不銹鋼(gang)管穿(chuan)過磁化線圈(quan)時(shi)會發(fa)生(sheng)如(ru)下(xia)兩種電(dian)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(gang)管切割磁力線而在其內部形成感生渦流。
2. 不銹鋼管(guan)磁介質在管(guan)頭(tou)進入(ru)磁化線圈和(he)管(guan)尾離開磁化線圈時，由于磁化線圈的磁通總量發生急劇變化，線圈中會產(chan)生感生電流(liu)。
一、鋼管內產生(sheng)(sheng)的感生(sheng)(sheng)渦流
不銹鋼管橫向缺陷漏磁(ci)(ci)檢測方法采用穿過式線(xian)圈(quan)(quan)產生(sheng)軸向磁(ci)(ci)化(hua)場，并(bing)(bing)在磁(ci)(ci)化(hua)線(xian)圈(quan)(quan)內布置檢測傳感(gan)器。當鋼管沿著軸向移動時，處于磁(ci)(ci)化(hua)線(xian)圈(quan)(quan)內的(de)不銹鋼管段被磁(ci)(ci)化(hua)至近飽和狀態，如存在缺陷將在鋼管表面(mian)產生(sheng)泄漏磁(ci)(ci)場，然后被磁(ci)(ci)敏感(gan)元件拾取(qu)并(bing)(bing)依次轉換(huan)為模擬(ni)信(xin)(xin)號和數字信(xin)(xin)號，最終由計算(suan)機信(xin)(xin)號處理(li)系統實施報警和分(fen)類。
如圖5-1所示，以(yi)鋼(gang)管軸線(xian)為中(zhong)(zhong)心建(jian)立(li)圓柱坐(zuo)標系(xi)。沿(yan)著鋼(gang)管運動方向，以(yi)磁(ci)(ci)化線(xian)圈為中(zhong)(zhong)心將鋼(gang)管劃分(fen)為進入(ru)(ru)區(qu)(qu)(qu)和離開(kai)區(qu)(qu)(qu)，在(zai)磁(ci)(ci)化線(xian)圈中(zhong)(zhong)施加如圖所示的磁(ci)(ci)化電流，磁(ci)(ci)力線(xian)分(fen)布特征為：在(zai)進入(ru)(ru)區(qu)(qu)(qu)磁(ci)(ci)力線(xian)從空氣中(zhong)(zhong)進入(ru)(ru)鋼(gang)管，并在(zai)磁(ci)(ci)化線(xian)圈中(zhong)(zhong)部匯聚(ju)，然后在(zai)離開(kai)區(qu)(qu)(qu)折射入(ru)(ru)空氣中(zhong)(zhong)。
如圖(tu)5-1所示，將磁感應(ying)強度(du)矢量B(r,z)分解(jie)為軸向(xiang)分量和(he)徑向(xiang)分量，即 B(r,z)=B2(r,z)+B,(r,z)
從圖5-1中可(ke)以看出，軸向分(fen)量B2(r,z)在(zai)進(jin)入(ru)(ru)區(qu)(qu)和離(li)開(kai)區(qu)(qu)方(fang)(fang)向一(yi)致，沿(yan)著鋼管前進(jin)方(fang)(fang)向，其強度在(zai)進(jin)入(ru)(ru)區(qu)(qu)逐漸(jian)增大，并在(zai)磁化(hua)線圈中部達到極大值，之(zhi)后在(zai)離(li)開(kai)區(qu)(qu)逐漸(jian)減小。徑向分(fen)量B,(r,z)在(zai)進(jin)入(ru)(ru)區(qu)(qu)方(fang)(fang)向指(zhi)向鋼管內部，并在(zai)磁化(hua)線圈中部發生轉變，在(zai)離(li)開(kai)區(qu)(qu)方(fang)(fang)向指(zhi)向鋼管外部。
為(wei)(wei)了研究(jiu)與鋼管同軸(zhou)(zhou)圓(yuan)環(huan)(huan)l(ro ,zo)的渦流分(fen)布，設圓(yuan)環(huan)(huan)半徑為(wei)(wei)ro，軸(zhou)(zhou)向位(wei)置為(wei)(wei)200根(gen)據楞次定律，當圓(yuan)環(huan)(huan)移動時，軸(zhou)(zhou)向分(fen)量B,(r,z)的強度變(bian)化導致(zhi)圓(yuan)環(huan)(huan)磁通(tong)量也發生(sheng)改(gai)變(bian)，從(cong)而在圓(yuan)環(huan)(huan)中產生(sheng)感生(sheng)電動勢。因磁化場為(wei)(wei)軸(zhou)(zhou)對(dui)稱(cheng)，建立圓(yuan)環(huan)(huan)感應電動勢方程為(wei)(wei)
