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     

纵差保护用导引电缆的应用和设计

本文针对供电线路中 ,当系统发生短路故障时 ,会产生较高的纵向感应电势 ,引起纵差保护装置误动 ,甚至电缆绝缘击穿这一现象 ,提出了抑制电磁干扰的对策 ,并由此设计研制了导引电缆。     

Improvement in cable rating calculations by consideration of dependence of losses on temperature

In this paper a new method is proposed that allows estimation of conductor temperature and cable losses as a function of conductor current and some parameters corresponding to the nominal loading conditions. Such parameters include cable rating and loss factors computed by the cable manufacturer for the laying conditions specified by the user. There are two major applications of the proposed approach: one relates to rating of power cables with current measurements alone and the other to the computation of the external thermal resistance with a nonunity load factor used in the Neher/McGrath approach. Both applications are examined in this paper.     

计及管道特性的调压室三维流场计算研究

本文对两侧各接有较长管道的调压室系统实现了管道特征线法和调压室三维非定常流动的联合计算,即建立了联合计算模型,其调压室底部与管道连接处通过迭代计算而获得有机衔接。将其结果与建立在一维压力平衡原则基础上的调压室（一维）模型的计算结果进行比较,在一维模型孔口阻尼取值合适时,两者计算结果有很好的一致性。验证了用调压室一维模型来描述调压室的动态特性,有较好的准确度。但混合模型的计算结果能反映调压室孔口等部位的结构形式对流动的影响,从而使结果能更基础地显示调压井真实的动态性能。     

The calculations of conductive noise and heating of the screen in a control cable

Lighting strokes and short circuits (SCs) are the main sources of conductive noise that propagates along control cables and can lead to the failure of microprocessor equipment in the protection and control systems of electric power substations. Two-sided grounding of the screen of a control cable substantially reduces the pulse and high-frequency conductive noise level, but leads to heating of the screen under short-circuit conditions. The existing standards determine the conductive noise and screen heating as a function of screen voltage that is suitable for a single cable. A more general case that takes into account the cable magnetic coupling with other conductors when current is used as a calculation parameter has been considered. The conductive noise at the first pulse of lightning current is determined using the transfer impedance “screen–cable core” or 3D cable model in the general case. To calculate the heating, the formula of GOST (State Standard) 28895-91, which is rejected in modern standards because of the assumption that short-circuit current is invariable (in fact, the current decreases with heating of the screen), has been used. Using this formula in a step algorithm leads to correct results. The cable magnetic coupling with other conductors is expressed as insertion impedance that increases the screen impedance and decreases the current and screen heating. A numerical experiment for a typical cable has shown that conductive noise and heating of the screen of the cable can be substantially reduced because of the parallel laying of conductors. It has been concluded that, to decrease the conductive noise and heating of the screen of a control cable, it is necessary to decrease the screen current.     

考虑生态流量的水库优化调度模型研究进展

总结了考虑生态流量的水库优化调度模型研究进展,对目前主要的优化模型进行了分类阐述,给出了通用的模型结构;结合生态流量研究的发展和调度实践,分析了各优化模型的优缺点,提出了可行的改进方法;对常用的优化方法进行了评述,重点介绍了遗传算法及其应用。在此基础上,讨论和辨析了此类优化调度模型的发展方向。     

A consideration of potentials of low‐density polyethylene using metallocene catalyst as insulator for power cable

We investigated the high‐field conduction, DC and impulse breakdown strength, space charge distribution, and tree inception voltage for three kinds of new low‐density polyethylene (LDPE) prepared using a metallocene catalyst (mLna, mLao, mLldao), linear LDPE prepared using a Ziegler catalyst (LLao), and LDPE prepared by a high‐pressure process (LDna). The dc and impulse breakdown strengths of LDPEs prepared using a metallocene catalyst were higher than those of LLao and LDna. The high‐field currents of LDPEs prepared using a metallocene catalyst were lower than those of LLao and LDna. A homo‐space charge was accumulated near the cathode in mLna. The tree inception voltage of mLna was higher than that of LDna. From these results, it is concluded that LDPE prepared using a metallocene catalyst has electrical insulating properties superior to the conventional LDPE and that the former has potential as a power cable insulator. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(4): 17–25, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1164     

