Dielectric liquids are widely used as electrical insulation industry area. Currently the insulating liquids which are typically employed in high-voltage (HV) systems are naphthenic mineral oils. However, stringent environmental protection regulations encourage operators of HV equipment to use more environmentally friendly liquids. There is also a strong demand for the development of industry which requires insulating liquids provide advanced dielectric properties. Natural and synthetic esters are considered as potential substitutes for traditional mineral oils due to their environmental friendly properties. Meanwhile a new approach to the modification of dielectric properties of insulating liquids has been introduced which is based on the addition of ultra-fine particles (with sub-micrometre dimensions) to insulating liquids (nanofluids). There are a number of published papers reported that nanfluids provide better thermal and breakdown properties than those of base liquids. However the full understanding of the breakdown properties of nanofluids is not completed. The comprehensive study of breakdown properties of nanofluids is required. In this thesis, the breakdown properties of mineral oil, ester, and nanofluids based on these liquids, developed using titanium dioxide (TiO₂) and boron nitride (BN) nanoparticles have been investigated. Nanofluids were prepared with various concentrations. The experiments have been designed and preformed: AC breakdown voltage, lightning impulse breakdown voltage, lightning impulse pre-breakdown time, and DC pre-breakdown current. The experimental results show that nanofluids with low concentration provide higher breakdown voltage as compare with those of base liquids. There is an ‘optimal’ concentration, nanofluids provide the highest AC, impulse breakdown voltage, and longest impulse pre-breakdown time as compare with those of other tested liquids. The measurement of DC pre-breakdown current in base liquids allowed calculation of the field distribution in liquids. As the pavement for further investigations, several potential mechanisms of nanoparticle influence on breakdown properties of nanofluid have been compared and discussed.

The remarkably increasing demand for communication systems has recently forced the research community to consider power line (PL) networks for data transmission, which is commonly referred to as power line communications(PLC). In particular, this technology becomes more attractive in harsh wireless environments where radio spectrum is scarce or/and propagation loss is high such as in underground structures and buildings with metal walls. PLC can support many applications such as home-networking, internet and smart grid. More specifically, PLC is considered the backbone of smart grids, not only because no extra wiring installation is required, but also because PLC is a through-grid technology which could reduce the reliance of the utility companies on third party connectivity and, consequently, overcome many security and privacy issues. On the other hand, since PLs were not designed for data transmission, communication signals over such channels can degrade tremendously. Contrary to many other communication channels, noise over PLs cannot be described as additive white Gaussian noise. It is rather categorized broadly into impulsive noise and background noise with the former being the most crucial element influencing PLC systems. With this in mind, this thesis will primarily focus on studying and developing advanced techniques and algorithms to reduce the severity of impulsive noise over PL channels. The contributions of this thesis are described as follows. Initially, a thorough review is provided to introduce and compare the challenges facing PLC, PL channel and noise modelling schemes, as well as some noise mitigation techniques. Next, novel approaches are proposed, with different degrees of effectiveness and complexity, to reduce the effect of impulsive noise in orthogonal frequency-division multiplexing (OFDM)-based PLC systems. Firstly, an adaptive hybrid preprocessing system is introduced to improve the performance of the conventional hybrid approach. In this respect, closed-form expressions for the output signal-to-noise ratio (SNR), probability of missed detection and probability of successful detection are derived. Secondly, and unlike existing works which are entirely based on countering impulsive noise at the receiver side, we show that if the OFDM signal is preprocessed at the transmitter side in such a way to minimize the signal peaks, the noise cancellation process can be made more efficient at the receiver. This is accomplished by applying a peak-to-average power ratio reduction scheme such as selective mapping. A closed-form expression for the probability of blanking error of this system is derived. Thirdly, to eliminate the estimation requirement problem of the short-term noise statistics associated with the aforementioned approaches, we propose the dynamic peak-based threshold estimation (DPTE) method. This method relies on utilizing the OFDM signal peak estimates with which optimal blanking is achieved irrespective of the noise parameters. In addition, to realize DPTE, a look-up table algorithm with uniform quantization is exploited and investigated in various system configurations. Furthermore, this thesis explores the performance of multi-carrier code division multiple access (MC-CDMA) systems over the multipath PL channel contaminated with Middleton class-A noise for various spreading codes, namely, Pseudonoise, Walsh-Hadamard and orthogonal poly-phase sequences. Different nonlinear preprocessors are implemented and the corresponding performance is evaluated in terms of the output SNR and symbol error rate.

