本文選題：增容改造　切入點：空間電荷　出處：《東北電力大學》2017年碩士論文

【摘要】：將交流電纜線路改為直流運行可以充分利用原有輸電走廊,最大限度地發(fā)揮原有輸電線路的輸送能力。而實際運行的交流XLPE電纜絕緣材料在設計時并沒有考慮空間電荷積累問題。直流電壓下,交流XLPE電纜中空間電荷積累嚴重,會造成局部的電場強度成倍增加,影響電纜的絕緣強度以及加速電纜絕緣的老化。為研究交流XLPE電纜在直流電壓下的空間電荷積累和電場分布特性,本文應用COMSOL多物理場仿真軟件,模擬了溫度梯度下電纜絕緣中的溫度場,并基于絕緣樣品電導率模型,研究了溫度梯度、場強、加壓時間及極性反轉(zhuǎn)等因素對66kV交流電纜的電場以及空間電荷行為的影響。直流穩(wěn)態(tài)電壓下,電纜絕緣中電場分布和空間電荷積累明顯受溫度梯度的影響。電場分布由絕緣材料的電導率所決定,在較高溫度梯度時可能出現(xiàn)電場分布翻轉(zhuǎn)現(xiàn)象;溫度梯度使得高溫側(cè)的空間電荷容易發(fā)生脫陷,加速了載流子向低溫側(cè)的遷移,導致了低溫側(cè)正負極性空間電荷的嚴重積累。當溫差為45℃、加壓8小時時,低溫側(cè)空間電荷密度達-0.15C/m~3,絕緣外側(cè)場強最大值為6.71 kV/mm,該數(shù)值低于66kV交流電纜絕緣的場強設計值。極性反轉(zhuǎn)電壓下,暫態(tài)電場分布取決于介電常數(shù)和電導率的共同作用,且以介電常數(shù)為主,暫態(tài)最大場強出現(xiàn)在纜芯附近,均大于其穩(wěn)態(tài)時的最大場強。暫態(tài)最大場強值與溫度梯度、電壓的幅值以及電壓極性反轉(zhuǎn)時間密切相關(guān),溫度梯度和電壓幅值越大,暫態(tài)最大場強越大;反轉(zhuǎn)時間越短,最大暫態(tài)場強越高,且暫態(tài)最大場強的位置越靠近纜芯導體。絕緣中載流子的定向遷移以及空間電荷的入陷、脫陷、中和、消散等行為使得極性反轉(zhuǎn)過程中該處正負極性空間電荷積累的總數(shù)量達到了動態(tài)最大值是導致最大暫態(tài)場強出現(xiàn)的根本原因。研究結(jié)果為66kV電纜線路改為直流運行時直流工作電壓的確定及未來直流配電網(wǎng)的構(gòu)建奠定了基礎。
[Abstract]:Changing AC cable line to DC operation can make full use of the original transmission corridor and maximize the transmission capacity of the original transmission line.However, space charge accumulation is not considered in the design of practical AC XLPE cable insulation materials.Under DC voltage, the accumulation of space charge in AC XLPE cable is serious, which will result in the increase of local electric field strength, which will affect the insulation strength of cable and accelerate the aging of cable insulation.In order to study the space charge accumulation and electric field distribution characteristics of AC XLPE cable under DC voltage, the temperature field in cable insulation under temperature gradient is simulated by using COMSOL multi-physical field simulation software, and based on the conductivity model of insulation sample.The effects of temperature gradient, field strength, pressure time and polarity reversal on the electric field and space charge behavior of 66kV AC cable were studied.The electric field distribution and space charge accumulation in cable insulation are obviously affected by temperature gradient under DC steady voltage.The electric field distribution is determined by the conductivity of the insulating material, and the electric field distribution may be reversed at a higher temperature gradient, which makes the space charge of the high temperature side prone to detrapping, and accelerates the migration of the carrier to the low temperature side.It leads to the serious accumulation of space charge in the low temperature side of positive and negative electrode.When the temperature difference is 45 鈩，

本文編號：1729015