A novel approach for fault location on transmission lines

A new approach for power transmission line fault location is investigated. The fault locator estimation is based on the noise generated by the fault in the sending-end current signal. The proposed scheme consists of a wavelet-based filter module, a Prony-based signal processor and an ANN-based estimator. Input data has been generated using the Alternative Transient Program (ATP). A three-phase, frequency-dependent (FD) transmission line model was used. The scheme is tested using data employed in the ANN training as well as new data sets. The proposed locator has a good level of accuracy     

Optimization of Hellenic overhead high-voltage transmission lines lightning protection

It is well known that the lightning protection of transmission lines is exclusively relying on their correct initial design. Although detailed engineering studies are usually performed by electric power utilities for the design of new transmission lines, there are reported cases where the design is based simply on tradition or on utilities’ standardization policy. In this paper, the lightning protection of high-voltage transmission lines is faced as an optimization problem where optimum design parameters are calculated for the lines, relating their cost with the lightning failures’ cost, aiming to reduce or even eliminate lightning failures. The optimization method considers all the available protection means, i.e. ground wires and surge arresters. In order to validate the effectiveness of the proposed method, it is applied on several operating Hellenic transmission lines of 150 kV carefully selected among others due to their high failure rates during lightning thunderstorms. The obtained optimum parameters, which reduce the failure rates caused by lightning are compared with the operating transmission lines’ existing parameters showing the usefulness of the method, which can prove to be a valuable tool for the studies of electric power system designers.     

Highly insulated window glazing

The paper is introduced by a short survey of heat-transfer processes through a double-glazed window system. Network calculations show the advantage of a double-glazed window including at least one heat-reflecting filter and an IR-trans-parent foil. In the optimum system with one foil, the U_L value is slightly below 1 W/m²K. Several insulating glazing systems with air and with krypton filling are compared, and all U_L values are calculated. the application of an IR-transparent foil to a solar collector is discussed, and the measured top losses are given.     

Mathematical modeling of agricultural fires beneath high voltage transmission lines

This paper presents a mathematical model for agricultural fires based on a multi-phase formulation. The model includes dehydration and pyrolysis of agricultural fuel and pyrolysis products. The model considers a homogeneous distribution of the agricultural solid fuel particles, interacting with the gas flow via source terms. These terms include: drag forces, production of water vapour and pyrolysis products, radiative and convective heat exchange. A multi-phase radiative transfer equation for absorbing-emitting medium is considered to account for the radiative heat exchange between the gas and solid phases of the fire. The main outputs of the present model are most important to study the influence of agricultural fire occurring beneath high voltage transmission lines. The agricultural fire causes a flashover due to the ambient temperature rise and soot accumulation on the insulator of these transmission lines. Numerical results of the present model are obtained for flat grassland fires to study the effects of wind velocity, solid fuel moisture content and ignition length on some selected fire outputs. These outputs include the temperature, velocity, soot volume fraction fields of the gas phase, together with fire propagation rate and flame geometry. The numerical results are compared to the available experimental work in the literature.     

Electric field analysis of hybrid ac/dc transmission lines

In recent years, the possibility for ac and dc transmission lines running parallel to each other, sharing the same right‐of‐way (ROW) or even the same tower has been increased. Design of such hybrid ac/dc networks requires a precise calculation of the electric field around and under them. This paper presents quantitative analysis of the electric field at 1 m height above ground surface for different hybrid ac/dc transmission lines. Lateral profiles for typical Egyptian 500, 220 and 132 kV after adding bipolar dc lines are presented. The paper also considers reconfiguration of a typical 220 kV Egyptian double‐circuit ac transmission line, in which one of the circuits is converted into ±220 kV bipolar dc line. Different reconfiguration alternatives are studied to choose the optimum arrangement. The charge simulation method (CSM) employing the superposition principle is used to calculate the RMS value of the electric field generated by hybrid ac/dc lines at any point in the space. The RMS values of the field are determined directly without dividing the ac supply cycle into a sufficient number of subintervals as it has been done before. Satisfactory agreement with the results measured and calculated before by other techniques, for some typical ac/dc lines, has been obtained. Copyright © 2000 John Wiley & Sons, Ltd.     