The research objective was to investigate the generation and collection of power generated in a distributed tidal generation site, and realise the most economic grid connection methodology for a practical installation. Current tidal steam prototype designs utilise variable speed gear boxes, power frequency converters and variable pitch blades in the nacelle, thus requiring complicated, heavy and expensive equipment in the nacelle. Moreover the variable blade pitch mechanism has a large power demand, and has to operate day after day submerged in water at depths between 30m – 80m. The approach taken in this research is to replace major cost components with much cheaper ones, as well as locating as many components as possible onshore where costs are less. This thesis investigates a novel tidal stream power generation system referred to as “passive rectification to a common DC-bus” where an array of 3-phase synchronous generators operating at diverse speeds are connected to a common DC bus via passive diode rectifiers. The proposed tidal stream topology shows that variable pitched blades, variable speed gearboxes and frequency converters in the nacelle can be replaced by a much simpler system that uses fixed pitch blades, a fixed ratio gearbox, generator excitation control system, and a diode bridge rectifier. These components are generally cheaper, lighter, have a lower power demand and are more reliable than the components they replace. Also some of the voltage and frequency conversion is carried out ashore where costs are less, in addition to the overall reduction in the number of components required as some of the components are shared by multiple devices. As a result system efficiency is maximised, in addition to facilitating a reduction in capital, installation and operational costs. Power conversion from the tidal generation power system to shore is achieved via passive rectification to a common DC-bus, thus system power regulation is achieved by individual generator field current control, to attain optimum system operation including, maximum power extraction, power limitation and stall control, in turn improving system reliability and controllability. Furthermore passive stall control via generator field current regulation eliminates the need for mechanical brakes which reduces cost and improves reliability. The feasibility of the proposed power generation system was carried out via computer simulations and later validated via small scale laboratory hardware simulations.

There is an increasing need for AC-DC converters to draw a pure sinusoidal current at near unity power factor from the AC mains. Most conventional power factor correcting systems employ PWM techniques to overcome the poor power factor being presented to the mains. However, the need for smaller and lighter power processing equipment has motivated the use of higher internal conversion frequencies in the past. In this context, resonant converters are becoming a viable alternative to the conventional PWM controlled power supplies. The thesis presents the implementation of active power factor correction in power supplies, using resonance mode techniques. It reviews the PWM power factor correction circuit topologies previously used. The possibility of converting these PWM topologies to resonant mode versions is discussed with a critical assessment as to the suitability of the semiconductor switching devices available today for deployment in these resonant mode supplies. The thesis also provides an overview of the methods used to model active semiconductor devices. The computer modelling is done using the PSpice microcomputer simulation program. The modifications that are needed to the built in MOSFET model in PSpice, when modeling high frequency circuits is discussed. A new two transistor model which replicates the action of a OTO thyristor is also presented. The new model enables the designer to estimate the device parameters with ease by adopting a short calculation and graphical design procedure, based on the manufacturer's data sheets. The need for a converter with a high efficiency, larger power/weight ratio, high input power factor with reduced line current distortion and reduced cost has led to the development of a new resonant mode converter topology, for power processing. The converter presents a near resistive load to the mains thus ensuring a high input power factor, while providing a stabilised de voltage at the output with a small lOOHz ripple. The supply is therefore ideal for preregulation applications. A description of the modes of operation and the analysis of the power circuit are included in the thesis. The possibility of using the converter for low output voltage applications is also discussed. The design of a 300W, 80kHz prototype model of this circuit is presented in the thesis. The design of the isolation transformer and other magnetic components are described in detail. The selection of circuit components and the design and implementation of the variable frequency control loop are also discussed. An evaluation of the experimental and computer simulated results obtained from the prototype model are included in the presentation. The thesis further presents a zero-current switching quasi-resonant flyback circuit topology with power factor correction. The reasons for using this topology for off-line power conversion applications are discussed. The use of a cascoded combination of a bipolar power transistor and two power MOSFETs i~ the configuration has enabled the circuit to process moderate levels of power while simultaneously switching at high frequencies. This fulfils the fundamental precondition for miniaturisation. It also provides a well regulated DC output voltage with a very small ripple while maintaining a high input power factor. The circuit is therefore ideal for use in mobile applications. A preliminary design of the above circuit, its analysis using PSpice, the design of the control circuit, current limiting and overcurrent protection circuitry and the implementation of closed-loop control are all included in the thesis. The experimental results obtained from a bread board model is also presented with an evaluation of the circuit performance. The power factor correction circuit is finally installed in this supply and the overall converter performance is assessed.