根據式（5-3），沿鋼(gang)(gang)管前進方(fang)(fang)向(xiang)，在進入區，軸(zhou)向(xiang)分(fen)(fen)量(liang)(liang)強(qiang)度逐(zhu)漸(jian)增強(qiang)，感生渦(wo)流(liu)(liu)方(fang)(fang)向(xiang)與(yu)原磁(ci)(ci)化(hua)電(dian)流(liu)(liu)方(fang)(fang)向(xiang)相反；在磁(ci)(ci)化(hua)線圈中(zhong)間位置，由于軸(zhou)向(xiang)分(fen)(fen)量(liang)(liang)變化(hua)率為零，故此部位無(wu)感生流(liu)(liu)產生；在離開區，軸(zhou)向(xiang)分(fen)(fen)量(liang)(liang)強(qiang)度由中(zhong)間最大值逐(zhu)漸(jian)減小，于是(shi)形成與(yu)原磁(ci)(ci)化(hua)電(dian)流(liu)(liu)方(fang)(fang)向(xiang)相同(tong)的(de)感生渦(wo)流(liu)(liu)，最終鋼(gang)(gang)管中(zhong)感生渦(wo)流(liu)(liu)分(fen)(fen)布(bu)如(ru)圖5-2a所(suo)示(shi)。如(ru)果改變磁(ci)(ci)化(hua)電(dian)流(liu)(liu)方(fang)(fang)向(xiang)，根據式（5-3），同(tong)樣可得出(chu)鋼(gang)(gang)管內感生渦(wo)流(liu)(liu)分(fen)(fen)布(bu)，如(ru)圖5-2b所(suo)示(shi)。
從(cong)圖5-2中(zhong)(zhong)可以看(kan)出，鋼(gang)(gang)管中(zhong)(zhong)感生(sheng)電(dian)流(liu)分布(bu)方向由(you)磁(ci)(ci)化(hua)(hua)(hua)(hua)電(dian)流(liu)方向和(he)鋼(gang)(gang)管運(yun)動方向共同(tong)決定。在(zai)進入區，鋼(gang)(gang)管中(zhong)(zhong)的感生(sheng)渦(wo)(wo)流(liu)J1與(yu)磁(ci)(ci)化(hua)(hua)(hua)(hua)電(dian)流(liu)方向相反(fan)；在(zai)磁(ci)(ci)化(hua)(hua)(hua)(hua)線圈中(zhong)(zhong)間位置(zhi)無感生(sheng)渦(wo)(wo)流(liu)產生(sheng)；在(zai)離開區，感生(sheng)渦(wo)(wo)流(liu)J2與(yu)磁(ci)(ci)化(hua)(hua)(hua)(hua)電(dian)流(liu)方向相同(tong)。從(cong)而，在(zai)感生(sheng)渦(wo)(wo)流(liu)產生(sheng)的磁(ci)(ci)場作用下，鋼(gang)(gang)管的磁(ci)(ci)化(hua)(hua)(hua)(hua)狀(zhuang)態將發生(sheng)變化(hua)(hua)(hua)(hua)。
建(jian)立如圖(tu)5-3所(suo)示的仿真模型(xing)。鋼(gang)管直徑為400mm、壁厚為15mm、長度(du)為3000mm，材質為25鋼(gang)（電(dian)導率為）。磁化線圈(quan)內徑為440mm、外徑為750mm、厚度(du)為160mm，磁化電(dian)流密度(du)iA／㎡，電(dian)流方向如圖(tu)5-3所(suo)示。
對不(bu)銹鋼管(guan)中(zhong)(zhong)的感生(sheng)(sheng)渦(wo)(wo)(wo)(wo)流(liu)(liu)(liu)(liu)(liu)分布(bu)進行仿真研究。磁化(hua)線圈(quan)固定不(bu)動(dong)(dong)，鋼管(guan)運(yun)行速度設(she)置為(wei)1m／s，不(bu)銹鋼管(guan)從左端(duan)進人(ren)并向(xiang)(xiang)右端(duan)移動(dong)(dong)，當鋼管(guan)中(zhong)(zhong)心(xin)與(yu)(yu)磁化(hua)線圈(quan)中(zhong)(zhong)心(xin)重(zhong)合時獲取感生(sheng)(sheng)渦(wo)(wo)(wo)(wo)流(liu)(liu)(liu)(liu)(liu)分布(bu)云圖(tu)，如圖(tu)5-4所(suo)示(shi)。