不銹鋼管穿過磁化線圈時會(hui)發生(sheng)如下(xia)兩種電磁感應現象:
1. 鋼管在橫向漏磁檢測磁化器內運動時,不銹鋼管(guan)切割磁力線而在其內部形成感生渦流。
2. 不銹鋼(gang)管(guan)磁(ci)介質在管(guan)頭進入磁(ci)化(hua)線(xian)圈(quan)和管(guan)尾離開磁(ci)化(hua)線(xian)圈(quan)時(shi),由于(yu)磁(ci)化(hua)線(xian)圈(quan)的磁(ci)通總量發(fa)生急(ji)劇變化(hua),線(xian)圈(quan)中會產生感生電流。
一、鋼管內產(chan)生的(de)感生渦流(liu)
不銹(xiu)鋼(gang)(gang)管橫(heng)向缺(que)陷(xian)漏磁(ci)檢(jian)(jian)測方法采用穿過(guo)式線(xian)(xian)圈(quan)產(chan)生(sheng)軸向磁(ci)化(hua)場,并(bing)在磁(ci)化(hua)線(xian)(xian)圈(quan)內(nei)布置檢(jian)(jian)測傳感器。當鋼(gang)(gang)管沿(yan)著(zhu)軸向移動時(shi),處于磁(ci)化(hua)線(xian)(xian)圈(quan)內(nei)的不銹(xiu)鋼(gang)(gang)管段被磁(ci)化(hua)至近飽(bao)和(he)狀態,如存在缺(que)陷(xian)將在鋼(gang)(gang)管表面產(chan)生(sheng)泄漏磁(ci)場,然后(hou)被磁(ci)敏感元(yuan)件(jian)拾取并(bing)依次(ci)轉換為模擬信號(hao)和(he)數(shu)字信號(hao),最終由計算機信號(hao)處理系統(tong)實施報警和(he)分類。
如(ru)圖(tu)5-1所(suo)示(shi),以(yi)鋼管軸線為中(zhong)心(xin)建立圓(yuan)柱坐標系(xi)。沿(yan)著鋼管運(yun)動方向(xiang),以(yi)磁(ci)(ci)化線圈(quan)為中(zhong)心(xin)將鋼管劃分為進(jin)入區和離開區,在磁(ci)(ci)化線圈(quan)中(zhong)施加如(ru)圖(tu)所(suo)示(shi)的磁(ci)(ci)化電流(liu),磁(ci)(ci)力線分布特征為:在進(jin)入區磁(ci)(ci)力線從空(kong)氣中(zhong)進(jin)入鋼管,并在磁(ci)(ci)化線圈(quan)中(zhong)部匯聚,然后在離開區折射入空(kong)氣中(zhong)。
如圖(tu)5-1所示,將磁(ci)感應(ying)強度矢(shi)量B(r,z)分(fen)(fen)解為(wei)軸(zhou)向分(fen)(fen)量和徑向分(fen)(fen)量,即 B(r,z)=B2(r,z)+B,(r,z)
從圖5-1中(zhong)可以看出(chu),軸向(xiang)分量B2(r,z)在進(jin)入(ru)區(qu)和(he)離(li)開區(qu)方(fang)向(xiang)一(yi)致(zhi),沿著鋼管(guan)前進(jin)方(fang)向(xiang),其(qi)強度在進(jin)入(ru)區(qu)逐漸增大,并(bing)在磁化線(xian)圈(quan)中(zhong)部達到極大值,之后在離(li)開區(qu)逐漸減小。徑向(xiang)分量B,(r,z)在進(jin)入(ru)區(qu)方(fang)向(xiang)指向(xiang)鋼管(guan)內部,并(bing)在磁化線(xian)圈(quan)中(zhong)部發生(sheng)轉變,在離(li)開區(qu)方(fang)向(xiang)指向(xiang)鋼管(guan)外部。
為(wei)了研究與鋼管同軸(zhou)圓(yuan)環(huan)(huan)l(ro ,zo)的渦流分布,設圓(yuan)環(huan)(huan)半徑為(wei)ro,軸(zhou)向位置為(wei)200根據楞次定律,當圓(yuan)環(huan)(huan)移(yi)動(dong)時,軸(zhou)向分量B,(r,z)的強度變化導致圓(yuan)環(huan)(huan)磁(ci)通(tong)量也發生(sheng)改變,從而在圓(yuan)環(huan)(huan)中產生(sheng)感生(sheng)電動(dong)勢(shi)。因磁(ci)化場為(wei)軸(zhou)對稱(cheng),建立圓(yuan)環(huan)(huan)感應電動(dong)勢(shi)方程(cheng)為(wei)
