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  • 1.
    Aagaard Fransson, Erik Johannes
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wall-Horgen, Tobias
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Building and Evaluating a 3D Scanning System for Measurementsand Estimation of Antennas and Propagation Channels2012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Wireless communications rely, among other things, on theunderstanding of the properties of the radio propagationchannel, the antennas and their interplay. Adequate measurementsare required to verify theoretical models and togain knowledge of the channel behavior and antenna performance.As a result of this master thesis we built a 3D fieldscanner measurement system to predict multipath propagationand to measure antenna characteristics. The 3Dscanner allows measuring a signal at the point of interestalong a line, on a surface or within a volume in space. In orderto evaluate the system, we have performed narrowbandchannel sounding measurements of the spatial distributionof waves impinging at an imaginary spherical sector. Datawas used to estimate the Angle-of-Arrivals (AoA) and amplitudeof the waves. An estimation method is presented tosolve the resulting inverse problem by means of regularizationwith truncated singular value decomposition. The regularizedsolution was then further improved with the helpof a successive interference cancellation algorithm. Beforeapplying the method to measurement data, it was testedon synthetic data to evaluate its performance as a functionof the noise level and the number of impinging waves. Inorder to minimize estimation errors it was also required tofind the phase center of the horn antenna used in the channelmeasurements. The task was accomplished by directmeasurements and by the regularization method, both resultsbeing in good agreement.

  • 2.
    Abid, Fahim
    et al.
    KTH.
    Ghorbani, Hossein
    Pourrahimi, Amir Masoud
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Edin, Hans Ezz
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Differences in morphology and polarization properties of heat-treated XLPE and LDPE insulation2016In: 2016 IEEE CONFERENCE ON ELECTRICAL INSULATION AND DIELECTRIC PHENOMENA (IEEE CEIDP), IEEE conference proceedings, 2016, 113-116 p.Conference paper (Refereed)
    Abstract [en]

    Cross-linked polyethylene (XLPE) is the most commonly used insulating material for extruded high voltage cable applications. Degassing is a heat-treatment process that is performed to remove methane from XLPE insulation which is formed during the crosslinking reactions as a by-product. Apart from removing methane, heat-treatment influences the electrical properties through changing the morphology due to annealing and also removal of polar crosslinking by-products. Scanning electron microscopy (SEM) is generally used to observe the changes in crystalline structure of the polymer. Frequency domain spectroscopy (FDS) is widely used to study polarization properties of dielectric materials. In this study these two methods are used for a comparative analysis of XLPE and LDPE subjected to different heat-treatment time, with or without a diffusion barrier. Electrical measurements are performed at room temperature. From the SEM imaging conducted after permanganate acid etching, formation of spherulites due to heat-treatment is not obvious in neither LDPE nor in XLPE. However, distinctions between LDPE and XLPE in SEM micrographs are evident. From studies with dielectric polarization spectroscopy, it is found that the LDPE samples are less sensitive to heat-treatment in comparison to the XLPE samples while dissipation factor of XLPE samples are influenced by the choice of pressing film used during sample preparation.

  • 3. Agheb, E.
    et al.
    Hashemi, E.
    Mousavi, Seyedali A.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hoidalen, H. K.
    Study of very fast transient overvoltages in air-cored pulsed transformers2012In: Compel, ISSN 0332-1649, Vol. 31, no 2, 658-669 p.Article in journal (Refereed)
    Abstract [en]

    Purpose - The purpose of this paper is to study very fast transient overvoltages (VFTOs) in the secondary winding of air-cored Tesla transformers and also study the resulting electric field stresses. Design/methodology/approach - An exhaustive model based on Multi-conductor Transmission Lines (MTLs) theory has been used. The governing telegraphist's equations have been solved by Finite Difference Time Domain (FDTD) method. Findings - The results demonstrated that there are some overvoltages at the end and middle turns that should be considered in insulation design. The magnitudes of these overvoltages are several times more than the steady state value of the corresponding turn which cause very high electric field stresses. Originality/value - The paper describes results obtained from an original and innovative implementation of FDTD method in transmission line modelling and is applied properly to air-cored pulse transformers.

