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  • 1.
    Aljure, Mauricio
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Becerra Garcia, Marley
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Karlsson, Mattias E.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymeric Materials.
    Streamer Inception from Ultra-Sharp Needles in Mineral Oil Based Nanofluids2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 8, article id 2064Article in journal (Refereed)
    Abstract [en]

    Positive and negative streamer inception voltages from ultra-sharp needle tips (with tip radii below 0.5 m) are measured in TiO2, SiO2, Al2O3, ZnO and C-60 nanofluids. The experiments are performed at several concentrations of nanoparticles dispersed in mineral oil. It is found that nanoparticles influence positive and negative streamers in different ways. TiO2, SiO2 and Al2O3 nanoparticles increase the positive streamer inception voltage only, whilst ZnO and C-60 nanoparticles augment the streamer inception voltages in both polarities. Using these results, the main hypotheses explaining the improvement in the dielectric strength of the host oil due to the presence of nanoparticles are analyzed. It is found that the water adsorption hypothesis of nanoparticles is consistent with the increments in the reported positive streamer inception voltages. It is also shown that the hypothesis of nanoparticles reducing the electron velocity by hopping transport mechanisms fails to explain the results obtained for negative streamers. Finally, the hypothesis of nanoparticles attaching electrons according to their charging characteristics is found to be consistent with the results hereby presented on negative streamers.

  • 2.
    Ao, Xianyu
    et al.
    South China Normal Univ, South China Acad Adv Optoelect, Ctr Opt & Electromagnet Res, Guangzhou 510006, Guangdong, Peoples R China..
    Xu, Xinan
    South China Normal Univ, South China Acad Adv Optoelect, Ctr Opt & Electromagnet Res, Guangzhou 510006, Guangdong, Peoples R China..
    Dong, Jinwu
    South China Normal Univ, South China Acad Adv Optoelect, Ctr Opt & Electromagnet Res, Guangzhou 510006, Guangdong, Peoples R China..
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. South China Normal Univ, South China Acad Adv Optoelect, Ctr Opt & Electromagnet Res, Guangzhou 510006, Guangdong, Peoples R China.;Zhejiang Univ, Natl Engn Res Ctr Opt Instruments, Ctr Opt & Electromagnet Res, JORCEP, Hangzhou 310058, Zhejiang, Peoples R China..
    Unidirectional Enhanced Emission from 2D Monolayer Suspended by Dielectric Pillar Array2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 41, p. 34817-34821Article in journal (Refereed)
    Abstract [en]

    Monolayers of transition metal dichalcogenides show great promise for optoelectronic devices as atomically thin semiconductors. Although dielectric or metal nanostructures have been extensively studied for tailoring and enhancing emission from monolayers, their applications are limited because of the mode concentrating inside the dielectric or the high optical losses in metals, together with the low quantum yield in monolayers. Here, we demonstrate that a metal-backed dielectric pillar array can suspend monolayers to increase the radiative recombination, and simultaneously, create strongly confined band-edge modes on surface directly accessible to monolayers. We observe unidirectional enhanced emission from WSe2 monolayers on polymer pillar array.

  • 3.
    Augustin, Tim
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. KTH Stockholm.
    Becerra, Marley
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Advanced Test Circuit for DC Circuit Breakers2018In: 20th European Conference on Power Electronics and Applications (EPE'18 ECCE EUROPE), 2018Conference paper (Refereed)
    Abstract [en]

    In future HVDC systems, many DC circuit breakers (DCCBs) will be required. In this paper, an advanced test circuit for DCCBs is described. A DC source is combined with a capacitor bank. In contrast to other test circuits, the proposed test circuit allows to replicate constant DC and temporary faults. In addition to conventional faults, this enables testing of auto-reclosing, proactive commutation, and complex test sequences combining all of these modes. The test circuit is easy to setup and also suitable for smaller research facilities. Experimental results from a down-scaled mock-up are included to demonstrate the capabilities of the test circuit.

  • 4.
    Augustin, Tim
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. KTH Stockholm.
    Magnusson, Jesper
    ABB Corporate Research, Västerås.
    Parekh, Mrunal
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    System Design of Fast Actuator for Vacuum Interrupter in DC Applications2018Conference paper (Refereed)
    Abstract [en]

    One of the major challenges of DC circuit breakers is the required fast mechanical actuator. In this paper, a Thomson coil actuator system for a vacuum interrupter is designed. Active damping is used to decelerate the moving contacts. Challenges are discussed, especially concerning the power supply needed for the Thomson coil actuator. The design philosophy is explained and FEM simulation results are presented. The results indicate that a wide range of combinations of drive circuit capacitance and voltage fulfill the requirements for armature acceleration. However, active damping requires a very careful selection of drive circuit voltage and timing of applied damping.

  • 5. Bangalore, P.
    et al.
    Letzgus, S.
    Patriksson, M.
    Bertling, Lina
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Analysis of SCADA data for early fault detection with application to the maintenance management of wind turbines2016In: CIGRE Session 46, CIGRE , 2016, p. 1-10Conference paper (Refereed)
    Abstract [en]

    During the past decade wind turbines have proven to be a promising source of renewable power. Wind turbines are generally placed in remote locations and are subject to harsh environmental conditions throughout their lifetimes. Consequently, the failures in wind turbines are expensive to repair and cause loss of revenue due to long down times. Asset management in wind turbines can aid in assessing and improving the reliability and availability of wind turbines, thereby making them more competitive. Maintenance policies play an important role in asset management and different maintenance models have been developed for wind turbine applications. Typically, mathematical models for maintenance optimization provide either an age based or a condition based preventive maintenance schedule. Age based preventive maintenance schedules provide the owner with the possibility to financially plan for maintenance activities for the entire lifetime of the wind turbine by providing the expected number of replacements for each component. However, age based preventive maintenance schedule may not consume the operating life of the wind turbine components to the maximum. Condition based maintenance scheduling has the advantage of better utilizing the operating life of the components. This paper proposes a wind turbine maintenance management framework which utilizes operation and maintenance data from different sources to combine the benefits of age based and condition based maintenance scheduling. This paper also presents an artificial neural network (ANN) based condition monitoring method which utilizes data from supervisory control and data acquisition (SCADA) system to detect failures in wind turbine components and systems. The procedures to construct ANN models for condition monitoring application are outlined. In order to demonstrate the effectiveness of the ANN based condition monitoring method it is applied to case studies from real wind turbines. Furthermore, a mathematical model called preventive maintenance schedule with interval costs (PMSPIC) is discussed and its application to a case study within the maintenance management framework is presented. The case study demonstrates the advantage of combining both the age based and condition based maintenance scheduling methods. 

  • 6.
    Bao, Fanglin
    et al.
    South China Normal Univ, Ctr Opt & Electromagnet Res, Guangdong Prov Key Lab Opt Informat Mat & Technol, South China Acad Adv Optoelect, Guangzhou 510006, Guangdong, Peoples R China..
    Shi, Kezhang
    Zhejiang Univ, Natl Engn Res Ctr Opt Instrumentat, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res,JORCEP,Coll Opt Sci &, Hangzhou 310058, Zhejiang, Peoples R China..
    Cao, Guanjun
    South China Normal Univ, Ctr Opt & Electromagnet Res, Guangdong Prov Key Lab Opt Informat Mat & Technol, South China Acad Adv Optoelect, Guangzhou 510006, Guangdong, Peoples R China..
    Evans, Julian S.
    Zhejiang Univ, Natl Engn Res Ctr Opt Instrumentat, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res,JORCEP,Coll Opt Sci &, Hangzhou 310058, Zhejiang, Peoples R China..
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. South China Normal Univ, Ctr Opt & Electromagnet Res, Guangdong Prov Key Lab Opt Informat Mat & Technol, South China Acad Adv Optoelect, Guangzhou 510006, Guangdong, Peoples R China.;Zhejiang Univ, Natl Engn Res Ctr Opt Instrumentat, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res,JORCEP,Coll Opt Sci &, Hangzhou 310058, Zhejiang, Peoples R China.
    Inhomogeneity-Induced Casimir Transport of Nanoparticles2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 13, article id 130401Article in journal (Refereed)
    Abstract [en]

    We propose a scheme for transporting nanoparticles immersed in a fluid, relying on quantum vacuum fluctuations. The mechanism lies in the inhomogeneity-induced lateral Casimir force between a nanoparticle and a gradient metasurface and the relaxation of the conventional Dzyaloshinskii-Lifshitz-Pitaevskii constraint, which allows quantum levitation for a broader class of material configurations. The velocity for a nanosphere levitated above a grating is calculated and can be up to a few microns per minute. The Born approximation gives general expressions for the Casimir energy which reveal size-selective transport. For any given metasurface, a certain particle-metasurface separation exists where the transport velocity peaks, forming a "Casimir passage." The sign and strength of the Casimir interactions can be tuned by the shapes of liquid-air menisci, potentially allowing real-time control of an otherwise passive force, and enabling interesting on-off or directional switching of the transport process.

