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As one of the most promising pathways in the transition period towards the low carbon economy, a large scale implementation of electric vehicles (EV) is expected in the near future. Concentration of EV charging in a small area or within a short time will dramatically affect the load demand profile, especially the peak load in the distribution network. As a result, distribution transformers are facing hazards of shortened lifetime due to extra loads, and direct failures caused by potential overloads. Considering the large number of distribution transformers and the massive investment involved, the adaptability of the population of distribution transformers under future EV scenarios should be assessed. In this thesis, an assessment strategy for the future adaptability of distribution transformer population under EV scenarios is introduced. Assessing the adaptability is to understand the impact of the hot-spot temperature, loss-of-life, expected lifetime and failure probability of each individual in the distribution transformer population. Determination of hot-spot temperature of distribution transformers is essential for the assessment. In order to achieve accurate prediction of hot-spot temperatures under EV scenarios, thermal parameters should be refined for individual distribution transformers so that their thermal characteristics can be reflected more accurately than using the generic values recommended for all distribution transformers in the IEC loading guide. Two methods for the refinement are proposed in this thesis. One method is to curve-fit hot-spot temperatures measured in the extended heat run test; and the other is to calculate each parameter with developed equations in the loading guide with standard heat run test results. The assessment strategy is introduced and demonstrated on a group of selected distribution transformers from the population under three EV scenarios, i.e. Business as usual (BAU), High-range and Extreme-range scenarios, which represent 0%, 32% and 58.9% EV penetration levels respectively. Results show that EV charging would be less concerned on the acceleration of thermal ageing than the direct failure due to breakdown caused by decrease of dielectric strength in an event of bubbling. Since the peak load and hot-spot temperature under EV scenarios only last for a short time and would be compensated by low values during the rest time of a day, which eventually leads to a moderate thermal ageing. Occasionally, severe over-ageing can be caused by extremely high hot-spot temperatures, and the lifetime will be reduced to an unacceptable level. However, on such occasions, hot-spot temperatures would be high enough to trigger bubbling and reduce the dielectric strength of transformer's insulation system to a level that is incapable of undertaking the voltage stress, which eventually causes breakdown of transformers. In terms of the failure probability, results show that no distribution transformers are facing failure risks due to bubbling under BAU scenario. Failure starts under High-range scenario. If transformers possessing a failure probability over 50% are identified as high risk, then 13% of investigated transformers are at high risk under High-range scenario, while it increases to 39% under Extreme-range scenario. It is found that the failure probability is dominantly controlled by the peak load, other factors such as transformer age and installation conditions are less influential. A threshold peak load of around 1.5 p.u. is observed that distinguishes transformers in high risk from others under Extreme-range scenario. This observation could be applied to assist the asset management under future EV scenarios that the peak load of distribution transformers should be restricted below 1.5 p.u. to prevent potential failure due to bubbling.

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No description available.

Este trabalho de pesquisa visa apresentar um processo de avaliação probabilística de integridade mecânica de elementos estruturais, e ilustra sua aplicação em situações de otimização dimensional de tais elementos. O processo apresentado é baseado na análise de confiabilidade por métodos analíticos, utilizando o diagrama de avaliação de falha (FAD) como critério de falha. A escolha da curva FAD como critério de falha visa padronizar a análise de confiabilidade estrutural, permitindo a sua aplicação tanto em simulações numéricas quanto em mapas utilizados para rápidas tomadas de decisão. Os métodos de análise e o processo apresentado são aplicados em casos de estudo para mostrar a influência da percepção probabilística nas tomadas de decisão de projeto e a importância da análise de risco no dimensionamento de sistemas estruturais. / This work intends to present a process for probabilistic assessment of mechanical integrity of structural elements, and illustrates its application in situations of dimensional optimization of such elements. The presented process is based on the reliability analysis by analytical methods, using the failure assessment diagram (FAD) as failure criteria. The choice of FAD curve as a failure criteria aims to standardize the structural reliability analysis, allowing its application both in numerical simulations and in chart maps used for fast decision making. The methods of analysis and the presented process are applied in case studies to show the influence of probabilistic perception on project decision making and the importance of risk analysis in the design of structural systems.

