Turbine, generator, system modeling and impact ofvariable-frequency ripple currents on torsional stressing of generatorsin Poland and Sweden: Lithuania/Poland and Sweden/Poland HVDC links

This paper analyzes rectifier ripple current superimposed on the direct current of a 600 MW asynchronous bipolar link between Lithuania and Poland and a 600 MW asynchronous monopolar link between Poland and Sweden in evaluating possible torsional vibrations in steam turbine-generator-exciter shafts. The studies are performed for machines in Northeastern Poland and in Southern Sweden close to the inverter station which are most at risk. Analyses are performed for the generators in Poland for the Lithuania/Poland link and for the generators in Sweden for the Poland/Sweden link. The paper examines system scaling factors for the Lithuania/Poland Link. It then examines AC system scaling factors and generator scaling factors for modulation product harmonic currents impressed on generators connected to the Swedish Grid Network by the inverter. Amplitude of shaft torsional torque due to resonant excitation imposed by the link on the generators in Sweden is evaluated for different scenarios of system and generator load. First, theory which relates magnitude of harmonic AC current injected into the AC system by the inverter is summarized. Dispersion of the injected harmonic AC current to proportion the current to individual generators is then reviewed, considering impedance of the generators, loads, and other system elements. Significance of simple and detailed shaft train models of machine shafts as well as approximate (Id, Iq) and detailed (2d, 3q) generator damper models on resonant torques is reviewed. Then, effects of both power factor and generator load on generator scaling factors is illustrated     

Preparing nurses for the inevitable: the New Madrid earthquake

Although this article discusses earthquake preparedness for the New Madrid seismic zone, registered nurses in any location will be on the front line as patient caregivers and managers in the event of a damaging earthquake. Two self-instructional modules were developed to educate registered nurses about earthquake preparedness. Statistical analyses of pretest and posttest scores from nurses who completed the modules and from nurses who participated in a control group reveal that the modules are effective educational tools. This information will make them more effective as nurses during and after an earthquake and emphasizes the need for their involvement in disaster mitigation and planning.     

Perspectives on the future of power generation and transmissionworldwide

A review is given of world-power demands, including energy-resource, environmental, technological, financial, and political aspects. International perspectives on the future of power generation and transmission to early in the next century in Germany, Italy, France, Japan, and the United States are provided. Discussed are nuclear power stations in Eastern Germany that are being closed down on safety grounds and the construction of semifinished nuclear plants that has been halted. Economic use of energy and combined heat and power is also evaluated. The Italian energy sector, which is the most import- and hydrocarbon-dependent of any of the major European economies, is discussed. Distribution of the generation between nuclear and hydro units in France is reviewed. International interconnections between France and European countries are discussed. Three major policy agendas for Japan are reviewed. A 1000-kV trunk line to transmit nuclear power to metropolitan areas that is under construction is also discussed. Proposed changes to Clean Air Acts to reduce SO₂ emissions from electric power generation in the United States are examined     

The Z4-linearity of Kerdock, Preparata, Goethals, andrelated codes

Certain notorious nonlinear binary codes contain more codewords than any known linear code. These include the codes constructed by Nordstrom-Robinson (1967), Kerdock (1972), Preparata (1968), Goethals (1974), and Delsarte-Goethals (1975). It is shown here that all these codes can be very simply constructed as binary images under the Gray map of linear codes over Z₄, the integers mod 4 (although this requires a slight modification of the Preparata and Goethals codes). The construction implies that all these binary codes are distance invariant. Duality in the Z₄ domain implies that the binary images have dual weight distributions. The Kerdock and “Preparata” codes are duals over Z₄-and the Nordstrom-Robinson code is self-dual-which explains why their weight distributions are dual to each other. The Kerdock and “Preparata” codes are Z₄-analogues of first-order Reed-Muller and extended Hamming codes, respectively. All these codes are extended cyclic codes over Z₄, which greatly simplifies encoding and decoding. An algebraic hard-decision decoding algorithm is given for the “Preparata” code and a Hadamard-transform soft-decision decoding algorithm for the I(Kerdock code. Binary first- and second-order Reed-Muller codes are also linear over Z₄ , but extended Hamming codes of length n⩾32 and the Golay code are not. Using Z₄-linearity, a new family of distance regular graphs are constructed on the cosets of the “Preparata” code     

Computer Programs for Fault Studies Using Symmetrical Components in Undergraduate and Postgraduate Teaching

ABSTRACT

The paper first reviews development of a digitial fault studies program for use in undergraduate and postgraduate teaching, highlighting aspects of program design. System data details: arrays containing details of system data: fault data; positive-, negative-, and zero-sequence network data; voltage arrays which store node voltages before and after the fault; corresponding current arrays; in addition to the file editor; routines for printing system data on screen or on paper; modifying system data; together with line data; and diagnostics are discussed for various shunt and series faults.

