土壤热湿传递下的直埋电缆载流量数值计算

针对土壤热湿过程对直埋电缆载流量的影响,修正土壤热湿耦合模型,联合MAXWELL方程组,建立电磁-热湿三场耦合模型。利用三场耦合模型和COMSOL Multiphysics软件按正交法计算不同敷设土壤类型、干密度和粒径下的YJV22 0.6/1 3×6直埋电缆载流量。通过对比正交计算结果的最大、最小载流量组的磁通密度、发热量、温度分布、含水率分布等,发现大载流量组的缆芯发热量较高,但电缆外表皮温度较低,使得直埋电缆内部热流密度较大,同时电缆周围土壤的导热系数和含水率较高,发生的湿分运移和相变较为微弱,使得缆芯的热量及时被导出。因此,土壤中的湿分运移和相变对于直埋电缆的载流量有一定提升作用。     

竖直U型埋管地热换热器热短路现象的影响参数分析

通过引入换热器出口最高流体温度的概念,对地源热泵竖直U型埋管地热换热器的热短路现象进行了量化,基于竖直U型埋管周围的瞬时有限元模型,对影响热短路现象的主要参数(支管间距和回填料导热系数)进行了模拟分析,得出了量化结果。结果表明,增大支管间距可降低换热器出口最高流体温度,减小由热短路现象引起的热损失;回填料的导热系数对热短路现象的影响较大,当回填料导热系数小于周围土壤的导热系数时,增大回填料导热系数对减小热短路损失有较大作用,而当回填料导热系数大于土壤导热系数时则作用不大,推荐使用导热系数与周围土壤导热系数接近的回填材料。     

Experimental study of thermal field deriving from an underground electrical power cable buried in non-homogeneous soils

The electrical cables ampacity mainly depends on the cable system operation temperature. To achieve a better cable utilization and reduce the conservativeness typically employed in buried cable design, an accurate evaluation of the heat dissipation through the cables and the surrounding soil is important. In the traditional method adopted by the International Electrotechnical Commission (IEC) and the Institute of Electrical and Electronics Engineers (IEEE) for the computation of the thermal resistance between an existing underground cable system and the external environment, it is still assumed that the soil is homogeneous and has uniform thermal conductivity. Numerical studies have been conducted to predict the temperature distribution around the cable for various configurations and thermal properties of the soil. The paper presents an experimental study conducted on a scale model to investigate the heat transfer of a buried cable, with different geometrical configurations and thermal properties of the soil, and to validate a simplified model proposed by the authors in 2012 for the calculation of the thermal resistance between the underground pipe or electrical cable and the ground surface, in cases where the filling of the trench is filled with layers of materials with different thermal properties. Results show that experimental data are in good agreement with the numerical ones.     

地下管道群中安装电缆的热状态及载流量评估

为了保证地下电缆可靠运行,电力部门通常的做法是在电缆表面安装温度传感器,对电缆的热状态进行直接监测。但是对于管道群中安装的电缆,如在安装时打碎已有管道既不安全也不经济,使温度传感器不得不安装在管道群的外表面,带来如何从远离电缆安装的温度传感器的数据中推测出电缆绝缘温度的问题。对此,提出了一种通过土壤热参数的估算来评估电缆绝缘热状态的方法,主要涉及有限元法和优化方法。通过实际应用于220 kV变电站入线的3条220 kV／250 MVA地下管道群电缆线路,对热状态进行精确评估,预测结果与实际测量值具有很好的一致性,证明了所提方法的有效性。     

长距离跨桥高压电缆的关键技术设计

在跨海大桥上敷设电力电缆不仅能够起到安全、可靠、经济地输送电能的目的,还能解决许多岛屿采用独立小发电系统,其发电成本高、可靠性低、环保效果差等问题。结合目前现有的桥梁上敷设电缆的设计经验,介绍了在进行桥梁上敷设高压电缆时在电缆热伸缩、桥梁伸缩与振动、电缆空间布置及电缆与其他管线相互影响等方面的关键技术设计,可对今后桥梁电缆的施工、运行提供借鉴。     