  • 4.
    Ahmed, Zeeshan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Analysis of Partial Discharge in OIP Bushing Models2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A high voltage bushing is a very important accessory of power transformers. Bushings are used to insulate high voltage conductors where they feed through steel tank of a power transformer. There are different sources of electric stress that may result in degradation of bushing. Partial discharges (PDs) are one of the main sources of electrical degradation. PDs occur due to defects in electrical insulations, and can lead to insulation failure. This thesis is composed of two parts. The first part deals with design of a 145 kV oil impregnated paper (OIP) bushing by using capacitive radial grading technique. In capacitive grading the foils of calculated length are placed at predetermined radial distance between the paper layers in order to distribute voltage and electric field uniformly between high voltage conductor and ground potential. A 145kV OIP bushing was designed according to dimensions of ABB GOE type bushing. After calculations, the 145 kV bushing geometry was modeled in COMSOL Multiphysics in order to analyze the voltage and electric field distribution in the bushing. In the second part of this thesis a scaled down model was designed using the capacitive radial grading technique. After designing, the scale down model was implemented in COMSOL in order to ensure that the voltage and electric field distribution should be similar to the full scale model of bushing. The scaled down bushing test model was made in laboratory by wrapping impregnated papers and foils on conductor tube according to calculated dimensions. These papers were impregnated with mineral oil. The test model was placed in an oil filled tube. Different defects were added in scale down bushing model and model was connected to PD measurement set up. PD inception voltage was measured and PD patterns were recorded on an insulation condition monitoring system (ICM). These patterns are analyzed in order to conclude about the signature of partial discharges in OIP bushings. From the PD pattern, the type and location of PDs can be concluded. PD patterns reveal that the main causes of PDs in OIP bushing can be gas filled cavities and surface discharges from foil edges.

  • 5.
    Alayon Glasunov, Andrés
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Prasad, S.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Experimental characterization of the propagation channel along a very large virtual array in a reverberation chamber2014In: Progress in Electromagnetics Research B, ISSN 1937-6472, no 59, 205-217 p.Article in journal (Refereed)
    Abstract [en]

    We show that the combined use of radio frequency absorbers and directive antennas can produce significant changes of the radio propagation channel properties along the positions of a virtual array inside a reverberation chamber. A multidimensional characterization of the channel was performed at 40 antenna positions with spacing of 0:233λ at 1 GHz. The average power, the Ricean K-factor, the coherence bandwidth, the r.m.s. delay spread, the mean delay, the beamforming power angle spectrum and array antenna correlation have been studied for different arrangements in the reverberation chamber. The analysis shows that the joint average over time and frequency channel behavior is, as expected, rather homogeneous along the very large array. However, individual realizations of the channel present a pronounced selective behavior in space, time and frequency with parameters varying along the positions of the virtual array suggesting that a heterogeneous behavior of the radio channels can be emulated in reverberation chambers. An important application of the presented study comprises testing of antenna array designs and algorithms in multipath environments. Further development may lead to Over The Air testing of Multiple Input Multiple Output antenna systems of various sizes, i.e., from small to very large arrays.

  • 6.
    Alayon Glazunov, Andres
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A Monte Carlo study on the diversity measure of a spherical volume2012In: Proceedings of 6th European Conference on Antennas and Propagation, EuCAP 2012, 2012, 21-24 p.Conference paper (Refereed)
    Abstract [en]

    In this paper we investigate the diversity measure ψ(R h) of MIMO (Multiple-Input Multiple-Output) channels based on the eigenvalues of the full-correlation matrix of the channel matrix R h. We apply this definition to antennas and channels based on the antenna scattering matrix and the spherical vector wave (svw) expansion of the electromagnetic fields. We derive bounds for this diversity measure in an isotropic propagation channel. We further analyze the diversity measure of a spherical volume occupied by decoupled λ/2-dipole antennas by means of Monte Carlo simulations assuming different polarizations, e.g., vertically or horizontally polarizations, 2 orthogonal polarizations and 3 orthogonal polarizations.

