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

【摘要】：將交流電纜線路改為直流運(yùn)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(shí)際運(yùn)行的交流XLPE電纜絕緣材料在設(shè)計(jì)時(shí)并沒(méi)有考慮空間電荷積累問(wèn)題。直流電壓下,交流XLPE電纜中空間電荷積累嚴(yán)重,會(huì)造成局部的電場(chǎng)強(qiáng)度成倍增加,影響電纜的絕緣強(qiáng)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(chǎng)分布特性,本文應(yīng)用COMSOL多物理場(chǎng)仿真軟件,模擬了溫度梯度下電纜絕緣中的溫度場(chǎng),并基于絕緣樣品電導(dǎo)率模型,研究了溫度梯度、場(chǎng)強(qiáng)、加壓時(shí)間及極性反轉(zhuǎn)等因素對(duì)66kV交流電纜的電場(chǎng)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(chǎng)分布和空間電荷積累明顯受溫度梯度的影響。電場(chǎng)分布由絕緣材料的電導(dǎo)率所決定,在較高溫度梯度時(shí)可能出現(xiàn)電場(chǎng)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(dǎo)致了低溫側(cè)正負(fù)極性空間電荷的嚴(yán)重積累。當(dāng)溫差為45℃、加壓8小時(shí)時(shí),低溫側(cè)空間電荷密度達(dá)-0.15C/m~3,絕緣外側(cè)場(chǎng)強(qiáng)最大值為6.71 kV/mm,該數(shù)值低于66kV交流電纜絕緣的場(chǎng)強(qiáng)設(shè)計(jì)值。極性反轉(zhuǎn)電壓下,暫態(tài)電場(chǎng)分布取決于介電常數(shù)和電導(dǎo)率的共同作用,且以介電常數(shù)為主,暫態(tài)最大場(chǎng)強(qiáng)出現(xiàn)在纜芯附近,均大于其穩(wěn)態(tài)時(shí)的最大場(chǎng)強(qiáng)。暫態(tài)最大場(chǎng)強(qiáng)值與溫度梯度、電壓的幅值以及電壓極性反轉(zhuǎn)時(shí)間密切相關(guān),溫度梯度和電壓幅值越大,暫態(tài)最大場(chǎng)強(qiáng)越大;反轉(zhuǎn)時(shí)間越短,最大暫態(tài)場(chǎng)強(qiáng)越高,且暫態(tài)最大場(chǎng)強(qiáng)的位置越靠近纜芯導(dǎo)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(guò)程中該處正負(fù)極性空間電荷積累的總數(shù)量達(dá)到了動(dòng)態(tài)最大值是導(dǎo)致最大暫態(tài)場(chǎng)強(qiáng)出現(xiàn)的根本原因。研究結(jié)果為66kV電纜線路改為直流運(yùn)行時(shí)直流工作電壓的確定及未來(lái)直流配電網(wǎng)的構(gòu)建奠定了基礎(chǔ)。
[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(hào)：1729015