电力电缆在线测温及载流量监测的研究进展与应用

介绍了国内外在电力电缆在线测温及载流量监测方面的研究进展,并对以电缆表面或绝缘表面温度折算线芯温度的相关理论及技术手段作了简要分析。国外应用实例的介绍显示了对电力电缆,尤其是高压/超高压电缆进行在线温度监测,以实时掌握电缆运行情况,保证安全运行,并在此基础上进行合理的负荷调度的重要性,也为国内运行部门提供了成功的运行经验。     

土壤源热泵U型垂直埋管传热过程的数值研究

针对土壤源热泵地下U型垂直埋管,建立了周围土壤的非稳态温度场的数学模型,并利用Matlab软件进行求解。通过对夏季制冷工况的模拟,研究了管内流量和回填材料对出水温度的影响,还研究了埋管间距和热作用半径对单位管长换热量的影响。     

Economics of cryocables

This paper examines the technical and economic feasibilities of: (1) using cryogenic hydrogen to cool a.c. cryoresistive or a.c. superconducting power transmission cables and, (2) delivering liquid hydrogen concurrently with cryoresistive or superconducting electrical power through a common cable. Cryogenic hydrogen coolant options considered are subcooled liquid and slush. Cryogenic nitrogen and helium coolants are also considered for cryoresistive and superconducting cables, respectively, to provide reference data for comparison with our H₂-coolant calculations. Thermodynamic analyses are performed to optimize the coolant flow rate and refrigerator spacing for each specific coolant, coolant fluid state, cable design, cable insulation quality and energy delivery option. The use of hydrogen as a coolant in electrical cables is discussed from a safety viewpoint.Helium-cooled and hydrogen-cooled superconducting power transmission lines are shown to be economically competitive and offer lower unit·transmission costs than conventional underground power lines. The hybrid hydrogen-superconducting cable concurrently transmits liquid hydrogen and electricity at the lowest unit cost of all cryocable energy systems examined. Hydrogen-cooled power lines and hybrid hydrogenelectric energy cables appear to be technically and economically feasible; however, they do not currently provide sufficient economic incentive to warrant the increased hazard of operation.     

海上风电场海底电缆防护方案研究

  [目的]  海底电缆防护是海上风电场建设的一种重要组成部分,海上风电中最大部分的保险理赔主要由于电缆事故造成。由于电缆路由线路较长,会穿过不同区域,每个区域的防护方案都不同。  [方法]  首先简单介绍海底电缆防护作法的基本情况,然后详细阐述了海底电缆登陆段防护方案,紧接着描述了海底电缆交越段防护方案以及电缆管附近的海缆防护方案,最后对海上风电场海底电缆防护方案进行总结。  [结果]  针对海底电缆登陆段,多采用套管保护、电缆沟与水平定向钻方案;针对海底电缆交越段,多在交越点采用垫块的方案;针对基础附近的海缆,主要采用J型管与弯曲限制器的方式。  [结论]  无论采用哪种方式,应高度重视海上风电场海底电缆的防护,确保海缆在运行期间的安全。     

Crossing quantities: How to compare electrical strength performances of insulation compounds for power cables

An innovative theory—derived from the “enlargement law”—about how to compare the breakdown performances of power cable insulation compounds is illustrated and applied herein. This theory enables the selection between two different compounds candidate for the insulation of power cables via dielectric strength tests performed on cable models. In particular, compound performances are investigated vs. cable length looking for the so-called crossing length, i.e. a crossover point between the performances of the two compounds, such that one of the two performs better above this length, and conversely the other below it. The application of this theory consists in a comparison between two EPR compounds, based on lightning impulse breakdown tests realized on mini-cables, and shows that the crossing length depends strongly on cable size and voltage rating. Therefore, the practical selection of the best compound must consider the typical installation lengths of real cables.     