  • 7.
    Becerra Garcia, Marley
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Long, Mengni
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Schulz, W.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    On the estimation of the lightning incidence to offshore wind farms2018In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 157, p. 211-226Article in journal (Refereed)
    Abstract [en]

    Field observations have shown that the frequency of dangerous lightning events to wind turbines, calculated according to the IEC standard 61400-24:2010, is grossly underestimated. This paper intends to critically revisit the evaluation of the incidence of downward lightning as well as self-initiated and other-triggered upward flashes to offshore wind power plants. Three different farms are used as case studies. The conditions for interception of stepped leaders in downward lightning and the initiation of upward lightning is evaluated with the Self-consistent Leader Inception and Propagation Model (SLIM). The analysis shows that only a small fraction of damages observed in the analysed farms can be attributed to downward lightning. It is also estimated that only a small fraction (less than 19%) of all active thunderstorms in the area of the analysed farms can generate sufficiently high thundercloud fields to self-initiate upward lightning. Furthermore, it is shown that upward flashes can be triggered even under low thundercloud fields once a sufficiently high electric field change is generated by a nearby lightning event. Despite of the uncertainties in the incidence evaluation, it is shown that upward flashes triggered by nearby positive cloud-to-ground flashes produce most of the dangerous lightning events to the case studies.

  • 8.
    Becerra Garcia, Marley
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Pettersson, Jonas
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Optical radiative properties of ablating polymers exposed to high-power arc plasmas2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 12, article id 125202Article in journal (Refereed)
    Abstract [en]

    The radiative properties of polymers exposed to high-intensity radiation are of importance for the numerical simulation of arc-induced ablation. The paper investigates the optical properties of polymethylmethacrylate PMMA and polyamide PA6 films exposed to high-power arc plasmas, which can cause ablation of the material. A four-flux radiative approximation is first used to estimate absorption and scattering coefficients of the tested materials in the ultraviolet (UV) and in the visible (VIS) ranges from spectrophotometric measurements. The temperature-induced variation of the collimated transmissivity of the polymers is also measured from room temperature to the glass temperature of PMMA and the melting temperature of PA6. Furthermore, band-averaged absorption and scattering coefficients of non-ablating and ablating polymers are estimated from the UV to the short-wavelength infrared (SWIR), covering the range of interest for the simulation of arc-induced ablation. These estimates are obtained from collimated transmissivities measured with an additional in situ photometric system that uses a high-power, transient arc plasma to both illuminate the samples and to induce ablation. It is shown that the increase in the bulk temperature of PA6 leads to a strong reversible increase in collimated transmissivity, significantly reducing the absorption and scattering coefficients of the material. A weaker but opposite effect of temperature on the optical properties is found in PMMA. As a consequence, it is suggested that the absorption coefficient of polymers used for arc-induced ablation estimates should not be taken directly from direct collimated transmissivity measurements at room temperature. The band-averaged radiation measurements also show that the layer of products released by ablation of PMMA produces scattering radiation losses mainly in the VIS-SWIR ranges, which are only a small fraction of the total incident arc radiation. In a similar manner, the ablation layer of PA6 leads to weak absorption radiation losses, although mainly in the UV range.

  • 9.
    Bessman, Alexander
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Soares, Rudi
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Software documentation for current-rippleequipment2018Report (Other (popular science, discussion, etc.))
  • 10.
    Björkqvist, Oskar
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Dahlberg, Oskar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Silver, Gustaf
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Kolitsidas, Christos
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Wireless Sensor Network Utilizing Radio-Frequency Energy Harvesting for Smart Building Applications2018In: IEEE Antennas & Propagation Magazine, ISSN 1045-9243, E-ISSN 1558-4143, Vol. 60, no 5, p. 124-136Article in journal (Refereed)
    Abstract [en]

    The scope of this article is to develop a modular radio-frequency (RF) energy-harvesting system for smart buildings that can act as a power source for sensing devices. Electromagnetic field-strength measurements at the main campus of the KTH Royal Institute of Technology in Stockholm, Sweden, were carried out to define the strength of the available ambient signals. Mainly two spectra were available for possible RF harvesting, i.e., two cellular bands [GSM1800 and third generation (3G)] and the 2.45-GHz Wi-Fi band. Based on these measurements, a modular approach for the system was adopted. The system is composed from two modules: 1) a Wi-Fi rectenna system composed of eight dual-polarized patch antennas and 16 rectifiers to produce eight differential voltage sources connected in series and 2) a cellular rectenna system composed of eight linear tapered slot antennas and eight rectifiers to produce four differential voltage sources connected in series. We propose an innovative multiple-input, single-output (MISO) wave rectifier that yields an efficient differential output. Both rectenna modules offer full azimuthal coverage and can operate either together or independently.

  • 11. Brazalez, A. A.
    et al.
    Manholm, L.
    Johansson, M.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Miao, Jingwei
    KTH.
    Investigation of a Ka-band Luneburg lens made of a glide-symmetric holey structure2017In: 2017 International Symposium on Antennas and Propagation, ISAP 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 1-2Conference paper (Refereed)
    Abstract [en]

    A Ka-band 2D flat-profiled Luneburg lens antenna implemented with a glide-symmetric holey structure is presented. The required refractive index for the lens design has been investigated via an analysis of the hole depth and the gap between the two metallic layers constituting the lens. The final unit cell is described and applied to create the complete metasurface Luneburg lens showing that a plane wave is obtained when feeding at an opposite arbitrary point with a discrete source.

  • 12. Brazalez, Astrid Algaba
    et al.
    Manholm, Lars
    Johansson, Martin
    Quevedo-Teruel, Oscar
    Miao, Jingwei
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Investigation of a Ka-band Luneburg Lens Made of a Glide-Symmetric Holey Structure2017In: 2017 INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION (ISAP 2017), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    A Ka-hand 2D flat-profiled Luneburg lens antenna implemented with a glide-symmetric holey structure is presented. The required refractive index for the lens design has been investigated via an analysis of the hole depth and the gap between the two metallic layers constituting the lens. The final unit cell is described and applied to create the complete metasurface Luneburg lens showing that a plane wave is obtained when feeding at an opposite arbitrary point with a discrete source.

  • 13.
    Bäckström, Hampus
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Design and Evaluation of V/UHF Satellite Communication Antennas for Naval Applications2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this master thesis, compact antenna design aimed towards naval applicationshave been designed, analyzed and evaluated. There is a recentinterest in the development of compact antennas to be used for smallersubmarine models, and with a smaller hull on a submarine, communicationand antenna systems must be adapted and minimized, which limitsantenna design. With two limiting cylindrical volumes with maximumallowed dimensions r = 10 cm, h = 50 cm and r = 5 cm, h = 90 cm,the antennas would operate on the upper to lower V/UHF band, radiatehemispherically and have a high RHCP purity. It was found that the mostappropriate antenna structure for both volumes was QHA design. Afterthe design and analysis process was completed, it was concluded that theshorter antenna design could meet all requirements set while the longerantenna design did not meet all requirements but could still establish agood communication link on the higher frequencies. Antenna prototypesbased on the produced design were constructed and measured and, despiteminor deviations, veried that the results obtained from this thesis werereliable.