根據式(5-3),沿鋼管(guan)前進(jin)方向(xiang)(xiang),在進(jin)入區,軸向(xiang)(xiang)分(fen)量強(qiang)度(du)(du)逐漸(jian)增強(qiang),感生(sheng)渦流方向(xiang)(xiang)與原磁(ci)(ci)(ci)化(hua)電(dian)流方向(xiang)(xiang)相(xiang)(xiang)反(fan);在磁(ci)(ci)(ci)化(hua)線圈中間位(wei)置,由于(yu)軸向(xiang)(xiang)分(fen)量變(bian)化(hua)率為零,故此部位(wei)無(wu)感生(sheng)流產生(sheng);在離開區,軸向(xiang)(xiang)分(fen)量強(qiang)度(du)(du)由中間最大值逐漸(jian)減小,于(yu)是形成與原磁(ci)(ci)(ci)化(hua)電(dian)流方向(xiang)(xiang)相(xiang)(xiang)同的感生(sheng)渦流,最終鋼管(guan)中感生(sheng)渦流分(fen)布(bu)如(ru)圖5-2a所(suo)示。如(ru)果改變(bian)磁(ci)(ci)(ci)化(hua)電(dian)流方向(xiang)(xiang),根據式(5-3),同樣可得出鋼管(guan)內感生(sheng)渦流分(fen)布(bu),如(ru)圖5-2b所(suo)示。
從圖(tu)5-2中(zhong)(zhong)可以看出,鋼管中(zhong)(zhong)感(gan)生電(dian)流(liu)分布方(fang)向(xiang)(xiang)由磁(ci)化(hua)(hua)電(dian)流(liu)方(fang)向(xiang)(xiang)和鋼管運動方(fang)向(xiang)(xiang)共同決定。在進(jin)入(ru)區,鋼管中(zhong)(zhong)的感(gan)生渦(wo)流(liu)J1與磁(ci)化(hua)(hua)電(dian)流(liu)方(fang)向(xiang)(xiang)相(xiang)反;在磁(ci)化(hua)(hua)線圈(quan)中(zhong)(zhong)間位置無(wu)感(gan)生渦(wo)流(liu)產生;在離(li)開區,感(gan)生渦(wo)流(liu)J2與磁(ci)化(hua)(hua)電(dian)流(liu)方(fang)向(xiang)(xiang)相(xiang)同。從而,在感(gan)生渦(wo)流(liu)產生的磁(ci)場作用下,鋼管的磁(ci)化(hua)(hua)狀態(tai)將發生變化(hua)(hua)。
建立如圖5-3所示的仿真模型。鋼管直(zhi)徑(jing)為(wei)(wei)(wei)(wei)400mm、壁厚(hou)(hou)為(wei)(wei)(wei)(wei)15mm、長度(du)(du)為(wei)(wei)(wei)(wei)3000mm,材(cai)質為(wei)(wei)(wei)(wei)25鋼(電(dian)(dian)導率為(wei)(wei)(wei)(wei))。磁化(hua)線圈(quan)內徑(jing)為(wei)(wei)(wei)(wei)440mm、外(wai)徑(jing)為(wei)(wei)(wei)(wei)750mm、厚(hou)(hou)度(du)(du)為(wei)(wei)(wei)(wei)160mm,磁化(hua)電(dian)(dian)流密(mi)度(du)(du)iA/㎡,電(dian)(dian)流方向如圖5-3所示。