從圖(tu)中(zhong)(zhong)可以(yi)看(kan)出(chu)，進入(ru)區(qu)(qu)(qu)的感生(sheng)(sheng)渦(wo)(wo)(wo)(wo)流(liu)(liu)(liu)(liu)(liu)方(fang)向(xiang)(xiang)與(yu)(yu)磁化(hua)電(dian)(dian)流(liu)(liu)(liu)(liu)(liu)方(fang)向(xiang)(xiang)相(xiang)(xiang)反，離開(kai)區(qu)(qu)(qu)的感生(sheng)(sheng)渦(wo)(wo)(wo)(wo)流(liu)(liu)(liu)(liu)(liu)方(fang)向(xiang)(xiang)與(yu)(yu)磁化(hua)電(dian)(dian)流(liu)(liu)(liu)(liu)(liu)方(fang)向(xiang)(xiang)相(xiang)(xiang)同(tong)，在線圈(quan)中(zhong)(zhong)部感生(sheng)(sheng)渦(wo)(wo)(wo)(wo)流(liu)(liu)(liu)(liu)(liu)幾乎為(wei)零。進入(ru)區(qu)(qu)(qu)和離開(kai)區(qu)(qu)(qu)的渦(wo)(wo)(wo)(wo)流(liu)(liu)(liu)(liu)(liu)分布(bu)相(xiang)(xiang)對于線圈(quan)呈(cheng)對稱(cheng)分布(bu)，方(fang)向(xiang)(xiang)相(xiang)(xiang)反，強度基本(ben)相(xiang)(xiang)同(tong)，仿真結果與(yu)(yu)圖(tu)5-2所(suo)示(shi)的渦(wo)(wo)(wo)(wo)流(liu)(liu)(liu)(liu)(liu)分布(bu)理論(lun)分析結論(lun)相(xiang)(xiang)同(tong)，其中(zhong)(zhong)感生(sheng)(sheng)渦(wo)(wo)(wo)(wo)流(liu)(liu)(liu)(liu)(liu)最大值為(wei)1.4×105A/㎡。
為(wei)了研(yan)究(jiu)感生渦(wo)(wo)流(liu)(liu)與不(bu)銹鋼管運(yun)(yun)行(xing)(xing)速(su)(su)度(du)的關系(xi)，分別取速(su)(su)度(du)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)仿真。當鋼管中部與磁化線圈(quan)重合時(shi)提取渦(wo)(wo)流(liu)(liu)密(mi)(mi)度(du)最大(da)值(zhi)和最小值(zhi)，繪制(zhi)成如圖(tu)5-5所示的渦(wo)(wo)流(liu)(liu)密(mi)(mi)度(du)與運(yun)(yun)行(xing)(xing)速(su)(su)度(du)關系(xi)曲線。從圖(tu)中可(ke)以看出，感生渦(wo)(wo)流(liu)(liu)與不(bu)銹鋼管運(yun)(yun)行(xing)(xing)速(su)(su)度(du)成近(jin)似正(zheng)比關系(xi)。鋼管低(di)速(su)(su)運(yun)(yun)動時(shi)感生渦(wo)(wo)流(liu)(liu)很小，可(ke)忽略(lve)不(bu)計(ji)；當運(yun)(yun)行(xing)(xing)速(su)(su)度(du)增(zeng)至50m／s時(shi)，渦(wo)(wo)流(liu)(liu)密(mi)(mi)度(du)為(wei)2。此時(shi)，感生渦(wo)(wo)流(liu)(liu)已接近(jin)傳導電(dian)流(liu)(liu)密(mi)(mi)度(du)。因此，高速(su)(su)運(yun)(yun)動時(shi)，感生渦(wo)(wo)流(liu)(liu)對鋼管漏(lou)磁檢測的影響不(bu)可(ke)忽視。
二、磁化(hua)線圈中產生的感(gan)生電流(liu)
