1,721,029 research outputs found
Managing Risks in Electrical Infrastructure Assets from a Strategic Perspective
No full textShould risks always be quantified before being managed? The answer is “yes” in the opinion of most asset managers in today’s electricity transmission and distribution companies, but “no” in modern theories of risk management. When the risks refer to reliability hazards of high-voltage assets, the answer to the above question is “yes, it should be, but not yet”. The first part of this thesis studies a typical cause of this situation: when data and knowledge on high-voltage assets are insufficient. Specifically, statistical methods were developed for analyzing life data of limit quantity and poor quality. For other types of data, the reliability data model and the knowledge maturity model were developed, as the tools to evaluate the progress towards risk-based asset management. When the risks on electrical infrastructure assets are long-term and stakeholder-oriented, the answer to the above question is probably “no”. In the second part of this thesis, these risks are modelled as “strategic risks”. Through adapting the theory of Klinke and Renn, the author identifies six types of strategic risks. Then, through developing our version of system diagram, the author provides asset managers with an analytical tool to manage the complexities and uncertainties caused by these strategic risks.Electrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Condition assessment of power cables using partial discharge diagnosis at damped AC voltages
No full textThe thesis focuses on the condition assessment of the distribution power cables, which have a very critical part in the distribution of electrical power over regional distances. The majority of the outages in the power system is related to the distribution cables, of which for more than 60% to internal defects. The material degradation in the power cables can be categorised into four local degradation processes, which are related to partial discharges. Partial discharge characteristics therefore provide sensitive parameters for detecting degradation processes. With partial discharge diagnostics, the insulation defects (discharge sources) can be pinpointed by "time domain reflectometry" to a specific component over the length of the cable system. To detect partial discharges external energising sources are required. In this thesis, damped AC voltages (temporarily attenuating AC voltages as a result of an oscillation obtained by means of an LC resonant circuit) are successfully investigated in this thesis as an effective energising method for partial discharge diagnostics. The compact and low weight measuring system results in a low noise level and high sensitivity in the field during the low power damped AC voltages with frequencies in the range of 100-500Hz for 100-200ms, for discharging defects in impregnated paper as well as polymeric cable insulation. The effects of the different test voltages on discharge activities are investigated by measuring different defect models in the laboratory and power cables in the field with 50Hz AC voltages, damped AC voltages at various frequencies and 0,1Hz voltages. It is shown that the test voltage shapes and frequencies do not have major influence on the values for the partial discharge parameters. Knowledge rules for condition assessment of the different insulation systems are developed. Statistical analysis of large amounts of measurement data are for this an effective and reliable method to determine experience norms (standard based on experience) for condition assessment. The various partial discharge properties relate to different aspects of the condition of a cable system and its components. The weighted combination of the various knowledge rules results in a methodology for decision making of maintaining cable systems.Electrical Engineering, Mathematics and Computer Scienc
Information Strategy for Decision Support in Maintaining High Voltage Infrastructures
No full textElectrical Engineering, Mathematics and Computer Scienc
Thermal and Electrical Properties of Nanocomposites, Including Material Properties
No full textThe research described in this thesis is part of a state-funded IOP-EMVT project in cooperation with industrial companies, aiming at the design, assessment and implementation of new, environmental friendly (e.g. oil and SF6 - free) solid dielectric materials. A large disadvantage of solid polymer dielectrics is their relatively low thermal conductivity. Therefore, the focus in this thesis is on if and how nanotechnology can improve the thermal conductivity without deteriorating existing electrical properties. Epoxy resin, which is very common polymer material in the electrical and power industry, has been used as a host to create new insulating materials: nanocomposites. In order to improve the thermal conductivity of epoxy resin, thermally conducting but electrically insulating nanofillers, such as aluminum and magnesium oxides (Al2O3 and MgO), silicon dioxide (SiO2), boron and aluminum nitrides (BN and AlN) were used to dope the polymer matrix. Good compatibility and adhesion was achieved by surface modification of the nanoparticles, using a silane coupling agent. Proper dispersion of nanoparticles is a vital factor for the final properties of nanocomposites. Good and stable dispersion of