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Over the last decade there has been a growing increase in research in the field of vibrational energy harvesting - devices which convert ambient vibrational energy into electrical energy. The major application area for such devices is as power sources for wireless sensors, thereby replacing currently used batteries which suffer from a finite lifespan and pose environmental issues during disposal. The vast majority of designs are cantilever beams comprising of piezoelectric layers having coverage identical to the substrate layer. It is evident from the literature that rudimentary work has been performed on design optimisation, with reliable and extensive parametric studies on geometry, especially piezoelectric layer coverage, being overlooked. As a result of this, outcomes from previous research are yet to be seen in designs for practical applications. In this work a versatile linear model is developed which can accurately predict the performance of cantilever piezoelectric energy harvesters. An integral part of the model uses a transfer matrix method to accommodate the difference in structural dynamics of both uniform and non-uniform structures with model validation provided through extensive experimental work. The linear model developed is used to carry out parametric studies on the geometry of three distinct energy harvester cases thereby providing comprehensive knowledge on key variables and geometrical changes which can improve performance. In one of the cases examined, an improvement in performance of over 100% is predicted by solely altering piezoelectric layer coverage. However, the load resistance, i.e. electrical condition, has a significant effect on the trends in generated power which led to work directed toward harvester optimisation in a more realistic electrical scenario. Investigation on harvester geometry whilst utilising an electrical scenario comprising of an energy storage medium is undertaken in this work. The developed model ensures the effects of electro-mechanical coupling remain and provides a solid basis from which users can readily apply model extensions through inclusion of further electrical components to resemble practical circuitry. Theoretically, for all examined case studies, improvements in performance were realised through alterations to piezoelectric layer dimensions with the most notable result indicating an improvement of over 200% during optimisation of piezoelectric layer length. In conjunction to theoretical findings, outcomes of extensive experimental work are provided in order to highlight the accuracy and reliability of the presented theoretical models in both electrical scenarios. Variation in mechanical damping magnitude plays a pivotal role throughout experimental testing and is one key factor in explaining why devices comprising of shorter piezoelectric layers have high performance. A methodology behind unbiased design comparisons is also provided in this work, and involves comparing devices with identical fundamental frequencies. The reasoning behind this approach is to allow for each device to perform as efficiently as possible in the same excitation scenario. Systematic alterations to multiple geometric parameters are used to achieve this. Geometric parameters such as the substrate thickness are observed to provide adequate frequency control. Using this approach, performance improvements from adjustments to piezoelectric coverage still remain. The occurrence of non-linearity in piezoelectric materials is a widely known phenomena and so lastly, a more robust model is provided which incorporates material and geometric non-linearity. This model is useful in determining dynamical responses of uniform and non-uniform piezoelectric energy harvesters when subjected to moderate-to-high acceleration levels. A thorough validation of the theoretical model is achieved using extensive experimental data obtained from a range of samples. For the harvester composition tested in this work, the occurrence of mild non-linearity at base acceleration levels as low as 1 meter per second squared is witnessed with softening behaviour causing the resonant frequency to decrease with base acceleration. In order to avoid reduced efficiency in the final application, the prediction of possible frequency shifts is vital during the design process.

The numbers of smaller scale distributed power generation units connected to the distribution networks of electricity utilities in the UK and elsewhere have grown significantly in recent years. Numerous economic and political drivers have stimulated this growth and continue to provide the environment for future growth in distributed generation. The simple fact that distributed generation is independent from the distribution utility complicates planning and operational tasks for the distribution network. The uncertainty relating to the number, location and type of distributed generating units to connect to the distribution network in the future makes distribution planning a particularly difficult activity. This thesis concerns the problem of distribution network and business planning in the era of distributed generation. A distributed generation strategic analysis framework is proposed to provide the required analytical capability and planning and decision making framework to enable distribution utilities to deal effectively with the challenges and opportunities presented to them by distributed generation. The distributed generation strategic analysis framework is based on the best features of modem planning and decision making methodologies and facilitates scenario based analysis across many utility strategic options and uncertainties. Case studies are presented and assessed to clearly illustrate the potential benefits of such an approach to distributed generation planning in the UK electricity supply industry.

