The changing process and trend of ground temperature around tower foundations of Qinghai-Tibet Power Transmission line

After the construction of Qinghai-Tibet Highway and Railway, the Qinghai-Tibet Power Transmission(QTPT) line is another major permafrost engineering project with new types of engineering structures. The changing process and trend of ground temperature around tower foundations are crucial for the stability of QTPT. We analyzed the change characteristics and tendencies of the ground temperature based on field monitoring data from 2010 to 2014. The results reveal that soil around the tower foundations froze and connected with the artificial permafrost induced during the construction of footings after the first freezing period, and the soil below the original permafrost table kept freezing in subsequent thawing periods. The ground temperature lowered to that of natural fields, fast or slowly for tower foundations with thermosyphons,while for tower foundations without thermosyphons, the increase in ground temperature resulted in higher temperature than that of natural fields. Also, the permafrost temperature and ice content are significant factors that influence the ground temperature around tower foundations. Specifically, the ground temperature around tower foundations in warm and ice-rich permafrost regions decreased slowly, while that in cold and ice poor permafrost regions cooled faster. Moreover, foundations types impacted the ground temperature, which consisted of different technical processes during construction and variant of tower footing structures. The revealed changing process and trend of the ground temperature is beneficial for evaluating the thermal regime evolution around tower foundations in the context of climate change.

Research on Total Electric Field for DC Lines Converted from Double-Circuit AC Lines

With rapid growth of power demand, transmission capacity is also in urgent need of upgrading. In some cases, converting existing AC transmission lines to DC lines can Improve the transmission capacity and reduce the construction investment. In this paper, the upstream finite element method was expanded to calculate the total electric field of same tower multi-circuit DC lines converted from double-circuit AC lines, and the validity of the algorithm was confirmed by experiments. Taking a DC line converted from a typical same tower 500 kV double-circuit AC transmission line as an example, the surface electric field and the ground total electric field in different pole conductor arrangement schemes were calculated and analyzed, and the critical height of pole conductors for DC lines in residential and non-residential area were determined. Then, the corridor width of DC and AC lines at critical height in residential and non-residential areas before and after AC-DC line transformation were compared. The results indicate that for DC lines converted from common 500 kV double-circuit AC lines, the ground total electric field can meet the requirements of corresponding standard with appropriate pole conductor arrangement schemes.

特高压重冰区地线支架脱冰动力响应安全性研究

为了探究特高压重冰区输电塔地线支架在脱冰动力荷载作用下的安全性,基于脱冰数值计算理论,建立了地线的脱冰数值模型和塔线耦合数值模型,研究了地线在不同工况下的脱冰动力响应和不同地线脱冰情况下铁塔地线支架的承载力安全性。脱冰研究表明:地线脱冰时,高差越大,脱冰产生的上拔力越大;档距越大,纵向不平衡张力越大;覆冰越厚,地线脱冰产生的纵向不平衡张力越大,产生的的上拔力越小。塔线耦合脱冰研究表明:多档模型下,地线脱冰时,悬垂直线塔地线支架正面和底部斜材存在应力比超限情况,现有设计方法偏于不安全;耐张塔地线支架不受脱冰动力响应控制。建议重覆冰区地线支架设计时仅考虑地线脱冰产生的上拔力影响,上拔力取地线最大使用张力的1.0%~5.0%,覆冰越厚,上拔荷载可越小,厚度为20 mm、30 mm、40 mm、50 mm、60 mm冰区的上拔荷载分别取为最大使用张力的4.0%~5.0%、3.0%~4.0%、2.5%~3.0%、2.0%~2.5%和1.0%~2.0%。

输电线路杆塔接地电阻测量装置设计

输电线路杆塔接地电阻测量对于电力运维人员是一项繁重的工作。为了实现在不解开接地引下线情况下即可测量杆塔的接地电阻,文章设计了一种新型输电线路杆塔接地电阻测量装置,该装置采用双钳法对接地电阻进行测量。首先,分析了新型输电线路接地电阻测量装置的原理;其次,采用模块化设计思路对接地电阻测量装置进行硬件设计;接着,对接地电阻测量装置进行软件设计,给出系统工作流程;最后,对所开发测量装置进行测试,所开发测量装置的测量值与精密电阻实际值误差在3%以内。