  • 7.
    Alayon Glazunov, Andres
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A survey of the application of the spherical vector wave mode expansion approach to antenna-channel interaction modeling2014In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 49, no 8, 663-679 p.Article in journal (Refereed)
    Abstract [en]

    This paper provides an overview of recent advances in the modeling, analysis, and measurements of interactions between antennas and the propagation channel in multiple antenna systems based on the spherical vector wave mode expansion of the electromagnetic field and the antenna scattering matrix. It demonstrates the importance and usefulness of this approach to gain further insights into a variety of topics such as physics-based propagation channel modeling, mean effective gain, channel correlation, propagation channel measurements, antenna measurements and testing, the number of degrees of freedom of the radio propagation channel, channel throughput, and diversity systems. The paper puts particular emphasis on the unified approach to antenna-channel analysis at the same time as the antenna and the channel influence are separated. Finally, the paper provides the first bibliography on the application of the spherical vector wave mode expansion of the electromagnetic field to antenna-channel interactions.

  • 8.
    Alayon Glazunov, Andres
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Expansion of the Kronecker and Keyhole Channels Into Spherical Vector Wave Modes2011In: IEEE Antennas and Wireless Propagation Letters, ISSN 1536-1225, E-ISSN 1548-5757, Vol. 10, 1112-1115 p.Article in journal (Refereed)
    Abstract [en]

    In this letter, we provide additional results on the expansion of wireless channels into spherical vector wave multipole modes. We specialize our results to multiple-input-multiple-output (MIMO) channels with Kronecker-product structure of the correlation matrix: 1) the Kronecker channel, and 2) the Keyhole channel. We show that the Kronecker or Keyhole structure of the multimode channel matrix implies the corresponding structure in the MIMO channel matrix. Moreover, we show that the separability of the joint probability distribution functions of the angle of arrival (AoA) and the angle of departure (AoD), i.e., the independence between the AoAs and the AoDs for co- and cross-polarized components results in a Kronecker-product structure of the full-correlation matrix of the multimode matrix for both the Kronecker and the Keyhole channels.

  • 9.
    Alayon Glazunov, Andres
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Maximum joint transmit-receive MRC gain with antennas exciting spherical vector wave modes up to order l2012In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 48, no 24, 1520-1521 p.Article in journal (Refereed)
    Abstract [en]

    Derived is the maximum joint transmit and receive maximum ratio combining (MRC) diversity gain in arbitrary MIMO (multiple-input multiple-output) wireless propagation channels and the corresponding transmit and receive antenna coefficients. Also provided are numerical examples addressing two generic MIMO channel models based on the Kronecker correlation model with Laplacian angle-of-arrival (AoA) and angle-of-departure (AoD) distributions. In the analysis, spherical vector wave multipole modes of order l are considered, including both TE and TM modes.