nanoparticles in polymer matrices have been achieved by mechanical mixing and ultrasonic vibration. The quality of the dispersion of nanoparticles was satisfactory for most of the nanocomposite samples. The fabricated composites were classified into three types, according to the average particle size and the extent of agglomerates observed inside the polymer matrix. Dielectric spectroscopy revealed that the relative permittivity of many nanocomposites is lower than that of the pure epoxy. This surprises, since the relative permittivity of the bulk materials of the fillers used is higher than that of the epoxy. The anomalous dielectric behaviour of nanocomposites was explained by the existence of an interface layer between polymer matrix and inorganic filler, and its influence on the macroscopic properties of the composite. The dielectric spectroscopy investigations demonstrated a reduction of the real and imaginary parts of the complex permittivity for all samples after subjecting the samples to postcuring. The postcuring process leads to evaporation of absorbed water and finalizes the process of epoxy curing. It was postulated that the interface polymer volume, which is affected by the alignment of polymer chains around surface treated nanoparticles, conducts the heat much better than an amorphous polymer that is not altered by nanoparticles. We proposed a three-phase Lewis-Nielsen model to fit the thermal conductivity behaviour of nanocomposites, which have a third phase of aligned polymer layers. The model fits the experimental data very well and takes the thermal resistance of the interface into account. Besides the interfacial layer and its nature, the size of the particles, their aspect ratio, crystal structure and alignment inside the polymer as well as surface modification are important aspects in determining the thermal conductivity of composites. Several ways are proposed to optimize the nanocomposite processing to enable scaling up to large industrial volumes. Finally, possible harmful effects of nanoparticles on health and required precautions for the workplace are discussed in the course of this thesis.High Voltage Technology & ManagenmentElectrical Engineering, Mathematics and Computer Scienc
On-load Tap Changer Diagnosis on High-Voltage Power Transformers using Dynamic Resistance Measurements
No full textHigh-voltage transformers have tap changers to regulate the voltage in the high-voltage network when the load changes. Those tap changers are subject to different degradation mechanisms and need regular maintenance. Various defects, like contact degradation, often remain undetected and the probability of maintenance errors cannot be neglected. Preventive diagnosis of dynamic resistance can be used to determine the contact condition and to check the basic function of the tap changer. This can guarantee that the high-voltage transformer can be put back into operation safely after maintenance. In addition, the information obtained can be used for condition-based maintenance. The research of Jur Erbrink elaborates on the condition assessment of tap changers using dynamic resistance measurements. He describes in his thesis the different ways in which the measurements can be performed and how this influences the measurement results. In particular it was emphasized that the dynamic resistance measurements at a lower the test current are more sensitive for long term aging effects. It is also investigated which defects can be detected and how the results can be interpreted.High Voltage Technology and ManagementElectrical Engineering, Mathematics and Computer Scienc
Applicability of recovery voltage and on-line partial discharge measurements for condition assessment of high voltage power transformers
No full textElectrical Engineering, Mathematics and Computer Scienc
Analysis of the Mechanisms Determining the Thermal and Electrical Properties of Epoxy Nanocomposites for High Voltage Applications
No full textThe addition of microsized fillers to polymers, in order to tailor their properties, has been extensively used in many industrial applications since the 1960s. The same approach applies to the field of electrical insulation. Epoxy resin is a widely used polymer in the electrical power sector, but it is usually loaded with microsized fillers, such as aluminum oxide and silicon dioxide, mainly to increase its thermal conductivity, improve its mechanical properties, and to decrease cost. Polymers with microsized fillers are called microcomposites. In the mid-1990s, a new type of polymeric composites for high voltage applications, the so-called nanocomposites, emerged. The main characteristic of these composites is the small filler size, which is smaller than 100 nm at least in one dimension. Since then, there has been a growing interest in the performance of polymeric nanocomposites for high voltage applications, including epoxy nanocomposites. The performance of nanocomposites is mainly related to the tremendous effective internal surface area of these materials because of the high surface-tovolume ratio of nanofillers. After 20 years of research, a significant amount of data has been generated which reflects the potential of nanodielectrics. It has been shown that nanofillers are capable of contributing to the improvement of both the thermal and electrical properties of polymers. However, the laboratory