【作者】 李振宇；

【导师】 赵学增； 王立国；

【作者基本信息】 哈尔滨工业大学 ， 机械电子工程， 2020， 博士

【摘要】 在某些特殊的气候条件下,空气中的过冷却水滴碰撞在输电线路的导线表面后,会冻结形成覆冰,这种现象即为输电线路覆冰。严重的覆冰灾害会引起塔杆倒塌和线路断线等事故,威胁输电线路的安全运行。因此,研究输电线路的覆冰形成机理,实现根据环境和线路参数来预测覆冰的增长速度,并结合融冰时间和融冰电流的计算,制定合理的覆冰防治策略,是降低覆冰对线路危害的重要手段。水滴在输电线路周围受外力作用产生运动轨迹变化,进而影响覆冰增长过程。对于输电线路,水滴在受到空气流场作用的同时,由于自身极化荷电,也会受电场力的影响。覆冰气候下的导线极易产生离子流电场,相对于原有电场更加复杂。因此,有必要研究离子流电场影响下的覆冰增长机理,建立更准确的覆冰增长模型。为了揭示离子流电场影响下的覆冰增长机理,基于改进的模拟电荷法和二阶迎风有限体积法,迭代计算离子流电场强度和空间电荷密度,并且在计算中考虑了风速的影响,使该方法更符合输电线路的实际运行情况,提升了离子流电场计算的速度和精度。设计了一个基于电晕笼的实验装置对离子流电场的计算结果进行验证。分析了电压、导线半径和风速对离子流电场的影响。在所建立的离子流电场计算方法的基础上,分析水滴在电场中的荷电过程,进一步计算了存在水滴的离子流电场。为了分析离子流电场作用下的覆冰增长机理,采用欧拉-拉格朗日法数值计算水滴在气体流场和离子流场中的运动轨迹,通过分析得到离子流电场影响覆冰增长的机理是荷电水滴在离子流电场的作用下,会增大水滴与导线之间的碰撞率,从而导致覆冰增长速度加快。在此基础上,提出考虑了离子流场的覆冰增长模型,设计了相应的实验,验证了该覆冰增长模型的准确性和离子流电场对覆冰增长的影响。基于电流焦耳热融冰方法,根据环境和线路参数计算融冰时间和融冰电流。分析了覆冰导线的热传递过程,基于覆冰导线温度分布的数值计算,通过融冰过程中覆冰的形状变化计算融冰时间。并且,根据所建立的考虑了离子流场的覆冰增长模型,将融冰过程中覆冰继续增长这一情况加以考虑,提出相应的融冰时间计算方法,并分别对无覆冰增长和覆冰增长两种情况下的融冰时间进行计算。根据线路的设计和运行要求,计算了最小和最大融冰电流。通过实验验证融冰时间的计算方法。研究了包括并联电容器无功补偿融冰、分裂导线融冰和交流、直流短路融冰的焦耳热融冰方法,作为覆冰防治方法的选择依据。根据本文提出的考虑了离子流场的覆冰增长模型,以及融冰时间和融冰电流的计算方法,提出了一种输电线路的覆冰防治策略,该策略以覆冰增长速度和覆冰防治功耗最小为目标实现覆冰防治策略,对覆冰线路的防冰和融冰进行选择,为输电线路的覆冰治理提供了参考。在66 k V线路上进行了现场融冰试验,对融冰时间计算和覆冰防治策略进行了验证。本文对输电线路覆冰增长机理和防治策略进行了研究,分析了离子流电场影响下的覆冰增长机理,在覆冰增长模型的碰撞率参数的计算中,加入了离子流电场的影响,提升了覆冰增长模型的准确性。给出了融冰过程中覆冰仍然增长情况下的融冰时间计算方法。基于本文研究成果建立的覆冰防治策略,可以通过环境和线路参数以及覆冰厚度,对线路的覆冰防治方式进行决策,减少覆冰防治过程中的功耗,提升覆冰防治的经济性。更多还原

【Abstract】 Icing of power transmission line occurs in special weather conditions result from the phenomenon that supercooled water drops in the atmosphere collide and freeze on conductor surface.Icing on transmission line will increase load bearing and stretch conductors which leads to mechanical injury,breaking down of transmission towers and conductor breaks may happen in serious ice disaster that threatens the safe operation of power transmission line.Therefore,it is necessa ry to analyze the formation mechanism of transmission line icing to predict the growth process based on parameters of meteorology and transmission line.Reasonable icing preventation and control will boost de-icing efficiency as well as mitigate the influence on normal operation of transmission line caused by de-icing work.Motion of the water drops near power transmission line is affected by external forces,thus the icing process will change.For the power transmission lines,water drops will be polarized,and their motion trajectories are governed by both the air flow field and electric field.Moreover,ion flow field is more likely to appear during the icing process on the transmission line surface,this leads to a more complicated electric field.Consequently,i t is necessary to investigate the icing process influenced by ion flow field,which is important for the establishment of ice accretion model.In this work,the ion flow field around transmission line is studied to discover the ice accretion process,a calculation method of ion flow field is presented.Enhanced charge simulation method is used for electric field,2^nd order upwind scheme finite volume method is employed for space charge density.Theseo variables are iteratively calculated until the criterio n is met.Anxperiment is conducted based on corona cage to verify the calculated result.Influcences of voltage level,conductor radius and wind speed on ion flow field are analyzed.According to the solution of ion flow field,ion flow field in presence o f water drops is calculated.For the purpose of analyzing th e ice accretion mechanism,Euler-Lagrange method is used to calculate the trajactories of water drops,then,the accuracy of accretion model is improved.Relative experiment is conductor for the verification of ice accretion model.Joul heat de-icing is a rapidly developing de-icing method,it removes the ice by adding the current of transmission line,the joul heat generated initialize the de-icing process and the ice will begin to melt.In jourl heat de-icing methods,it is nessecary to calculate the de-icing time and de-icing current in accordance to environmental and conductor parametersHeat balance equation is established in line with the analysis of heat transfer process of ice-coated conductor.Critical icing and de-icing conditions are given,and the calculation method of critical icing preventation current and critical de-icing current are calculated.The time cost of de-icing is evaluated combining numerically solved temperature distributi on and the change of geometric shape of the gap inside melting ice.In addition,maximum and minimum de-icing current is calculated in accordance with the heat balance equation and the design requisite of transmission line.Relevant experiment are conducte d to verify the time cost of de-icing.In this work,different joule heat de-icing methods are introduced consists of their theories and applications,and the de-icing strategy is proposed accordingly.The condition of transmission line icing is predicted in line with the weather prognosis,line parameters,the ice accretion model and de-icing current introduced by this work.Additionally,the criterion of ice preventation and de-icing operation and the process of de-icing strategy is presented based on the calculation of de-icing time and de-icing current,the principle is to minimize the power consumption during the de-icing operation.Meteorological parameters of certain period are used as a background to apply and examine the de-icing strategy,besides,to find the optimal de-icing solution.Eventually,practical experiment is conducted in 66 k V transmission line to verify the feasibility of the de-icing method introduced in this paper.In summary,this work studied the ice accretion process and de-icing process,the mechanism of ice accretion affected by ion flow field,thus the ice accretion model will be more accurate.On the other hand,it boosts the the range of the application of de-icing method,enables the calculation in such circumstance where the ice keeps growing in the process of de-icing period.According to the research result,an icing preventation and control scheme is established to determetin the ice preventation and control method between ice preventation method and de-icing method.更多还原