特高压输电线路下方工频电磁场的研究

以前苏联特高压输电线路为模型，利用CDEGS软件包对影响线路下方地面以上的工频电场的对地高度、相间距离、分裂导线的根数、分裂间距、子导线直径等各种因素进行了仿真，得出升高相导线对地高度、减小相间距离、减少分裂根数、缩短分裂间距、选择小截面子导线均可以减小地面场强，其中提高输电线路对地高度的效果最明显。另外，还提出在相导线与地面之间安装屏蔽线的方法，并对架设2、3、5和7根屏蔽线的情况进行了仿真，仿真结果表明安装屏蔽线能明显地减小地面场强。     

特高压输电线路电磁环境研究的matlab实现

利用matlab软件对交流特高压输电线路的工频电场、工频磁场进行了详细的仿真研究,分别介绍了仿真模型的建立方法和程序的具体模块,并采用算例进行仿真,仿真结果表明,避雷线对输电线周围电磁场没有太大影响,而导线对地高度越高,地面附近的电场强度越弱。由此结果可见,采用增加导线对地高度等措施可以减小输电线路下的工频电场。仿真结果对特高压输电线路的建设有一定的指导意义。     

Impact of German Energiewende on transmission lines in the central European region

This paper analyses the impacts of the growth of renewable energy production and German nuclear phase-out on the electricity transmission systems in Central Europe. The principal concern is the significant disparity between the growth of renewable production and the pace at which new transmission lines for the transport of electricity have been built, especially in Germany. This imbalance profoundly endangers the system stability and reliability in the whole region. The assessment of these impacts on the transmission grid is analysed by the direct current load flow model ELMOD. Two development scenarios for the year 2025 are evaluated by 3 representative weeks. The results illustrate the issue from three different perspectives. First, the distribution of loads in the grids is shown. Second, hourly patterns during particular weeks are analysed. Third, a geographical decomposition is made, and problematic regions are identified. The high solar or wind power generation decrease the periods of very low transmission load and increase the mid- and high load on the transmission lines. High solar feed-in has less detrimental impacts on the transmission grid than high wind feed-in. High wind feed-in burdens the transmission lines in the north-south direction in Germany and water-pump-storage areas in Austria.     

Performance of antisolar insulated roof system

Rooms with concrete slab roofs directly exposed to the sun become unbearably hot during summer and very cold during winter. Huge amounts of energy are required to keep them comfortable. Application of thermal insulation on roofs significantly reduces energy required for heating and cooling. The effectiveness of roof insulations may be further enhanced if a layer of antisolar coating is applied on top of the insulation. The antisolar coating reflects most of the incident sunlight and prevents the roof from heating up. This reduces the daily cycles of thermal expansion and contraction which cause cracks in the roof slabs for the rainwater to leak through. The antisolar coating prolongs the useful life of the building structure as well as the life of the insulation that evaporates with heat. The method of application of the antisolar coating has been specially developed to eliminate thermal bridges formed between the edges of the tiles. This report presents the results of an experiment conducted at the Attock Refinery Limited (ARL) Rawalpindi to assess the performance of the antisolar insulated roof system. Record of the room temperature before and after the installation of the system shows a significant reduction in the indoor temperature. The room occupants, who used to experience a very high thermal stress after 10:30 am in spite of the 1.5-ton air conditioner operating in the room, felt much relieved after the installation. They had to turn back the thermostat of the air conditioner and even had to switch it off occasionally. A detailed thermal analysis of the room shows that cost of an antisolar system is paid back in less than a year in the form of savings of energy required for air-conditioning in summer and for gas heating in winter. In addition, the system prevents the addition of 150 kg per year of green house gases to the atmosphere for each square meter of the area covered by the system. It also provides a quieter environment by reducing the operational duration of the air-conditioning and gas heating appliances.     

Internally insulated pipes for district-cooling systems

A method is presented whereby, for any set of prescribed conditions, an optimal thickness of a thermally insulating internal lining may be determined for pipes to be used for the conveyance of chilled water. The optimum investigated in this paper corresponds with the minimum total rate off energy dissipation costs as a result of refrigeration and pumping. The overall optimal design cannot be decided at this juncture without a knowledge of such unknowns as the capital cost of internally lining the pipe.     

Thermal explosion theory for partially insulated reactants

Thermal stability of reacting masses of slab and cylindrical form, having parts of their surfaces insulated and the remainder offering no resistance to heat transfer, is investigated; only symmetrically heated reactants are considered. It is assumed that the ratio of insulation size to slab width or cylindrical radius is small; perturbation expansions are used to determine the critical Frank-Kamenetskii parameter as a series in terms of this ratio.     

Vehicular storage of hydrogen in insulated pressure vessels

This paper describes an alternative technology for storing hydrogen fuel onboard vehicles. Insulated pressure vessels are cryogenic capable vessels that can accept cryogenic liquid hydrogen, cryogenic compressed gas or compressed hydrogen gas at ambient temperature. Insulated pressure vessels offer advantages over conventional storage approaches. Insulated pressure vessels are more compact and require less carbon fiber than compressed hydrogen vessels. They have lower evaporative losses than liquid hydrogen tanks, and are lighter than metal hydrides.

The paper outlines the advantages of insulated pressure vessels and describes the experimental and analytical work conducted to verify that insulated pressure vessels can be safely used for vehicular hydrogen storage. Insulated pressure vessels have successfully completed a series of certification tests. A series of tests have been selected as a starting point toward developing a certification procedure. An insulated pressure vessel has been installed in a hydrogen fueled truck and tested over a six month period.     

