European transmission interconnection: Eurasian power grid

The existing EHV/UHV installations and principal network configurations in Europe and the Soviet Union are described, focusing on the gap between them. It is argued that this gap can be closed by proven techniques, resulting in a completely interconnected Eurasian power grid. The possibilities for energy exchange that would result and the resulting advantages are discussed     

Re-thinking the power transmission model for sub-Saharan Africa

A vision for a United States of Africa has been advocated since the dawn of independence by, among others, pioneers like Kwame Nkrumah, Gamal Abdel Nasser and Julius Nyerere. More recently the idea gained new momentum, through such initiatives as the New Partnership for African Development (NEPAD) and the African Union (AU) to create a single market of Africa’s 750 million people that is competitive within itself and within the global economy. This would be achieved through a deliberate, systematic and concerted effort to integrate, upgrade and modernize infrastructure that would offer the required catalyst for economic growth. However, the prioritization by African policy makers of a grand plan to link up the entire African continent’s electric power grid networks would appear to be incompatible with 21st century thinking. The specifications for a centrally managed power grid were made by Nicola Tesla in 1883 and have served the power industry for over 125 years but are now obsolete in the era of digital micro-electronics and smart grid concepts. This paper examines some issues that surround the evolution of sub-Sahara African regional power pools and highlights the anomalies and perhaps wrong timing around the conceptualization and prioritization of grand inter-state power grids. The authors then propose an alternative model that conforms to a new and more sustainable paradigm in electricity supply economics. The proposals are however not meant to provide a panacea but it is hoped that the article will ignite a debate that will lead to a lasting solution.     

Health and safety issues for microwave power transmission

A general public perception that microwaves are hazardous has been a key obstacle for acceptance of microwave power transmission (MPT). This perception will eventually dissipate and then attention will focus on a real technical problem, that of interference (RFI). This can range from perceptible through annoying to hazardous. A program of actions is proposed to accelerate the goal of public acceptance of MPT.In this paper, a historical review shows that the solar power satellite (SPS) was reviewed a number of times relative to potential microwave exposure hazards. In all cases, no “show-stopper” was found but often the shibboleth “more research is needed” was aired. It is shown that standards for safe exposure to microwaves are the most important asset in convincing an audience that microwave exposure associated with MPT or SPS is safe. Standard-setting, world-wide, is shown to converge towards rational limits that are supportive of the MPT/SPS concepts. In recent times there has been the proposed substitute of “risk communication” (“prudent avoidance”). This is an unwise substitute for standards.Other aspects of microwave exposure standards are the new interface with RFI—hence the need for a rational division of responsibility between the radiators and the victim devices, like medical electronics—using both radiation limits and susceptibility limits. Beneficial applications of microwave exposure are being developed.Several studies are recommended which could put into perspective the likelihood of improbable events that represent “catastrophe”—e.g. the inadvertent focusing of a great amount of energy into inhabited areas.     

Superconducting power transmission: The perils and promise

The development of bulk electricity transmission systems must be considered in the light of changing growth rates, increasing resistance to EHV overhead transmission and the tendency to concentrate generation in fewer sites. Helium-cooled, or superconducting, cables possess technical characteristics which will make them suitable as utility network components for power transmission over distances of ten to several hundred miles. These properties are illustrated by considering two applications in existing electrical networks. The first is a 43 mile system to transmit 4800 MVA and the second is a potential application under study in Pennsylvania to transmit 10,000 MVA over a distance of 350 miles or so. Helium-cooled versions of these transmission systems were designed to permit technical and economic evaluations.The major groups and institutions throughout the world engaged in the development of helium-cooled cables are listed and aspects of the technical approaches are briefly described.     