  • 14.
    Chen, Qiao
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Southeast Univ, State Key Lab Millimeter Wave, Nanjing 210096, Jiangsu, Peoples R China..
    Ghasemifard, Fatemeh
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Dispersion Analysis of Coaxial Line Loaded with Twist-Symmetric Half-Rings2018In: 2018 IEEE International Workshop on Antenna Technology, iWAT2018 - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

    A coaxial line with half-rings connected to its external conductor is proposed in this paper, to investigate the dispersion properties of a twist-symmetric electromagnetic configuration. We demonstrate that the propagating modes in a twist-symmetric structure are more linear than a conventional structure. Additionally, the bandgap at the Brillouin zone boundaries can be manipulated by tuning the relative angular orientation or translation of the rings. This tuning is equivalent to changing the order of the twist symmetry from 4- to 2-fold. Our proposed geometry finds potential application in fully-metallic reconfigurable filters and phase shifters.

  • 15.
    Chen, Qiao
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Southeast Univ, State Key Lab Millimeter Waves, Nanjing 210096, Jiangsu, Peoples R China.
    Ghasemifard, Fatemeh
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Valerio, Guido
    Sorbonne Univ, Lab Elect & Electromagnetisme, F-75005 Paris, France..
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Modeling and Dispersion Analysis of Coaxial Lines With Higher Symmetries2018In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 66, no 10, p. 4338-4345Article in journal (Refereed)
    Abstract [en]

    In this paper, 1-D periodic structures possessing higher symmetries are proposed and investigated in terms of their dispersion properties. The proposed structures are coaxial lines with coaxial rings periodically loaded on their inner or outer conductors. The higher symmetries, namely, glide and twist symmetries, are obtained by performing an additional geometrical operation within the unit cell of the periodic structure. We demonstrate that the propagating modes exhibit a lower frequency dispersion in higher symmetric coaxial lines. Moreover, the conventional stopbands of periodic structures at their Brillouin zone boundaries can be controlled by breaking the higher symmetry or changing the order of the twist symmetry. A circuit-based analytical method is proposed to calculate the dispersion diagram of the glide-symmetric coaxial lines. The results are validated with a full-wave simulation. Moreover, several prototypes of the twist-symmetric coaxial lines are manufactured and measured. A remarkable agreement is achieved between the measurements and simulations, validating the theoretical results. The proposed structures find potential applications in leaky-wave antennas and fully metallic reconfigurable filters and phase shifters.

  • 16.
    Cui, Yue
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Bangalore, Pramod
    Greenbyte AB, Gothenburg, Sweden..
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    An Anomaly Detection Approach Using Wavelet Transform and Artificial Neural Networks for Condition Monitoring of Wind Turbines' Gearboxes2018In: 2018 POWER SYSTEMS COMPUTATION CONFERENCE (PSCC), IEEE , 2018Conference paper (Refereed)
    Abstract [en]

    This paper presents an anomaly detection approach using artificial neural networks and the wavelet transform for the condition monitoring of wind turbines. The method aims to attain early anomaly detection and to prevent possible false alarms under healthy operations. In the approach, nonlinear autoregressive neural networks are used to estimate the temperature signals of the gearbox. The Mahalanobis distances are then calculated to measure the deviations between the current states and healthy operations. Next, the wavelet transform is applied to remove noisy signals in the distance values. Finally, the operation information is considered together with the refined distance values to detect potential anomalies. The proposed approach has been tested with the real data of three 2 MW wind turbines in Sweden. The results show that the approach can detect possible anomalies before failure events occur and avoid reporting alarms under healthy operations.

  • 17.
    Cui, Yue
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Bangalore, Pramod
    Greenbyte AB, Gothenburg, Sweden..
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    An Anomaly Detection Approach Using Wavelet Transform and Artificial Neural Networks for Condition Monitoring of Wind Turbines' Gearboxes2018In: 2018 POWER SYSTEMS COMPUTATION CONFERENCE (PSCC), IEEE , 2018Conference paper (Refereed)
    Abstract [en]

    This paper presents an anomaly detection approach using artificial neural networks and the wavelet transform for the condition monitoring of wind turbines. The method aims to attain early anomaly detection and to prevent possible false alarms under healthy operations. In the approach, nonlinear autoregressive neural networks are used to estimate the temperature signals of the gearbox. The Mahalanobis distances are then calculated to measure the deviations between the current states and healthy operations. Next, the wavelet transform is applied to remove noisy signals in the distance values. Finally, the operation information is considered together with the refined distance values to detect potential anomalies. The proposed approach has been tested with the real data of three 2 MW wind turbines in Sweden. The results show that the approach can detect possible anomalies before failure events occur and avoid reporting alarms under healthy operations.

  • 18.
    Duvnjak Zarkovic, Sanja
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    On the Security of Electricity Supply in Power Distribution Systems2018In: 2018 IEEE International Conference on Probabilistic Methods Applied to Power Systems (PMAPS), IEEE conference proceedings, 2018, article id 8440489Conference paper (Refereed)
    Abstract [en]

    Security of electricity supply has become a fundamental requirement for modern societies. However, attempts to define and evaluate security of supply have differed from one another. This paper reviews relevant studies in order to give a comprehensive explanation of the security of supply concept. The paper includes theory, assessment, methodology, regulations, data and practical issues associated with the security of supply and power system reliability. Special focus is given to the methodologies used for improving the reliability and security of supply in power distribution systems.

  • 19.
    Ebrahimpouri, Mahsa
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH Royal Inst Technol, Sch Elect Engn, S-10044 Stockholm, Sweden..
    Brazalez, Astrid Algaba
    Ericsson AB, Ericsson Res, S-41756 Gothenburg, Sweden..
    Manholm, Lars
    Ericsson AB, Ericsson Res, S-41756 Gothenburg, Sweden..
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Using Glide-Symmetric Holes to Reduce Leakage Between Waveguide Flanges2018In: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 28, no 6, p. 473-475Article in journal (Refereed)
    Abstract [en]

    In this letter, a novel cost-effective flange is proposed to prevent the leakage created by undesired air gaps between flanges of two mating waveguides. The cause of an undesired gap can be surface curvature, dirt, human mistakes, or misalignment. Our proposal consists of machining glide-symmetric holes around the waveguide aperture on the flanges. Due to the glide symmetry properties, an identical pattern of the holes is possible at both sides, thus becoming glide-symmetric when they are mated together.

  • 20.
    Estanqueiro, Ana
    et al.
    National Laboratory on Energy and Geology (LNEG).
    Ahlrot, Claes
    E.ON AB.
    Duque, Joaquim
    National Laboratory on Energy and Geology (LNEG).
    Santos, Duarte
    National Laboratory on Energy and Geology (LNEG).
    Gentle, Jake P.
    Idaho National Laboratory (INL).
    Abboud, Alexander W.
    Idaho National Laboratory (INL).
    Morozovska, Kateryna
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Söder, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Kanefendt, Thomas
    Fraunhofer IEE.
    DLR use for optimization of network design withvery large wind (and VRE) penetration2018Conference paper (Refereed)
    Abstract [en]

    Due to the stochastic nature of wind and clouds,the integration of wind and PV generation in the powersystem poses serious challenges to the long-term planning oftransmission systems. Grid reinforcements always involverelevant direct costs while the average load factor of the windand solar PV dedicated transmission lines is usually low.Additionally, in very windy sites, the same high windresource that produces large amounts of wind generation andmay congest the transmission lines transporting it to distantconsumption centres may also have a beneficial effect inincreasing the transmission capacity of those lines. In fact, theoccurrence of wind not only contributes to the loading of theconnecting line, but also increases the line capacity, via theconvective cooling of the cables - one of the main heattransfer mechanisms in conductor heat balance; in otherwords, higher winds speeds contribute to faster cooling ofconductor and therefore higher conductor’s capacitypotential. In this paper the existing methodologies tocharacterize those thermal effects in electrical cables - usuallyreferred as dynamic line rating (DLR) - are applied to severalIEA Task 25 countries case studies to characterize thetechnical value of the dynamic operation of thermallycongested lines, as well as its potential economic benefits.

  • 21.
    Ghasemifard, Fatemeh
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Periodic Structures with Higher Symmetries: Analysis and Applications2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, periodic structures with higher symmetries are studied. Their wave propagation characteristics are investigated and their potential applications are discussed. 

    Higher-symmetric periodic structures are described with an additional geometrical operation beyond a translation operator. Two particular types of higher symmetry are glide and twist symmetries. Glide-symmetric periodic structures remain invariant under a translation of half a period followed by a reflection with respect to a glide plane. Twist-symmetric periodic structures remain invariant under a translation along followed by a rotation around a twist axis. 

