基于热电耦合的10kV XLPE地下电缆群温度场数值计算

利用有限元计算了地下电缆的焦耳损耗和温度场分布,利用迭代法实现地下电缆温度场和电磁场间的耦合计算,提高了地下电缆温度场计算的精度,利用迭代法确定地下电缆的载流量。本文对地下直埋多芯电缆群的温度场进行了计算,并给出了相应的载流量。耦合计算结果比非耦合计算结果更接近试验结果,完全满足工程实际的需要。     

地下电缆群稳态温度场和载流量计算新方法

根据地表对流和深层土壤温度不变的原则,将地下电缆群开域温度场等效为闭域温度场,应用有限元分析了给定电缆负荷电流的地下电缆群闭域温度场分布.采用热路法将电缆金属套损耗归算到电缆导体,应用调和平均法对电缆导体外的薄层进行处理,最终将电缆等效为导体和外护两层结构,减少了剖分节点数,提高了计算精度和收敛速度.采用弦截法计算了地下电缆群载流量.试验和计算结果表明,利用有限元计算地下电缆群温度场和载流量满足工程实际需求.     

电缆温度场的有限元分析

针对地下电缆结构和敷设过程中影响地下电缆输送能力的问题,应采取有效的方法对电缆的载流量和温度场进行准确分析计算.根据传热学原理,提出用有限元方法分析给定电缆负荷载流量和地下电缆温度场分布较为适宜.将该方法与IEC标准进行对比,完全符合要求.     

单芯电缆实时载流量计算方法研究

以电缆温度在线监测为基础,结合实时负荷数据和温度信息,采用有限元方法,对单芯电缆温度场进行分析,实时计算地下电缆的温度场和载流量。该计算方法考虑了外部土壤热阻的实时计算和更新,用环境温度、表面温度和实时负荷来间接计算。实验表明:该方法能准确获取电缆温度场和实时载流量,对提高电缆运行可靠性和输送能力具有重要意义。     

基于有限元法的地下电缆群温度场及载流量的仿真计算

结合传热学知识对地下直埋电缆温度场进行分析,构造出热传导方程和边界条件后,采用专业有限元软件建立了3根直埋单芯电缆的温度场模型,计算区域采用三角形单元剖分法。对电缆温度场分布及载流量的确定采用对分法进行迭代求解。通过仿真,分析了影响土壤直埋电缆载流量的各个因素以及各因素对载流量的影响规律,为工程实际提供了参考依据。     

10kV配网电缆温度场和载流量计算分析

为确保电缆能安全、正常工作,又充分发挥电缆的输送能力,采用精确方法预计地下电缆的载流量具有重要意义。针对10 kV配网常用三芯电力电缆,结合传热知识对10 kV配网直埋电缆温度场进行分析,构造出载流量和热流密度间的换算关系和边界条件,建立直埋三芯电力电缆的温度场模型,对电缆温度场和载流量进行仿真计算。在此基础上,基于IEC 60857给出的解析计算式进行验证分析,误差不超过0.6%,且与Q/GDW 512—2010《电力电缆线路运行规程》中规定的载流量值相差不大,误差不超过4%。最后,利用建立的地下直埋电缆温度场模型,分析了影响土壤直埋电缆载流量的影响因素及各因素对载流量的影响规律,为工程实际提供参考依据。     

地下电缆群暂态温度场和短时载流量数值计算方法

利用有限差分法将地下电缆群暂态过程分为离散的时间步,然后利用有限元法分析每一时间步的地下电缆群温度场分布,给出了土壤直埋电缆群的暂态温度场分布。在此基础上,利用牛顿迭代法计算了土壤直埋电缆群的短时载流量。试验和计算结果表明,利用有限差分和有限元计算地下电缆群暂态温度场和短时载流量为工程实际提供了一种新的计算方法。     