基于离子流效应的同塔双回直流线路地线融冰感应过电压分析与抑制措施

针对某±500 kV同塔双回直流输电线路,在“一回停运、一回运行”工况下进行停运线路地线融冰时,感应电压过大导致融冰装置故障、自动接线装置和避雷器击穿受损情况,研究建立了静电耦合和空间离子流效应综合作用的停运线路过电压计算模型。按6种工况计算分析了带电运行回路导线不同起晕电压时在停运线路上感应的过电压水平,同时综合考虑过电压抑制水平和线路能量,提出了加装5 kΩ接地高阻的过电压抑制措施,可实现将超过100 kV感应电压抑制到20 kV以下,并经实际线路融冰操作,验证了其有效性。

基于有限元方法的山地输电杆塔接地特性分析

为深入研究山地输电杆塔的接地特性,运用有限元方法对杆塔基础、接地体、土壤介质建模,分析不同接地参数、不同环境工况下的接地特性。结果表明:土壤电阻率和接地体长度对接地电阻有较大影响;接地体所处的土壤环境对接地电阻有较大影响,可考虑在接地体周边实施降阻措施;高频条件下,随着导体阻抗增大,高频电流沿导体传播难度增大,电流更易从电流注入点附近散流,工程中可考虑在电流入地点附近实施降阻措施。本文研究可为实际工程中地表电位测算和防雷、降阻设计提供参考。

输电线路杆塔接地状态在线监测技术探索

接地保护措施是确保输电线路安全供电的关键环节。目前,电网系统大多依赖人工方式来监测杆塔接地情况,但在险峻地形和恶劣天气条件下,人工测量存在较多不便,且测量步骤烦琐,难以及时发现故障点,因此研究智能化实时监测技术成为迫切需求。因此,文章提出一种输电线路杆塔接地状态在线监测方法,通过测量故障出现点的接地电位和入地电流,归一化处理形态各异的接地模式,并利用平均电位计算接地电阻。同时,通过比较故障检测装置中的电流阈值与杆塔接地电流,可以判断接地是否出现故障。实证分析表明,该方法能够较为准确地判断接地电阻和故障部位,且具有较高的准确性。该研究不仅有助于提升电网输电线路的安全性,还为智能化实时监测技术的发展提供有益的探索。

一起220 kV同塔双回线跨线事故保护动作的分析

介绍了一起同塔双回线C相受雷电反击导致接地故障,后续雷电过电压致使其中一条线已经分开的开关C相断口击穿的事故。通过对保护装置动作报告、故障时序及故障录波器波形记录的分析,准确判断出开关内部击穿的事实,避免了重大二次事故的发生。提出故障发生后要多源信息融合判断,深入了解故障发生的各项因素,结合故障波形分析,以便更加快速地对故障产生的原因及可能导致的后果做出合理正确的判断。

接地装置降阻率及经济性分析

架空电力线路降低雷电事故的主要措施之一是减小杆塔接地电阻。分析了4种接地网需要的导体长度和对应减小杆塔接地电阻的效果,并进行了经济分析和总结,对电力技术从业人员具有一定参考价值。

110 kV输电线路设计研究

结合实际工程,介绍110 kV输电线路的设计。通过前期设计人员对路径方案的规划对比,导线的技术经济对比,地线的远期配置,以及选择适应工程所需的杆塔和基础模型,来保证工程设计的质量更优。通过合理地选择线路路径、导线和地线参数、气象条件,进而合理地选取典型设计中的铁塔模块等,使得设计方案更合理,以达到工程经济技术指标更优,更加符合国家电网有限公司对输变电工程提出的“环境友好型、资源节约型”等方面的建设要求。