Computer programs have been developed to enable the coordination of fuses and overcurrent relays for radial power systems under estimated fault current conditions. The grading curves for these protection devices can be produced on a graphics terminal and a hard copy can be obtained. Additional programs have also been developed which could be used to assess the validity of relay settings (obtained under the above conditions) when the transient effect is included. Modelling of a current transformer is included because transformer saturation may occur if the fault current is high, and hence the secondary current is distorted. Experiments were carried out to confirm that distorted currents will affect the relay operating time, and it is shown that if the relay current contains only a small percentage of harmonic distortion, the relay operating time is increased. System equations were arranged to enable the model to predict fault currents with a generator transformer incorporated in the system, and also to include the effect of circuit breaker opening, arcing resistance, and earthing resistance. A fictitious field winding was included to enable more accurate prediction of fault currents when the system is operating at both lagging and leading power factors prior to the occurrence of the fault.

Type 11 hot corrosion has been identified as a major life limiting factor of gas turbine components in the topping cycle of coal fired combined cycle power plant. Impurities in the coal combustion gases provide the environmental contaminants necessary for type 11 hot corrosion to occur. It is the purpose of the present study to develop corrosion lifting models such that corrosion rates and thus component lives in coal fired combined cycle plant gas turbines may be accurately predicted thus minimising efficiency losses and plant downtime due to corrosion related problems. Type 11 hot corrosion has been shown to follow bi11lodal distributions which cannot be modelled using the well known mathematical models. It has been shown that a probabilistic approach to modelling is appropriate and that the Gumbel Type I extreme value model of maxima can be used to model the maximum extreme corrosion data This is appropriate as it is the maximum extreme corrosion which in life limiting in the plant gas turbine. Basic corrosion data has been generated through a series of laboratory hot corrosion tests designed to simulate the ambient conditions within the plant gas turbine. The variables having most influence on the corrosion process have been identified as ; temperature, thermal cycling, alkali (Na + K) metal sulphate deposition rate, S02 and HCl in the ambient atmosphere. The corrosion models have been developed from this data which accurately predict the type 11 hot corrosion rates observed in the coal fired gas turbine of a combined cycle power plant.

Cyprus is an island in the Mediterranean Sea. It has an isolated electricity grid and energy system which is fully reliant on imported fossil fuels. Burning fossil fuels for electricity generation has a negative impact on the environment due to the greenhouse gas emissions and importing the fuels places a huge burden on the economy of the country and a risk in terms of the electricity supply security of the island. One way to reduce dependency on imported fuels is to implement renewable energy solutions in the island. There are many studies assessing the availability of renewable energy sources, evaluating future electricity demand and investigating methods of demand reduction in Cyprus but there are a very limited number of studies specifically produced for Cyprus that address the integration and cost of renewable energy sources and explore their effects on the grid system. This thesis illustrates the big picture of Cyprus in terms of availability of exploitable renewable energy sources, current electricity generation and electricity demand characteristics. In order to address the grid code barrier, the grid codes of developed European countries are investigated. From this research, amendments to the current grid are produced. These additional mandatory codes will form the infrastructure for renewable energy projects and bring knowledge to the current system operator from other experienced countries. In addition renewable energy technologies worldwide are investigated in terms of output capacity, energy pricing, investment, and operation costs. Pricing and cost information is applied to the case of Cyprus. By further optimizing the technologies appropriately to Cyprus conditions, current and future cost analysis is produced. By producing reliable data on the cost and performance of renewable energy technologies the significant barrier to the uptake of these technologies is lowered. This will enable governments and financial bodies to arrive at an accurate assessment of which renewable energy technologies are the most appropriate for their particular circumstances.

No description available.

No description available.