回填土质对埋地热油管道传热影响的研究

针对不同导热系数的土样回填管沟,忽略管道轴向温降建立二维非稳态传热模型,环境温度采用周期性边界条件。利用有限容积法,对方程进行离散,数值模拟了管道投产第一年内正常运行非稳态传热过程,同时应用"焓-多孔度"技术,并考虑原油凝固潜热对温降的影响,数值模拟了管道停输非稳态温降过程。结果表明:采用导热系数相对较小的土质回填管沟,管壁及保温层外壁热流密度明显减小,而且回填区温度较高散热较慢,由计算的安全停输时间可知,回填土质导热系数越小安全停输时间越长,模拟结果符合实际。     

DEFORMATION OF AN INFINITELY LONG,DC CABLE WITH TEMPERATURE-DEPENDENT ELECTRIC CONDUCTIVITY OF THE INSULATION

We investigate the deformation of an infinitely long, circular cylindrical electric conductor carrying a uniform axial current, for the case when the electric conductivity of the coating is temperature dependent. This model conforms with the real situation for many of the existing modern dc cables with polyethylene coating. The distributions of temperature, magnetic field, stresses, and displacements in the cable are obtained and discussed under a thermal radiation condition at the boundary of the cable. In particular, it appears that there is a critical temperature for the ambient medium to the cable, above which no solution for the steady heat problem can exist and the thermal equilibrium of the cable is no longer fulfilled. A formula for the calculation of this critical value is given, which may turn out to be of practical importance for a reliable design of the cable. The obtained results also show that the electric conductivity of the coating strictly decreases as one moves from the core to the boundary of the cable in conformity with the behavior of temperature. Some numerical results are presented.     

Superconducting transmission cables

The discovery of high-temperature superconductivity (HTS) in 1986-1988 rekindled interest in superconducting power transmission cables. Many projects are underway around the world to study the use of HTS power transmission cables. The siting and environmental issues facing the expansion of transmission capacity have become increasingly more difficult with time. The HTS power cable may be able to address some of these issues, especially in urban areas, where HTS retrofits of existing conventional cables can increase capacity substantially without increasing the footprint of the cable right of way. Several of the cable projects employing HTS are discussed in this article     

An improved non-adiabatic FEM model of a line-to-earth fault in buried power cables

It is shown in this paper that the non-adiabatic nature of phase-to-earth fault thermodynamics in buried power cables can be modelled in an even more precise manner by using the FEM. The nonlinear FEM model has been created on the basis of an authentic case of fault caused by a previous mechanical damage of the cable sheath and insulation, as well as heat sources, thermo-physical and electrical material properties as functions of temperature and time. The proposed model is applicable to power cables of all voltage levels with different polymer insulations laid in soils with changeable moisture content, as well as to the dry arc tracking or wet arc tracking phenomena in PVC-insulated cables.     

西北750 kV示范工程输电线路OPGW光缆防振特性的研究

介绍了光纤复合架空地线(OPGW)光缆在国内第一个超高压西北750 kV官亭-兰州东输电线路的应用。结合西北750 kV输电线路的特点和对OPGW的要求,描述了750 kV输电线路OPGW光缆的结构设计的特点,同时通过750 kV官亭-兰州东输电线路大档距OPGW光缆防振特性的研究,为西北750 kV输电线路1 235m大档距OPGW光缆推荐了满足技术条件的直线档防振方案,并提供了测试结果及分析意见,对探索和积累750 kV超高压等级上OPGW光缆的设计和运行经验具有现实意义。     

基于寿命的电缆群载流能力优化研究

采用周期性条件计算得到的载流量能提高电缆的载流能力,在周期性载流量的基础上提出一种周期性寿命最大允许电流模型。鉴于电缆周期性寿命最大允许电流与电缆寿命之间互相影响,采用多目标粒子群算法,考虑电缆的互为热源效应,以电缆群的平均寿命和平均周期性寿命最大允许电流为目标函数,在改进周期性载流量设置方法的基础上提出周期性寿命最大允许电流设置方法,然后对电缆群中每条回路的周期性寿命最大允许电流和寿命进行优化,从而找到电缆群的优化运行方式,并深入研究了电热联合老化对两个目标函数的影响。     

Analysis and suppression measures of lightning transient overvoltage in the signal cable of wind turbines