對(dui)不銹(xiu)鋼(gang)管中(zhong)(zhong)(zhong)的感(gan)生(sheng)渦(wo)流(liu)(liu)分(fen)布(bu)(bu)(bu)進行仿(fang)真研究。磁(ci)化(hua)(hua)線(xian)圈(quan)固定不動,鋼(gang)管運(yun)行速度設置為(wei)1m/s,不銹(xiu)鋼(gang)管從左(zuo)端進人并向(xiang)(xiang)(xiang)右端移動,當鋼(gang)管中(zhong)(zhong)(zhong)心與磁(ci)化(hua)(hua)線(xian)圈(quan)中(zhong)(zhong)(zhong)心重合時獲取(qu)感(gan)生(sheng)渦(wo)流(liu)(liu)分(fen)布(bu)(bu)(bu)云圖,如圖5-4所示。從圖中(zhong)(zhong)(zhong)可以(yi)看(kan)出,進入區(qu)(qu)(qu)的感(gan)生(sheng)渦(wo)流(liu)(liu)方(fang)(fang)向(xiang)(xiang)(xiang)與磁(ci)化(hua)(hua)電流(liu)(liu)方(fang)(fang)向(xiang)(xiang)(xiang)相(xiang)反,離開區(qu)(qu)(qu)的感(gan)生(sheng)渦(wo)流(liu)(liu)方(fang)(fang)向(xiang)(xiang)(xiang)與磁(ci)化(hua)(hua)電流(liu)(liu)方(fang)(fang)向(xiang)(xiang)(xiang)相(xiang)同,在(zai)線(xian)圈(quan)中(zhong)(zhong)(zhong)部感(gan)生(sheng)渦(wo)流(liu)(liu)幾乎為(wei)零。進入區(qu)(qu)(qu)和離開區(qu)(qu)(qu)的渦(wo)流(liu)(liu)分(fen)布(bu)(bu)(bu)相(xiang)對(dui)于(yu)線(xian)圈(quan)呈對(dui)稱分(fen)布(bu)(bu)(bu),方(fang)(fang)向(xiang)(xiang)(xiang)相(xiang)反,強度基本相(xiang)同,仿(fang)真結(jie)果與圖5-2所示的渦(wo)流(liu)(liu)分(fen)布(bu)(bu)(bu)理論(lun)分(fen)析(xi)結(jie)論(lun)相(xiang)同,其中(zhong)(zhong)(zhong)感(gan)生(sheng)渦(wo)流(liu)(liu)最大值為(wei)1.4×105A/㎡。
為了研究感生渦流(liu)(liu)(liu)與不(bu)銹鋼管(guan)運行(xing)(xing)(xing)速(su)度的(de)關系,分別取(qu)速(su)度0.1m/s、1m/s、2m/s、5m/s、8m/s、10m/s、20m/s、30m/s、40m/s和50m/s進行(xing)(xing)(xing)仿真。當(dang)鋼管(guan)中(zhong)(zhong)部與磁(ci)化線(xian)圈(quan)重合時提取(qu)渦流(liu)(liu)(liu)密度最大值和最小值,繪制(zhi)成(cheng)如圖(tu)5-5所示的(de)渦流(liu)(liu)(liu)密度與運行(xing)(xing)(xing)速(su)度關系曲線(xian)。從圖(tu)中(zhong)(zhong)可以看(kan)出,感生渦流(liu)(liu)(liu)與不(bu)銹鋼管(guan)運行(xing)(xing)(xing)速(su)度成(cheng)近似(si)正比關系。鋼管(guan)低速(su)運動(dong)時感生渦流(liu)(liu)(liu)很小,可忽略不(bu)計;當(dang)運行(xing)(xing)(xing)速(su)度增至50m/s時,渦流(liu)(liu)(liu)密度為2。此(ci)時,感生渦流(liu)(liu)(liu)已接近傳導電流(liu)(liu)(liu)密度。因(yin)此(ci),高速(su)運動(dong)時,感生渦流(liu)(liu)(liu)對鋼管(guan)漏磁(ci)檢測(ce)的(de)影(ying)響不(bu)可忽視。
二(er)、磁化線(xian)圈中產生的感生電流