基于PSpice仿真的SLD控制电路降额设计

降额设计是电路可靠性设计中的一种常用方法,通过降额设计可以达到降低器件基本失效率、提高产品使用可靠性的目的.传统的降额设计存在计算量大、耗时长、是一种"静态"分析方法、无法估计器件瞬态应力的缺点,基于PSpice仿真的降额设计可以准确分析电路中各个器件的瞬态电应力和器件结温,同时在仿真软件中设置器件的Smoke参数、降额因子,可以直接输出所有器件的应力分析和降额情况,从而大大提高了降额设计的准确性和效率.本文采用OrCAD公司PSpice软件中的Smoke高级分析模块,对光纤陀螺光源(SLD)的驱动电路和温控电路的降额设计进行了仿真,验证了该方案的可行性,从而为电路的降额设计提供了一种新的手段,说明在Smoke分析基础上进行降额设计的研究具有重要的实用意义.     

考虑电压稳定约束含风电场的电网动态最优潮流研究

电压稳定性是风电场的并网运行后所需考虑的一个重要问题.在传统优化潮流的基础上,将改进后的电压稳定性指标引入到优化算法之中,研究了多时段不同穿透功率下的动态优化潮流.根据风力异步电动机的特性方程,将其模型与原始一对偶内点算法算法相结合,推导得出了考虑电压稳定约束含风电场的电力系统动态最优潮流计算的内点算法.该算法可有效保持内点法的收敛快、鲁棒性等优点,实现对系统的优化.最后,考虑不同穿透功率,对算例系统进行了优化计算,分析了风电场对系统的经济性和电压稳定性方面的影响.通过算例分析,得出了一些相关的结论.     

Determination of the reduction factor for feeding cable lines consisting of three single-core cables

The paper presents an original analytical procedure for the determination of the ground fault current distribution in the cases when a feeding line is composed of three single-core cables. The procedure takes into account the existence of all three cable sheaths as the return path for the ground-fault current. The reduction factor for these types of cables as given by the cable manufacturer takes into consideration only the existence of the metal sheath of a faulted single-core cable. As a consequence of that, the estimations of the safety conditions (step and touch voltages) on the grounding systems of the supplied stations are too severe. For the high-voltage cables, a certain, sufficiently low reduction factor achieved by an increase of the sheath cross-section can be demanded from the manufacturer. In both cases, too conservative values for the reduction factor lead to unnecessary expenditures. The quantitative analysis performed in this paper shows that the reduction factor for three single-core cables belonging to the same line is significantly lower in comparison to the situation when each of these cables is treated separately.     

发热电缆在住宅低温地板辐射采暖和管道保温中的应用

本文介绍了发热电缆的特点，阐述了如何应用发热电缆进行住宅低温地饭辐射采暖和管道伴热的设计?     

Critical heat flowrates in subcooled flow boiling

Matters related to calculating critical heat flowrates during boiling in a highly subcooled flow are considered. Existing data on heat transfer for swirl flow with one-sided heating are analyzed, and a formula for calculating critical heat flowrates is proposed. The conditions under which the thermodynamic limit of boiling is reached are analyzed.     

空调系统用平行流换热器的失效分析

随着原材料价格上涨、空调产品能效标准的不断提升,在空调系统中采用平行流换热器,是目前降成本并提高能效最有前途的形式之一.但因为平行流换热器的特殊形式,也容易出现比如芯体堵、芯体泄露、抗腐蚀性差以及用于热泵时结霜后融霜水不能完全排除等问题.对此,本文简单分析平行流换热器的失效原因,并提出相应的处理措施.     

Mathematical modeling of nonstationary processes of heat and mass transfer in a rectangular cable channel

This work is devoted to solving the problem of heat and mass transfer in a rectangular cable channel laid in the earth mass, taking into account the electric and magnetic dynamics processes in the metal elements of the power cable. The current load of power cables depends on the temperature field in the cable construction, which in turn the following factors influence: the conditions of heat transfer, thermal characteristics of the materials used, the induced currents in a metal screen of power cables, etc. The proposed mathematical model of the processes of complex heat and mass transfer is based on the laws of conservation of mass, momentum, and energy. For the electrodynamics problem, equations of current density and a magnetic potential vector based on Maxwell equations are used. The problem was solved numerically under conditions of natural convection with taking into account the radiant energy by the finite element method in the Ansys Fluent software package. As a result, the power of heat losses in the metal structural elements of the power cable and the velocity and temperature fields in the cable channel were calculated. The temperature fields in the cable channel are presented and analyzed depending on the location of power cables. The different operating modes of the cable line are discussed. To analyze the heat processes in the cable channel, the nonstationary problem defining the heating time of cable lines to the limit values is solved. The heating curves of the cable lines operating in unsteady mode are obtained. The maximum operating time of the cable line in an overload and short circuit is determined.     