    In a periodic structure with a higher symmetry, in which the higher order modes are excited, the frequency dispersion of the first mode is dramatically reduced. This feature overcomes the bandwidth limitations of conventional periodic structures. Therefore, higher-symmetric periodic structures can be employed for designing wideband metasurface-based antennas. For example, holey glide-symmetric metallic structures can be used to design low loss, wideband flat Luneburg lens antennas at millimeter waves, which find application in 5G communication systems. In addition, holey glide-symmetric structures can be exploited as low cost electromagnetic band gap (EBG) structures at millimeter waves, due to a wider stop-band achievable compared to non-glide-symmetric surfaces. 

    However, these attractive dispersive features can be obtained if holey surfaces are strongly coupled, so higher-order modes produce a considerable coupling between glide-symmetric holes. Hence, these structures cannot be analyzed using common homogenization methods based on the transverse resonance method. Thus, in this thesis, a mode matching formulation, taking the generalized Floquet theorem into account, is applied to analyze glide-symmetric holey periodic structures with arbitrary shape of the hole. Applying the generalized Floquet theorem, the computational domain is reduced to half of the unit cell. The method is faster and more efficient than the commercial software such as CST Microwave Studio. In addition, the proposed method provides a physical insight about the symmetry of Floquet modes propagating in these structures. 

    Moreover, in this thesis, the effect of twist symmetry and polar glide symmetry applied to a coaxial line loaded with holes is explained. A rigorous definition of polar glide symmetry, which is equivalent to glide symmetry in a cylindrical coordinate, is presented. It is demonstrated that the twist and polar glide symmetries provide an additional degree of freedom to engineer the dispersion characteristics of periodic structures. In addition, it is demonstrated that the combination of these two symmetries provides the possibility of designing reconfigurable filters. Finally, mimicking the twist symmetry effect in a flat structure possessing glide symmetry is investigated. The results demonstrate that the dispersion properties associated with twist symmetry can be mimicked in flat structures.

     

  • 22.
    Ghasemifard, Fatemeh
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Dispersion Analysis of 2-D Glide-Symmetric Corrugated Metasurfaces Using Mode-Matching Technique2018In: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 28, no 1, p. 1-3Article in journal (Refereed)
    Abstract [en]

    In this letter, wave propagation in 2-D doubled corrugated metasurfaces, including glide-symmetric corrugated metasurfaces, embedded in a thin parallel plate waveguide have been analyzed using the mode matching method. The general dispersion equation for propagation at different directions is derived and dispersion surfaces have been obtained for three different cases. The results are in good agreement with reference results obtained using CST Microwave Studio. Moreover, the method is accurate and computationally much faster than CST Microwave Studio and similar commercial software.

  • 23.
    Ghasemifard, Fatemeh
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Twist and Polar Glide Symmetries: an Additional Degree of Freedom to Control the Propagation Characteristics of Periodic Structures2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8Article in journal (Refereed)
    Abstract [en]

    New high-frequency 5G and satellite communication systems require fully-metallic antennas and electromagnetic components. These components can be implemented with truncated versions of periodic structures. In order to achieve the desired performance of these future devices, it is of crucial importance to have a precise control of the propagation properties, i.e. the frequency dispersion behavior and stop-bands. Here, we demonstrate the potential use of higher symmetries to diminish the frequency dispersion of periodic structures and control the width of stop-bands with a new type of fully-metallic transmission line, which is loaded with holes on a twist-symmetric configuration. Simulated and experimental results confirm the intrinsic link between the propagation characteristics and the symmetries of a periodic structure. Additionally, we provide a definitive explanation of the recently discovered polar glide symmetry and its potential combination with twist symmetries to produce low-dispersive materials and reconfigurable stop-bands. The promising properties of these structures are demonstrated with a fully-metallic reconfigurable filter, which could be used for future high-frequency 5G and satellite communication systems.

  • 24.
    Ghorbani, Hossein
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Characterization of Conduction and Polarization Properties of HVDC Cable XLPE Insulation Materials2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    High voltage direct current (HVDC) cables with extruded insulation system were introduced in 1998. Since then this technology has been growing rapidly with many installations that are today operational at voltages up to 320 kV. With fast developments during the last few years, extruded DC cable systems for operation voltages as high as 640 kV are now commercially available.

    Due to the importance of DC conductivity in the distribution of electrical field across the cable insulation, a good understanding of the DC conduction physics is of key importance to the design of robust HVDC cables. Currently, crosslinked polyethylene (XLPE) is the dominating material used in the insulation system of extruded DC cables. Since XLPE includes peroxide decomposition products (PDP), understanding their role on conduction behavior of the insulation system has been of great interest. The PDP and other chemical species can move in the system through diffusion which makes the characterization of cable insulation more challenging. Besides, like other semi-crystalline polymers, morphology of the XLPE evolves with temperature and over time. These changes in the material pose challenges to their electrical characterization by requiring stringent control of parameters during preparation, storage and measurement.

    In this work, different electrical characterization techniques relevant to polymeric insulation materials are discussed highlighting their applications and limitations. A set of considerations during preparation, storage and measurement of polymeric samples is listed and implemented in the studies. The design and performance of a high voltage DC conductivity measurement setup is evaluated.

    Thick low density polyethylene (LDPE) and XLPE press molded plaque samples together with plaque samples extracted from cable insulation are prepared and studied using the high voltage DC conductivity measurement setup. Conductivity measurements are done both under static and dynamic temperature programs. Different preparations and test programs are used and the results are analyzed and compared.

    Investigations show that the type of protective press film used during press molding of samples can strongly influence the results and using polyethylene terephthalate (PET) film appears to lead to the higher measured conductivity levels. Studies with dynamic temperature program reveal a non-monotonic temperature dependence of apparent DC conductivity of samples with certain

    preparation which to the author’s best of knowledge has not been previously

    reported in the literature.

    Studies on XLPE and LDPE plaque samples with different heat-treatments show that the behavior of conductivity during thermal dynamics depends on the type of the press film. Upon degassing, samples pressed with PET film show a decline of conductivity at all temperatures and a reduction of the non-monotonic behavior. Based on the results from the experiments, a set of hypotheses as potential explanation of this behavior is put forward and discussed.

  • 25.
    Ghorbani, Hossein
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Influence of press films on conduction in polyethylene plaque samples2016In: Dielectrics (ICD), 2016 IEEE International Conference on, France: Institute of Electrical and Electronics Engineers (IEEE), 2016, article id 16250905Conference paper (Refereed)
    Abstract [en]

    Press molded plaque samples are commonly used for characterization of polymeric insulation materials. Such samples are prepared by pressing polymer granulates sandwiched between two layers of protective press films at high temperatures and pressures. Polyethylene terephthalate (PET) film is a common press film since it tolerates high temperatures, acts as a good diffusion barrier and can be separated from the molded polyethylene sample easily. In this work, studies are performed on the influence of the pressing film on the dielectric properties of press molded polyethylene insulation samples. Volume resistivity is measured under high voltage DC at different conditions on samples pressed using different press films and different preparations. Furthermore, PEA measurements under high voltage DC is performed on plaque samples press molded with different press films. It is found that press molding using PET film leads to a considerably higher apparent conductivity of the samples in comparison to using aluminum foil. Choice of press film, also influences the space charge measurement results. It is concluded that the influence of the press film used during sample preparation cannot be neglected and this effect should be evaluated carefully in material characterization research. According to the results in this work, aluminum foil seems to be a better option as a press film in comparison to PET press film.

  • 26.
    Ghorbani, Hossein
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Long-term conductivity decrease of polyethylene and polypropylene insulation materials2017In: IEEE Transactions on Dielectrics and Electrical Insulation, ISSN 1070-9878, Vol. 24, no 3, p. 1485-1493Article in journal (Refereed)
    Abstract [en]

    This work summarizes the results of a number of DC conductivity measurement studies on polypropylene (PP), low density polyethylene (LDPE), and cross linked polyethylene (XLPE). The main observation is that under apparently time-constant external conditions (voltage, temperature, etc.) no steady-state direct current (DC) was established even after very long measurement times. Nevertheless, this behavior seems to exhibit some common systematic features, and since the experiments were performed with different equipment at different R&D labs in different years by different teams, simple measurement artefacts can be excluded. One observation is that there are two electric field regimes with slightly different behavior, separated by crossover field of about 10-15 kV/mm. In this work we focus on the high-field region, where the main observation is that the conductance slowly decays sub-linearly with time, I~ t-n, with 0.3 <; n <; 1, n mostly around 0.5. We provide experimental indications that this behavior is rather independent of the presence of 1) the voltage and 2) the peroxide decomposition products (in PE). The observations are in favor of an underlying thermally driven relaxation process related to structural changes (morphology, free volume) of the polymer. A main implication of the results is that the use of steady-state conductivity values for the characterization of certain polymer insulation is not appropriate and instead the decaying behavior of the conduction current must be considered.

