器(qi)(qi)運行時的可靠性。