Calculation of economic transmission connection capacity for wind power generation

Applications for the connection of large-scale wind power generation to transmission networks are presenting new issues both for transmission system planners and generation developers. One of the major problems faced is the assessment of transmission system capacity requirements for the export of power from areas with high penetration of variable and intermittent sources of generation such as wind power. A method for evaluating the required transmission connection capacity from an area dominated by wind generation to the main interconnected system is presented, based on historical time series data for both wind power generation output and the demand in the group. The operational implications for the transmission system and generation owners are evaluated using a cost-benefit approach. The method is demonstrated for a number of network situations. Conclusions are drawn about the value of the method and, more generally, about the trade-off between investment in transmission capacity and curtailment of wind generation under favourable wind conditions     

The history of wireless power transmission

The history of wireless power transmission at microwave frequencies is reviewed with emphasis upon the time period starting with the post World War II efforts to use the new microwave technology developed during the war. A nationally televised demonstration of a microwave powered helicopter at the Spencer Laboratory of the Raytheon Co., in 1964 was the result of these early efforts and broadly introduced the concept of wireless power transmission to scientific and engineering communities and to the public. Subsequent development efforts centered on improving the efficiency of the interconversion of d.c. and microwave power at the ends of the system to reach a demonstrated overall d.c. to d.c. system efficiency of 54% in 1974. The response to the requirements of applications such as the Solar Power Satellite and high altitude microwave powered aircraft have changed the direction of technology development and greatly expanded the technology base. Recent and current efforts are centered on examining the use of higher frequencies than the baseline 2.45 GHz, and in reducing the system costs at 2.45 GHz.     

基于PSASP和Power Factory的分解协调式输配一体化潮流计算

大量分布式电源的并网改变了配电网单向潮流特性,输电网和配电网之间的耦合更加紧密,电力系统呈现出主配网一体化的特点。文章提出了基于分解协调的主配一体化潮流计算方法,分别采用PSASP和Power Factory进行输电网和配电网的计算,设计了主网和配网潮流的边界协调方程,并采用Jacobian-Free Newton-GMRES(m)方法进行求解。测试结果表明,文章所提方法收敛性较好,计算精度高。     

大功率、高效率油田用液力传动装置的研制

通过对现有钻机传动装置的优缺点进行分析,结合液力传动的特点,相继开发了大功率、高效率的YO750、YO7503偶合器传动箱。使油田动力机组的效率提高了14个百分点,大大节省了燃油消耗,提高了动力机组及传动部件的寿命。     

Cool thinking: Unlocking earth's energy

The ground is as universal as air and solar radiation. Over the past twenty years, as the hunt for natural low-carbon energy sources has intensified, there has been an increased endeavour to investigate and develop both earth and ground water thermal energy storage and usage. Bill Holdsworth reports on some recent pioneering developments in the Netherlands and UK.     

A new method for determining reference compensating currents of thethree-phase shunt active power filter

Among various solutions to electric power quality problems, the use of a shunt active power filter (SAPF) has been proven as an effective method to compensate reactive power and to mitigate harmonic currents of nonlinear loads. When designing a SAPF, it is crucial to generate reference currents for determining actual compensating current injections to the point of common coupling. In contrast to the conventional instantaneous reactive power theory that needs coordinate transformations, the new method proposed in this paper is to determine reference compensating currents based on the balance of the instantaneous reactive and active power generated in the SAPF. It is shown that the proposed method is suitable for reactive and harmonic power compensation by using a SAPF. In addition to maintaining the sinusoidal source currents, this method also eliminates the need for installing an energy storage device for reactive power compensation as well as the DC source for the harmonic compensation in the active power filter. Therefore, a simpler design of the SAPF with the minimal line losses can be expected     

Estimating the power potential of tidal currents and the impact of power extraction on flow speeds