  • 27.
    Ghorbani, Hossein
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Observation of non-monotonic dependence of leakage current with temperature during thermal cycling2016In: IEEE Electrical Insulation Conference (EIC), 2016, Montreal: Institute of Electrical and Electronics Engineers (IEEE), 2016, article id 16263557Conference paper (Refereed)
    Abstract [en]

    Conductivity under high voltage DC, is one of the most important characteristics of insulating materials used as insulation in HVDC applications. The volume conductivity of the insulation can be measured on press molded plaque samples by applying DC voltage and measuring the leakage current passing through the insulation. Such measurements are often performed at constant temperatures and constant voltage levels. In this work, the leakage current is measured on 1 mm thick press molded low density polyethylene (LDPE) and crosslinked polyethylene (XLPE) samples under DC voltage of 30 kV while the different temperature conditions including thermal cycling with temperatures between room temperature and 90 °C is applied. While the obtained results with constant temperature are in good agreement with the previously reported measurements, during thermal transients an interesting phenomenon was observed. Based on the theories and previously reported measurements, the leakage current is expected to have an Arrhenius dependence to temperature. But in the new experiments during thermal transients, the leakage current shows a non-monotonic temperature dependence and during heating and cooling, peaks are observed in the measured leakage current. It was discovered that the behavior of leakage current is influenced by the type of protective film used during sample preparation and using PET film leads to a higher apparent conductivity than using aluminum foil. A non-monotonic temperature dependence is observed in samples pressed using PET film while samples pressed with aluminum foil exhibit an Arrhenius temperature dependence.

  • 28. Gong, Y.
    et al.
    Yang, B.
    Zhang, D.
    Hong, X.
    Lu, Y.
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. South China Normal University, Guangzhou, China.
    Chen, Jiajia
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Optical Network Laboratory (ON Lab). South China Normal University, Guangzhou, China.
    Crosstalk-aware multiple-AWG based optical interconnects for datacenter networks2018In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 426, p. 151-157Article in journal (Refereed)
    Abstract [en]

    This paper proposes a crosstalk-aware passive optical interconnect architecture based on multiple arrayed waveguide gratings (AWGs). With two-stage cascaded AWGs, it can realize the communications not only within but also among the clusters for large-scale datacenters. To overcome serious crosstalk in multiple-AWG based optical interconnects, crosstalk suppression schemes are proposed. Proof-of-concept experiments are carried out to verify the necessity and feasibility of the proposed crosstalk suppression schemes for multiple-AWG based optical interconnects.

  • 29.
    Habib, Md Zakaria
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Wang, Jianping
    Li, YouYi
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Phase Shift Compensation Method for the Line Differential Protection on UHV-AC Transmission Lines2018Conference paper (Refereed)
    Abstract [en]

    Line differential protection is popular for its good selectivity and simplicity as long as there is a dependable communication system between the two ends of the line. However, the sensitivity needs to be compromised when traditional line differential scheme is applied for UHV-AC lines because of the large charging current. This paper presents a study of the impact of UHV transmission line characteristics on line differential protection and a proposed solution based on compensation of the phase shift that exists between the sending and receiving end currents.

  • 30.
    Hartono, Aryudha
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Microgrid Safety and Protection Strategies2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    One of the challenging issues with the Microgrid is that the bidirectional power flow providedby the distributed generator (DG) which modify the fault current level. Furthermore, theinverter based-renewable energy source (IB-RES) limits the total fault current contributionto the grid due to its thermal capability. Since Microgrid should be able to operate in gridconnectedand islanded mode, protection strategies are needed to solve this challenging issue.By only having IB-RES and battery storage system, the fault condition and normaloperation cannot be distinguished. Apart from fault clearing issue, there is a consideration tostudy the fault isolation in the Microgrid under the limited fault current provided by IB-RES.To have fault isolation capability, the intelligent electrical device (IED) is needed. The firststep is to find a method that can detect a fault under the fault level modification constraint.This thesis presents a zero and negative sequence current protection to detect a fault.However, to make it selective, this protection will be applied directionally. It is common thatthe distribution grid has unbalanced load operation, thus providing zero and negativesequence component in the grid. To apply the directional zero and negative sequence currentprotection, the unbalanced load flow is simulated to distinguish the fault and normaloperation under unbalanced load condition.Safety and regulation are discussed briefly in this thesis. It is important that each of theIB-RES has fault ride-through (FRT) capability that follows a regulation. However, thisregulation is expected to have a coordination with the proposed protection in the Microgridso the reliability, selectivity, and sensitivity can be achieved in grid-connected and islandedmode. This thesis shows the coordination between fuses, IED, and inverter FRT capability.After providing a protection strategy, the adaptability of the proposed protection isassessed regarding of Microgrid expansion. The result shows that by applying the schemeand following the grading margin requirement that is presented in this thesis, the Microgridexpansion will not disrupt the proposed protection coordination. Since it is known that thedistribution grid is expanding its load capacity and microgeneration in continuous basis, it isconvenient that the proposed protection in the IED is expected to be adaptable, means that ithas a fixed IED setting when the grid is expanded. The analysis is performed by electrical transient analysis program (ETAP) and MatlabSimulink. The short circuit analysis, sequence-of-operation, and unbalanced load flow aresimulated by ETAP, while the protection stability is simulated by Matlab Simulink.

  • 31.
    He, Sailing
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Song, J.
    He, J. -J
    Dai, D.
    Planar waveguide multiplexers/demultiplexers in optical networks: From improved designs to applications2016In: VLSI Micro-and Nanophotonics: Science, Technology, and Applications, CRC Press , 2016Chapter in book (Other academic)
  • 32. He, Wang
    et al.
    Xu, Bo
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Gustafsson, Mats
    Ying, Zhinong
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    RF Compliance Study of Temperature Elevation in Human Head Model Around 28 GHz for 5G User Equipment Application: Simulation Analysis2018In: IEEE Access, E-ISSN 2169-3536, Vol. 6Article in journal (Refereed)
    Abstract [en]

    The crowdedness of current cellular bands and the demand for higher transmission speed prompt the use of the millimeter-wave spectrum for the next-generation mobile communication. In the millimeter-wave frequencies, the dosimetric quantity for human exposure to electromagnetic fields changes from the specific absorption rate to incident power density. In this paper, we used 28-GHz beam-steering patch arrays, a dipole antenna, and plane waves to investigate the temperature elevation in a multi-layer model of human head and its correlation with power density metrics. The power density averaged over one square-centimeter in free space and the peak temperature elevation in tissue at 28 GHz have good correlation. The peak temperature elevation indicated by the power density averaged one square-centimeter also agrees well with the peak temperature elevation induced by the plane waves. The results show that the averaging area of a few square-centimeters may be a good candidate for the spatial-average power density. The findings provide valuable input to the ongoing revision and updating of relevant safety standards and guidelines.

  • 33.
    Jürgensen, Jan Henning
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH Royal Institute of Technology.
    Individual Failure Rate Modelling and Exploratory Failure Data Analysis for Power System Components2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A set of vital societal functions such as health and safety are necessary for today's society to function and to secure the life of its individuals. Infrastructure is required to provide and maintain these functions. This for society critical infrastructure includes electronic communication technology, transport systems, oil \& gas supply, water supply, and the supply of electric power. The electric power system plays a central role in the critical infrastructure since it is required to operate all others. Therefore, outages in the power system can have severe consequences not solely for the supply of electricity but also for the supply of water, gas, and food. To provide a reliable and safe power supply, power system operators are applying asset management strategies to investigate, plan, maintain, and utilize the system and its components while improving the performance under its own financial constraints.