New analytical solution for heat transfer in insulated wires

In this paper we investigate the heat transfer from pin-fins of infinite length made of a high thermal conductivity core with a low thermal conductivity coating. Considering a two-dimensional thermal field in the coating and a one-dimensional field in the core, an exact, analytical solution is presented for this geometry, previously not available in the literature. This solution is obtained in the form of an infinite series, but its first term can serve as an excellent approximation of practical problems under a wide range of conditions. In particular, the new model is appropriate to assist design engineers in calculating heat transfer losses from insulated wires, which can be conceived as infinitely long composite fins. The first term approximation is at once different and improves upon the traditional one-dimensional formula. Both approximations are compared vs. the exact series solution in order to establish their limits of validity. We have computed heat transfer losses for different combinations of core/coating pairs and typical geometric ratios pertaining to commercial electric wires. The figures show that the new solution produces better results than the traditional approach, especially for Bi < 1 × 10^?2 with relative errors below 1.35%. Thus, the new expedient proposed in this paper brings along a remarkable improvement, gaining accuracy and at the same time retaining a suitable simplicity.     

新型全绝缘熔断器在配电变压器中的应用

新型全绝缘高压喷射式熔断器是广泛应用在10kV架空配电开关柜的保护和开关设备,目前广泛采用的跌落式熔断器具有触头裸露、绝缘水平低、拉合操作有一定危险性等弊端,基于此,研发了适用于国内要求的熔断器,将绝缘防护性能和操作安全性均较常规的熔断器进行了较大改进,并按国内要求大幅提高了开断能力和耐压水平,可以拉合负荷电流,结合实际要求提出了全面的试验标准,并成功地通过了试验挂网运行。     

Laminar flows of heavy-fuel oils through internally insulated pipelines

For slow flows of hot oils through large diameter horizontal pipelines, natural convection currents within the oils affect the rates of heat transfer from the pipelines. This phenomenon is taken account of in the presented predictions of the optimal internal thicknesses of the pipes' thermally insulating liners, corresponding to the least rates of financial expenditure upon energy. The recommended average temperatures for the transmission of the oil through short pipelines are also predicted for a range of conditions commonly encountered.     

A new transparently insulated, bifacially irradiated solar flat-plate collector

A new type of transparently insulated flat-plate collector was developed. It reaches higher efficiencies at low irradiation values or high operating temperatures than any other collector type known. Both sides of its absorber are covered with transparent insulation material and both sides are irradiated. Thus, the heat losses of the collector related to the total absorber area are distinctly reduced. An optical efficiency of η₀ = 0.72 and a temperature dependent U-value of U(ΔT) = (0.95 + 0.0076 ΔTK⁻¹) W m⁻² K⁻¹ were measured with an outdoor test facility. The bifacial-absorber collector is considered to be the best option for the DHW system of the energetically self-sufficient solar house in Freiburg because of its outstanding winter performance.     

Numerical simulation of a building with one transparently insulated wall

A numerical simulation model is developed to study the thermal performance of an outdoor test-room with one Transparently Insulated (TI) wall. The thermal behavior of the room is examined under different control strategies for the shading device. Simulation results indicate significant energy savings. However, appropriate control strategies are required to prevent overheating of the room and discomfort.     

Aerogel and krypton insulated evacuated flat-plate collector for process heat production

We investigated the reduction of gas heat conduction in evacuated flat-plate collectors with operating pressures between 10³ and 10⁴ Pa. In stationary heat loss experiments with a real-size model the pressure dependency of the thermal losses was examined for air, krypton and for a nanostructured SiO₂-aerogel powder insulation between absorber and rear side of the casing. The theory for pressure dependent gaseous conduction was validated. Due to its high molecular mass, krypton as filling gas reduces gaseous conduction by 65% in the continuum range with respect to air. In a low emissive EFPC where gas conduction losses are comparable to radiative losses, the reduction in the total losses is about 30%. In principle, with unpacked aerogel the heat conduction could be reduced further: the nanostructures affect the gaseous heat conduction to be nearly totally suppressed below 10² Pa, because the mean free path of the gas is large compared to the pore dimensions of the aerogel. However, the applied packaging of PTFE-fabric compensates the excellent properties of the insulant due to solid conduction in the fabric.     

Efficient pumping of hot liquids through horizontal, internally insulated pipes

An optimal thickness exists for the internal, thermally-insulating lining of each length of pipe through which a hot liquid is pumped. Corresponding to this condition, a minimum total rate of energy loss from the pipe and pump occurs. The analysis presented in this paper enables the optimal thickness of insulant to be predicted as a function of the liquid properties and pipeline characteristics (e.g. roughness of the lining/liquid interface) for various assumptions.