當不銹鋼管(guan)端(duan)部進入和離開磁(ci)(ci)(ci)化(hua)(hua)(hua)線(xian)(xian)(xian)(xian)圈(quan)時(shi)，線(xian)(xian)(xian)(xian)圈(quan)中(zhong)(zhong)的磁(ci)(ci)(ci)通(tong)(tong)量(liang)發生(sheng)(sheng)(sheng)(sheng)變化(hua)(hua)(hua)而(er)產生(sheng)(sheng)(sheng)(sheng)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)(dian)流(liu)(liu)(liu)(liu)。設磁(ci)(ci)(ci)化(hua)(hua)(hua)電(dian)(dian)(dian)源提供的電(dian)(dian)(dian)壓(ya)為(wei)(wei)(wei)Uo，磁(ci)(ci)(ci)化(hua)(hua)(hua)線(xian)(xian)(xian)(xian)圈(quan)電(dian)(dian)(dian)阻為(wei)(wei)(wei)R，則(ze)磁(ci)(ci)(ci)化(hua)(hua)(hua)電(dian)(dian)(dian)源在線(xian)(xian)(xian)(xian)圈(quan)中(zhong)(zhong)產生(sheng)(sheng)(sheng)(sheng)的初始(shi)傳導(dao)電(dian)(dian)(dian)流(liu)(liu)(liu)(liu)為(wei)(wei)(wei)Io=Uo/RR。磁(ci)(ci)(ci)化(hua)(hua)(hua)線(xian)(xian)(xian)(xian)圈(quan)通(tong)(tong)過的磁(ci)(ci)(ci)通(tong)(tong)總量(liang)為(wei)(wei)(wei)Φ，當磁(ci)(ci)(ci)化(hua)(hua)(hua)線(xian)(xian)(xian)(xian)圈(quan)中(zhong)(zhong)磁(ci)(ci)(ci)通(tong)(tong)總量(liang)發生(sheng)(sheng)(sheng)(sheng)變化(hua)(hua)(hua)時(shi)，根據楞次(ci)定律，線(xian)(xian)(xian)(xian)圈(quan)中(zhong)(zhong)將產生(sheng)(sheng)(sheng)(sheng)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)(dian)動勢，對應的感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)(dian)流(liu)(liu)(liu)(liu)磁(ci)(ci)(ci)化(hua)(hua)(hua)線(xian)(xian)(xian)(xian)圈(quan)中(zhong)(zhong)通(tong)(tong)過的電(dian)(dian)(dian)流(liu)(liu)(liu)(liu)I為(wei)(wei)(wei)初始(shi)傳導(dao)電(dian)(dian)(dian)流(liu)(liu)(liu)(liu)和感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)(dian)流(liu)(liu)(liu)(liu)之和，即
當(dang)線(xian)圈(quan)(quan)中沒有鋼管時，磁(ci)(ci)(ci)(ci)化(hua)線(xian)圈(quan)(quan)磁(ci)(ci)(ci)(ci)通(tong)總量(liang)為線(xian)圈(quan)(quan)自身產(chan)生的靜態磁(ci)(ci)(ci)(ci)通(tong)量(liang)，其與磁(ci)(ci)(ci)(ci)化(hua)電流(liu)強度成正比，當(dang)磁(ci)(ci)(ci)(ci)化(hua)電流(liu)不變時，線(xian)圈(quan)(quan)磁(ci)(ci)(ci)(ci)通(tong)總量(liang)也不發生變化(hua)。此時線(xian)圈(quan)(quan)中通(tong)過的電流(liu)為磁(ci)(ci)(ci)(ci)化(hua)電源產(chan)生的初始磁(ci)(ci)(ci)(ci)化(hua)傳導(dao)電流(liu)
當管(guan)(guan)頭進(jin)入(ru)磁(ci)(ci)化(hua)線(xian)圈時(shi)，具有高磁(ci)(ci)導率的鋼(gang)管(guan)(guan)磁(ci)(ci)介質(zhi)進(jin)入(ru)磁(ci)(ci)化(hua)線(xian)圈內部，使得線(xian)圈內部的磁(ci)(ci)通(tong)總量增大。根據式（5-4），磁(ci)(ci)化(hua)線(xian)圈中會產生與初始磁(ci)(ci)化(hua)傳導電流(liu)方向相反的感生電流(liu)，此(ci)時(shi)線(xian)圈中通(tong)過的電流(liu)為，如圖(tu)5-6a所示。
