Resistance heating of steel conductors of circular cross-section

The object of this thesis is to develop a method for calculating the losses developed in steel conductors of circular cross-section and at temperatures below 100oC, by the direct passage of a sinusoidally alternating current. Three cases are considered. 1. Isolated solid or tubular conductor. 2. Concentric arrangement of tube and solid return conductor. 3. Concentric arrangement of two tubes. These cases find applications in process temperature maintenance of pipelines, resistance heating of bars and design of bus-bars. The problems associated with the non-linearity of steel are examined. Resistance heating of bars and methods of surface heating of pipelines are briefly described. Magnetic-linear solutions based on Maxwell's equations are critically examined and conditions under which various formulae apply investigated. The conditions under which a tube is electrically equivalent to a solid conductor and to a semi-infinite plate are derived. Existing solutions for the calculation of losses in isolated steel conductors of circular cross-section are reviewed, evaluated and compared. Two methods of solution are developed for the three cases considered. The first is based on the magnetic-linear solutions and offers an alternative to the available methods which are not universal. The second solution extends the existing B/H step-function approximation method to small diameter conductors and to tubes in isolation or in a concentric arrangement. A comprehensive experimental investigation is presented for cases 1 and 2 above which confirms the validity of the proposed methods of solution. These are further supported by experimental results reported in the literature. Good agreement is obtained between measured and calculated loss values for surface field strengths beyond the linear part of the d.c. magnetisation characteristic. It is also shown that there is a difference in the electrical behaviour of a small diameter conductor or thin tube under resistance or induction heating conditions.

A detailed study of the mechanical and electrical aspects of microparticle impact phenomena

An experimental and theoretical study of the impact behaviour of charged microparticles in a high voltage vacuum gap has been carried out to investigate under controlled conditions the role of low velocity microparticles (ζ 500 ms-1) in initiating electrical breakdown in such gaps. This has involved developing a unique (UHV) low-velocity source of micron-sized charged particles to study the underlying mechanical and electrical aspects of micro-particle impact on a range of target materials e.g. Pb, Ti, C, stainless-steel and mica etc., having atomically clean or oxidised surfaces. Argon-ion etching and electron-beam heating has been used for in-situ surface treatment and ellipsometry for characterising the target surfaces. An associated sphere/plane theoretical model has been developed for detailed analysis of the many complex electrical (in-flight in-field emission, M.I.M. tunnelling and ohmic conduction) and mechanical (impact dynamics, deformation and heating) phenomena that are involved when a microparticle closely approaches and impacts on a plane target. In each instance the influence of parameters such as particle radius, particle/target impact velocity, surface field, surface condition and material has been determined.

Studies on the thermal decomposition behaviour, kinetics and electrical conductivity of the non-isothermal decomposition of pyridine mono carboxylic acids and some of their transition metal complexes

The thesis is divided into four chapters. They are: introduction, experimental, results and discussion about the free ligands and results and discussion about the complexes. The First Chapter, the introductory chapter, is a general introduction to the study of solid state reactions. The Second Chapter is devoted to the materials and experimental methods that have been used for carrying out tile experiments. TIle Third Chapter is concerned with the characterisations of free ligands (Picolinic acid, nicotinic acid, and isonicotinic acid) by using elemental analysis, IR spectra, X-ray diffraction, and mass spectra. Additionally, the thermal behaviour of free ligands in air has been studied by means of thermogravimetry (TG), derivative thermogravimetry (DTG), and differential scanning calorimetry (DSC) measurements. The behaviour of thermal decomposition of the three free ligands was not identical Finally, a computer program has been used for kinetic evaluation of non-isothermal differential scanning calorimetry data according to a composite and single heating rate methods in comparison with the methods due to Ozawa and Kissinger methods. The most probable reaction mechanism for the free ligands was the Avrami-Erofeev equation (A) that described the solid-state nucleation-growth mechanism. The activation parameters of the decomposition reaction for free ligands were calculated and the results of different methods of data analysis were compared and discussed. The Fourth Chapter, the final chapter, deals with the preparation of cobalt, nickel, and copper with mono-pyridine carboxylic acids in aqueous solution. The prepared complexes have been characterised by analyses, IR spectra, X-ray diffraction, magnetic moments, and electronic spectra. The stoichiometry of these compounds was ML2x(H20), (where M = metal ion, L = organic ligand and x = water molecule). The environments of cobalt, nickel, and copper nicotinates and the environments of cobalt and nickel picolinates were octahedral, whereas the environment of copper picolinate [Cu(PA)2] was tetragonal. However, the environments of cobalt, nickel, and copper isonicotinates were polymeric octahedral structures. The morphological changes that occurred throughout the decomposition were followed by SEM observation. TG, DTG, and DSC measurements have studied the thermal behaviour of the prepared complexes in air. During the degradation processes of the hydrated complexes, the crystallisation water molecules were lost in one or two steps. This was also followed by loss of organic ligands and the metal oxides remained. Comparison between the DTG temperatures of the first and second steps of the dehydration suggested that the water of crystallisation was more strongly bonded with anion in Ni(II) complexes than in the complexes of Co(II) and Cu(II). The intermediate products of decomposition were not identified. The most probable reaction mechanism for the prepared complexes was also Avrami-Erofeev equation (A) characteristic of solid-state nucleation-growth mechanism. The tempemture dependence of conductivity using direct current was determined for cobalt, nickel, Cl.nd copper isonicotinates. An activation energy (ΔΕ), the activation energy (ΔΕ ) were calculated.The ternperature and frequency dependence of conductivity, the frequency dependence of dielectric constant, and the dielectric loss for nickel isonicotinate were determined by using altemating current. The value of s paralneter and the value of'density of state [N(Ef)] were calculated. Keyword Thermal decomposition, kinetic, electrical conduclion, pyridine rnono~ carboxylic acid, cOlnplex, transition metal compJex.

