1,721,135 research outputs found
Analysis of Thermo-Mechanical Stresses in Joints and Cables
No full textThe landscape of the power sector is undergoing a significant transformation. The growing demand for energy, the depletion of world’s fossil energy resources and the greenhouse effect are well-recognized challenges for the power sector. Through the integration of renewable resources to the energy mix, the power sector is becoming cleaner and more affordable. A fundamental requirement to handle these new developments is to have an efficient transmission and distribution network. Effective transmission and distribution of electricity depends on the condition of underground power cables and joints. Any malfunction in these elements can affect the reliability of the entire grid and this could have an economic impact on the system. Undoubtedly, having an efficient and reliable transmission network implies the need to know and determine the electrical, thermal and mechanical limits of cable systems (cable + accessory). The stresses affecting the service performance of cable system may be classified as thermal, electrical, mechanical and chemical or a combination of the aforementioned. The contributory effects of thermo-mechanical stresses on the degradation of cable joints have gained great attention. Correct expectation of the thermo-mechanical behaviour of all the components in the cable system allows optimisation of both the performance and reliability of these components while maintaining the component life. This research explores some aspects of the thermo-mechanical stresses inside the cable system components in more depth. This work investigates thermomechanical stresses in silicone rubber pre-moulded cable joints and in three core submarine export cables.It is known that the electrical breakdown strength of insulation interfaces in cable joints depends on the mechanical pressure. Based on the literature, it has been shown that increasing the mechanical pressure in cable joints at the interface is important for ensuring high electrical breakdown strength. However, there is no clear benchmark for interface pressure, and little knowledge about how the thermal behaviour of the cable system will affect it. Furthermore, there is no correlation between interface pressure and different parameters such as material strain, temperature, thickness and elastic modulus. In this research, the mechanical design of solid-solid interface in cable joints is studied to evaluate the main effects of the relevant parameters. More specifically, a model is developed using the finite element method to calculate mechanical stresses based on a non-linear elastic model. In addition, an improved analytical approach is developed to determine the changes in interface pressure during operation. This proposed analytical approach takes proper account of material properties and their changes with temperature. The analytical algorithm is validated using finite element method. The use of a more realistic interface pressure model increases the integrity of the cable joint design and better enables industry professionals and system operators to determine the limits of their system during operation.In three-core cables, the cores are subjected to higher internal thermo-mechanical stresses than single core cables since each core is expected to be more restricted. The effect of internal thermo-mechanical stresses on the electrical performance of the three-core cable should be examined properly, but is often neglected. During electrical testing of AC submarine cables, only one core of a three-core cable could be tested. In this thesis, the internal thermo-mechanical stresses generated inside a single core and a three core cable are examined. In particular, a 2D thermo-mechanical coupled model is developed using finite element modelling. The model is analysed through thermo-mechanical analysis, to investigate how the thermally induced deformations could affect the electrical performance of the cable. This study demonstrates the significance of testing the full three core submarine cable with armour rather than testing only one single core
Thermo-mechanical analysis of solid interfaces in HVAC cable joints
No full textMechanical stresses affect the electrical performance of solid-solid interfaces in highvoltage cable joints. This paper assesses the influence of insulation material mechanical properties and temperature on interface pressure. Based on a hyper-elastic model, the mechanical stresses inside silicone rubber joint tube were determined. Circumferential stresses can reach 50% of the silicone rubber tensile strength at normal pre-operation expansion ratios. An analytical method to determine the thermally induced mechanical stress during operation is presented and its accuracy is confirmed using finite element method. This method is modified to account for the variation of the mechanical properties with temperature. This paper shows that circumferential stresses at the interface increase as temperature drops, which may have a significant impact on theelectrical performance of the interface during operation
The temperature dependence of insulation mechanical properties and its effect on interface pressure in cable joints
No full textContact pressure is a vital factor that controls the interfacial electrical breakdown strength. Loss of interface pressure between cable insulation and joint insulation must be avoided in practice to ensure a long life span of power cable joints.The contact pressure depends on the temperature profile in the bulk material, the thermal characteristics and the mechanical properties of the insulation materials. In this paper, a mathematical model using the thermo-elastic equations was developed to estimate the contact pressure taking into account how the mechanical properties (elastic modulus and thermal expansion) change with temperature, along with a realistic radial temperature profile. Twodifferent approaches are compared, one using finite element analysis and the other using a set of differential equations which may be solved without the need for proprietary software
Effect of short circuit currents on thermo-mechanical properties of insulated cables
No full textCables are expected to have the ability to safely carry the rated short circuit current during abnormal dynamic conditions, such that a through fault does not damage the whole cable. For XLPE insulated cables, the maximum temperature during short circuits should not exceed 250 °C. This temperature must not adversely affect the conductor or the lead sheath. However, the effect of the thermo-mechanical stresses generated on the speed of degradation of the insulation system is of great importance. This paper analyses the influence of short circuit current on the interface between the cable sheath and insulation. Based on the theory of elasticity, a finite element thermomechanical model is proposed of a single core cable, incorporating temperature-dependent properties. The model demonstrates the importance of the mechanical properties of the insulation material, which plays a critical role in understanding the internal thermomechanical stresses within a cable
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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