當不銹鋼管端部進入(ru)和(he)離開磁(ci)化(hua)線圈(quan)時(shi),線圈(quan)中的磁(ci)通(tong)量(liang)發(fa)(fa)生(sheng)(sheng)變化(hua)而產(chan)(chan)生(sheng)(sheng)感(gan)(gan)生(sheng)(sheng)電(dian)流(liu)。設磁(ci)化(hua)電(dian)源(yuan)提供的電(dian)壓為Uo,磁(ci)化(hua)線圈(quan)電(dian)阻為R,則磁(ci)化(hua)電(dian)源(yuan)在線圈(quan)中產(chan)(chan)生(sheng)(sheng)的初始(shi)傳導電(dian)流(liu)為Io=Uo/RR。磁(ci)化(hua)線圈(quan)通(tong)過(guo)的磁(ci)通(tong)總(zong)量(liang)為Φ,當磁(ci)化(hua)線圈(quan)中磁(ci)通(tong)總(zong)量(liang)發(fa)(fa)生(sheng)(sheng)變化(hua)時(shi),根(gen)據楞次定律,線圈(quan)中將(jiang)產(chan)(chan)生(sheng)(sheng)感(gan)(gan)生(sheng)(sheng)電(dian)動勢,對應的感(gan)(gan)生(sheng)(sheng)電(dian)流(liu)磁(ci)化(hua)線圈(quan)中通(tong)過(guo)的電(dian)流(liu)I為初始(shi)傳導電(dian)流(liu)和(he)感(gan)(gan)生(sheng)(sheng)電(dian)流(liu)之和(he),即
當(dang)線(xian)(xian)圈(quan)(quan)中沒有(you)鋼管時,磁(ci)(ci)化(hua)線(xian)(xian)圈(quan)(quan)磁(ci)(ci)通(tong)總量為線(xian)(xian)圈(quan)(quan)自(zi)身產生(sheng)(sheng)的靜態磁(ci)(ci)通(tong)量,其與磁(ci)(ci)化(hua)電流強(qiang)度成正比(bi),當(dang)磁(ci)(ci)化(hua)電流不變時,線(xian)(xian)圈(quan)(quan)磁(ci)(ci)通(tong)總量也不發生(sheng)(sheng)變化(hua)。此時線(xian)(xian)圈(quan)(quan)中通(tong)過的電流為磁(ci)(ci)化(hua)電源產生(sheng)(sheng)的初始磁(ci)(ci)化(hua)傳(chuan)導電流
當管(guan)頭進入磁(ci)化線(xian)(xian)圈(quan)(quan)時(shi),具有高(gao)磁(ci)導(dao)率的(de)鋼管(guan)磁(ci)介質進入磁(ci)化線(xian)(xian)圈(quan)(quan)內(nei)部(bu)(bu),使(shi)得(de)線(xian)(xian)圈(quan)(quan)內(nei)部(bu)(bu)的(de)磁(ci)通總量增大。根據式(5-4),磁(ci)化線(xian)(xian)圈(quan)(quan)中(zhong)會產生(sheng)與初始磁(ci)化傳(chuan)導(dao)電流(liu)(liu)方向相反的(de)感生(sheng)電流(liu)(liu),此時(shi)線(xian)(xian)圈(quan)(quan)中(zhong)通過(guo)的(de)電流(liu)(liu)為(wei),如圖(tu)5-6a所示。
當管(guan)體通(tong)過磁(ci)化線圈(quan)時(shi)(shi),線圈(quan)內(nei)部磁(ci)介質總(zong)量及分布(bu)特性基(ji)本不(bu)變,從(cong)而線圈(quan)內(nei)部的(de)磁(ci)通(tong)總(zong)量也保持(chi)恒定。根據式(5-4),磁(ci)化線圈(quan)基(ji)本無(wu)感生電流(liu)產生,此時(shi)(shi),磁(ci)化線圈(quan)中通(tong)過的(de)電流(liu)與無(wu)鋼管(guan)時(shi)(shi)相同,為磁(ci)化電源產生的(de)初(chu)始磁(ci)化傳導(dao)電流(liu)1=,如(ru)圖5-6b所(suo)示。
