| 1. |
- Gustafsson, Stefan, et al.
(författare)
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Electromagnetic dispersion modeling and measurements for HVDC power cables
- 2014
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Ingår i: IEEE Transactions on Power Delivery. - : IEEE Press. - 0885-8977 .- 1937-4208. ; 29:6, s. 2439-2447
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides a general framework for electromagnetic (EM) modeling, sensitivity analysis, computation, and measurements regarding the wave propagation characteristics of high-voltage direct-current (HVDC) power cables. The modeling is motivated by the potential use with transient analysis, partial-discharge measurements, fault localization and monitoring, and is focused on very long (10 km or more) HVDC power cables with transients propagating in the low-frequency regime of about 0-100 kHz. An exact dispersion relation is formulated together with a discussion on practical aspects regarding the computation of the propagation constant. Experimental time-domain measurement data from an 80-km-long HVDC power cable are used to validate the electromagnetic model, and a mismatch calibration procedure is devised to account for the connection between the measurement equipment and the cable. Quantitative sensitivity analysis is devised to study the impact of parameter uncertainty on wave propagation characteristics. The sensitivity analysis can be used to study how material choices affect the propagation characteristics, and to indicate which material parameters need to be identified accurately in order to achieve accurate fault localization. The analysis shows that the sensitivity of the propagation constant due to a change in the conductivity in the three metallic layers (the inner conductor, the intermediate lead shield, and the outer steel armor) is comparable to the sensitivity with respect to the permittivity of the insulating layer. Hence, proper modeling of the EM fields inside the metallic layers is crucial in the low-frequency regime of 0-100 kHz.
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| 2. |
- Nordebo, Sven, et al.
(författare)
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Low-frequency dispersion characteristics of a multilayered coaxial cable
- 2013
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Ingår i: Journal of Engineering Mathematics. - : Springer Netherlands. - 0022-0833 .- 1573-2703. ; 83:1, s. 169-184
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides an exact asymptotic analysis regarding the low-frequency dispersion characteristics of a multilayered coaxial cable. A layer-recursive description of the dispersion function is derived that is well suited for asymptotic analysis. The recursion is based on two well-behaved (meromorphic) subdeterminants defined by a perfectly electrically conducting (PEC) and a perfectly magnetically conducting termination, respectively. For an open waveguide structure, the dispersion function is a combination of two such functions, and there is only one branch point that is related to the exterior domain. It is shown that if there is one isolating layer and a PEC outer shield, then the classical Weierstrass preparation theorem can be used to prove that the low-frequency behavior of the propagation constant is governed by the square root of the complex frequency, and an exact analytical expression for the dominating term of the asymptotic expansion is derived. It is furthermore shown that the same asymptotic expansion is valid to its lowest order even if the outer shield has finite conductivity and there is an infinite exterior region with finite nonzero conductivity. As a practical application of the theory, a high-voltage direct current (HVDC) power cable is analyzed and a numerical solution to the dispersion relation is validated by comparisons with the asymptotic analysis. The comparison reveals that the low-frequency dispersion characteristics of the power cable is very complicated and a first-order asymptotic approximation is valid only at extremely low frequencies (below 1 Hz). It is noted that the only way to come to this conclusion is to actually perform the asymptotic analysis. Hence, for practical modeling purposes, such as with fault localization, an accurate numerical solution to the dispersion relation is necessary and the asymptotic analysis is useful as a validation tool.
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| 3. |
- Bybrant, M. C., et al.
