Structural integrity of power transformers

The subject of this thesis is to study the mechanical integrity and performance of insulation materials used in power transformers under short circuit conditions. There are a number of methods to calculate short circuit forces in the literature. These methods were developed to determine the magnetic properties related to the short circuit condition and cannot be used in the open circuit condition due to the assumption of infinitely permeable core. To this end, a new solution strategy is introduced which is able to calculate magnetic properties of power transformers both in open circuit and in short circuit conditions. A solution was derived utilizing transform techniques and multiple connected permeable regions can now be solved. Mechanical failure modes of transformer winding are presented and new solution methods are introduced for some failure modes. Dynamic representation of the transformer winding is achieved by treating the winding turn by turn. Particular attention is given to stress calculations of Continuously Transposed Cable (CTC) and resin bonded CTC. Digital Image Correlation (DIC) technique maps the strain distribution on the test specimen and the strain distribution can be extracted at any cross section of interest. 3‐D DIC technique is used to determine the response of transformerboard material under tensional and bending loads and material properties are determined. It is also shown that the DIC method provides much more accurate results compared to strain gauges due to its manufacturing technique. DIC results are used to determine material properties related to both tensional and bending type loading conditions. Resin laminate wood is also compared to transformerboard. Viscoelastic properties of transformerboard are examined. Because a short circuit event is dynamic in nature, storage and loss modulus of transformerboard are determined as a function of temperature and frequency under cyclic loading conditions. Conventional creep test setups cannot be used for transformerboard. A test setup is designed to measure creep curves of transformerboard. The test setup measures the creep curves both in oil and in air and the displacements are recorded automatically. Tests are performed at a wide range of temperatures encountered in real service conditions of transformerboard material. The developed method can be introduced in PC codes to determine the magnetic properties related to the magnetic field. Also the method can be used to determine turn to turn or disc to disc mutual inductances of a transformer. Electromagnetic forces calculated with the introduced method are also more accurate than the methods developed earlier. Methods to calculate mechanical stresses acting on transformer components are also reviewed and new solution techniques for some failure modes are developed. Mechanical performance of insulation materials under tension and bending type loadings are measured and monitored using DIC technique. Finally, time dependent material properties of the transformerboard under constant and cyclic loading conditions are determined. Both analytical and experimental techniques are utilized to determine the material properties of the transformer components and their behaviour under different loading conditions. New solution techniques are developed and the material behaviour of the insulation materials under different loading conditions is determined. With the data obtained and solutions developed, mechanical stress calculations of the power transformer components can be made more accurately

Impact of Embedded Carbon Fiber Heating Panel on the Structural/Mechanical Performance of Roadway Pavement

INE/AUTC 12.3

Integration and Conventional Systems at STAR

At the beginning of the design and construction of the STAR Detector, the collaboration assigned a team of physicists and engineers the responsibility of coordinating the construction of the detector. This group managed the general space assignments for each sub-system and coordinated the assembly and planning for the detector. Furthermore, as this group was the only STAR group with the responsibility of looking at the system as a whole, the collaboration assigned it several tasks that spanned the different sub-detectors. These items included grounding, rack layout, cable distribution, electrical, power and water, and safety systems. This paper describes these systems and their performance.Comment: 17 pages, 6 figures, Contribution to a NIM Volume Dedicated to the Detectors and the Accelerator at RHI

Degradation of the compression strength of spacers made of high-density pressboard used in power transformers under the influence of thermal ageing

The structural components inside power transformers are commonly made of high-density pressboard, due to its suitable mechanical and dielectric properties. Among these components are the spacers used in the windings of transformers, which are subjected to compressive loading during operation. The spacers are immersed in dielectric liquid and subjected to high temperatures and chemical reactions during the lifespan of the transformer, which result in the degradation of their dielectric and mechanical properties. The performance and reliability of the power transformer greatly depends on its mechanical integrity, so it is necessary to understand how ageing degrades the mechanical response of the high-density pressboard. In this study, spacers made of high-density pressboard and pieces of copper conductor were immersed in uninhibited paraffinic oil and aged at 150 °C for different periods of time, trying to realistically represent the process suffered by a power transformer during its whole lifespan. The evolution caused by the thermal ageing over some chemical parameters (acidity and moisture content) and dielectric properties (AC breakdown voltage, dielectric dissipation factor, resistivity and degree of polymerisation) of the oil and the pressboard was studied experimentally. Compressive mechanical tests were performed on samples of the aged high-density pressboard, and the compressive stiffness during the ageing process was related with other chemical and dielectric parameters