當管(guan)體通(tong)過磁(ci)(ci)化線(xian)圈時(shi)，線(xian)圈內(nei)部磁(ci)(ci)介質總(zong)量及分布特(te)性基本不變，從而線(xian)圈內(nei)部的磁(ci)(ci)通(tong)總(zong)量也保持(chi)恒定。根(gen)據式（5-4），磁(ci)(ci)化線(xian)圈基本無(wu)(wu)感生電流(liu)(liu)產(chan)生，此時(shi)，磁(ci)(ci)化線(xian)圈中通(tong)過的電流(liu)(liu)與無(wu)(wu)鋼管(guan)時(shi)相同，為磁(ci)(ci)化電源產(chan)生的初始磁(ci)(ci)化傳導電流(liu)(liu)1＝，如(ru)圖(tu)5-6b所示。
當管(guan)尾離開(kai)磁(ci)化線(xian)(xian)(xian)圈(quan)時(shi)，由(you)于線(xian)(xian)(xian)圈(quan)內(nei)部的高磁(ci)導(dao)率磁(ci)介(jie)質(zhi)不斷(duan)減少，導(dao)致(zhi)磁(ci)化線(xian)(xian)(xian)圈(quan)的磁(ci)通總量也(ye)不斷(duan)減少。根據式（5-4），磁(ci)化線(xian)(xian)(xian)圈(quan)中會產生與初始磁(ci)化傳導(dao)電流(liu)方向相同的感生電流(liu)，此時(shi)線(xian)(xian)(xian)圈(quan)中通過的電流(liu)為，如圖5-6c所(suo)示。
不銹鋼管內的(de)(de)磁(ci)(ci)(ci)場(chang)包括：磁(ci)(ci)(ci)化(hua)線(xian)圈(quan)通過電流(liu)I產(chan)生(sheng)的(de)(de)磁(ci)(ci)(ci)場(chang)和鋼管中(zhong)(zhong)感生(sheng)渦流(liu)J形成的(de)(de)磁(ci)(ci)(ci)場(chang)。磁(ci)(ci)(ci)化(hua)線(xian)圈(quan)的(de)(de)磁(ci)(ci)(ci)通總量包含了由(you)感生(sheng)渦流(liu)J產(chan)生(sheng)的(de)(de)部分磁(ci)(ci)(ci)通量，因此鋼管中(zhong)(zhong)的(de)(de)渦流(liu)效(xiao)應會對磁(ci)(ci)(ci)化(hua)線(xian)圈(quan)中(zhong)(zhong)的(de)(de)感生(sheng)電流(liu)產(chan)生(sheng)一定影響。
采用如圖(tu)5-3所示模型，進一步研究(jiu)磁(ci)(ci)化(hua)線(xian)(xian)(xian)圈(quan)中(zhong)(zhong)產生(sheng)(sheng)(sheng)的感(gan)(gan)生(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)變化(hua)規律。其中(zhong)(zhong)，線(xian)(xian)(xian)圈(quan)匝數為600匝，磁(ci)(ci)化(hua)電(dian)(dian)流(liu)(liu)為5A。當鋼管(guan)(guan)管(guan)(guan)頭(tou)、管(guan)(guan)體和(he)管(guan)(guan)尾分(fen)別(bie)與(yu)磁(ci)(ci)化(hua)線(xian)(xian)(xian)圈(quan)耦合時(shi)提取磁(ci)(ci)化(hua)線(xian)(xian)(xian)圈(quan)內部產生(sheng)(sheng)(sheng)的感(gan)(gan)生(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)，如圖(tu)5-7所示。仿真(zhen)分(fen)兩種：一是考(kao)慮鋼管(guan)(guan)渦(wo)(wo)流(liu)(liu)效(xiao)應時(shi)分(fen)析線(xian)(xian)(xian)圈(quan)感(gan)(gan)生(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)與(yu)運(yun)動(dong)(dong)速度(du)的關系(xi)，二是忽略(lve)鋼管(guan)(guan)渦(wo)(wo)流(liu)(liu)效(xiao)應而單(dan)獨分(fen)析線(xian)(xian)(xian)圈(quan)感(gan)(gan)生(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)與(yu)鋼管(guan)(guan)運(yun)動(dong)(dong)速度(du)關系(xi)。