Design of Experiment (DOE) is a technique used to make effective and controlled experimentation and simulations, it helps in reducing the number of simulation runs. This will be very helpful in heterogeneous systems, since simulating such system is costing a lot of CPU resources and computations which leads to prohibitive simulation's time. Energy harvesting system is one of these heterogeneous (multi-physics) systems that contains components from different domains such as electrical both analogue and digital, mechanical, magnetic and thermal; simulating this type of system will result in prohibitive cost unless utilising the power of DOE. In addition to that, DOE enables mathematical modeling to study the behavior of these systems and enable optimising performance of these complex systems efficiently.
Design of Experiment (DOE) is a technique used to make effective and controlled experimentation and simulations, it helps in reducing the number of simulation runs. This will be very helpful in heterogeneous systems, since simulating such system is costing a lot of CPU resources and computations which leads to prohibitive simulation's time. Energy harvesting system is one of these heterogeneous (multi-physics) systems that contains components from different domains such as electrical both analogue and digital, mechanical, magnetic and thermal; simulating this this type of system will result in prohibitive cost unless utilising the power of DOE. In addition to that, DOE enables mathematical modeling to study the behavior of these systems and enable optimising performance of these complex systems efficiently.
Interest is rapidly increasing regarding the application of partial discharge (PD) diagnostics for the task of condition monitoring of HV plant. Put simply, utilities require the tools and fundamental understanding to interpret on-line PD data and relate it to the health of their assets. This project aims to investigate the PD generated by a specific type of three-phase distribution cable: that of paper insulated lead covered construction (PILC). This specific design of cable is of great interest to the utilities that operate Londons' distribution network as it is widely used and is approaching the end of its operational life - significant increases in failure rates have already been identified. An improved understanding of the relationship between PD activity and the various failure mechanisms associated to this cable design is key to accurate analysis in the future.
An experiment has been designed and constructed with the capability of stressing cable sections in a manner similar to circuits in the field. A number of cable samples have been fabricated with defects that are known to reduce the service life of operational circuits. The hope being that the signals generated by these samples under known laboratory conditions, will exhibit similar characteristics to those generated in the field. Therefore, any discrimination or characterisation algorithms that we develop using the experimental data should be readily transferrable to currently operational systems.
Existing induction based harvesting devices power by ambient vibrations are designed around an inertial mass mounted on a spring systems. Such arrangements are linear resonators with very simple structures and strong amplification at their resonant frequency. However they have one major limitation namely their very narrow resonant peak, this translates in very low power generation when the excitation frequency (ambient vibrations) deviates for the resonant frequency of the spring-mass system. Different strategies have been studied to widen the bandwidth of such devices but all of them complicate the simple mass-spring system of such devices. In this project a magnetic circuit is added to the induction devices as it will increase the coupling between the mechanical and electrical domain, however this addition will not complicate the mass-spring system structure of the device. The addition of the of the magnetic circuit will complicate however the design and analysis part, as the linear behaviour of the system is modified and FEM models of the device coupled with a system simulation will be needed to fully characterize the induction harvester. The losses in the magnetic circuit have to be also properly characterised and accounted to fully understand the benefits of the iron core. The possibility to create a bi-stable device in this configuration will be also investigated.
Oil is an important part in power transformers. It serves as both the electrical insulation and coolant and is in contact with metals and the paper insulation. Contaminants such as metal filings or cellulosic residual can be formed in the oil, especially for the transformers with aged paper insulation. These contaminants could form a bridge under the influence of the applied electric field. The bridge may potentially act as a conducting path between two different potentials within the transformer structure, leading to partial discharges or insulation failure. Experimental studies of contaminants motion under both dc and ac voltages will be done in the project. In addition to live optical observation and capturing of bridging phenomena between two electrodes in oil under different voltages, contamination levels and oil and paper insulation conditions, electrical conduction currents and partial discharges will also be measured simultaneously during bridging. These experimental results should allow one to establish a good understanding of contamination and its relation to electrical performance and pre-breakdown phenomena. To aid the understanding of bridging dynamics in the contaminated oil, a numerical model of particle movements and their accumulation at high field regions will be developed. It will be based on the hydrodynamic drift-diffusion approximation for the particles motion under dielectrophoresis force.
