摘要:
高压干式直流套管运行中内部径向电场、温度场分布是表征套管性能的重要参数,关系着套管芯子的长期安全稳定运行。套管中心导杆欧姆发热和绝缘介质焦耳发热是芯子内部存在温度梯度分布的主要原因,且绝缘介质电导率与温度密切相关,而直流条件下电场分布又取决于电导率,因此高压直流套管电场与温度场的计算是一个相互耦合的过程。鉴于此,首先建立套管芯体圆柱模型,并进行半解析理论公式推导,实现了电场和温度场的解耦计算。在此基础上,提出了有限元电热耦合模型和计算流程,并将电热耦合理论模型与有限元模型在实际套管结构下的电场、温度场计算结果进行对比,两者吻合较好,证明了有限元电热耦合模型的有效性。进一步将有限元模型推广到与实际套管芯子结构相同的圆锥模型,计算了某干式直流套管芯子内部电场、温度场分布,并对芯子外轮廓结构进行了优化设计。优化目标为在额定运行条件下,套管最热点温度接近90℃,且套管径向场强最大值约为3.5 kV/mm,分布较均匀。最后对该干式直流套管样机进行了温升和电性能试验,证明了优化设计方案的可行性。提出的电热耦合理论、有限元模型,以及电热解耦计算方法和芯子优化设计流程可以为高压干式直流套管的研制提供参考。
Abstract:
Distribution of radial electric and temperature field is an important parameter to characterize performance of resin impregnated paper（RIP） high voltage direct current（HVDC） bushings.Moreover,it has a direct connection with long-term operation performance of bushing condenser.Ohmic heating of inner conductor and joule heating of insulation medium can establish temperature gradient inside bushing condenser.In addition,conductivity of insulation media is closely related with temperature and E-field distribution depends on conductivity under static DC application,so computation of electric and temperature field in HVDC bushing is a mutual coupling process.In the paper,cylinder model of bushing condenser was established,and derivation of semi-analytical theory formula was also conducted to achieve decoupling calculation of electric and temperature field.Based on this,finite element electro-thermal coupling model and calculation process were proposed,and the results under these two models in actual bushing structure have been compared.The results are in good agreement which proving validity of finite element electro-thermal coupling model.Then finite element model was used in cone model which is much closer to actual condenser structure.Moreover,optimization design for condenser outer contour structure was also conducted to make sure that the hottest-spot temperature is close to 90 ℃ under rated operating condition,and maximum radial E-field strength is approximately equal to 3.5 kV/mm and distributed uniformly.Finally,temperature rise and electrical performance test were carried out on a RIP HVDC bushing prototype,which canverify the feasibility of optimized design.The electro-thermal coupling theory and FEM model proposed in this paper,as well as electro-thermal decoupling calculation method and condenser optimization design process have good theoretical guiding significance for development of higher voltage RIP DC bushings.
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