地下电缆载流量评估影响因素数值分析

利用有限元法对影响地下电缆温度场分布的地表空气温度、电缆埋地深度、土壤热阻系数、有无回填土、电缆排列方式、电缆接地方式等因素进行了分析,利用弦截法计算地下电缆群载流量,给出电缆载流量随各项参数变化的关系,为根据实际环境和敷设条件选择合适的电缆载流量提供依据。     

基于有限元法的排管敷设电缆温度场和载流量的计算研究

电力行业长期以来使用IEC 60287标准对地下电缆温度场和载流量进行计算,但该方法只适用于简单条件下的结果计算,不适用于过程分析。为研究排管敷设电缆工作时温度场和载流量之间的相互关系,为分析不同外界条件对温度场和载流量的影响情况,利用有限元法建立了排管敷设电缆温度场的仿真模型,对电缆的温度和载流量进行计算和分析。用IEC 60287标准对仿真模型进行验算,验证了仿真模型的有效性和准确性。由仿真结果可知,电缆工作时热量呈辐射型向四周传递,最终经过地表和左右远处土壤进行散热;管道内部受空气影响而难以散热。对地表温度、电缆间距和埋深等参数进行调整,分析了不同外界条件对排管敷设电缆温度场和载流量的影响,得出电缆间距在0.5 m、埋设深度在1.5 m以内时,调整间距和埋深会对电缆的温度和载流量产生较大影响。     

有限元法对电力电缆载流量影响因素的分析

地下电缆的载流量是决定电缆输送能力的一个重要参数,提高地下电缆的输送能力,对电缆的载流量和温度场进行准确分析具有重要意义。为此,利用有限元法对影响电力电缆载流量的空气温度、土壤温度、土壤热阻系数、电缆布置间距等因素进行分析,计算电力电缆的载流量并分析其与各项参数变化的关系,为工程在线分析提供参考依据。     

管道内填充导热介质提高电缆载流量

电力电缆排管敷设时,因预埋管中空气热阻较大,使其载流量比直埋方式的载流量有显著下降。为提高预埋管敷设方式下电缆输送能力,可向管道内填充导热介质以改善管道的散热状况。采用基于坐标组合的有限差分法,编制了电缆排管敷设温度场和载流量通用计算程序。程序计算结果与模拟试验及现场试验结果相符。计算结果表明,单回路电缆填充导热介质可提高载流量约5.6%,降低缆芯温度约7°C。多回路电缆由于电缆间的互热效应,填充导热介质对提高载流量的作用显著减小。管道内填充导热介质,可降低电缆运行温度,提高电缆输送能力。     

基于FEM的直埋电缆载流量与外部环境关系的计算

利用有限元法对有外部热源的直埋电缆区域进行剖分,计算了给定电缆负荷的温度场.利用对分法计算了导体温度等于绝缘长期耐受温度时的电缆负荷,确定了有外部热源和地表空气温度变化时的直埋电缆的载流量.计算结果给出了电缆载流量随电缆与外部热源间距的变化规律,以及电缆载流量随地表空气温度的变化规律,为工程实际提供了参考依据.     

Rating power cables in wrapped cable trays

Conductor temperatures for a given ampacity loading is a function of ambient temperature inside the tray. In other words, the ampacity of cables included in these tray systems has to be rated at the ambient temperature inside the tray. Cable overheating and eventual failure can result if cables are overloaded or not derated for operation. IPCEA Pub. No. 54-440/WC lists cable ampacities in air ambient temperature of 40°C. Cables operating at temperatures above this have to be derated accordingly. An algorithm is presented for determining ambient temperatures in the cable tray for conditions of natural air convection with different cable loading. Hence, derated cable ampacities can be derived from those at 40°C. Although at present, there is no industry standard for wrapped cable trays, the method used here can be used to develop such a standard     