    One approach to increase the reliability of the power grid while decreasing costs is maintenance planning, scheduling, and optimization. To optimize maintenance, a reliability measure for power system components is required. The failure rate, which is the probability of failure in a predefined interval, is utilized in maintenance optimization. Thus far, an average failure rate has been assigned to all components of the same type due to a shortage of component failure data. However, this limits the accuracy of maintenance techniques since the component heterogeneity is neglected. Moreover, the actual failure rate is being underrated or overrated and it is a challenge to identify the impact of conducted maintenance tasks.

    This thesis presents how the failure rate accuracy can be improved despite limited failure data available. Firstly, an introduction to failure rate modelling theory, concepts, and definitions is given to provide a common understanding for the later chapters and papers. Secondly, regression models are presented which can be used to model, predict, and characterise the failure rate and failure intensity for power system components. The Cox regression and regression models for count data are applied to two case studies of disconnector and circuit breaker failure data. The results contribute to an improved modelling of the failure rate on individual level but also improve the understanding of risk factor's impact on component failures. However, the aforementioned regression models have rarely been applied in the power system domain due to the limited failure data. Thirdly, the necessity to distinguish between population and individual failure rates is illustrated and risk factors and methods are presented, which are frequently used in failure rate modelling. Moreover, the thesis presents a method to calculate and predict individual failure rates despite the occurrence of actual failures which is of particular advantage for new components.

  • 34.
    Jürgensen, Jan Henning
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Nordström, Lars
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Estimation of Individual Failure Rates for Power System Components based on Risk Functions2018Manuscript (preprint) (Other academic)
    Abstract [en]

    The failure rate is essential in power system reliability assessment and thus far it has been commonly assumed as constant. This is a basic approach that delivers reasonable results. However, this approach neglects the heterogeneity in component populations which has a negative impact on the accuracy of the failure rate. This paper proposes a method based on risk functions, which describes the risk behaviour of condition measurements over time, to compute individual failure rates within populations. The method is applied to a population of 12 power transformers on transmission level. The computed individual failure rates depict the impact of maintenance and that power transformers with long operation times have a higher failure rate. Moreover, the paper presents a procedure based on the proposed approach to forecast failure rates. Finally, the individual failure rates are calculated over a specified prediction horizon and depicted with a 95\% confidence interval.

  • 35.
    Kazemi, Noj
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Circuit analysis of a parallel plate waveguide2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this work was to model a four-port waveguide as a simple circuit,by first starting with a two-port then a three-port waveguide. Duethat the work was based on Nathan Marcuvitz book Waveguide handbook,an analytical solution for the circuit parameters was desired. In order toobtain an analytical solution three methods were studied; the Variationalmethod, the Integral equation method and the Static method. Out of thesethree methods the latter was chosen, because its strength of simplifying theboundary conditions. The goal to model a four-port and a three-portedwaveguide was too complicated. This led to that the goal was changed totrying to get a higher accuracy on the existing circuit model for a two-portwaveguide, by solving an extension to the circuit parameter. This was donebecause Marcuvitz only treated the first two modes correctly and it was notclear if the circuit model was stable for the higher orders of Taylor series. Inthe end a circuit model for a waveguide with an iris that treats the first 16modes correctly was solved. By looking at the dispersive properties of thecircuit a comparison with simulation software CST Microwave Studio couldbe done, which resulted in that the circuit model gave good results up to2b/ < 1. It was also showed that the accuracy was about the same as thecircuit model found in Waveguide handbook, but it can be mentioned thatthe accuracy is minimally better for the circuit model that was developed inthis work. Something that was discovered in this work is that the restrictionmentioned in Waveguide handbook for the case when the window is centeredis unreliable, it should be 2b/ < 1. It also appeared that the circuit modelremained stable for higher orders of the Taylor series, in this case up to the16:th order.

  • 36.
    Kubyshkina, Elena
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Ab initio modelling of interfaces in nanocomposites for high voltage insulation2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Dielectric nanocomposite materials have been experimentally proven to have properties that are beneficial in applications for efficient energy transport. However, today there are still no empirical models or rules that can predict the performance of a certain combination of materials in the nanocomposite, and there are also no definitive explanations of their dielectric behavior. A deeper understanding of the phenomena behind these materials' response to an applied electric field can open new possibilities for improvement of the insulating properties of nanocomposites.

    The goal of this work is to locate the key processes that are responsible for dielectric performance. The methodology of the study is based on ab initio technology, that relies solely on the knowledge of chemical and structural composition of the material. In this work, the charge-related properties of nanocomposite interfaces are studied. The primary material of the study is chosen to be polyethylene-based composite with magnesium oxide nanoparticles.

    The impact of the nanoparticle crystal surface termination and its silane treatment on the electronic structure of the interface between MgO and polyethylene are investigated here. Moreover, the effects of presence of carboxyl defect and water molecule near the interface are considered in this work as well.

    Based on the calculated electronic structure data, a model for charge dynamics is proposed. The model explains mechanisms for conductivity and space charge reduction in nanocomposites, but also predicts an increase in thermal stress and susceptibility for chemical defects. It is suggested here that the suppression mechanisms for space charge and conductivity in nanocomposites are inherently unstable and can also accelerate material aging.

  • 37.
    Kubyshkina, Elena
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Unge, Mikael
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymeric Materials. ABB Corporate Research.
    Impact of interfacial structure on charge dynamics in nanocomposite dielectricsManuscript (preprint) (Other academic)
  • 38. Li, Borui
    et al.
    Sun, Fei
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Reducing the dimensions of acoustic devices using anti-acoustic-null media2018In: APPLIED PHYSICS EXPRESS, ISSN 1882-0778, Vol. 11, no 2, article id 024301Article in journal (Refereed)
    Abstract [en]

    An anti-acoustic-null medium (anti-ANM), a special homogeneous medium with anisotropic mass density, is designed by transformation acoustics (TA). Anti-ANM can greatly compress acoustic space along the direction of its main axis, where the size compression ratio is extremely large. This special feature can be utilized to reduce the geometric dimensions of classic acoustic devices. For example, the height of a parabolic acoustic reflector can be greatly reduced. We also design a brass-air structure on the basis of the effective medium theory to materialize the anti-ANM in a broadband frequency range. Numerical simulations verify the performance of the proposed anti-ANM.

  • 39. Li, Fang
    et al.
    Zhu, Huilin
    Xu, Jie
    Gao, Qianqian
    Guo, Huan
    Wu, Shijing
    Li, Xinge
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Lie Detection Using fNIRS Monitoring of Inhibition-Related Brain Regions Discriminates Infrequent but not Frequent Liars2018In: Frontiers in Human Neuroscience, ISSN 1662-5161, E-ISSN 1662-5161, Vol. 12, article id 71Article in journal (Refereed)
    Abstract [en]

    Functional near-infrared spectroscopy (fNIRS) was used to test whether monitoring inhibition-related brain regions is a feasible method for detecting both infrequent liars and frequent liars. Thirty-two participants were divided into two groups: the deceptive group (liars) and the non-deceptive group (ND group, innocents). All the participants were required to undergo a simulated interrogation by a computer. The participants from the deceptive group were instructed to tell a mix of lies and truths and those of the ND group were instructed always to tell the truth. Based on the number of deceptions, the participants of the deceptive group were further divided into a infrequently deceptive group (IFD group, infrequent liars) and a frequently deceptive group (FD group, frequent liars). The infrequent liars exhibited greater neural activities than the frequent liars and the innocents in the left middle frontal gyrus (MFG) when performing the deception detection tasks. While performing deception detection tasks, infrequent liars showed significantly greater neural activation in the left MFG than the baseline, but frequent liars and innocents did not exhibit this pattern of neural activation in any area of inhibition-related brain regions. The results of individual analysis showed an acceptable accuracy of detecting infrequent liars, but an unacceptable accuracy of detecting frequent liars. These results suggest that using fNIRS monitoring of inhibition-related brain regions is feasible for detecting infrequent liars, for whom deception may be more effortful and therefore more physiologically marked, but not frequent liars.

