| 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. |
- Hamon, Camille, et al.
(författare)
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A Stochastic Optimal Power Flow Problem With Stability Constraints-Part I : Approximating the Stability Boundary
- 2013
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Ingår i: IEEE Transactions on Power Systems. - 0885-8950 .- 1558-0679. ; 28:2, s. 1839-1848
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Tidskriftsartikel (refereegranskat)abstract
- Stochastic optimal power flow can provide the system operator with adequate strategies for controlling the power flow to maintain secure operation under stochastic parameter variations. One limitation of stochastic optimal power flow has been that only line flows have been used as security constraints. In many systems voltage stability and small-signal stability also play an important role in constraining the operation. In this paper we aim to extend the stochastic optimal power flow problem to include constraints for voltage stability as well as small-signal stability. This is done by approximating the voltage stability and small-signal stability constraint boundaries with second-order approximations in parameter space. Then we refine methods from mathematical finance to be able to estimate the probability of violating the constraints. In this first part of the paper, we derive second-order approximations of stability boundaries in parameter space. In the second part, the approximations will be used to solve a stochastic optimal power flow problem.
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| 3. |
- Ivanenko, Yevhen, et al.
(författare)
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Quasi-Herglotz functions and convex optimization
- 2020
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Ingår i: Royal Society Open Science. - : The Royal Society Publishing. - 2054-5703. ; 7:1, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- We introduce the set of quasi-Herglotz functions and demonstrate that it has properties useful in the modelling of non-passive systems. The linear space of quasi-Herglotz functions constitutes a natural extension of the convex cone of Herglotz functions. It consists of differences of Herglotz functions and we show that several of the important properties and modelling perspectives are inherited by the new set of quasi-Herglotz functions. In particular, this applies to their integral representations, the associated integral identities or sum rules (with adequate additional assumptions), their boundary values on the real axis and the associated approximation theory. Numerical examples are included to demonstrate the modelling of a non-passive gain medium formulated as a convex optimization problem, where the generating measure is modelled by using a finite expansion of B-splines and point masses.
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| 4. |
- Nedic, Mitja, et al.
(författare)
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Herglotz functions and applications in electromagnetics
- 2020
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Ingår i: Advances in Mathematical Methods for Electromagnetics. - : Institution of Engineering and Technology. - 9781785613845 - 9781785613852 ; , s. 491-514
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Herglotz functions inevitably appear in pure mathematics, mathematical physics, and engineering with a wide range of applications. In particular, they are the pertinent functions to model passive systems, and thus appear in modeling of electromagnetic phenomena in circuits, antennas, materials, and scattering. In this chapter, we review the basic theory of Herglotz functions and its applications to determine sum rules and physical bounds for passive systems.
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| 5. |
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| 6. |
- Nordebo, Sven, et al.
(författare)
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Passive approximation and optimization
- 2015
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Ingår i: Progress in Electromagnetics Research Symposium (PIERS). - 9781934142295 ; , s. 84-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Perninge, Magnus, et al.
(författare)
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A Stochastic Optimal Power Flow Problem With Stability Constraints-Part II : The Optimization Problem
- 2013
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Ingår i: IEEE Transactions on Power Systems. - 0885-8950 .- 1558-0679. ; 28:2, s. 1849-1857
-
Tidskriftsartikel (refereegranskat)abstract
- Stochastic optimal power flow can provide the system operator with adequate strategies for controlling the power flow to maintain secure operation under stochastic parameter variations. One limitation of stochastic optimal power flow has been that only limits on line flows have been used as stability constraints. In many systems voltage stability and small-signal stability also play an important role in constraining the operation. In this paper we aim to extend the stochastic optimal power flow problem to include constraints for voltage stability as well as small-signal stability. This is done by approximating the voltage stability and small-signal stability constraint surfaces with second-order approximations in parameter space. Then we refine methods from mathematical finance to be able to estimate the probability of violating the constraints. In this, the second part of the paper, we look at how Cornish-Fisher expansion combined with a method of excluding sets that are counted twice, can be used to estimate the probability of violating the stability constraints. We then show in a numerical example how this leads to an efficient solution method for the stochastic optimal power flow problem.
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| 8. |
- Perninge, Magnus, 1980-, et al.
(författare)
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Approximating a post-contingency stable operation region in parameter space through time-domain simulation
- 2013
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Ingår i: Proceedings of IREP Symposium. - : IEEE. - 9781479901999
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Konferensbidrag (refereegranskat)abstract
- Operating criteria for power systems, such as the (N - 1)-criterion, are often based on evaluating whether the system is vulnerable to a specific set of contingencies. Therefore, a major part of power system security is concerned with establishing regions in parameter space where the system is vulnerable to specific contingencies. In this article we exploit the possibility of using Monte Carlo simulations to build an approximation of the region, in parameter space, where the power system will remain stable following a given contingency.
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| 9. |
- Perninge, Magnus
(författare)
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Approximating the loadability surface in the presence of SNB-SLL corner points
- 2013
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Ingår i: Electric power systems research. - : Elsevier BV. - 0378-7796 .- 1873-2046. ; 96, s. 64-74
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Tidskriftsartikel (refereegranskat)abstract
- Power system voltage security assessment is generally applied by considering the power system loadability surface. For a large power system, the loadability surface is a complicated hyper-surface in parameter space, and local approximations are a necessity for any analysis. Unfortunately, inequality constraints due to for example generator overexitation limiters, and higher codimension bifurcations, make the loadability surface non-smooth. One situation that is particularly difficult to handle is when a saddle-node bifurcation surface intersects a switching loadability limit surface. In this article we intend to investigate how several local approximations can be combined to obtain an adequate approximation of the loadability surface near such intersections.
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| 10. |
- Baglee, David, et al.
(författare)
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How can SMEs adopt a new method to advanced maintenance strategies : A Case study approach
- 2018
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Ingår i: Conference Proceedings: 30th International Conference on Condition Monitoring and Diagnostic Engineering Management (COMADEM 2017). - : University of Central Lancashire. - 9781909755154 ; , s. 155-162
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Konferensbidrag (refereegranskat)abstract
- Maintenance is crucial to manufacturing operations. In many organisations, the production equipmentrepresents the majority of invested capital, and deterioration of these facilities and equipment increasesproduction costs, reduces product quality. Over recent years the importance of maintenance, and thereforemaintenance management, within manufacturing organisations has grown. The maintenance function hasbecome an increasingly important and complex activity, particularly as automation increases. Theopportunity exists for many organisations to benefit substantially through improvements to theircompetitiveness and profitability by adopting a new approach to maintenance management. Several toolsand technologies including Condition Based Maintenance (CBM), Reliability Centred Maintenance (RCM)and more recently e-maintenance have developed under the heading of Advanced Maintenance Strategies.However, the adoption of advanced maintenance strategies and their potential benefits are usuallydemonstrated in large organisations. Unfortunately, the majority of organisations are constrained by thelack of knowledge and understanding on the requirements, which need to be in place before adopting anadvanced maintenance strategy. These are usually classified as Small and Medium Sized Enterprises(SMEs).The research strategy is based on ‘empirical iterations’ using survey secondary data, experts’ interviewsinformation and multiple case studies. The results show that there is a set of recommendations, whichstrongly influence the implementation of an Advanced Maintenance Strategy (AMS) with a Small toMedium Enterprise (SME). Organisations require a structured and integrative approach in order to takeadvantage of a new approach to maintenance management. This paper will propose recommendations forintegrating an AMS into the organisation and provide evidence of a successful implementation.
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