Power Line Communication (PLC) has the potential to become the preferred technique for providing broadband to homes and offices with the advantage of eliminating the need for new wiring infrastructure and reducing the cost. Power line grids, however, present a hostile channel for data communication, since the fundamental purpose of the power line channel was only the transmission of electric power at 50/60 Hz frequencies. The development of PLC systems for providing broadband applications requires an adequate knowledge of the power line channel characteristics. Various types of noise and multipath effects are some of the limitations for power line channels which need to be considered carefully in designing PLC systems. An effect of an impulsive noise characterized with short durations is identified as one of the major impairment in PLC system. Orthogonal Frequency Division Multiplexing (OFDM) technique is one of the modulation approaches which has been regarded as the modulation technique for PLC systems by most researchers in the field and is used in this research study work. This is because it provides high robustness against impulsive noise and minimizes the effects of multipath. In case of impulsive noise affecting the OFDM system, this effect is spread over multiple subcarriers due to Discrete Fourier Transform (DFT) at the receiver. Hence, each of the transmitted communication symbols is only affected by a fraction of the impulsive noise. In order to achieve reliable results for data transmission, a proper power line channel with various noise models must be used in the investigations. In this research study work, a multipath model which has been widely accepted by many researchers in the field and practically proven in the Tanzanian power line system is used as the model for the power line channel. The effects of different scenarios such as variations in direct path length, path number, branch length and load on the channel frequency response are investigated in this research work. Simulation results indicate the suitability of multi-carrier modulation technique such as an OFDM over the power line channels. To represent the actual noise scenario in the power line channel, an impulsive noise and background noise are classified as the two main noise sources. A Middleton class A noise is modelled as an impulsive noise, whereas the background noise is modelled as an Additive White Gaussian Noise (AWGN). The performance of PLC system based on OFDM is investigated under Middleton Class A and AWGN noise scenarios. It is observed that Bit Error Rate (BER) for the impulsive noise is higher than the background noise. Since channel coding can enhance the transmission in a communication system, Block code and convolutional codes have been studied in this research work. The hamming code chosen as a type of the block code, whereas the Trellis Coded Modulation (TCM) selected from the category of the convolutional channel codes and modelled in Matlab2013b. Although TCM code produces improvements in the Signal-to-Noise Ratio (SNR), they do not perform well with Middleton class A noise. A rectangular 16-QAM TCM based on OFDM provides better BER rate compared to the general TCM.

The development of modern process industries, and increasingly fierce competition in the world market, has inevitably led to new demands on process control from industrial sectors. An important question for process control is how to secure the security operation of complex industries. The power system is one of the most complex industrial systems in the world, and faults in transmission lines pose a threat to the safe and stable operation of power systems. An inspection and monitoring system for transmission lines is proposed in this thesis, and, as a case study, a comprehensive early-warning scheme for assessing the icing condition of transmission lines with probability density function (PDF) based image recognition technology is carried out. In addition, fault location technologies for both transmission lines and distribution networks are discussed as another important component of the operational security of power systems. These provide fault location methods based on distribution characteristics of faulty currents in optical ground wire (OPGW) and the travelling wave scheme with distribution generations. Finally, control algorithms for optimising the power distribution network are also discussed. Cooperative control, based upon physical network connectivity, is proposed. This is used to maintain a group of generators operating at the identical ratio in terms of their available power, which is known as fair utilisation.