當管(guan)尾離開磁(ci)(ci)化線(xian)(xian)圈(quan)(quan)(quan)(quan)時,由于線(xian)(xian)圈(quan)(quan)(quan)(quan)內部的(de)(de)高磁(ci)(ci)導率磁(ci)(ci)介質不斷減(jian)少(shao),導致(zhi)磁(ci)(ci)化線(xian)(xian)圈(quan)(quan)(quan)(quan)的(de)(de)磁(ci)(ci)通總(zong)量也不斷減(jian)少(shao)。根據式(5-4),磁(ci)(ci)化線(xian)(xian)圈(quan)(quan)(quan)(quan)中(zhong)會產生(sheng)與初始(shi)磁(ci)(ci)化傳導電流(liu)方向相同(tong)的(de)(de)感生(sheng)電流(liu),此時線(xian)(xian)圈(quan)(quan)(quan)(quan)中(zhong)通過的(de)(de)電流(liu)為(wei),如圖(tu)5-6c所示。
不銹鋼管(guan)內的磁(ci)場包(bao)(bao)括:磁(ci)化線圈通過電(dian)流I產(chan)生(sheng)(sheng)的磁(ci)場和鋼管(guan)中感生(sheng)(sheng)渦流J形成的磁(ci)場。磁(ci)化線圈的磁(ci)通總量(liang)包(bao)(bao)含了(le)由感生(sheng)(sheng)渦流J產(chan)生(sheng)(sheng)的部分磁(ci)通量(liang),因此鋼管(guan)中的渦流效應會對磁(ci)化線圈中的感生(sheng)(sheng)電(dian)流產(chan)生(sheng)(sheng)一定(ding)影響。
采用如(ru)(ru)圖5-3所示(shi)(shi)模型,進一步研究磁(ci)化(hua)(hua)(hua)線(xian)圈中產(chan)(chan)生(sheng)的(de)感(gan)(gan)(gan)生(sheng)電(dian)(dian)流(liu)(liu)(liu)變化(hua)(hua)(hua)規律。其(qi)中,線(xian)圈匝數(shu)為600匝,磁(ci)化(hua)(hua)(hua)電(dian)(dian)流(liu)(liu)(liu)為5A。當鋼(gang)管(guan)管(guan)頭(tou)、管(guan)體和(he)管(guan)尾(wei)分(fen)別(bie)與磁(ci)化(hua)(hua)(hua)線(xian)圈耦合時(shi)提取(qu)磁(ci)化(hua)(hua)(hua)線(xian)圈內部產(chan)(chan)生(sheng)的(de)感(gan)(gan)(gan)生(sheng)電(dian)(dian)流(liu)(liu)(liu),如(ru)(ru)圖5-7所示(shi)(shi)。仿真分(fen)兩種:一是考慮鋼(gang)管(guan)渦(wo)流(liu)(liu)(liu)效應時(shi)分(fen)析線(xian)圈感(gan)(gan)(gan)生(sheng)電(dian)(dian)流(liu)(liu)(liu)與運(yun)動速(su)(su)度(du)的(de)關(guan)系,二是忽略鋼(gang)管(guan)渦(wo)流(liu)(liu)(liu)效應而單獨分(fen)析線(xian)圈感(gan)(gan)(gan)生(sheng)電(dian)(dian)流(liu)(liu)(liu)與鋼(gang)管(guan)運(yun)動速(su)(su)度(du)關(guan)系。分(fen)別(bie)取(qu)速(su)(su)度(du)0.1m/s、1m/s、2m/s、5m/s、8m/s、10m/s、20m/s、30m/s、40m/和(he)50m/s進行仿真,獲(huo)得如(ru)(ru)圖5-8所示(shi)(shi)的(de)磁(ci)化(hua)(hua)(hua)線(xian)圈感(gan)(gan)(gan)生(sheng)電(dian)(dian)流(liu)(liu)(liu)與運(yun)動速(su)(su)度(du)關(guan)系曲線(xian)。