Choosing configurations of transmission line tower grounding by back flashover probability value

There is a considerable number of works devoted to electrical characteristics of grounding. These characteristics are important in general. However, in application to grounding of transmission line towers they are not enough to determine what grounding construction is preferable in some particular case, because these characteristics are calculated or measured apart from the grounded object, and only limited number of current （or voltage） source waveforms is used. This paper indicates reasons in favor of the fact that to choose the optimum design of grounding, the calculation model should include the tower as it is. The probability of back flashover, which provides both qualitative and quantitative estimate of the grounding structure efficiency, can be taken as the criterion for the grounding design. The insulation flashover probability is calculated on the basis of engineering method, which evaluates breakdown strength of insulation for nonstandard waveshapes, and probability data on lightning currents. Different approaches are examined for identifying the back flashover probability, as not only amplitudes but also other parameters can be taken into account. Finite-difference time-domain method is used for calculations of transients. It is found that lightning current waveform can greatly influence calculated back flashover probability value.

Response of a transmission tower-line system at a canyon site to spatially varying ground motions

Collapses of transmission towers were often observed in previous large earthquakes such as the Chi-Chi earthquake in Taiwan and Wenchuan earthquake in Sichuan,China. These collapses were partially caused by the pulling forces from the transmission lines generated from out-of-phase responses of the adjacent towers owing to spatially varying earthquake ground motions. In this paper,a 3D finite element model of the transmission tower-line system is established considering the geometric nonlinearity of transmission lines. The nonlinear responses of the structural system at a canyon site are analyzed subjected to spatially varying ground motions. The spatial variations of ground motion associated with the wave passage,coherency loss,and local site effects are given. The spatially varying ground motions are simulated stochastically based on an empirical coherency loss function and a filtered Tajimi-Kanai power spectral density function. The site effect is considered by a transfer function derived from 1D wave propagation theory. Compared with structural responses calculated using the uniform ground motion and delayed excitations,numerical results indicate that seismic responses of transmission towers and power lines are amplified when considering spatially varying ground motions including site effects. Each factor of ground motion spatial variations has a significant effect on the seismic response of the structure,especially for the local site effect. Therefore,neglecting the earthquake ground motion spatial variations may lead to a substantial underestimation of the response of transmission tower-line system during strong earthquakes. Each effect of ground motion spatial variations should be incorporated in seismic analysis of the structural system.

特高压直流入地电流对附近杆塔地网腐蚀评估

为了有效开展直流入地电流对交流电网的影响评估,指导特高压直流接地极工程的选址建设,以国家电网公司正在建设的±800kV某特高压直流输电工程接地极(址)及邻近500kV交流输电线路杆塔实际参数为例,采用接地仿真计算软件建立了相应的极址土壤模型和线路电气模型,对流入输电线路各杆塔接地体的直流电流及分布特性进行了全面、系统的研究,根据接地极在设计寿命内的总安时数和运行方式计算得到了单基杆塔接地体的腐蚀量,分析表明杆塔地网腐蚀量与接地极运行的安时数、流出该基杆塔接地体的电流值以及使该基杆塔接地体电流流出时接地极的运行时间成正比,且主要集中在接地体的末端,建议应根据极址土壤电阻率参数和系统额定电流来确定接地极与输电线路的最小距离要求。该成果可用于指导直流接地极设计中类似问题的研究。

输电杆塔接地电阻测量新方法及误差分析

简要介绍了几种常用的输电杆塔接地电阻的测量方法与仪器,指出其存在的缺陷。为克服目前接地电阻测量中所存在的弊端,提出一种新的测量方法和模型,并给出了具体算法。通过仿真分析,给出了影响测量准确性的几个重要因素,并得出简化的误差修正公式。修正后的结果表明, 新方法合理,测量精度较高。最后,针对新方法实际应用中的检验问题,给出了相应的标定方法。