The use of polymeric power cables for high voltage direct current HVDC has become increasingly popular for renewable power sources such as offshore wind farms. The long term reliability of polymeric cables operating under DC conditions is still unknown and therefore of concern to the industry. However, there is no an explicit consideration of how the injected charges can cause effects to the prediction of the life-time. Thus, it is important to develop an ageing model can assist of understanding the effect of these charges on the insulating material. Regarding to the polymeric material that are used as an electrical insulation, the presence of space charges could be the consequence of material degradations that are thermally activated and accelerated by the presence of electric field. The dynamics of space charge, therefore, can be potentially used to characterise the material. In this direction, an ageing model in which parameters have clear physical meanings has been developed and applied to the material to extrapolate the lifetime. The kinetic equation has been established based on charge trapping and detrapping of the injected charge from electrodes. The local electromechanical energy stored in the region surrounding the trap reduces the trap depth with a value related to the electric field. At a level where the internal electric field exceeds the detrapping field in the material, an electron can be efficiently detrapped and the released energy per detrapped charge can cause a weak bond or chain scission i.e. material degradation. The model has been applied to the electro-thermally aged low density polyethylene LDPE film samples. To evaluate the damages structure during ageing process, a simulation work was performed on the developed ageing model to investigate the susceptibility of such parameters that can cause an explicit effect to the ageing process. The simulation work is performed on a two-dimensional square grid that is assumed to represent a part of the insulating material. The mesh structure is divided using the finite element method. Based on the nature of polyethylene, its structure is semi-crystalline with a spatially varying morphology. Consequently, each bond in the grid is assigned a set of parameter values. One of these parameters is the critical fraction of trapped charges C*, which needs to be reached in order to fail a bond. It is chosen at random values from a range centred on the characteristic value obtained from the experimental results. This indicates that the insulation life at varying parameter C* is lower than its characteristic value.

This thesis focuses on the development of the wireless applications for Ambient Assisted Living (AAL) system, the energy harvesting technique for powering the passive sensors in the building environment, and the flexible screen printed coils for Wireless Power Transfer (WPT) system to provide the power for a body-area sensor network in an AAL system. The AAL provides safe environments around assisted peoples and help them maintain independent living. The applications in AAL include the fixed monitor sensor in building environment and the wearable sensor on users body area. For supplying power for the applications of AAL wireless power supply provides the power without cables while offers a more environmentally friendly solution. Compared with energy harvesting technology, WPT is capable of supplying more power without increasing the size of the device. In this work, a solar powered PIR sensor demonstrates that the energy harvesting technique for a passive sensor application for the fixed monitor sensor in building environment, which can work for up to 16 hours without ambient energy input. For the on-body area application, the flexible coils are employed in the WPT system because of the comfort requirement. The coils are printed on 65/35 polyester/cotton textile with a Fabink-UV-IF1 interface layer coating. The interface layer provides a relatively flat and smooth surface to prevent the permeation of the conductive paste into the textile and allows the printing of finer profile coils, and the flexibility and breathability of textile can be remained. The measured inductances of the printed flexible coils are 3.9 μH for single layer. The design of the printed coil minimises the coil’s parasitic capacitance, which is less than 25 pF, and consequently increase the self-resonant frequency of the printed coil. A 5 V 1.51 W DC output has been achieved by a wireless power transfer system using the printed flexible coils with Qi standard circuitry; a DC-DC efficiency of 38% has been measured. It has been compared with the system employed with Qi standard wound copper coils which has the recorded 52% DC-DC efficiency.