In overwhelming majority of the petroleum or petrochemical plants, pressure vessels and process piping play important roles among the major elements of static equipments. So, based on the integrity of safety management for the petroleum or petrochemical plants and reduction of the operation risks, some objective schemes of the systematic failure evaluations and assessments should be established in order to optimize the resources of inspection and maintenance. However, performing the inspections based on the conventional methodologies, some uncontrolled factors which caused by the environments and inspection methods may exist and affect the assessment of the estimated corrosion rate. If the influences of the uncontrolled factors were not considered and compensated in the assessment of the estimated corrosion rate, some underestimate or unreasonable results would be obtained which lead potential risks may exist in the plants. Moreover, the measured data of some parameters, for example, operation pressure, corrosion condition, allowable stress, which were used to evaluate the estimated corrosion rate of the pressure components may exhibit a normal or non-normal distribution. Under such circumferences, if one used the nominal values of the measured parameters to assessment the safety conditions of the pressure components, potential risks may exist in the petroleum or petrochemical plants at the final stage of long-term operation. With an eye to obtain more conservative and objective assess results for pressure equipments in the long-term operation, three subjects will be differentiated between the evaluation of estimated corrosion rate, failure probability of pressure vessels and pressure safety valve (PSVs). First, based on the pressure boundaries suffered from general corrosion, a statistical methodology was proposed to modify the assessment of estimated corrosion rates for the pressure components in conventional methodology. Furthermore, the obtained results of the estimated corrosion rates will be used to assess the failure probability of pressure components based on the upper limited value. By adopting First Order Second Moment (FOSM) method, the failure probability was approached for the pressure components in long term operation. Moreover, for the sake of optimize the inspection and maintenance resources based on the acceptable risk of the plant owners, typical semi-quantitative risk based inspection (RBI) methodology to each pressure vessel are proposed in safety management based on the approached failure probability. Besides, the final protection for the pressure equipments when the pressure systems were upset - pressure safety valves (PSVs), are also play important roles to system evaluation and safety management for pressurized system. So, follow the semi-quantitative RBI methodology, the objective evaluation schemes together with the suggested inspection interval were conservatively established. Based on the conclusion of the studies, few pressure components with high failure probability will raise the operation risk of the pressurized system. It is an effective way to reduce the operation risk of the pressurized system by shift the limited resource of inspection/maintenance on the pressure components with high risk and obtain further control with effective strategies. Moreover, the conclusion also shows the prospective inspection intervals of PSVs which time-based strategy according to the local regulations (2-year based) should be change to condition-based strategy to reduce the operation risk.

Este trabalho de pesquisa visa apresentar um processo de avaliação probabilística de integridade mecânica de elementos estruturais, e ilustra sua aplicação em situações de otimização dimensional de tais elementos. O processo apresentado é baseado na análise de confiabilidade por métodos analíticos, utilizando o diagrama de avaliação de falha (FAD) como critério de falha. A escolha da curva FAD como critério de falha visa padronizar a análise de confiabilidade estrutural, permitindo a sua aplicação tanto em simulações numéricas quanto em mapas utilizados para rápidas tomadas de decisão. Os métodos de análise e o processo apresentado são aplicados em casos de estudo para mostrar a influência da percepção probabilística nas tomadas de decisão de projeto e a importância da análise de risco no dimensionamento de sistemas estruturais. / This work intends to present a process for probabilistic assessment of mechanical integrity of structural elements, and illustrates its application in situations of dimensional optimization of such elements. The presented process is based on the reliability analysis by analytical methods, using the failure assessment diagram (FAD) as failure criteria. The choice of FAD curve as a failure criteria aims to standardize the structural reliability analysis, allowing its application both in numerical simulations and in chart maps used for fast decision making. The methods of analysis and the presented process are applied in case studies to show the influence of probabilistic perception on project decision making and the importance of risk analysis in the design of structural systems.

No description available.

No description available.

No description available.