  • 10.
    Alayon Glazunov, Andres
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Kolmonen, Veli-Matti
    Aalto University, Finland.
    Laitinen, Tommi
    Aalto University, Finland.
    MIMO Over-the-Air Testing2012In: LTE-Advanced and Next Generation Wireless Networks: Channel Modelling and Propagation, Chichester, U.K.: John Wiley & Sons, 2012, 411-441 p.Chapter in book (Refereed)
  • 11.
    Alayon Glazunov, Andres
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lai, Zhihua
    Ranplan Wireless Network Design Ltd., United Kingdom.
    Zhang, Jie
    University of Sheffield, United Kingdom.
    Outdoor-Indoor Channel2012In: LTE-Advanced and Next Generation Wireless Networks: Channel Modelling and Propagation, Chichester, U.K.: John Wiley & Sons, 2012, 123-151 p.Chapter in book (Refereed)
  • 12.
    Alayon Glazunov, Andres
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Prasad, Sathyaveer
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bolin, Thomas
    Prytz, Kjell
    Impact of Scattering Within a Multipath Simulator Antenna Array on the Ricean Fading Distribution Parameters in OTA Testing2014In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 0096-1973, Vol. 62, no 6, 3257-3269 p.Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate the unwanted scattering that exists within the multipath simulator (MPS) array antennas employed in over the air (OTA) testing of mobile terminals. The impact of scattering is evaluated in terms of the measurement uncertainty of the average received power and the Ricean K-factor. The maximum ratio combining diversity is investigated for a generic device under test comprising two half-wavelength dipole antennas. We provide closed-form expressions for the uncertainties of the average received power and the Ricean K-factor for a uniform circular array of MPS antennas and a 2-D uniformly distributed angle-of-arrival spectrum. We also derive the maximum number of MPS antennas and the minimum ring radius of the MPS system as a function of the separation between the most distant antenna elements if the device under test employs a uniform linear array. As a result, we provide design guidelines for MPS array in terms of the number antennas, the radius of the MPS array and the wavelength of the carrier frequency.

  • 13.
    Alayon Glazunov, Andres
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Zhang, Jie
    University of Bedfordshire.
    Clustering impact on the statistics of the multipole expansion coefficients of a wireless channel2011In: Progress in Electromagnetics Research Symposium, 2011, 603-607 p.Conference paper (Refereed)
    Abstract [en]

    It has been widely known that experimental results show that multipath components seem to arrive at the receiver in concentrated groups. These groups of multipath components, or clusters, are usually a result of scattering from large physical structures. Their impact on the capacity of Multiple-Input Multiple-Output (MIMO) systems has been widely studied. However, their impact on the spherical vector waves (svw) expansion of the propagation channel has not yet been addressed in the literature. As we have recently shown, a svw expansion provides a compact and straightforward representation of both antennas and channels. This can potentially facilitate designing antennas tailored to take advantage of the spatial and polarimetric characteristics of the propagation environment, which is essential to the deployment of efficient wireless networks. In this paper, we therefore study the impact of clustering on the first and second order statistics of the multimode expansion coefficients. We adopt the simulation approach to exemplify our results and provide numerical examples.

  • 14.
    Alayon Glazunov, Andres
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Zhang, Jie
    The University of Sheffield.
    On Some Optimal MIMO Antenna Coefficients in Multipath Channels2011In: Progress in Electromagnetics Research B, ISSN 1937-6472, Vol. 35, 87-109 p.Article in journal (Refereed)
    Abstract [en]

    This paper derives some optimum transmit and receive antenna coefficients in wireless multipath channels based on the spherical vector wave multimode expansion of the multiple-input multiple-output (MIMO) channel matrix. The derived antenna coefficients satisfy the following specific optimization criteria: (i) maximum MIMO mean effective link gain (link MEG) based on the multimode channel realizations or (ii) maximum MIMO link MEG based on the multimode correlation matrix or (iii) correlation minimization by diagonalization of the MIMO full-correlation matrix. It is shown that the proposed approach leads to matrix equations belonging to the nearest Kronecker product (NKP) problem family, which in general have no trivial solution. However, we show that exact solutions are provided to the posed NKP problems under the assumption of the Kronecker model for the MIMO full-correlation matrix. The results are illustrated by numerical examples. The proposed approach is a complement to existing antenna pattern analysis methods.

  • 15.
    Alayon Glazunov, Andres
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Zhang, Jie
    Lund University.
    Some Examples of Uncorrelated Antenna Radiation Patterns for MIMO Applications2011In: Progress in Electromagnetics Research Symposium, 2011, 598-602 p.Conference paper (Refereed)
    Abstract [en]

    In this paper, we provide some examples of an approach resulting in uncorrelatedantenna radiation patterns at both ends of a MIMO (Multiple-Input Multiple-Output) wireless link in a given propagation channel. The patterns of antennas exciting dipole or dipole and quadrupole TE and TM modes are analyzed for two generic MIMO channel models based on the Kronecker correlation model with Laplacian angle-of-arrival (AoA) and angle-of-departure (AoD) distributions. The presented results are of a fundamental nature and essential to achieve the promise of MIMO systems.