Many power transmission systems are under pressure from increasing load demand as well as changes in power flows due to the evolution of the power market and the integration of renewable energy generations. At the same time, limited finance for installing new cables and the difficulties in reinforcement of existing circuits in urban areas incentivize transmission operators around the world to find ways to maximize the flexibility and usage of their existing transmission network. As a result, it is crucial to adopt new current rating methods which are able to optimize asset utilization, minimize risk and reduce the constraint costs incurred by transmission system operators. Historically, most cable thermal ratings are continuous ratings, with fixed seasonal values for a certain cable circuit. They are based on worst-case assumptions and are not able to consider the real-time environmental conditions. The ignorance of the real-time change in environmental conditions, which control the rate of heat dissipation from the cable, makes continuous ratings generally conservative. However, the rating values can also be optimistic for some extreme situations such as thermal runaway in the soil around the cables, which might cause overheating. Several dynamic rating systems have been applied to the existing underground cable in practice by using online monitoring data. Some worst case assumptions used in conventional cable rating standards have been removed. Such systems have been reported to deliver increases of 5-20% in cable current capacity. However, most existing dynamic rating systems can only determine a short-term rating at the current time step. It would be valuable for transmission operators to know the short-term rating in advance to assist in day-ahead planning. To solve this problem, a predicted rating system, which is capable of providing network operators with accurate short term current ratings at the day ahead stage, has been developed in this work. This novel cable rating concept integrates a day-ahead load forecasting system into the dynamic rating system to provide the time-limited short-term rating calculated forward from any point within the next 24 hours. Some shortcomings of existing rating methods for different kind of insulated cable installations have been detected and overcome. More suitable models have been built, compromising between accuracy and solution speed to fit them into the predicted rating system. A day-ahead load forecasting system has been built by using the Support Vector Regression (SVR) method. Dynamic thermal models are used to translate the load prediction into thermal prediction 24 hours ahead. Thus, the time-limited short-term ratings can then be calculated 24hrs ahead, based on the predicted load data and cable temperature data. In addition, an error estimation system has been integrated to estimate the predicted conductor temperature error quickly, thus increases the reliability of the predicted rating system. Utilizing this predicted rating system has the double benefit of reducing variations in dynamic ratings (which makes them difficult to plan with), while reducing the risk of thermally overloading the cable, thus prematurely ageing the dielectric. For a large scale transmission network, the dynamic rating and predicted rating systems for all the cable circuits might require huge amounts of computation and very long solution times, which make their application impractical and infeasible. The idea of using a machine learning method, such as Support Vector Regression, has been shown to dramatically reduce the solution time for dynamic rating calculations.

Charge build up under high voltage DC is a significant concern in the transmission system as its presence may distort the local electric field. By chemically treat polymeric insulation via direct fluorination, and plasma enhanced fluorination process, the charge transport characteristics of the material can be modified. In doing so, excellent surface properties similar to those of fluoropolymers can be attained without compromising the bulk properties of the original polymeric insulation. The change in chemical components at the surface of polymeric insulation should lead to a corresponding change in dielectric properties at the surface and consequently may suppress the occurrences of charge build up. In this research, epoxy resin samples with various surface fluorinating conditions were formulated and treated. The samples then were characterised by SEM and EDX analysis, Raman spectroscopy, and DC surface conductivity measurements. To further explain the effects of fluorination treatment, modelling of the electric field and current density distribution had been carried out. Surface potential decay tests from corona discharge, as well as PEA measurements, show that there is a significant change in decay characteristics with the introduction of surface fluorinated layer. The decay mechanisms responsible for the observed phenomena were thoroughly discussed. The effect of moisture absorption on the treated surface was studied and proved to be the limiting factor in the improvement of dielectric properties of fluorination treatment. Finally, surface DC flashover test using a pair of finger electrodes were performed. This research proved that the introduction of the fluorinated surface layer on epoxy resins does play a major role in improving the surface dielectric properties for the use as insulation spacer in high voltage DC GIS systems.