Plasma electrolytic oxidation (PEO) is a novel surface engineering technology, allowing relatively thick oxide coatings to be formed on metal parts. The process is superficially similar to the more familiar hard anodizing. The substrate is immersed in an aqueous electrolyte and a high potential, usually AC, is applied to it. The voltage between substrate and electrolyte rapidly rises as the native oxide thickens, and within a few minutes reaches several hundred volts. Sparks then start to appear on the surface, and this persists throughout processing. Recent work at Cambridge has confirmed that these are optically active plasmas, with durations ranging from tens to hundreds of microsecond, and peak temperatures up to ~10,000 K. These discharges allow oxide growth to proceed, so as to produce films with thicknesses of up to 100 microns or more. Moreover, the discharge events have a profound effect on coating microstructure, and hence on its physical and mechanical properties. Itââ¬â¢s thus possible to produce thick, strong coatings, extending the utility of such oxide films to encompass protection in tribologically and chemically aggressive environments, and also to offer significant thermal barrier function. The process is particularly effective on Al, on which it can generate thick, highly-adherent, hard and wear-resistant coatings.
Among the attractions of the process are that it involves very few health or safety hazards, with the electrolytes required containing neither the concentrated sulphuric acid nor the chromate ions necessary for hard anodizing. PEO coatings can be grown using solutions as simple and dilute as 0.02 M KOH, and are generally so mild that they do not require special chemical disposal, since they are less harmful than many household cleaning products. This is an advantage of increasing significance. Furthermore, coatings of uniform thickness can quickly and easily be produced on components with complex surface geometry, over a wide range of sizes, with no requirement for chambers or special environments. This cannot be said of most other coating techniques, such as thermal spraying, ion beam plating, sputtering etc.
In view of these advantages, PEO has recently attracted intense commercial and academic interest. Much of the research carried out hitherto has been aimed at characterisation of the coatings, and process optimisation through empirical observation. While several attempts have been made to explore the underlying coating formation mechanisms, many basic questions remain unanswered. Progress has been made in observation of discharge characteristics. Nevertheless, the development of an integrated and comprehensive model of the process remains to be achieved. In the project use of recently-developed plasma analysis techniques, focussing on single discharge events, will allow these characteristics to be monitored as a function of the processing conditions.
What can optical emission spectra tell us about PEO plasma in individual discharges? Optical emission spectra arise from the decay of excited electronic states of atoms and molecules in a hot gas or plasma. Provided that the plasma is optically thin, the strength of the emission lines is proportional to the product of the number of atoms or molecules in the excited state and the constant rate at which these decay to the lower state. If the decay rate constants are known, the measured strength of the lines can be used to estimate the relative abundance of the excited states. The relative strength of lines from different molecular species gives information about the composition of the plasma, while the relative strength of lines from the same species gives information about temperature.
This project aims to develop tools for the rating and technical assessment of high power HVDC cable systems with mass impregnated insulation. The calculation of current ratings for DC cable is significantly more complex than that for AC cable. The rating is often determined by electric stress constraints rather than considerations of thermal ageing. Ratings are also strongly influenced by thermally induced pressure transients within the cable. In some cases the rating of the cable can be restricted by the cable being too cold, requiring different calculation approaches to AC cable where the main criterion is the maximum conductor temperature.
The project intends to develop a comprehensive framework for the rating of HVDC MI cable circuits, making use of techniques such as multiphysics modelling to examine the complex interactions of thermal and electrical stresses. The modelling of transient thermal conditions and the behaviour of the cable insulation under reversals of power flow will provide guidance for the development of dynamic rating algorithms and operational regimes suitable for high power HVDC cable circuits. Consideration will also be given to the effects of polarity reversals to ensure that the best use can be made of HVDC network links in the future.