A simple method for estimating the potential of currents in tidal channels to produce power is presented. The method only requires measurement of the peak tidal volume transport through the channel without turbines, along with a bottom drag coefficient and the channel’s dimensions. A recent existing method for estimating potential requires measurements of the undisturbed transport as well as water levels at both ends of the channel to give the head loss. The adaptation of the existing method presented here exploits analytic solutions for the transport and optimal farm drag coefficient and does not require measurement of the head loss. The equations presented allow both the channel’s potential and the flow reduction due to power extraction to be estimated using a calculator. Thus the presented method has much of the ease of use of the older KE flux method, but is more reliable as it includes retardation of the flow by the turbines. The presented method can be used for the initial assessment of channels to determine if the additional measurements required to use the existing method are warranted. It can also be used where the headloss in the channel is too small to measure reliably. The presented equations enable the maximum power available to be simply traded off against environmentally acceptable flow speed reduction. The presented method is applied to two example channels. Cook Strait NZ has an estimated potential of 15 GW, while the entrance channel to Kaipara Harbour has a potential between 110 MW and 240 MW.     

Electrical power generation from ocean currents in the Straits of Florida: Some environmental considerations

Ocean currents contain a remarkable amount of kinetic energy and have potential worldwide capability. Initial tests to harness current power focus on the Straits of Florida where the Florida Current has a total flow capacity of about 30 × 10⁶ m³ s⁻¹. Generation of clean electricity from ocean currents off southeast Florida is based on a power extractor comprising open-center turbine technology. This innovative turbine provides safe passage for fish and other aquatic species. The water-column array of energy production units (EPUs) will have a 350 km² footprint, based on a 600 m (10 rotor diameters) downstream separation distance between EPUs with a lateral separation of 400 m. Water depths for the EPU field are in the range of 100–500 m. With such a large area of water column and benthic habitat utilized, environmental concerns must be overcome, including routing of transmission lines to shore. Risks and vulnerabilities of the proposed ocean current generated electricity include failure of individual EPUs and damage to sensitive coastal marine environments during installation.     

An overview of power transmission systems in China

In the past 20 years, China's economy has grown rapidly, but so has the country's power industry. This paper provides a comprehensive introduction on the current status and the future development of the power transmission systems and grids, which include HVAC and HVDC transmissions, regional power grids and grid interconnections, several important operational issues, e.g., stability problems that China's power grids face, new technologies for increasing transmission capacity, and stabilizing the grids, and so on. Under the constructed UHVAC and UHVDC, some pilot projects and planned future development of UHVAC and UHVDC transmission systems are also introduced.     

Solar thermal power system based on optical transmission

In the solar tower concept, a multiplicity of mass produced heliostats reflect sunlight to a an elevated central receiver where it is absorbed as heat and transported to the ground. This paper presents the results of an NSF/RANN funded study of the technical and economic feasibility of this approach for powering a 10–500 MW electrical generator. A computer model of the collector system is described and results illustrative of the high performance of the system are presented. Detailed heliostat design studies have shown a silvered float glass mirror supported on a welded steel grid and guided in elevation and azimuth by a receiver oriented optical sensor and feedback circuit can be mass produced economically. Conceptual designs of the tower and receiver show them to be a minor cost component. With careful attention to thermal cycle fatigue, the receiver will present only a minor technical risk. The cost of electricity in the intermediate load range is competitive with the upper range of fossil fuel costs.     

可逆流光伏与市电联合供电能量管理研究

针对光伏直流供电系统的能量变动性,提出了使用市电作为直流负载的能量补偿来源。系统由光伏电池、市电、移相全桥变换器、PWM整流器组成。在光伏发电能量大于负载所需时,将多余的能量馈送电网;在光伏发电能量不足时,由市网补充。系统的核心是实现光伏、市电、负载三者之间的能量管理。文章首先对整个供电系统进行了分析,然后讨论了系统的不同工作模式,最后提出了市电的能量补偿控制策略。仿真和实验表明所提的系统结构和控制策略能够实现市电与光伏供电系统的稳定联合供电。     

Status of international experimentation in wireless power transmission

An overall view of past, present and proposed wireless power transmission projects is presented. Activities in the United States, Canada, France, the former Soviet Union and Japan are highlighted. The recent Japan-U.S. space to space wireless power transmission demonstration ISY-METS is described. Japan's recent feasibility study for large-scale space solar power transmission for terrestrial use is examined. In particular, proposals for utility experimentation and the use of wireless power transmission for telecommunications platforms are discussed.     