  • 16.
    Aljure, M.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, M.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pallon, L. K. H.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Electrical conduction currents of a mineral oil-based nanofluid in needle-plane configuration2016In: 2016 IEEE CONFERENCE ON ELECTRICAL INSULATION AND DIELECTRIC PHENOMENA (IEEE CEIDP), IEEE conference proceedings, 2016, 687-690 p.Conference paper (Refereed)
    Abstract [en]

    We present experiments and simulations on the electrical conduction currents of purified transformer oil with and without surface-modified MgO nanoparticles. Results show that on the injection regime of the voltage-current characteristics, nanoparticles increase the charge production in the fluid. It is also found that the conduction currents in the space-charge-limited regime increased at a lower rate as a function of the voltage in the presence of nanoparticles. The numerical simulations suggest electron attachment is increased due to the nanoparticles, leading to larger accumulation of negative ionic space charge close to the needle in the space-charge-limited regime. It is concluded that electron attachment may be significantly increased with nanoparticles, becoming an important process of electrical conduction in nanofluids.

  • 17.
    Aljure, Mauricio
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. ABB Corporate Research, Sweden.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Simulation of the electrical conduction of cyclohexane with TiO2 nanoparticles2014In: Proceedings of the 2014 IEEE 18th International Conference on Dielectric Liquids, ICDL 2014, IEEE , 2014, 6893119- p.Conference paper (Refereed)
    Abstract [en]

    Nanoparticles mixed with transformer oil can potentially increase the breakdown strength of the base liquid. Unfortunately, the basic physical mechanisms leading to such improvement are still not clear. This paper implements two existing theories to model the electrical conduction of cyclohexane with TiO2 nanoparticles in a needle to plane configuration. The generation and drift of carriers in the liquid are simulated by coupling the continuity equations for electrons, positive ions, negative ions, and nanoparticles with Poisson's equation for the electric field. The current-voltage characteristics are simulated and compared with the case of pure cyclohexane. The nanoparticles are modeled as either absorbers of electrons or as source of shallow traps in the fluid, according to the existing theories. The simulations show that the considered theories predict no significant effect of nanoparticles added to cyclohexane on the conduction current from a negative point electrode in steady state or under transient conditions.

  • 18.
    Amaya Maldonado, Sergio
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Efficient analysis of 2D antenna arraysusing the ASM-MBF method2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The analysis of large-scaled 2D finite planar arrays with the Method of Momentsrelying on the RWG basis functions requires a huge amount of memory for saving theequation system and a long computation time for solving the surface current distribu-tion. In this project, the Array Scanning Method - Macro Basis Function (ASM-MBF)method created by Craeye is implemented in an existing MoM’s code in order to verifythe reduction of the equation system keeping a good accuracy. Some improvementshave been implemented in the existing code in order to analyze arrays with rectangularand skew lattices. The time spent in the impedance matrix construction has also beenreduced. A program for solving 2D infinite arrays has been created for obtaining theinfinite surface current distributions necessary for the implementation of the ASM-MBF method. Finally, the definitive program has been tested with arrays of dipoleand bowtie antennas. In both cases, the computation time is reduced without affectingthe accuracy of the input impedance.