performance of nanocomposites is inconsistent and unpredictable. These are the main factors which inhibit the applicability of nanodielectrics. Important challenges in the field of epoxy nanocomposites should be overcome before nanodielectrics can be produced on an industrial level. The most important challenge is related to the dubious reproducibility of the nanocomposite performance which is closely related to sample homogeneity. Thus, the effectiveness of separating the nanoparticles from each other and the homogeneous incorporation of them into the polymer matrix are expected to affect the performance of nanocomposites. However, the extent to which the behavior of nanocomposites is influenced by sample homogeneity is not well defined. In this thesis, a number of epoxy nanocomposites and mesocomposites were synthesized aiming at the analysis of the parameters which influence their thermal and electrical properties. The analysis includes the thermal and electrical conductivity, dielectric response, and breakdown strength under both AC and DC electric fields. The experimental results demonstrate the important role of interfaces in the behavior of epoxy nanocomposites. Based on the experimental results, important parameters for determining the performance of nanocomposites are suggested to be the polymer re-organization and water uptake. The former is related to the influence of nanofillers on the polymer structure, i.e., the areas in the vicinity of nanofillers are assumed to exhibita different behavior from the rest of the polymer matrix. The uptake of water is related mainly to the hydrophilic nature of nanofillers and plays a significant role in the electrical performance of nanocomposites. Apart from the aforementioned mechanisms, the presence of structural imperfections should not be neglected as they affect both the thermal and electrical properties of epoxy nanocomposites. Additionally to the experimental part, models were developed for both the relative permittivity and thermal conductivity of nanocomposites. The models are based on the two aforementioned parameters; polymer re-organization in the vicinity of nanofillers and water uptake due to the hydrophilicity of nanofillers. The main characteristic of both models is the use of the same structure which strengthens the validity of the assumptions. The experimental results are in good agreement with the model results. Also, a large part of the thesis is devoted to the evaluation of the influence of sample homogeneity on the performance of nanocomposites. For this purpose, nanocomposites with different synthesis techniques were fabricated. The results suggest that the thermal conductivity, dielectric response, and breakdown strength (AC and DC) of epoxy nanocomposites are not significantly influenced by the nanoparticle distribution. This observation suggests that high levels of reproducibility can be achieved when the particles are similarly dispersed and differently distributed. Finally, hybrid composites which combine both microsized and nanosized fillers were fabricated, tested, and analyzed. This type of composites is more likely to be employed in industry as epoxy resin in its pure form is rarely used for high voltage applications. It is usually reinforced with high loadings of microparticles. Microcomposites reinforced only with a small amount of nanofillers, i.e., less than 1 % by volume, show a significant thermal and electrical improvement.Electrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Space charge and partial discharge phenomena in high voltage DC devices
No full textElectrical Engineering, Mathematics and Computer Scienc
Partial Discharge Diagnosis of High-Voltage Gas-Insulated Systems
No full textElectrical Engineering, Mathematics and Computer Scienc
Multi-Agent Model-Based Optimization for Future Electrical Grids
No full textThe electricity grid is one of the most complex systems created by human beings. It consists of an intricate network of components such as generators, transmission and distribution lines, transformers, breakers, various controllers, and various measurement and monitoring systems. The grid has been going through significant changes in past decades with new technological developments, deregulation, distributed generation, smart grid, and asset management. A synergy of these new developments has contributed to a better grid by improving its reliability and performance. However, the efficient coordination between various components of the grid and various new developments has been a constant challenge. For instance, new components that are introduced in the grid often have state of the art measurement and monitoring systems whereas the aging components have limited measurement and monitoring systems. We need to maintain the balance between these new and old technologies such that the new developments should be exploited to their full extent and the old systems should be reinforced such that their operational life could be extended without affecting their reliability significantly. Due to the complexity of the grid control, a centralized control of every component and every aspect of the grid is practically impossible. A distributed control system provides the ability to simplify the complexity of the grid control problem while solving the complex problem of coordination between its sub-systems. A distributed