Ampacity of diversely loaded cables in covered and uncovered trays

The existing code for ampacity of cables in a tray does not account for load diversity among the cables and it does not consider the presence of tray covers. This paper provides two factors that can be used to determine ampacity values for these two cases. These factors can be used in conjunction with existing code ampacity values so that cable ampacities can be calculated for diversely loaded, covered and uncovered trays. Also, the case of a few heavily loaded cables in an otherwise lightly loaded tray is addressed. This particular situation can produce nonconservative ampacity values if treated with a one-dimensional heat transfer model. The problem of both load diversity, and the presence of a cover are addressed with a computer code that has been described in previous papers. The computer model is designed to provide conservative ampacity values by assuming that the more highly-loaded cables are placed along the tray centerline and the lightly-loaded cables are positioned on the outer surfaces of the cable bundle. In this way the heavily-loaded cables are insulated from the environment and thus the program calculates a conservative cable temperature. The factors that account for load diversity show that a small percentage of cables in the tray can be loaded significantly beyond the code allowable ampacity value if the remainder of the cables are lightly loaded or unenergized. On the other hand, the code-allowable ampacity must be reduced by up to 25% when a solid cover is placed over the tray     

Probabilistic Determination of Power Cable Ampacity

ABSTRACT

A probabilistic evaluation of the ampacity of naturally cooled and forced-cooled 300 KV underground cables has been carried out from the deterministic sensitivity studies of cable ampacities. The results show that probabilistic studies of cable ampacities should be carried out because deterministic studies give conservative results.     

Temperature rise of submarine cable on riser poles

Results of outdoor temperature-rise tests on submarine power cables installed under guards on riser pole are presented. Test data were used to determine ampacities for three steel-wire armored distribution class cables under specific solar radiation conditions. The measured data also compared well with results from an existing cable ampacity computer program. Some discrepancies, however, indicated that the program predictions could be improved if eddy-current and hysteresis losses were considered in the calculation method used for single-phase cables on riser poles. For a valid comparison between measurements and calculations, it was necessary to account for limitations in the existing computation method by conditioning some program inputs. Consequently, a technique was developed for deriving a single-valued program input that would represent the effect of time-varying solar radiation. A thermal circuit used to determine the transient response of the cable/guard system is presented, along with values for the thermal parameters of three submarine cables. A revised method used to calculate the external heat dissipation coefficient for vertical cable guards is also described     

Ampacities of power cables wound on reels

This paper presents a mathematical model that is capable of calculating the ampacity of a wide variety of power cable designs consisting of an arbitrary number of layers on a cable reel. The model considers round cables with copper conductors. The validity and accuracy of the ampacity model were verified by comparing the predicted temperature distribution within the reel with measured temperatures collected during an extensive testing program conducted at the US Bureau of Mines (USBM). The mathematical model predicted a temperature distribution within the cable layers that was very close to the measured variation in temperature. The value of the program is illustrated by calculating ampacities for several copper conductor sizes     

Calculation of conductor temperatures and ampacities of cablesystems using a generalized finite difference model

The objective of this study is the development of generalized two-dimensional finite-difference model (FDM) for the calculation of conductor temperatures and ampacities of a cable-system with separation between the cables ranging from direct contact to a finite distance. The heat-sources or sinks which are the conductors are represented in the model as a two-dimensional finite-difference thermal resistance mesh, which is solved by iteration using the digital computer. The effects on conductor temperature due to skin effect, eddy currents, and associated losses have also been included in the analysis for completeness     

Power cable thermal analysis with consideration of heat andmoisture transfer in the soil

A method of numerically modeling coupled heat and moisture flow around power cables in steady-state and transient conditions that is based on the Philip and DeVries model for flow in soils is presented. The method has been implemented in a computer program for an IBM or compatible personal computer that utilizes the Galerkin finite-element method. The program uses sparsity-based algorithms that can handle large finite-element grid structures and calculate accurately the steady-state and transient temperatures, moisture distributions, and isothermal contours for power cables buried in media containing complex configurations of soil, boundaries, heat sources and sinks. The program has been validated by data from field tests, which show good agreement between predicted and measured results