  • 19.
    Aminlashgari, Nina
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. ABB, Sweden.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. ABB, Sweden.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Characterization of degradation fragments released by arc-induced ablation of polymers in air2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 5, 055502Article in journal (Refereed)
    Abstract [en]

    Polymers exposed to high intensity arc plasmas release material in a process called arc-induced ablation. In order to investigate the degradation fragments released due to this process, two different polymeric materials, poly(oxymethylene) copolymer (POM-C) and poly(methyl methacrylate) (PMMA), were exposed to a transient, high-power arc plasma in air. A small fraction of the ablated material drifting away from the arcing volume was deposited on a fixed glass substrate during the total duration of a 2 kA ac current semicycle. In addition, another fraction of the released material was deposited on a second moving substrate to obtain a time-resolved streak 'image' of the arc-induced ablation process. For the first time, mass spectra of degradation fragments produced by arc-induced ablation were obtained from the material deposited on the substrates by using laser desorption ionization time-of-flight mass spectrometry (LDI-ToF-MS). It was found that oligomers with mean molecular weight ranging between 400 and 600 Da were released from the surface of the studied polymers. The obtained spectra suggest that the detected degradation fragments of POM could be released by random chain scission of the polymer backbone. In turn, random chain scission and splitting-off the side groups are suggested as the main chemical mechanism leading to the release of PMMA fragments under arc-induced ablation.

  • 20. Anatory, Justinian
    et al.
    Theethayi, Nelson
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Channel Characterization for Indoor Power-Line Networks2009In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 0885-8877, Vol. 24, no 4, 1883-1888 p.Article in journal (Refereed)
    Abstract [en]

    Power-line networks are promising mediums by which broadband services can be offered, such as Internet services, voice over Internet protocol, digital entertainment, etc. In this paper, an analysis of delay spread, coherence bandwidth, channel capacity, and averaged delay in the frequency bands up to 100 MHz for typical indoor power-line networks are studied. Earlier studies for indoor power-line networks considered frequencies up to 30 MHz only and earlier works have shown that at these frequency bands, the data rates are generally low and are inefficient for digital entertainment in comparison with wireless local-area networks standards, such as IEEE 802.11n. In this paper, it is shown that at 100 MHz, the average channel capacity for typical indoor power-line networks can be up to 2 Gb/s and it is found that by increasing the number of branches in the link between transmitting and receiving ends, the average channel capacity decreases from 2 Gb/s to 1 Gb/s (when the number of branches was increased by four times for a power spectral density of 60 dBm/Hz). At the same time, the coherence bandwidth decreased from 209.45 kHz to 137.41 kHz, which is much better than the coherence bandwidths corresponding to 30-MHz systems. It is therefore recommended to operate the indoor power-line networks at 100-MHz bandwidths for a wide variety of broadband services.

  • 21. Anatory, Justinian
    et al.
    Theethayi, Nelson
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Effects of Multipath on OFDM Systems for Indoor Broadband Power-Line Communication Networks2009In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 0885-8877, Vol. 24, no 3, 1190-1197 p.Article in journal (Refereed)
    Abstract [en]

    Power-line networks are an excellent infrastructure for broadband data transmission. However, various multipaths within a broadband power-line communication (BPLC) system exist due to stochastic changes in the network load impedances, branches, etc. This further affects network performance. This paper attempts to investigate the performance of indoor channels of a BPLC system that uses orthogonal frequency-division multiplexing (OFDM) techniques. It is observed that when a branch is added in the link between the sending and receiving end of an indoor channel, an average of 4-dB power loss is found. Additionally, when the terminal impedances of the branch change from the line characteristic impedance to impedance of lower values, the power loss (signal-to-noise ratio) is about 0.67 dB/Omega. On the contrary, for every increase in the terminal impedances by 100 Omega, above the line characteristic impedance, the power loss is 0.1. dB/Omega. When the line terminal impedances are close to short or open circuits, OFDM techniques show degraded performance. This situation is also observed when the number of branches increases. In this paper, it is shown that to overcome such performance degradation, the concatenated Reed-Solomon codes/interleaved Viterbi methods can be used. The observations presented in the paper could be useful for an efficient design of a BPLC system that uses OFDM techniques.