Epoxy resins have been used extensively as the dielectric and the mechanical support in solid insulation systems, such as electrical machines. Recently, thanks to the development of nanotechnology, epoxy nanocomposites have been expected to be potential candidates to replace the base resin. However, the effects of nano-fillers have been controversial, in both positive and negative ways. It is believed that the properties of nanocomposites are related to the surface chemistry of nano-fillers. The incorporation of nano-fillers with large interfacial areas into epoxy matrices may also modify the cure behaviour of the system, through introducing additional chemical reactions between moieties on the nano-filler surfaces and reactants thereby change the chemical balance of the original system. This project sets out to investigate the effects of stoichiometry and the nature of the interfacial areas of treated silica particles of various sizes on the properties of an epoxy-based system, and hence, provide a more comprehensive insight into the relationships between formulating reactants and incorporating fillers with the formed molecular architecture, which is associated with the end properties of products.
Smart fabrics and interactive textiles (SFIT) are defined as textiles that are able to sense stimuli from the environment and react or adapt to them in a predetermined way. For example, smart textiles/garments can incorporate sensors/actuators, processing and communications for use in applications such as health monitoring, consumer products and in the automotive sector. Smart fabrics and interactive textiles represent the next generation of fabrics and the potential opportunities for exploiting them are enormous. During recent involvement with the textiles community and talking in particular to developers of smart fabrics and intelligent clothing, it has become clear that a major obstacle towards integrating electronic functionality into fabrics is the portable power supply required. For example, whilst conductive tracks can be printed onto, or conductive yarns woven into, a fabric, the power supply for any integrated device is presently a standard battery. This requires conventional connection and must be repeatedly replaced and removed during washing. No matter how integrated the functionality of the fabric becomes, at present there is no alternative to powering the system using discrete batteries.
Energy harvesting (also known as energy scavenging) is concerned with the conversion of ambient energy present in the environment into electricity. Energy Harvesting is now a significant research topic with conferences such as PowerMEMS, IEEE MEMS, Transducers, DTIP and Eurosensors featuring at least one session on the subject. Energy harvesters do not have the energy density (energy stored for a given volume) of a battery but offer the attraction of an integrated power supply that will last the lifetime of the application and will not require recharging or replacement. This project will focus on harvesting energy from two sources: kinetic and thermal energy all of which have been identified as promising approaches for powering mobile electronics.
- Kinetic Energy Harvesting - For example, there is a large amount of kinetic energy available from human motion. Human motion characterised by large amplitude, low frequency movements that can also exert large forces. It has been estimated that 67W of energy are available in each step .
- Thermal Energy Harvesting - Harvesting of energy from heat sources (such as the human body) can be achieved by the conversion of thermal gradients to electrical energy using the Seebeck effect. There has been interest in the generation of power from body heat as a means to power wearable devices. For example Seiko have produced a wrist watch powered by body heat. Reported results for power densities achieved from micro-fabricated devices are 0.14 microW/mm^2 from a 700 mm^2 device for a temperature difference of 5 K, which is typically achievable for wearable applications.
The proposal involves using rapid printing processes and active printed inks to achieve energy harvesting fabrics. This will result in a low cost, easy to design, flexible and rapid way to realise energy harvesting textiles/garments. Both inkjet and screen printed are fully accepted processes widely used in the textile industry for depositing patterns. The proposed screen and inkjet printing processes have many benefits including low-cost, repeatability, flexibility, suitability for small/medium series and mass production, short development time, compatibility with a wide range of textiles and the capability of depositing a wide range of materials. The inks and associated printing parameters will be researched to enable the bespoke design and layout of the energy harvesting films in the application being addressed. The research will provide a toolbox of materials and processes suitable for a range of different fabrics that enable a user to develop the energy harvesting fabric best suited to their requirements.
The OpenMentor Technology Transfer (OMtetra) project addresses the JISC call in appropriately exploiting technology-enhanced assessment and feedback to enable more authentic and more useful feedback on assignment performance, thus improving assessment quality, enhancing the student experience, and supporting staff. It will do this by packaging the JISC-funded OpenMentor technology innovation of the Open University and supporting its transfer to two external institutions -the University of Southampton and King's College London - where it will be developed to address their identified needs to improve student feedback.
The potential impact of the OMtetra project is profound. There is currently no tool with the simple yet compelling "value proposition" of OpenMentor: to take a set of marked assignments, profile the feedback provided, and support the tutor in reflecting upon and improving that feedback.
The project will embed sustainability in a community of users, seeded at the originating institutions and reaching out to all interested practitioners both in the UK and world-wide, providing community access and tools to ensure the continued development and use of OpenMentor.