A Sampling Approach for Intentional Islanding of Distributed Generation

This paper proposes an innovative way of making a decision to island (or synchronize) distributed generators when operating conditions of a distribution system are varied. Islanding decisions are made when a network undergoes disturbances. In this approach, there is a decision-making mechanism, which samples states of the network operating condition to either synchronize or island in an identified period of time. Decision making is achieved through extended sequential sampling, which manages generator states within specific time periods. The approach can minimize the duration of islanded operation and manage generators' re-connection to the grid. Use of the proposed mechanism and sampling approach offer benefits over conventional relays; incorrect operations due to errors in measurements are reduced because the operational actions are not based on a single decision sample, but instead rely on extended sequential sampling over a number of samples. A case study is investigated using the IEEE 30-bus test system and the results are presented for this new approach     

Value of security: modeling time-dependent phenomena and weather conditions

Deterministic security criteria provide a degree of security that may be insufficient under some operating conditions and excessive for others. To determine an appropriate level of security, one should perform a probabilistic cost/benefit analysis that balances the cost of the security margin against its benefits, i.e., the expected societal cost of the avoided outages. This paper shows how a previously published method based on Monte Carlo simulation can be enhanced to take into account time-dependent phenomena (TDP) such as cascade tripping of elements due to overloads, malfunction of the protection system, and potential power system instabilities. In addition, the importance of using failure rates that reflect the weather conditions is discussed. Studies based on the South-Western part of the transmission network of England and Wales demonstrate the validity of the models that have been developed.     

Dye-sensitized solar cell with the hole collector p-CuSCN deposited from a solution in n-propyl sulphide

A method is devised for the deposition of CuSCN on ruthenium bipyridyl dye coated nanocrystalline TiO₂ films from a solution in n-propyl sulphide. The dye-sensitized solid state photovoltaic cell formed was found to yield higher short-circuit photocurrent, open-circuit voltage and efficiency compared to the cells made with CuSCN by other deposition techniques. Factors affecting the stability of the cell are investigated.     

Effect of various coal gas contaminants on the performance of solid oxide fuel cells: Part III. Synergistic effects

The coal-derived gas from a coal gasifier contains multiple contaminants, and their synergistic effects may not be simply the additive influences of individual contaminants. The present work presents the results of a study of the synergistic effects of four contaminants of major concern—S, As, P, and Cl, at the ppm level and in combinations of two, three, or four kinds—on the performance of Ni-YSZ/YSZ/LSM solid oxide fuel cells. The results indicate that both cell performance and morphology differ significantly in cells exposed to a single contaminant, and that cell performance is not simply the additive influence of each contaminant. Synergistic effects can be very destructive (accelerated degradation or even cell failure) when S is in the presence with As/P, but can also be beneficial (stabilization in power density variations over time or a slowed degradation rate) when Cl is present with other contaminants. Cl can even partially restore performance loss when it is introduced after P is already present. Therefore, with the addition of Cl the tolerance limit of SOFCs for the other three contaminants can be greatly increased. We speculate that the affinity of the contaminants to Ni catalyst increases in the following order: As < P < Cl. The interactions between and among these contaminants and possible mechanisms for their destructive and beneficial synergistic effects are discussed.     

Virtual MIMO-based cooperative communication for energy-constrained wireless sensor networks

An energy-efficient virtual multiple-input multiple-output (MIMO)-based communication architecture is proposed for distributed and cooperative wireless sensor networks. Assuming a space-time block coding (STBC) based MIMO system, the energy and delay efficiencies of the proposed scheme are derived using semi-analytic techniques. The dependence of these efficiency values on physical channel propagation parameters, fading coherence time and the amount of required training is also investigated. The results show that with judicious choice of design parameters the virtual MIMO technique can be made to provide significant energy and delay efficiencies, even after allowing for additional training overheads.     

Comparison of risk-based and deterministic security assessments

The traditional N - 1 security criterion provides only a limited perspective on the actual level of security of a power system and a risk-based approach to security assessment provides considerably more information on which to base operating decisions. It further argues that this risk should be measured in terms of expected outage costs to the consumers. Furthermore, the risk calculation should not be limited to the consideration of a predefined set of contingencies but should factor in the actual probabilities of outages leading to load disconnections. A case study based on the IEEE-Reliability Test System shows that different operating points on the system's deterministic security boundary have very different levels of risk. For a given operating point, the risk level changes considerably between fair, average and bad weather conditions. Finally, the paper shows how, using adaptive deterministic security boundaries, it is possible to compare the cost and benefit of relaxing operating limits.     

Computer-aided facility layout — A status report

In this paper, an up-to-date review of literature on computer-aided techniques in plant layout is presented. Mathematical models in the area fall into categories of quadratic assignment models, set covering problem, integer and mixed integer programming models, nonlinear programming models and graph theoretic models. The algorithms are optimal or heuristic. The heuristic algorithms considered are construction, improvement, hybrid and fuzzy-set based algorithms. Special considerations are given to multi-criteria models/algorithms and algorithms based on artificial intelligence which are either pure expert systems or hybrid methods. Important issues in facility layout are also discussed. Deficiencies in current methods may be overcome by the use of AI based tools. More research is required in this area.     

Formation and reactivity of nitrides. III. Boron,aluminium and silicon nitrides

The reactivities of boron, aluminium and silicon nitrides have been compared. Samples of these nitrides have been converted to oxides by being calcined in air. Changes in phase composition, surface area, crystallite and aggregate sizes have been correlated with oxidation time and temperature. Crystallites of alumina, α-Al₂O₃, split off from the remaining aluminium nitride before they sinter and inhibit further oxidation. The diboron trioxide, B₂O₃, and silica, SiO₂ (α-cristobalite), immediately act as mineralisers for the remaining boron and silicon nitrides, and progressively retard the oxidations.     

Formation and reactivity of nitrides II. Calcium and magnesium nitrides and calcium cyanamide

Samples of calcium and magnesium nitrides have been prepared and hydrolysed ‘dry’ with water vapour and steam or ‘wet’ with liquid water. Changes in phase composition, surface area, crystallite and aggregate sizes have been correlated with hydrolysis conditions and compared with ‘dry’ and ‘wet’ hydration of lime and magnesia. The reactions involve the splitting of nitride and oxide crystallites and the subsequent ageing of the newly formed calcium and magnesium hydroxides. Hydrolysis of calcium cyanamide has been studied similarly. The intermediate product, hydrated lime, has been separately reacted with urea solutions and gives calcitic rhombs having a wide crystallite size range.     

Versatile multispectral microscope based on light emitting diodes

We describe the development of a novel multispectral microscope, based on light-emitting diodes, capable of acquiring megapixel images in thirteen spectral bands from the ultraviolet to the near infrared. The system captures images and spectra in transmittance, reflectance, and scattering modes. We present as examples of applications ground truth measurements for remote sensing and parasitology diagnostics. The system is a general purpose scientific instrument that could be used to develop dedicated simplified instruments with optimal bands and mode selection.