  • 22. Anatory, Justinian
    et al.
    Theethayi, Nelson
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Performance of Underground Cables That Use OFDM Systems for Broadband Power-Line Communications2009In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 0885-8877, Vol. 24, no 4, 1889-1897 p.Article in journal (Refereed)
    Abstract [en]

    Power-line networks are proposed for broadband data transmission. The presence of multipaths within the broadband power-line communication (BPLC) system, due to stochastic changes in the network load impedances, branches, etc. pose a real challenge as it affects network performance. This paper attempts to investigate the performance of an orthogonal frequency-division multiplexing (OFDM)-based BPLC system that uses underground cables. It is found that when a branch is added in the link between the sending and receiving end, there is an average of 4-dB power loss. In addition, when the terminal impedances of the branches that are connected to the link between the transmitting and receiving end vary from line characteristic impedance to low-impedance values, the power loss (signal-to-noise ratio) is about 0.35 dB/Omega. On the contrary, for an increase in the terminal impedances by 100 Omega above line characteristic impedance, the power loss is 0.23 dB/Omega. When the branch terminal impedances are close to short or open circuits, OFDM techniques show degraded performance. This situation is also observed when the number of branches increases. It is shown that to overcome degraded network performance, the concatenated Reed-Solomon codes/interleaved Viterbi methods can be used, which could be used for an efficient design of the BPLC system that uses OFDM techniques.

  • 23. Anatory, Justinian
    et al.
    Theethayi, Nelson
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Mvungi, Nerey H.
    A Broadband Power-Line Communication System Design Scheme for Typical Tanzanian Low-Voltage Network2009In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 0885-8877, Vol. 24, no 3, 1218-1224 p.Article in journal (Refereed)
    Abstract [en]

    Information and communications technologies (ICTs) are gaining importance in developing countries. Power-line network is a potential infrastructure for ICT services provision. Power-lines are highly interconnected network with stochastic variation in number of branches. Under such distributed network conditions the design of a broadband power-line communication (BPLC) system is a challenge. In this paper a case study of an actual power-line network, representative of a low-voltage BPLC channel in Dar es Salaam, Tanzania is considered. We shall investigate the performance of such a low-voltage channel that uses orthogonal frequency division multiplexing (OFDM) technique with binary phase shift keying (BPSK) modulation scheme for communication. For sensitivity analysis, three different transmitter locations were chosen and receiver points were varied to identify the possible degraded performance scenarios. Analysis show that in the frequency bands of 100 MHz, the channel delay spread for such networks is about 4 mu s, giving a maximum number of subchannels 4096 with 512 cyclic prefix. To improve the degraded performance scenarios, the concatenated Reed Solomon outer code with punctured convolution inner code was applied to the network. It was found that when the branches were terminated by its corresponding characteristic impedances the performance is improved by 1.0-20 dB compared to a corresponding uncoded system. On the contrary for a coded system when the branches were terminated either in low or higher impedances compared to branch characteristic impedances the improvement was greater than 2-15 dB. This study demonstrates that the specification proposed by IEEE-802.16 Broadband wireless access working groups can be used for performance improvement of distributed low-voltage systems.

  • 24.
    Anusuya Thiruchelvan, Niveditha
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Design of an antenna for automotive communication in FM band2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Antennas used for FM transmission in radio stations are too large and to fit in the same for vehicular communication is inconceivable, considering the dimensional aspects. The product “EVAM System” is used for automotive communication in emergency vehicles. This product uses FM band for transmission of traffic information to the surrounding vehicle. The FM antennas normally installed on the vehicles are used for reception. The radiation efficiency of these antennas is too low and VSWR is too large. Thus, the FM reception antennas reflect the power at large scale, damaging the product as a result. The main objective of this thesis is to design a low-profile antenna, which can be mounted on the emergency vehicle as demanded by H&E Solutions AB. In addition to the dimensional requirements, the antenna should also satisfy the specified performance characteristics. These specifications are explained in detail and a design that best suits the product is developed considering both dimensional and performance characteristics.