(författare)
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Celiac disease can be predicted by high levels of tissue transglutaminase antibodies in children and adolescents with type 1 diabetes
- 2021
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Ingår i: Pediatric Diabetes. - : Hindawi Limited. - 1399-543X .- 1399-5448. ; 22:3, s. 417-424
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Tidskriftsartikel (refereegranskat)abstract
- Objectives Children with type 1 diabetes (T1D) are not included in guidelines regarding diagnosis criteria for celiac disease (CD) without a diagnostic biopsy, due to lack of data. We explored whether tissue transglutaminase antibodies (anti-tTG) that were >= 10 times the upper limit of normal (10x ULN) predicted CD in T1D. Methods Data from the Swedish prospective Better Diabetes Diagnosis study was used, and 2035 children and adolescents with T1D diagnosed between 2005-2010 were included. Of these, 32 had been diagnosed with CD before T1D. The children without CD were repeatedly screened for CD using anti-tTG antibodies of immunoglobulin type A. In addition, their human leukocyte antigen (HLA) were genotyped. All children with positive anti-tTG were advised to undergo biopsy. Biopsies were performed on 119 children and graded using the Marsh-Oberhuber classification. Results All of the 60 children with anti-tTG >= 10x ULN had CD verified by biopsies. The degree of mucosal damage correlated with anti-tTG levels. Among 2003 screened children, 6.9% had positive anti-tTG and 5.6% were confirmed CD. The overall CD prevalence, when including the 32 children with CD before T1D, was 7.0% (145/2035). All but one of the children diagnosed with CD had HLA-DQ2 and/or DQ8. Conclusions As all screened children and adolescents with T1D with tissue transglutaminase antibodies above 10 times the positive value 10x ULN had CD, we propose that the guidelines for diagnosing CD in screened children, when biopsies can be omitted, should also apply to children and adolescents with T1D as a noninvasive method.
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| 4. |
- Gopinath, Varun, et al.
(författare)
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Collaborative Assembly on a Continuously Moving Line - An Automotive Case Study
- 2018
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Ingår i: 28TH INTERNATIONAL CONFERENCE ON FLEXIBLE AUTOMATION AND INTELLIGENT MANUFACTURING (FAIM2018): GLOBAL INTEGRATION OF INTELLIGENT MANUFACTURING AND SMART INDUSTRY FOR GOOD OF HUMANITY. - : ELSEVIER SCIENCE BV. ; 17, s. 985-992
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Konferensbidrag (refereegranskat)abstract
- Collaborative operation is a state in which a purposely designed robot system and an operator work within a collaborative workspace. To ensure a safe working environment, safety standards suggest conducting a task-based risk assessment followed by risk reduction to reduce the risks to an acceptable level. In this article, an automotive case study will be used to understand safety issues associated with collaborative operations with large industrial robots. Based on this case study, a layout of the collaborative workstation, in terms of workspaces and tasks, which is the outcome of a risk assessment program will be presented. The first critical step in risk assessment is hazard identification, which can allow the risk assessing team to evaluate the hazards and suggest measures to mitigate the risks. Therefore, the hazards identified during the risk assessment program will also be detailed along with measures to mitigate the risks and is expected to complement our understanding of the nature of hazards associated with collaborative operations with large industrial robots. (C) 2018 The Authors. Published by Elsevier B.V.
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| 5. |
- Gopinath, Varun, 1982-, et al.
(författare)
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Safe Collaborative Assembly on a Continuously Moving Line with Large Industrial Robots
- 2021
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Ingår i: Robotics and Computer-Integrated Manufacturing. - : Elsevier. - 0736-5845 .- 1879-2537. ; 67
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Tidskriftsartikel (refereegranskat)abstract
- Robot safety standards defines Collaborative Operation as a state in which purposely designed robots work in direct cooperation with a human within a defined workspace. That is, an operator and an industrial robot complete assembly tasks at the collaborative workspace. A prerequisite to ensuring safety during all phases of operation is an understanding of the nature of hazards pertinent to collaborative systems. An automotive assembly station, where plastic panels are assembled on a continuously moving line, formed the basis for research operations meant to understand safety issues when a large industrial robot aids an operator in assembly tasks. This led to the development of a laboratory demonstrator whose design and functioning will be presented in this article. Additionally, the hazards identified during risk assessment along with measures to mitigate the associated risks will be presented in order to highlight the nature of hazards pertinent to collaborative systems.
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