  • 40. Li, Shichao
    et al.
    Sun, Fei
    An, Di
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Increasing Efficiency of a Wireless Energy Transfer System by Spatial Translational Transformation2018In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 33, no 4, p. 3325-3332Article in journal (Refereed)
    Abstract [en]

    A magnetic translational projector (MTP) designed by transformation optics is applied to improve energy transfer efficiency in a wireless power transfer (WPT) system. Our numerical simulation results showtheMTP can greatly enhance energy transfer efficiency (e.g., nearly two orders, compared to the case without our MTP) in the WPT system, which is much larger than that of a previous method (i.e., using magnetic super-lens). A 3-D reduced MTPcomposed of layered isotropicmagnetic materials is designed, whose performance is verified by our 3-D numerical simulation in 10 MHz. The influence of loss in metamaterial on the performance of the proposed MTP is also studied, which shows that the MTP can still enhance energy transfer efficiency when loss exists. Further simulation is also carried out to show that the function of the MTP is not sensitive to large perturbation. Finally, detailed experimental suggestion for implementing the simplified MTP, which is composed of layered medium is given and then verified by our numerical simulation.

  • 41.
    Li, Zongbao
    et al.
    South China Normal Univ, South China Acad Adv Optoelect, Ctr Opt & Electromagnet Res, Guangzhou 510006, Guangdong, Peoples R China.;Tongren Univ, Sch Mat & Chem Engn, Tongren 554300, Guizhou, Peoples R China..
    Yang, Jianxin
    South China Normal Univ, South China Acad Adv Optoelect, Ctr Opt & Electromagnet Res, Guangzhou 510006, Guangdong, Peoples R China..
    Shi, Meng
    Qufu Normal Univ, Sch Prov Key Lab Laser Polarizat & Informat Techn, Jining 273165, Shandong, Peoples R China..
    Yang, Liu
    Zhejiang Univ, Natl Engn Res Ctr Opt Instrumentat, Ctr Opt & Electromagnet Res, JORCEP, Hangzhou 310058, Zhejiang, Peoples R China..
    Cheng, Yupeng
    South China Normal Univ, South China Acad Adv Optoelect, Ctr Opt & Electromagnet Res, Guangzhou 510006, Guangdong, Peoples R China..
    Hu, Xiaowen
    South China Normal Univ, South China Acad Adv Optoelect, Ctr Opt & Electromagnet Res, Guangzhou 510006, Guangdong, Peoples R China..
    Jiang, Xiaofang
    South China Normal Univ, South China Acad Adv Optoelect, Ctr Opt & Electromagnet Res, Guangzhou 510006, Guangdong, Peoples R China..
    Xing, Xiaobo
    South China Normal Univ, South China Acad Adv Optoelect, Ctr Opt & Electromagnet Res, Guangzhou 510006, Guangdong, Peoples R China.;South China Normal Univ, Coll Biophoton, MOE Key Lab Laser Life Sci, Guangzhou 510631, Guangdong, Peoples R China.;South China Normal Univ, Coll Biophoton, Inst Laser Life Sci, Guangzhou 510631, Guangdong, Peoples R China..
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Upconversion Luminescence of Graphene Oxide through Hybrid Waveguide2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 29, p. 16866-16871Article in journal (Refereed)
    Abstract [en]

    Phonon-assisted upconversion is a promising way to generate short-wavelength emissions under excitation of long wavelength based on unique anti-Stokes luminescence properties. Graphene oxide nanosheets (GONs) exhibit excellent optical properties owing to quantum confinement and edge effects, which have driven research into fundamental principles and potential applications. Here, we experimentally demonstrate upconversion emission by exciting an easily fabricated GON hybrid waveguide (GHVV) with enhanced photothermal effects. The results reveal different origins of short-wavelength range and long-wavelength range in the upconversion spectra, whereas the emissive surface defects of GONs and GHW structure play significant roles in the behavior of photoluminescence. Introducing other upconversion materials to promote emission efficiency, the hybrid waveguide system might readily provide the possibility for the construction of upconversion fiber lasers and remote control of the upconversion luminescence.

  • 42.
    Lindberg, Martin
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Mode Matching Analysis of One-Dimensional Periodic Structures2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis, we analyze the electromagnetic wave propagation in waveguidestructuresexhibiting periodical geometry, including glide symmetry. The analysisis performed using a mode matching technique which correlates the different modecoefficients from separate but, connected regions in the structure. This technique isused to obtain the dispersion diagrams for two one-dimensional periodic structures:a glide-symmetric corrugated metasurface and a coaxial line loaded with periodicholes. The mode matching formulation is presented in Cartesian and cylindricalcoordinate system for the former and the later, respectively. The mode matchingresults are compared to simulated results obtained from the Eigenmode Solver inCST Microwave Studio and are found to agree very well.

  • 43.
    Liu, Lipeng
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    On the critical charge required for positive leader inception in long air gaps2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 3, article id 035202Article in journal (Refereed)
    Abstract [en]

    The amount of the electric charge injected by the streamer corona bursts during the stage of leader inception determines the energy deposited to thermalize the corona stem into a leader segment. This paper is aimed at investigating the critical charge required for positive leader inception in air by using a thermo-hydrodynamic model with a detailed kinetic scheme. In order to simplify the analysis and to speed up the simulation, a reduced kinetic scheme for air is proposed. Numerical comparisons show that the reduced scheme can obtain almost the same results as the previous comprehensive kinetic scheme but with only half of the number of species and reactions. The thermo-hydrodynamic model with the reduced kinetics is then used to solve the radial dynamics of a single stem heated by current pulses typical of streamer corona bursts. The critical charge necessary for the direct transition of a first streamer corona into a leader under electrodes with large curvature radius is estimated between 0.08 and 0.5 uC per stem. Furthermore, the simulation shows that the gas heating of corona stem formed from electrodes with small curvature radius is mainly determined by the total accumulated charge injected by previous streamer corona bursts and the length of the dark periods in between the current pulses. The shape and the number of the corona current pulses in the discharge also play a role and their effects are discussed. It is suggested that the transition into a leader is triggered when a secondary streamer burst is initiated after the gas temperature is increased by the heating of previous streamers to about 1200 K. In addition, it is found that the heating produced by the charge injected by previous streamer corona bursts can be neglected if the dark period to the next burst is larger than few hundreds of  for a corona stem with moderate initial stem radius. This indicates that the critical charge criterion obtained from laboratory experiments does not hold to evaluate the inception of positive leaders under conditions when long dark periods are present.

  • 44.
    Liu, Wen
    et al.
    Zhejiang Univ, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Wang, Yalun
    Zhejiang Univ, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Han, Xiao
    Jilin Univ, State Key Lab Supramol Struct & Mat, Changchun 130012, Jilin, Peoples R China..
    Lu, Ping
    Jilin Univ, State Key Lab Supramol Struct & Mat, Changchun 130012, Jilin, Peoples R China..
    Zhu, Liang
    Zhejiang Univ, Interdisciplinary Inst Neurosci & Technol, Hangzhou 310058, Zhejiang, Peoples R China..
    Sun, Chaowei
    Zhejiang Univ, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Qian, Jun
    Zhejiang Univ, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Zhejiang Univ, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China.
    Fluorescence resonance energy transfer (FRET) based nanoparticles composed of AIE luminogens and NIR dyes with enhanced three-photon near-infrared emission for in vivo brain angiography2018In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 10, no 21, p. 10025-10032Article in journal (Refereed)
    Abstract [en]

    Near-infrared (NIR) fluorescence is very important for high-contrast biological imaging of high-scattering tissues such as brain tissue. Unfortunately, commercial NIR dyes are excited usually by visible light, and their multi-photon absorption (MPA) cross-sections are small. Here, we design new co-encapsulated NIR nanoparticles (NPs) with a large three-photon (3PA) absorption cross-section. A form of aggregation-induced emission (AIE) luminogen (AIEgen), 2,3-bis(4-(diphenylamino)-[1,1-biphenyl]-4-yl) fumaronitrile (TPATCN), is introduced as the donor, and a form of NIR dye, silicon 2,3-naphthalocyanine bis-(trihexylsilyloxide) (NIR775), is adopted as the acceptor. Under the excitation of a 1550 nm fs laser, TPATCN-NIR775 NPs demonstrated a bright three-photon fluorescence centered at 785 nm. The energy transfer efficiency of the TPATCN-NIR775 NPs was calculated to be as high as 90%, which could be attributed to the good spectral overlap between the emission of TPATCN and the absorption of NIR775. By injection with TPATCN-NIR775 NPs, a vivid 3D reconstruction of mouse brain vasculature was obtained with even small blood vessels clearly visualized. The design strategy used for the co-encapsulated AIE-NIR NPs would be helpful in synthesizing more NIR probes for deep-tissue biological imaging in the future.