分(fen)別(bie)取速度(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(zhen)，獲得如圖(tu)5-8所示的磁(ci)(ci)化(hua)線(xian)(xian)(xian)圈(quan)感(gan)(gan)生(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)與(yu)運(yun)動(dong)(dong)速度(du)關系(xi)曲線(xian)(xian)(xian)。其中(zhong)(zhong)I1csI2cs和(he)I3cs分(fen)別(bie)為考(kao)慮鋼管(guan)(guan)渦(wo)(wo)流(liu)(liu)效(xiao)應時(shi)在管(guan)(guan)頭(tou)、管(guan)(guan)體和(he)管(guan)(guan)尾處線(xian)(xian)(xian)圈(quan)中(zhong)(zhong)產生(sheng)(sheng)(sheng)的感(gan)(gan)生(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)，11cI2c和(he)I3c分(fen)別(bie)為忽略(lve)不銹鋼管(guan)(guan)渦(wo)(wo)流(liu)(liu)效(xiao)應時(shi)磁(ci)(ci)化(hua)線(xian)(xian)(xian)圈(quan)中(zhong)(zhong)產生(sheng)(sheng)(sheng)的感(gan)(gan)生(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)。
圖5-8所示的(de)(de)(de)仿真結(jie)果(guo)與(yu)圖5-6所示的(de)(de)(de)理論分析結(jie)論相(xiang)同：當(dang)管(guan)(guan)(guan)頭(tou)進入磁化(hua)(hua)線(xian)(xian)圈(quan)時(shi)(shi)，線(xian)(xian)圈(quan)中(zhong)(zhong)產生(sheng)(sheng)(sheng)(sheng)的(de)(de)(de)感(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)幅值為負(fu)，即(ji)與(yu)磁化(hua)(hua)電(dian)流(liu)方(fang)向相(xiang)反(fan)(fan)；當(dang)管(guan)(guan)(guan)體(ti)通(tong)(tong)過磁化(hua)(hua)線(xian)(xian)圈(quan)時(shi)(shi)，線(xian)(xian)圈(quan)中(zhong)(zhong)基(ji)本無感(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)產生(sheng)(sheng)(sheng)(sheng)；隨著管(guan)(guan)(guan)尾(wei)(wei)離開(kai)磁化(hua)(hua)線(xian)(xian)圈(quan)，此時(shi)(shi)線(xian)(xian)圈(quan)中(zhong)(zhong)產生(sheng)(sheng)(sheng)(sheng)與(yu)磁化(hua)(hua)電(dian)流(liu)方(fang)向相(xiang)同的(de)(de)(de)感(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)。