Improved routines which employ complex impedances to represent generators, transformers and transmission lines on the more common PC's are explained. Phase voltages and currents for both shunt and series faults which illustrate the effect of the more common approximations such as neglecting system resistance or approximating complex impedance to constant angle impedance in shunt and series faults are made.     

Performance of HVDC Converters in Enhancing Transient Stability of Power Systems and in the Torsional Stressing of Generator Shafts Due to Balanced and Unbalanced Operation of the Rectifier

This paper examines performance of HVDC converters with respect to real and reactive power at the inverter or rectifier following a command for power injected into or taken from the AC system to enhance power system stability. It also considers the effect balanced and unbalanced operation of inverters in asynchronous links has on torsional stressing of large turbine-generator shafts. First a 6-pulse bridge is modeledto determine characteristics for reactive power at both the inverter and rectifier as a function of AC power at the inverter or rectifier. Responses for real and reactive power following transient commands for AC real power are determined for a range of commands for real power to enhance transient performance of the power system. The characteristics relate to a link with typical parameters rated at 200 MW ~ 1000 MW. Performance of a 12-pulse bridge configuration that was modeled is then summarized. Noncharacteristic harmonic currents injected by the inverter into the AC system due to balanced and unbalanced operation of the rectifier in an asynchronous link is then reviewed. Excitation of turbine-generator shaft torsional vibrations by noncharacteristic currents injected into the AC system on account of balanced and unbalanced operation of the rectifier is then discussed.     

Integrating renewable energy sources into European grids

This paper examines the integration of new sources of renewable energy into the power systems in Europe—challenges and possible solutions, application of wind power prediction tools for power system operation, new tasks that create new solutions for communication in distribution systems, wind power in Greece, integration of dispersed generation in Denmark, wind power in The Netherlands, EdF and distributed energy resources in France, and new renewable sources in Italy. The paper also examines the European Commission Technology Platform’s vision paper on Electricity Networks of the Future that was published in January 2006. In this respect, drivers towards Smart Grids, Grids today, and key challenges for Smart Grids of the Future are critically assessed.     

Assessment of alternative energy sources for generation ofelectricity in the UK following privatisation of the electricity supplyindustry

The structure of the industry in Europe is reviewed along with profiles of electricity generation in Europe and the UK. The size, geographic location, and time scale of future electricity demand in the UK are evaluated, and shortfalls between estimated demand and predicted generation are assessed. Alternative energy sources are examined. These include tidal power from the proposed Severn Estuary Scheme, development of pumped storage such as that proposed at Craigroyston above Loch Lomond, small-scale hydro using low head hydro-turbines permitting development of previously uneconomic schemes on rivers, wind power from wind farms which would utilize the favorable wind patterns which exist in the UK, use of North Sea gas for combined cycle plant, development of small-scale coal-fired stations, particularly those which use the more efficient and cleaner fluidized bed system, and utilizing wave power     

Feasibility of Iceland/United Kingdom HVDC submarine cable link

The authors address: market considerations, including forecasts for the development of electricity supply in the United Kingdom with cost of electricity from new plant; investments for the development of hydro resources in Iceland, supply of submarine cables, overhead transmission lines, and rectifier/inverter plant; marine environment, installation of cables, and cable repair; rectifier/inverter station equipment; high-voltage direct-current (HVDC) overhead transmission lines; and overall availability of the link. It is shown that: there should be no major difficulties in the manufacture and laying of submarine cables of the length and type necessary for the link; the availability of the connection should be at least equal to that of a new coal or nuclear plant; and the cost of energy delivered would be very competitive with that from new coal or nuclear power stations     

A new approach to layered space-time coding and signal processing

The information-theoretic capacity of multiple antenna systems has been shown to be significantly higher than that of single antenna systems in Rayleigh-fading channels. In an attempt to realize this capacity, Foschini (1996) proposed the layered space-time architecture. This scheme was argued to asymptotically achieve a lower bound on the capacity. Another line of work has focused on the design of channel codes that exploit the spatial diversity provided by multiple transmit antennas (Tarokh et al. 1998, Hammons and Gamal 2000). In this paper, we take a fresh look at the problem of designing multiple-input-multiple-output (MIMO) wireless systems. First, we develop a generalized framework for the design of layered space-time systems. Then, we present a novel layered architecture that combines efficient algebraic code design with iterative signal processing techniques. This novel layered system is referred to as the threaded space-time (TST) architecture. The TST architecture provides more flexibility in the tradeoff between power efficiency, bandwidth efficiency, and receiver complexity. It also allows for exploiting the temporal diversity provided by time-varying fading channels. Simulation results are provided for the various techniques that demonstrate the superiority of the proposed TST architecture over both the diagonal layered space-time architecture in Foschini (1996) and the multilayering approach (Tarokh et al. (1999).