FTLD线形测温电缆在电厂电缆沟火灾报警系统中的应用

针对大坝发电有限责任公司#1～#4机组电缆沟火灾报警系统存在的问题,通过对当前各种以测温电缆与感温电缆为主要检测元件的火灾报警系统工作原理及性能进行分析比较,提出以美国进口的线形温度探测器--FTLD测温电缆作为系统主要检测元件组成的火灾预警系统,可连续实时监测电缆沟内各区域的最高温度,克服传统的"点式"温度传感器只能探测"某点"温度以及感温电缆只能输出开关量信号,在火灾已发生,达到定温点后才能发出报警信号的不足。使用该系统对大坝#1～#4机组电缆沟火灾报警系统及防火门自动关闭系统进行完善后,系统维护量大大减少,可靠性大大提高。     

High-frequency modeling for cable and induction motor overvoltage studies in long cable drives

High-frequency simulation models for power cables and motors are key tools to aid a better understanding of the overvoltage problem in pulsewidth modulation drives with long feeders. In this paper, frequency responses of the cable characteristic and the motor input impedances are obtained experimentally and suitable models are developed to match the experimental results. Several lumped segments incorporating a lossy representation of the line are used to model the cable. The cable and induction motor models may be implemented using a computational tool such as MATLAB, thereby providing a convenient method to analyze the overvoltage phenomena. Simulation and experimental results are presented for a typical 3-hp induction motor, showing the suitability of the developed simulation models. The most promising dv/dt filter networks are also investigated through simulation analysis, and a design approach based on a tradeoff between filter losses and motor peak voltage is proposed. Experimental results of an RC filter placed at the motor terminals demonstrate the validity of the simulation models.     

热流计校准装置测量控制系统的建立

对采用绝对法的检零式箔加热热流源进行了改进,建立了校准热阻式热流计的整套新控制装置。采用PID调节实现主加热器与辅助加热器之间绝热面的零热流控制,基于LabVIEW软件平台实现整个装置的自动化控制、数据采集及处理。对检零热流计的热损失进行了实验评价和修正。校准结果因控制系统引起的标准不确定度优于1%。     

考虑电压因素的电力系统输电阻塞调度

针对开放输电环境下出现的由于电压稳定因素造成的输电阻塞问题,提出了一种考虑电压稳定的输电阻塞调度方法.该方法在传统的最优潮流优化算法的基础上,用负荷裕度指标作为系统电压稳定性的指示器,结合连续潮流算法对系统在正常状态和N-1事故状态下的电压稳定性进行分析,如果出现由于电压稳定约束造成的输电阻塞问题,将计算发电机有功出力对负荷裕度的灵敏度指标,以此作为依据调节发电机有功出力来增大系统负荷裕度,解决输电阻塞问题.该算法在6节点系统的应用效果表明了其有效性.     

用极低频以局放和损耗因数测量来鉴定中压电缆的新成果

引　言本文介绍采用一个 0 .1周正弦波极低频电源诊断系统进行现场试验的真实结果。这一采用新技术的新型诊断工具为地下电缆系统和电网的用户提供高效的测量步骤以判断老化特性、更换的需要程度以及更精确的投资规划预测。此外 ,远在击穿发生前这个方法提供了适时更换和对初期故障的预测。普遍使用这种诊断工具可以戏剧般地降低拥有者的投资 ,更换、维护和‘停电’的成本 ,同时可以得到较高的系统可靠性和配电的冗余度。以往 ,中压和高压电缆是用直流做试验的。它的好处是现场试验设备重量轻、便携带、使用方便和经济。在引入如聚乙烯、交…