根(gen)據楞次定律，線(xian)(xian)圈(quan)中(zhong)(zhong)產生(sheng)(sheng)(sheng)(sheng)的(de)(de)(de)感(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)會(hui)阻礙線(xian)(xian)圈(quan)磁通(tong)(tong)量的(de)(de)(de)變化(hua)(hua)：當(dang)管(guan)(guan)(guan)頭(tou)進入磁化(hua)(hua)線(xian)(xian)圈(quan)時(shi)(shi)，線(xian)(xian)圈(quan)中(zhong)(zhong)會(hui)產生(sheng)(sheng)(sheng)(sheng)反(fan)(fan)向感(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)來阻礙磁通(tong)(tong)量的(de)(de)(de)增大(da)；當(dang)管(guan)(guan)(guan)體(ti)與(yu)磁化(hua)(hua)線(xian)(xian)圈(quan)耦合時(shi)(shi)，由于(yu)線(xian)(xian)圈(quan)磁通(tong)(tong)量基(ji)本不(bu)變而(er)無感(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)產生(sheng)(sheng)(sheng)(sheng)；當(dang)管(guan)(guan)(guan)尾(wei)(wei)離開(kai)磁化(hua)(hua)線(xian)(xian)圈(quan)時(shi)(shi)，線(xian)(xian)圈(quan)中(zhong)(zhong)會(hui)產生(sheng)(sheng)(sheng)(sheng)同向感(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)來阻礙磁通(tong)(tong)量的(de)(de)(de)減小。
另外(wai)，從圖(tu)5-8中可以看出，在運行速(su)度較低(di)時，磁化線(xian)(xian)圈中感生(sheng)電流隨著速(su)度的(de)(de)增加而(er)快速(su)上升；當速(su)度達到一定幅值時，磁化線(xian)(xian)圈中的(de)(de)感生(sheng)電流基本保持(chi)不變(bian)(bian)。因為感生(sheng)電流只(zhi)能(neng)減緩磁化線(xian)(xian)圈磁通量的(de)(de)變(bian)(bian)化速(su)度，而(er)不能(neng)改(gai)變(bian)(bian)磁通量的(de)(de)變(bian)(bian)化趨勢。
從(cong)圖5-8中(zhong)還(huan)可(ke)以(yi)看出，鋼(gang)管(guan)中(zhong)的(de)渦流會削弱磁(ci)化(hua)線(xian)圈中(zhong)產生的(de)感生電流，根據楞次定律(lv)，鋼(gang)(gang)管(guan)(guan)中(zhong)的(de)渦流(liu)同(tong)樣會阻(zu)(zu)礙(ai)鋼(gang)(gang)管(guan)(guan)中(zhong)磁(ci)(ci)(ci)(ci)通(tong)(tong)(tong)量的(de)變(bian)化(hua)(hua)。當不銹(xiu)鋼(gang)(gang)管(guan)(guan)進入和離開磁(ci)(ci)(ci)(ci)化(hua)(hua)線(xian)圈(quan)時，鋼(gang)(gang)管(guan)(guan)中(zhong)的(de)磁(ci)(ci)(ci)(ci)通(tong)(tong)(tong)量變(bian)化(hua)(hua)規律(lv)同(tong)樣先(xian)增(zeng)大(da)后減小。由于磁(ci)(ci)(ci)(ci)化(hua)(hua)線(xian)圈(quan)磁(ci)(ci)(ci)(ci)通(tong)(tong)(tong)總量包(bao)含了(le)(le)不銹(xiu)鋼(gang)(gang)管(guan)(guan)磁(ci)(ci)(ci)(ci)通(tong)(tong)(tong)量，所以，感生渦流(liu)在(zai)阻(zu)(zu)礙(ai)鋼(gang)(gang)管(guan)(guan)磁(ci)(ci)(ci)(ci)通(tong)(tong)(tong)量變(bian)化(hua)(hua)的(de)同(tong)時也(ye)阻(zu)(zu)礙(ai)了(le)(le)線(xian)圈(quan)磁(ci)(ci)(ci)(ci)通(tong)(tong)(tong)量的(de)變(bian)化(hua)(hua)速率(lv)，最(zui)終(zhong)削弱了(le)(le)線(xian)圈(quan)感生電流(liu)的(de)強(qiang)度。