Lightning strikes are a major threat to the secure operation of wind turbines. When lightning strikes a wind turbine, the lightning current flows through the blade and the tower and then the induced overvoltage will damage sensors and signal cables. In this study, a comprehensive transient surge impedance model of a wind turbine was built to analyze the causes of the overvoltage in the signal cable. The model that studies the overvoltage caused by both capacitive coupling and electromagnetic induction included the blade, nacelle, tower, signal cable, power cable, and grounding system using π networks. The influences of the cable shielding layer, soil resistivity, and lightning current waveform on the overvoltage were also analyzed. Then, 2 overvoltage suppression measures, ie, grounding at 2 ends of the outer shielding layer and installation of a surge protective device, were tested. Results show that a signal cable with double shielding layers reduced the overvoltage in the signal cable, and higher soil resistivity resulted in increased voltage on the tower base. In addition, the peak and the front time of the lightning current significantly influenced the overvoltage on the tower and the cable. The effectiveness of the 2 suppression measures was also verified. The calculation results will provide guidance for a reasonable lightning protection design.     

XLPE电缆绝缘老化与剩余寿命评估的试验方法

电缆投入运行后.绝缘会受到电、热、机械、水分等因素的作用而发生老化,影响电缆的运行可靠性和使用寿命.XLPE电缆的绝缘状态与剩余寿命的评估是目前的热点问题,相对于定性的分析,对电缆剩余寿命的定量评估更有实际价值.文章总结了XLPE电缆绝缘老化机理并调研了几种定量分析电缆剩余寿命的方法:击穿电压对比法,介质损耗因素法和直流泄漏电流法.可为从事电缆运行情况和寿命研究的技术人员提供参考.     

Evaporating system for cryogenic support of long length HTS power cables

The paper deals with an analysis of the results of theoretical and experimental research on an evaporating system for cryogenic support as supplied to long length thermostatting channels of high-temperature superconducting (HTS) cables and hybrid power transmission lines as well as thermal control systems for cryogenic components in aircraft fuel tanks during long-term spaceflights. Experimental evidence for nitrogen and hydrogen are presented here. The importance of such research for practical application in developing modern cryostatting systems has been highlighted.The design of an experimental hybrid power transmission line for studying thermostatting of superconducting power cables has been considered in the paper. The transmission line contains three sections with different types of thermal insulation and current leads providing high current supply to superconducting threads with minimum external heat inflow. The unique experimental data on heat inflows from the outer surface of the transmission line in different sections has been obtained by the authors. It is shown that it may be possible to compensate fully for external heat inflow to a cryogenic line as well as to lower the temperature of a cryogenic coolant in the section with an evaporating system for cryogenic support. In order to determine the possible length of the cryostatting work field of a long length superconducting cable, estimates of using liquid nitrogen and liquid hydrogen as a working fluid for various mass flow rates of the coolant feed have been made via the mathematical model describing physical processes in a thermostatting channel using an evaporating system for cryogenic support. Calculation data on changes in the length of the long length temperature cryostat, pressure and cooling capacity of the evaporating cryostat system has been obtained.     

电缆中空间电荷的测量与特性研究

交联聚乙烯电力电缆因其优异的电气性能,现已广泛应用于电力系统输配电线路中,然而由于绝缘本体中空间电荷的存在,会畸变局部场强,进而导致绝缘老化和击穿,因此研究电缆本体绝缘中空间电荷的分布具有重大意义。目前针对固体绝缘电介质,电声脉冲法测量空间电荷由于无损和方便等优势,在国内外被广泛采用。鉴于此,介绍了电声脉冲法的测量原理,并且结合实际运行情况中电缆线芯和外半导体之间存在温度差,通过穿心升流变压器和接触式温度传感器控制线芯温度,改进测量下电极形状以适应不同厚度和半径的电缆本体绝缘,设计了一套能够用于电缆本体的空间电荷测量装置,并进行了不同温度下的实际测量,实验结果表明,温度对声信号在介质中的传播速度以及空间电荷的注入影响明显。