其(qi)中I1csI2cs和(he)I3cs分(fen)別(bie)為考慮鋼(gang)管(guan)渦(wo)流(liu)(liu)(liu)效應時(shi)在管(guan)頭(tou)、管(guan)體和(he)管(guan)尾(wei)處線(xian)圈中產(chan)(chan)生(sheng)的(de)感(gan)(gan)(gan)生(sheng)電(dian)(dian)流(liu)(liu)(liu),11cI2c和(he)I3c分(fen)別(bie)為忽略不銹(xiu)鋼(gang)管(guan)渦(wo)流(liu)(liu)(liu)效應時(shi)磁(ci)化(hua)(hua)(hua)線(xian)圈中產(chan)(chan)生(sheng)的(de)感(gan)(gan)(gan)生(sheng)電(dian)(dian)流(liu)(liu)(liu)。
圖5-8所示的(de)仿(fang)真結(jie)果與(yu)(yu)圖5-6所示的(de)理論(lun)分(fen)析結(jie)論(lun)相同(tong):當(dang)管頭進入磁(ci)(ci)化(hua)(hua)線(xian)(xian)(xian)(xian)(xian)圈(quan)時(shi),線(xian)(xian)(xian)(xian)(xian)圈(quan)中產(chan)(chan)(chan)生(sheng)(sheng)(sheng)(sheng)的(de)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)(liu)幅值為負,即與(yu)(yu)磁(ci)(ci)化(hua)(hua)電(dian)流(liu)(liu)方向(xiang)相反;當(dang)管體(ti)通過磁(ci)(ci)化(hua)(hua)線(xian)(xian)(xian)(xian)(xian)圈(quan)時(shi),線(xian)(xian)(xian)(xian)(xian)圈(quan)中基(ji)本無(wu)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)(liu)產(chan)(chan)(chan)生(sheng)(sheng)(sheng)(sheng);隨著管尾(wei)離(li)開(kai)磁(ci)(ci)化(hua)(hua)線(xian)(xian)(xian)(xian)(xian)圈(quan),此時(shi)線(xian)(xian)(xian)(xian)(xian)圈(quan)中產(chan)(chan)(chan)生(sheng)(sheng)(sheng)(sheng)與(yu)(yu)磁(ci)(ci)化(hua)(hua)電(dian)流(liu)(liu)方向(xiang)相同(tong)的(de)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)(liu)。根據(ju)楞次定律,線(xian)(xian)(xian)(xian)(xian)圈(quan)中產(chan)(chan)(chan)生(sheng)(sheng)(sheng)(sheng)的(de)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)(liu)會(hui)阻礙(ai)線(xian)(xian)(xian)(xian)(xian)圈(quan)磁(ci)(ci)通量(liang)(liang)(liang)的(de)變化(hua)(hua):當(dang)管頭進入磁(ci)(ci)化(hua)(hua)線(xian)(xian)(xian)(xian)(xian)圈(quan)時(shi),線(xian)(xian)(xian)(xian)(xian)圈(quan)中會(hui)產(chan)(chan)(chan)生(sheng)(sheng)(sheng)(sheng)反向(xiang)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