Long term test of buried gas insulated transmission lines (GIL)

Transmitting high amounts of electrical power with an underground transmission installation requires high performance systems with low losses due to thermal effects. Gas insulated transmission lines (GIL) are an excellent means of transmitting power in such a way. An analysis using the FEM-method (ANSYS) was carried out to study the unsteady state behaviour of buried GIL. In a long duration test the GIL the calculated results were compared to the results of the measurement to check the accuracy of the numerical model so that it could be used for the design and improvement of future applications.     

考虑大规模风电外送的半波长输电系统稳态电压控制方法

大规模可再生能源可以通过半波长输电线路实现远距离传输.本文针对考虑大规模风电外送场景的半波长传输系统提出了一种改进的稳态电压控制方法.首先,基于长线路分布参数模型推导出半波长线路特殊的电压分布规律.在二级电压控制层面,基于其电压特性,提出考虑对主导节点电压参考值跟踪的同时,通过限制半波长线路的无功传输实现对沿线稳态过电...     

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.     

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.     

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.     

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。     

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。     

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.     

Magnetic field of high‐phase order and compact transmission lines

Research has been conducted in high phase order (HPO) power transmission wherein 6 or 12 phases are used to transmit power in less physical space and with reduced environmental effects than conventional designs. In this paper, existing 3‐phase double circuit transmission lines (TL) are reconfigured to 6‐phase systems for the purpose of calculating and comparing the magnetic field of both systems. The magnetic field of several single‐phase configurations; flat, vertical, delta and inverted‐delta with the same degree of compaction is calculated and analysed at 1m height above the ground level. The magnetic field of the inverted‐delta arrangement, which showed the lowest field profile, is compared with the magnetic field of 6‐ and 12‐phase TLs having the same degree of line compaction and current loading conditions. The three systems are analysed when their lowest conductors had the same clearance to ground in one case and when their highest conductor positions were matched in another case. A comparison between 12‐, 6‐ and 3‐phase double circuit TLs having the same degree of compaction, the same phase voltage, the same clearance to ground and the same current per conductor is made to demonstrate if HPO lines reduce fields or not. The 6‐ and 12‐phase lines are raised while keeping their conductors within the space, which would be taken by the conductors of the double circuit line. In this case, the highest conductor positions of the two systems are matched and the magnetic field is recomputed to conclude the results. The vector magnetic field potential concept, as extended to HPO transmission lines, together with a flexible developed computer program are used to calculate and present the magnetic flux density components profiles around the mentioned systems. Copyright © 2002 John Wiley & Sons, Ltd.     

The economic value of transmission lines and the implications for planning models

Many connections between economic efficiency, regulation, the environment and energy markets are evident in the planning for transmission upgrades in an electricity network. Transmission owners have to make decisions about investing in new assets while facing uncertainty in the generation plans, regulatory and environmental constraints, and current system endowments. In this paper, we demonstrate an analytical method for determining the economic value of individual transmission lines in a meshed network by calculating the total welfare effects for the system. While many regulators believe that traditional congestion rents provide the correct incentives for investing in transmission upgrades, we show that the uncertainty in system conditions breaks down this paradigm. The analysis uses an existing Security Constrained Optimal Power Flow (SCOPF) model and a test network to demonstrate how the method can be used to determine the welfare effects of changing the capacity of selected transmission lines. The results show that a substantial portion of the economic benefits for an individual line may come from maintaining system reliability when equipment failures occur. Furthermore, these benefits can change dramatically when inherently intermittent sources of renewable generation are added to a network, and the changes in benefits are not captured effectively by changes in the expected congestion rents.     

Bargaining local compensation payments for the installation of new power transmission lines

This paper analyzes transmission system operator (TSO)-host community negotiations over an efficient and socially-optimal compensation payment for the installation of new electric power transmission lines. We consider that the TSO has an incentive to negotiate over a transfer that will become a function of final demand. We thus develop a bargaining game within a vertical relationship framework to include the distribution system operator (DSO) and the end-users at the downside of the bargaining problem. We determine the equilibrium of the game, for three negotiation protocols (sequential, bilateral, and multilateral) as an alternative to the non-cooperative situation. We show that when the number of municipalities involved in the process is higher than 5, the multilateral bargaining procedure is the most profitable for all agents, including the municipalities. Inversely, when the number of municipalities is lower than 5, different cases can arise. A single municipality will prefer the non-cooperative outcome while municipalities will prefer the sequential case when there are 2 or the bilateral case when there are 3 or 4. However, from the TSO standpoint and for the society, multilateral negotiations are always the best outcome.     

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.     

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.     

Distance protection of EHV long transmission lines considering compensation degree of shunt reactor

This study investigated the feasibility of distance protection in extra-high voltage (EHV) networks. In long-distance transmission lines, the distributed parameter characteristic of the EHV network is obvious. When a fault occurs far away from the measurement site, the measured impedance might not be directly proportional to the fault distance, and the protection domain of distance protection will be decreased. The detailed theory inferred and proven in this paper reveals that this phenomenon is widespread in EHV transmission lines. The results indicate that the protection domain error is greatly reduced by the application of the shunt reactor. Overall, simulation results show that the proposed method is effective for impedance relay, considering different characteristics, different lengths of lines, and compensation degrees.     

Analysis on the fault characteristics of three-phase short-circuit for half-wavelength AC transmission lines

Half-wavelength AC transmission (HWACT) is an ultra-long distance AC transmission technology, whose electrical distance is close to half-wavelength at the system power frequency. It is very important for the construction and operation of HWACT to analyze its fault features and corresponding protection technology. In this paper, the steady-state voltage and current characteristics of the bus bar and fault point and the steady-state overvoltage distribution along the line will be analyzed when a three-phase symmetrical short-circuit fault occurs on an HWACT line. On this basis, the three-phase fault characteristics for longer transmission lines are also studied.     

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.     

Fiber Bragg grating monitors for thermal and stress of the composite insulators in transmission lines

Running composite insulators are prone to failure due to their harsh surrounding work environment, which directly affects the safe operation of transmission lines. This paper puts forward the method of using fiber Bragg grating (FBG) as the monitors to parameters correlated with thermal and stress of the composite insulators in transmission lines at working status. Firstly, monitoring points are found out by the mechanical test on composite insulator samples. Secondly, based on the monitoring theory, this paper introduces the feasibility design frame of the composite insulator with FBG implanted in the rod and the online monitor system. At last, it describes applications of this monitor system in the field of transmission lines.