system is modular in nature and this system could be introduced to the grid in incremental phases within large networks. Multi-agent control can be used in the grid to realize a distributed system. Using agent theory, a concept of an intelligent component is described in this thesis. The intelligent component has the ability to make intelligent decisions based on the state of the component. With developments in measurement and monitoring technologies, we are better informed of the state of the grid components. By using these systems, we have the ability to better predict the health state of the grid components. There has also been significant developments in understanding how the health state of the grid components evolves over their lifetime. A model of the health state coupled with the new measurement and monitoring system allows us to predict the health state of the system. A framework of model-based optimization is included in the intelligent component. This framework consists of a predictive health model. An optimization is performed based on the prediction of the health model and the control decision of the intelligent component is made on the basis of this optimization. In order to solve the whole problem of the electricity grid, the intelligent components need to collaborate within each other. A concept of an intelligent network is also proposed in this thesis. In the intelligent network concept, a hierarchical structure of intelligent components has been developed. In order to optimize their global performance, the intelligent components need to collaborate with each other. The intelligent components within this hierarchical structure coordinate by exchanging their local states and their future plans. Coordination within intelligent network is only possible if all their intelligent components can communicate effectively. For this, an information interface was developed. The interface is particularly of importance in the electricity grid as different control systems used within the grid are often developed by different vendors. Common Information Model (CIM) has been deployed in the grid for network control, data exchange, and energy management systems. This CIM is further developed in this thesis so that it can accommodate the concept of the intelligent component and the intelligent network developed in this thesis. A case study of dynamic loading of transformers is used to illustrate the concept. The example is used throughout the thesis to demonstrate applicability of concepts of the intelligent component, the intelligent networks and the information interface. A dynamic loading scheme of transformer is developed based on the concept of intelligent components. A predictive health model for the top-oil temperature and the hot-spot temperature is developed. The predictive heath model predicts the top-oil temperature and the hot-spot temperature based on the loading of the transformer. An optimization method is developed which gives the dynamic rating of the transformer based on these predictions. The dynamic loading (DL) agent, developed here, could make local decisions on its dynamic rating based on the predicted loading of the transformer. This dynamic loading is applied in a electricity grid to illustrate the concept of intelligent networks. Multiple transformers within the grid have their own dynamic loading agents. An optimal power flow (OPF) agent is developed which controls the grid based on an optimal power flow algorithm. The OPF agent obtains the dynamic ratings from the dynamic loading agents of the transformers. Based on these dynamic ratings, the OPF agent controls the power flow of the grid. The OPF agent also sends predicted loadings of the transformers to its DL agents. These predicted loading is used by the dynamic loading agents which use this information for the next time step. The information interface is also described for this intelligent network implementation. In order to communicate dynamic ratings and predicted loadings of transformers, an extension to the CIM is developed. The workflow of the intelligent agent and its interaction with the extended CIM is also demonstrated. It is concluded that the use of the predictive health model enables the optimization for the future prediction horizon. The intelligent component concept is modular in nature which is useful for the electricity grid. The intelligent network concept effectively combines intelligent components within it. The framework developed in this thesis is also demonstrated with examples of dynamic loading of transformers within an electricity network in which the loading of the transformers are increased by 50 % of its nominal rating. Possible future extension of the predictive health model to include other electrical components models such as cables, circuit breakers, and generators, etc. is also discussed. A suggestion on the implementation phases of the concept developed in this thesis is also presented. It is suggested that the concept would be practical to be implemented in gradual phases to the electricity grid. New developments are also a potential opportunity for the implementation of the concept as the marginal cost is minimal for introducing the concept.High-Voltage Components and Power Systems groupElectrical Engineering, Mathematics and Computer Scienc
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