)(liu)來阻礙(ai)磁(ci)(ci)通量(liang)(liang)(liang)的(de)增大;當(dang)管體(ti)與(yu)(yu)磁(ci)(ci)化(hua)(hua)線(xian)(xian)(xian)(xian)(xian)圈(quan)耦合時(shi),由于線(xian)(xian)(xian)(xian)(xian)圈(quan)磁(ci)(ci)通量(liang)(liang)(liang)基(ji)本不(bu)變而無(wu)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)(liu)產(chan)(chan)(chan)生(sheng)(sheng)(sheng)(sheng);當(dang)管尾(wei)離(li)開(kai)磁(ci)(ci)化(hua)(hua)線(xian)(xian)(xian)(xian)(xian)圈(quan)時(shi),線(xian)(xian)(xian)(xian)(xian)圈(quan)中會(hui)產(chan)(chan)(chan)生(sheng)(sheng)(sheng)(sheng)同(tong)向(xiang)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)(liu)來阻礙(ai)磁(ci)(ci)通量(liang)(liang)(liang)的(de)減小(xiao)。
另(ling)外,從圖5-8中(zhong)可以(yi)看出(chu),在運行速(su)度較低時,磁(ci)化(hua)(hua)線圈(quan)中(zhong)感生(sheng)(sheng)電流隨著速(su)度的(de)增加而快(kuai)速(su)上升;當速(su)度達到一定幅值(zhi)時,磁(ci)化(hua)(hua)線圈(quan)中(zhong)的(de)感生(sheng)(sheng)電流基本(ben)保持不(bu)變(bian)(bian)。因為感生(sheng)(sheng)電流只能減(jian)緩磁(ci)化(hua)(hua)線圈(quan)磁(ci)通量的(de)變(bian)(bian)化(hua)(hua)速(su)度,而不(bu)能改(gai)變(bian)(bian)磁(ci)通量的(de)變(bian)(bian)化(hua)(hua)趨勢(shi)。
從圖5-8中還可以看出,鋼管中的渦流會(hui)削弱磁化線圈中產生的感生電流,根據楞次定律(lv),鋼(gang)管中的(de)渦流(liu)同(tong)樣(yang)會阻礙鋼(gang)管中磁(ci)(ci)(ci)通(tong)(tong)量(liang)的(de)變(bian)(bian)(bian)(bian)化(hua)。當(dang)不銹鋼(gang)管進入和離開(kai)磁(ci)(ci)(ci)化(hua)線(xian)(xian)圈(quan)(quan)時,鋼(gang)管中的(de)磁(ci)(ci)(ci)通(tong)(tong)量(liang)變(bian)(bian)(bian)(bian)化(hua)規(gui)律(lv)同(tong)樣(yang)先增(zeng)大后減小。由于磁(ci)(ci)(ci)化(hua)線(xian)(xian)圈(quan)(quan)磁(ci)(ci)(ci)通(tong)(tong)總(zong)量(liang)包含了不銹鋼(gang)管磁(ci)(ci)(ci)通(tong)(tong)量(liang),所以,感生(sheng)渦流(liu)在阻礙鋼(gang)管磁(ci)(ci)(ci)通(tong)(tong)量(liang)變(bian)(bian)(bian)(bian)化(hua)的(de)同(tong)時也阻礙了線(xian)(xian)圈(quan)(quan)磁(ci)(ci)(ci)通(tong)(tong)量(liang)的(de)變(bian)(bian)(bian)(bian)化(hua)速率,最(zui)終削弱了線(xian)(xian)圈(quan)(quan)感生(sheng)電流(liu)的(de)強度。