输电线路杆塔接地电阻的简化计算

输电线路杆塔接地设计中,通常应用经验公式计算杆塔接地电阻,计算精度有限。为此,考虑到接地导体扩散电流的不均匀性,对接地导体进行分段处理,计算各分段导体的自电阻系数和互电阻系数,进而求得接地导体的接地电阻。可根据精度要求确定分段数量,分段数量越多,计算精度越高。最后分析了输电线路杆塔常用的射线接地体、双环形接地体分别在不同土壤电阻率、导体半径、埋设深度等条件下的接地电阻,可为接地体优化设计和型式选择提供参考。

500kV输电线路杆塔接地电阻季节变化特性测量与分析

输电线路杆塔接地电阻测量是线路防雷的一项重要工作内容,而杆塔接地电阻随降雨量的季节性变化而变化。采用三极法在不同月份对杆塔接地电阻进行测量,分析降雨量、温度、地形、土壤类型等因素对杆塔接地电阻的影响,探讨不同因素对季节系数的影响机制。测量与分析结果表明:500kV输电线路杆塔接地电阻出现季节性变化最主要影响因素是不同季节降雨量的变化,并由所测数据分析地形对接地电阻季节性变化的影响,给出该地区平地和坡地的接地电阻季节影响系数。

输电线路杆塔接地装置冲击接地电阻特性研究

针对目前输电线路杆塔接地装置存在的遭受雷击时不能满足性能要求的问题,通过模拟计算,对多种接地装置的冲击接地电阻特性进行了分析,揭示了冲击接地电阻与雷电流波形、土壤电阻率、放射状导体长度的关系,设计了适合输电线路杆塔的接地装置结构.

山区110kV线路雷击事故分析及对策

通过对山区送电线路雷害事故的分析,得出了山区雷害主要是雷击杆塔或避雷线造成的反击事故。雷击事故主要发生在水库、水塘附近的突出山顶上;高山的山坡或半坡向阳的山脊上;电阻率高的土壤区和附近无树木等山丘突出处。地形坡度较陡的杆塔外边侧绝缘子、大转角杆塔外侧绝缘子串和大档距两端杆塔也易遭雷击闪络。采取杆塔降阻、装设线路避雷器、侧向避雷针和加强绝缘等多种措施后,防雷保护效果较好。

OPGW架空输电系统任一点接地短路电流分布的研究

架空输电线路发生接地短路时,短路电流在光纤复合架空地线(OPGW)上的分布对电力系统有重要影响。传统计算OPGW线上短路电流的方法大多采用工程简化计算和基于序分量法的计算,并且只考虑接地短路发生在杆塔处的情形,计算结果过于粗糙。为此提出了基于相分量模型对全线任一点接地短路电流计算的方法。分别提出接地短路发生在杆塔处和杆塔间不同的数学模型,进一步求解相导线和OPGW每一级档距上的电流。数值算例验证了在杆塔处接地短路分流模型的正确性,杆塔处接地短路的分流结果进一步验证了杆塔间接地短路分流模型的正确性,并在实际工程中进行了应用。对于复杂的OPGW架空输电系统,基于相分量模型的计算方法能够准确计算全线任一点发生接地短路时,OPGW线上短路电流的分布情况。

输电线路杆塔及接地体雷电冲击响应分析

雷击是造成输电线路跳闸的主要原因,研究输电线路及接地体的雷电冲击响应具有十分重要的意义。为此,笔者运用电磁分析软件CDEGS建立了500 kV双回路自立式输电线路杆塔雷电冲击模型,分析不同雷电流波形、不同杆塔参数、不同土壤电阻率和不同接地体长度下输电线路杆塔及接地体上雷电冲击响应规律。计算结果表明,雷击杆塔塔顶时,避雷线分流大小与土壤电阻率成正比关系,雷电流过大将导致绝缘子击穿;雷电流波前时间越短、横担越窄、杆塔越高、土壤电阻越大、接地体越短,雷击时塔顶和接地体冲击电压峰值越高;在高土壤电阻率地区通过增长接地体长度、降低土壤电阻率能有效降低塔顶和接地体电位。