A study of the electrical and optical properties of unhydrogenated neon-sputtered amorphous silicon

Films of amorphous silicon (a-Si) were prepared by r.f. sputtering in a Ne plasma without the addition of hydrogen or a halogen. The d.c. dark electrical conductivity, he optical gap and the photoconductivity of the films were investigated for a range of preparation conditions, the sputtering gas pressure, P, the target-substrate spacing, d, the self-bias voltage, Vsb, on the target and the substrate temperature, Ts. The dependence of the electrical and optical properties on these conditions showed that various combinations of P, d and Vsb, at a constant Ts, giving the same product (Pd/V sb) result in films with similar properties, provided that P, d and Vsb remain vithin a certain range. Variation of Pd/Vsb between about 0.2 and 0.8 rrTorr.cm!V varied the dark conductivity over about 4 orders of magnitude, the optical gap by 0.5 eV and the photoconductivity over 4-5 orders of magnitude. This is attributed to controlling the density-of-states distribution in the mobility gap. The temperature-dependence of photoconductivity and the photoresponse of undoped films are in support of this conclusion. Films prepared at relatively high (Pd/Vsb) values and Ts=300 ºc: exhibited low dark-conductivity and high thermal activation energy, optical gap and photoresponse, characteristic properties of a 'low density-of-states material. P-type doping with group-Ill elements (Al, B and Ga) by sputtering from a composite target or from a predoped target (B-.doped) was investigated. The systematic variation of room-temperature conductivity over many orders of magnitude and a Fermi-level shift of about 0.7 eV towards the valence-band edge suggest that substitutional doping had taken place. The effects of preparation conditions on doping efficiency were also investigated. The post-deposition annealing of undoped and doped films were studied for a temperature range from 250 ºC to 470 ºC. It was shown that annealing enhanced the doping efficiency considerably, although it had little effect on the basic material (a-Si) prepared at the optimum conditions (Pd/Vsb=0.8 mTorr.cm/V and Ts=300 $ºC). Preliminary experiments on devices imply potential applications of the present material, such as p-n and MS junctions.

Voltage control on an uninhabited autonomous vehicle electrical distribution system

More-electric vehicle technology is becoming prevalent in a number of transportation systems because of its ability to improve efficiency and reduce costs. This paper examines the specific case of an Uninhabited Autonomous Vehicle (UAV), and the system topology and control elements required to achieve adequate dc distribution voltage bus regulation. Voltage control methods are investigated and a droop control scheme is implemented on the system. Simulation results are also presented.

Public policy and electrical-grid sector innovation

Purpose – This paper aims to investigate the manner in which technological innovation in the European electrical-grid sector has developed by focusing, in particular, on the effect of public policy on innovation. To achieve this aim, this paper highlights how technological innovation and development progressed from the 1960s to the 1980s, and contrasts this period with the deregulated/privatization environment. Design/methodology/approach – The paper is based on a series of in-depth multiple company case studies of grid companies, some of their suppliers and other actors in their broader business network. Empirical data were collected through 55 interviews. Findings – The authors find that a phase of mutual collaboration was encouraged in the first period, which led to strong technological innovation with a focus on product quality and the development of functionality. Buyers played a pivotal role in the development of products and posed technical requirements. In contrast, the current role of the buyer has transformed principally into one of evaluating competing bids for specific projects. Today, buyers face increasing pressure to substantially lower CO2 emissions and transform the energy grid system. These goals are difficult to achieve without a new way of thinking about innovation. Research limitations/implications – Models to achieve innovation must not only focus on individual research projects; instead, the innovation should be factored into normal business dealings in the supply chain. Practical implications – We propose that policymakers and regulators need to: accommodate for innovation and address the collaborative elements of innovation when developing policies and regulations. Furthermore, regulators have the option of either developing a strategic vision for the electrical-grid network or incorporating sustainability into the evaluation of electrical grids and, thus, consumers’ willingness to pay. Originality/value – This paper makes a distinctive contribution in the area of innovation for electrical grids. Our paper shows how innovation and the development of new technology for electrical grids changed over time. Furthermore, this paper describes the energy sector in terms of a business network comprising the different actors involved in innovation and development and, thus, their role in the energy supply chain.