  • 45. Liu, Y.
    et al.
    Sun, F.
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH, School of Engineering Sciences (SCI), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Controlling lightwave in Riemann space by merging geometrical optics with transformation optics2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, no 1, article id 514Article in journal (Refereed)
    Abstract [en]

    In geometrical optical design, we only need to choose a suitable combination of lenses, prims, and mirrors to design an optical path. It is a simple and classic method for engineers. However, people cannot design fantastical optical devices such as invisibility cloaks, optical wormholes, etc. by geometrical optics. Transformation optics has paved the way for these complicated designs. However, controlling the propagation of light by transformation optics is not a direct design process like geometrical optics. In this study, a novel mixed method for optical design is proposed which has both the simplicity of classic geometrical optics and the flexibility of transformation optics. This mixed method overcomes the limitations of classic optical design; at the same time, it gives intuitive guidance for optical design by transformation optics. Three novel optical devices with fantastic functions have been designed using this mixed method, including asymmetrical transmissions, bidirectional focusing, and bidirectional cloaking. These optical devices cannot be implemented by classic optics alone and are also too complicated to be designed by pure transformation optics. Numerical simulations based on both the ray tracing method and full-wave simulation method are carried out to verify the performance of these three optical devices.

  • 46.
    Ludvig-Osipov, Andrei
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Evaluation of the Electric Polarizability for Planar Frequency-Selective Arrays2018In: IEEE Antennas and Wireless Propagation Letters, ISSN 1536-1225, E-ISSN 1548-5757, Vol. 17, no 7, p. 1158-1161Article in journal (Refereed)
    Abstract [en]

    This letter presents a method to evaluate the static electric polarizability of 2-D infinitely periodic metal patch arrays with dielectric substrate. Static polarizabilities are used in several design applications for periodic structures such as estimation of the bandwidth limitations for frequency-selective structures or prediction of the radiation properties for antenna arrays. The main features of the proposed method are its numerical efficiency and a deep insight into the physics of the fields interacting with the structure. We provide derivation and analysis of the method, and its verification against two another commercial solver-based approaches for various structure geometries. Additionally, we suggest the guidelines for applying the method to bandwidth optimization of frequency-selective structures and illustrate this with an example.

  • 47.
    Mahidhar, G. D. P.
    et al.
    Indian Inst Technol Madras, Dept Elect Engn, Madras 600036, Tamil Nadu, India..
    Sarathi, R.
    Indian Inst Technol Madras, Dept Elect Engn, Madras 600036, Tamil Nadu, India..
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Edin, Hans Ezz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Study on Performance of Silica Nanoparticle Dispersed Synthetic Ester Oil under AC and DC Voltages2018In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 25, no 5, p. 1958-1966Article in journal (Refereed)
    Abstract [en]

    Synthetic ester oil (SEO) is becoming a replacement for mineral oil in transformers due to its biodegradability and for its better insulation properties. Silica nanoparticles dispersed in SEO can increase its corona inception voltage (CIV) and breakdown voltage compared to pure SEO. Physico-chemical studies were carried out to understand the characteristics of nanoparticles and nanofluids. Methodical experimental studies were carried out to understand the corona discharge activity in SEO based nanofluid. A ultra-high frequency (UHF) sensor was used to identify corona activity and it is concluded that the UHF signal radiated from corona activity in SEO and nanoparticle dispersed SEO have a bandwidth in the range of 700 MHz to 2 GHz. A comparative study on the CIV of SEO and nanofluid under harmonic AC voltages has been carried out, which indicates a reduction in the CIV as the total harmonic distortion of the supply voltage increases. Phase resolved partial discharge analysis indicates that the magnitude of discharges formed in nanofluid is much lower than in the SEO. Comparative statistical analysis are made with the breakdown voltages of the synthetic ester oil and nanofluid. A comparative analysis on the energy of the UHF signal due to the corona discharges is performed.

  • 48.
    Majlund, Åsa
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Konsekvensanalys av olika förändringar i intäktsrams-regleringen avseende hänsyn till leveranssäkerhet2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The distribution of electricity is a natural monopoly. The infrastructure of the electricity grid is divided into areas and the distribution system operator (DSO) has concession for the distribution of the defined area. The concession is governed by laws and regulation.The Swedish Energy Markets Inspectorate (Ei) is the national regulatory authority. The continuity of supply of electricity is a part of the regulation. The incentive is given by a revenue cap regulation which may result in a reward or penalty.The performance indicators are a measure of the continuity of supply and used in the calculation of the revenue cap regulation.The Master thesis aims to specify the possible consequences for the electricity distribution system operators and their customers utilizing the electricity grid in case of a change of the current methods used to measure the continuity of supply in Sweden.With the current methods, the Ei regulation for year 2016-2019, is the continuity of supply in the local electrical grid estimated from a view where each disruption is treated equal and therefore is SAIFI and SAIDI used. In the regional electrical grid is another method used to measure the continuity of supply, estimated from a view where the loss of supplied energy is considered, therefore uses PNS and ENS. In the documentation is the term ILE used for ENS and ILEffekt for PNS.The Master thesis is constructed to analyze new performance indicators for the local and regional distribution grid. The new performance indicator is the mathematically instrument to measure the continuity of supply and is supported by analytically advantages and disadvantages.The result shows the choice of performance indicators cause a great impact in the revenue cap regulation. AIT, AIF corresponds to ENS and PNS, respectively, divided by power. The three most important results are given by:1. Mathematical and theoretical results show that ENS, PNS are not good indicators individually or in combination with SAIDI, SAIFI and CEMI4 as power consumption within each customer group varies in the local electrical grid.In the regional electrical grid, power consumption may also vary between the norm period and the supervisory period, which means that ENS, PNS can sometimes be misleading.2. The inclusion of power disruption over 12 hours generate stronger incentives in the regulation. Because it requires long term planning to avoid interruptions exceeding 12 hours. The difference is shown mainly in local electrical grid with the indicators SAIDI, SAIFI and CEMI4 and gives a slight increase in rewards in the regulation. This affects the DSO’s and their customers with a marginal difference.3. In the short term, the introduction of AIT, AIF as quality indicators means that customers who consume more power within their customer group get higher-value interruptions. An interruption of a high-consumption customer would then be prioritized compared to a customer with a lower consumption. One way to counteract this is to use CEMI4, in order to capture these customers' interruptions in the regulation.In the long term, the regulation does not become cyclically sensitive, meaning that reasonable rewards or penalties are made. This should benefit a long-term planning of the electrical grid, as the DSO’s do not have to compensate for this.

  • 49.
    Malmström, Johan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Saab Surveillance, S-17588 Stockholm, Sweden.
    Derivation of Reaction Theorems for Scattered Fields2018In: IEEE Antennas and Wireless Propagation Letters, ISSN 1536-1225, E-ISSN 1548-5757, Vol. 17, no 10, p. 1876-1880Article in journal (Refereed)
    Abstract [en]

    Two novel formulations of the reaction are derived. The formulations decompose the electromagnetic fields in scattered components based on the location of the sources of the scattered fields. It is shown that some of the scattering components do not contribute to the reaction. The novel formulations of the reaction are derived by excluding these noncontributing components from the classical reaction formulations. The correctness of one of the formulations is verified with a numerical example. It is observed from one of the novel formulations that the first-order scattered fields do not contribute to the reaction. This result legitimizes the approximation to neglect multiple scattering, which is a common assumption when using reaction theorems. The novel formulations are also important for a conceptual understanding of the reaction.

  • 50.
    Malmström, Johan
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Holter, Henrik
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    On Mutual Coupling and Coupling Paths between Antennas Using the Reaction Theorem2018In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 60, no 6, p. 2037-2040Article in journal (Refereed)
    Abstract [en]

    The reaction theorem is applied to antenna coupling problems. It is shown that the reaction theorem can be used to calculate the mutual impedance between antennas, when the electromagnetic fields are known on a plane that separates the two antennas in two disjoint regions. We also show that coupling paths between the antennas can be visualized on the separation plane, by using intermediate results from the reaction theorem. The coupling paths are visualized based on the fields generated by each of the two antennas, and only take into account the energy that is actually transfered between the antennas. The visualization of coupling paths is useful for understanding how the coupling between the antennas is distributed in space.

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