含柔性直流输电的海上风电场群无功控制策略

大规模海上风电场集群并网将对电力系统静态电压稳定产生影响。文章通过研究电网侧发生电压跌落或者上升,提出含柔性直流输电海上风电场集群的协同无功控制策略。该策略以电网故障节点电压快速恢复为目标,考虑了柔性直流输电方式的特点,充分利用交流海底电缆的输电特性,采用就地控制和远方控制相结合的无功控制策略。该策略首先确定含交直流柔性输电系统中的无功控制节点,并计算各节点相对电压跌落或上升节点的电压/无功灵敏度,然后基于无功补偿装置的运行状态、系统潮流分布,求解各节点控制的最大容量,最后利用遗传算法确定各控制节点的无功控制量。以改进IEEE 39节点系统为算例进行了仿真分析,结果表明,该策略提高了海上风电场集群对电网电压的支撑作用。     

Challenges facing the European power transmission tariffs: The case of inter-TSO compensation

This article draws attention to problems important for all EU power consumers—the unfairness in individual payments for power transmission and in the cross-border subsidy element in the mechanism of Inter-Transmission System Operators (TSO) Compensation (ITC). A brief review of power transmission tariffs brings out the structure of the problems. A short retrospection explains their growth. The essence of the ITC mechanism is explained and existing shortcomings are illustrated. The deficiencies of existing regulations for transmission pricing are analyzed. In the light of this analysis, the ITC problem is reconsidered and defined more precisely. The basic prerequisites to an ITC reformulation process are presented. The main principles of a new simple, transparent and equitable approach are suggested, in accordance with the contemporary legal positions and functions of the TSOs.     

Bridging the scales: A conceptual model for coordinated expansion of renewable power generation,transmission and storage

To analyze the challenge of large-scale integration of renewables during the next decades, we present a conceptual power system model that bridges the gap between long term investment allocation and short-term system operation decisions. It integrates dynamic investments in generation, transmission and storage capacities as well as short-term variability and spatial distribution of supply and demand in a single intertemporal optimization framework. Large-scale grid topology, power flow distributions and storage requirements are determined endogenously. Results obtained with a three region model application indicate that adequate and timely investments in transmission and storage capacities are of great importance. Delaying these investments, which are less costly than investments in generation capacities, leads to system-wide indirect effects, such as non-optimal siting of renewable generation capacities, decreasing generation shares of renewables, increasing residual emissions and hence higher overall costs.     

Electricity transmission tariffs for large-scale wind power consumption in western Gansu province,China

Large-scale wind power transmission presents the power system with several challenges. The determination of the transmission tariff and the cost-sharing issue are potential obstacles which may influence the development of wind power. This paper analyses the incremental cost to the power system for long-distance transmission of wind power, considers the fixed and variable properties of the incremental cost and the risk of fluctuations in the cost, and establishes a comprehensive risk-based pricing model for long-distance transmission of large-scale wind power electricity. Gansu Province in China has abundant wind resources, so we use the Jiuquan wind power integration and the ±800 kV Gansu-Zhuzhou direct current (DC) power transmission as examples to test the validity of the model. The conclusions are as follows: the allowances for access grid connection cost should be separately estimated for the large-scale wind power base and long-distance transmission; and the long-distance transmission pricing of large-scale wind power should apply a two-part electricity transmission pricing system, in order to eliminate the volatility risk inherent in each simple allocation method, and the fixed and variable characteristics of the transmission cost. The transmission price must include compensation for depreciation, operation and maintenance costs, and also a reasonable return on investment, in order to offer an effective incentive and guidance mechanism for enterprises’ business development.