Impact Assessment of Hypothesized Cyberattacks on Interconnected Bulk Power Systems

The first-ever Ukraine cyberattack on power grid has proven its devastation by hacking into their critical cyber assets. With administrative privileges accessing substation networks/local control centers, one intelligent way of coordinated cyberattacks is to execute a series of disruptive switching executions on multiple substations using compromised supervisory control and data acquisition (SCADA) systems. These actions can cause significant impacts to an interconnected power grid. Unlike the previous power blackouts, such high-impact initiating events can aggravate operating conditions, initiating instability that may lead to system-wide cascading failure. A systemic evaluation of "nightmare" scenarios is highly desirable for asset owners to manage and prioritize the maintenance and investment in protecting their cyberinfrastructure. This survey paper is a conceptual expansion of real-time monitoring, anomaly detection, impact analyses, and mitigation (RAIM) framework that emphasizes on the resulting impacts, both on steady-state and dynamic aspects of power system stability. Hypothetically, we associate the combinatorial analyses of steady state on substations/components outages and dynamics of the sequential switching orders as part of the permutation. The expanded framework includes (1) critical/noncritical combination verification, (2) cascade confirmation, and (3) combination re-evaluation. This paper ends with a discussion of the open issues for metrics and future design pertaining the impact quantification of cyber-related contingencies

Consumer health protection and Information and Communication Technology

The environmental emergencies, the alimentary crisis, the increase of chronic illnesses, pushes the consumers to seek informative channels often also "virtual" as a reassurance for their own health, for the salubriousness of food and above all as a direct channel with the enterprises. For these last, then, it becomes fundamental to look at the information, to the virtual nets, and to the Information and Communication Technologies (ICTs) especially as powerful means of communication. Therefore, the work analyzes the role that the ICTs develop in the productive sector of ‘Mozzarella di Bufala Campana’, a particularly important product for the economy of the Region but in crisis because installed in a context of environmental emergencies that have seriously compromise the trust of the consumer, worried about the implications for the health. Particularly, the work proposes a survey both on the dairies that on the consumers with the purpose to appraise the propensity of the first ones to use Internet in their own strategies of web marketing and the importance of such tool, for the seconds, in presence of a situation of alarm for the health.Health, consumer protection, food quality, Information and Communication Technologies., Agricultural and Food Policy, Food Consumption/Nutrition/Food Safety,

Power transformer under short-circuit fault conditions: A multiphysics approach

Transformers’ windings experience mechanical loads from electromagnetic forces due to the currents they carry. During normal operation, the resulting stresses and strains have minor influence, therefore they do not represent the significant risk to the devices’ integrity. However, transformers can suffer from high sudden short-circuit currents that are several times higher than those during the normal operation. These short-circuit currents are a significant threat, not only from an electrical but also from the structural integrity point of view. In this paper, coupled electromagnetic and structural mechanics simulations are carried out to evaluate short-circuit fault risks in a comprehensive and accurate way

Power transformer under short-circuit fault conditions: A multiphysics approach

Transformers’ windings experience mechanical loads from electromagnetic forces due to the currents they carry. During normal operation, the resulting stresses and strains have minor influence, therefore they do not represent the significant risk to the devices’ integrity. However, transformers can suffer from high sudden short-circuit currents that are several times higher than those during the normal operation. These short-circuit currents are a significant threat, not only from an electrical but also from the structural integrity point of view. In this paper, coupled electromagnetic and structural mechanics simulations are carried out to evaluate short-circuit fault risks in a comprehensive and accurate way

Structural health monitoring for wind turbine foundations

The construction of onshore wind turbines has rapidly been increasing as the UK attempts to meet its renewable energy targets. As the UK’s future energy depends more on wind farms, safety and security are critical to the success of this renewable energy source. Structural integrity of the tower and its components is a critical element of this security of supply. With the stochastic nature of the load regime a bespoke low cost structural health monitoring system is required to monitor integrity of the concrete foundation supporting the tower. This paper presents an assessment of ‘embedded can’ style foundation failure modes in large onshore wind turbines and proposes a novel condition based monitoring solution to aid in early warning of failure. The most common failure modes are discussed and a low-cost remote monitoring system is presented