  • 25. Ao, X. Y.
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Negative refraction of left-handed behavior in porous alumina with infiltrated silver at an optical wavelength2005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 87, no 10Article in journal (Refereed)
  • 26. Ao, X. Y.
    et al.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Polarization beam splitters based on a two-dimensional photonic crystal of negative refraction2005In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 16, 2152-2154 p.Article in journal (Refereed)
  • 27. Ao, Xianyu
    et al.
    Tong, Xili
    Kim, Dong Sik
    Zhang, Lianbing
    Knez, Mato
    Mueller, Frank
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Schmidt, Volker
    Black silicon with controllable macropore array for enhanced photoelectrochemical performance2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, no 11, 111901- p.Article in journal (Refereed)
    Abstract [en]

    Macroporous silicon with multiscale texture for reflection suppression and light trapping was achieved through a controllable electrochemical etching process. It was coated with TiO2 by atomic layer deposition, and used as the photoanode in photocatalytic water splitting. A conformal pn-junction was also built-in in order to split water without external bias. A 45% enhancement in photocurrent density was observed after black silicon etching. In comparison with nano-structured silicon, the etching process here has neither metal contamination nor requirement of vacuum facilities.

  • 28. Ao, Xianyu
    et al.
    Wang, Xuyue
    Yin, Guanbo
    Dang, Kangkang
    Xue, Yali
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Zhejiang University, China.
    Broadband Metallic Absorber on a Non-Planar Substrate2015In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 11, no 13, 1526-1530 p.Article in journal (Refereed)
    Abstract [en]

    Absorbers for visible and near-infrared light are realized by depositing a thin iron layer on arrays of cones which are replicated from a porous template. The replicated conic structure itself is of several micrometers and ineffective at antireflection, but the subsequent deposition of iron on top generates nanometer-size columnar structures, and thus broadband absorption enhancement is achieved.

  • 29. Arafat, Y.
    et al.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Gustafsson, P. -A
    Experience from real tests on multiple smart meter switching2015In: IEEE PES Innovative Smart Grid Technologies Conference Europe, 2015, no JanuaryConference paper (Refereed)
    Abstract [en]

    Smart Meters (SMs) offer remote switching functionalities to the Distribution System Operators (DSOs). The DSO can switch the breaker of the SM of any customer remotely whenever needed. The DSOs are currently applying this technique for customers typically one by one when customers are changing their addresses or when contracts are terminated. The breaker functionalities of the SMs could be used for multiple customers, thereby opening up new possibilities to balance electricity consumption and production. How the technology has been functioning in practice has, however, not been fully investigated with regard to multiple SM switching. In this paper, the experience from real tests on simultaneous multiple SM switching is presented. The tests have been conducted to observe the effect of SM switching on power quality (PQ). Power Quality Meters (PQMs) had been used both at the substation as well as the customer level to measure the PQ during SM switching. This paper presents the results by showing current measurements during switching ON and OFF of multiple SMs belonging to each substation.

  • 30. Arafat, Y.
    et al.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Gustafsson, P. -A
    Field test on multiple Smart Meter switching to study the effect on power quality at customers level2015In: 2015 IEEE Eindhoven PowerTech, PowerTech 2015, IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    Smart Meters (SMs) are undergoing an increasing deployment all over the world and have been introduced to several regions. The SMs generally have remotely accessible breakers which offer remote switching functionalities to the Distribution System Operators (DSOs). The DSOs have the possibility of using this unique functionality of SMs for various future applications, e.g., switching some loads during peak loads crisis or outage management during natural disasters. Under these conditions, the DSO can disconnect selected customers by using SM switching while continuing power supply to risk customers and emergency service providers. During multiple SM switching, the power quality (PQ) of the connected loads might be affected. This paper presents results on the impact of multiple SM switching at customer level. Data are used from a field test on multiple SM switching from a DSO in Sweden. The number of customers in this test was higher compared to the previous two tests of the work. Moreover, all customers in the selected test area were not switched in this test. Almost half of the customers in the test area were disconnected remotely using SMs while the other half of the customers remained connected with power supply to investigate the impact of SMs switching in a different way. This work observed some transient events during the SMs switching. Voltage quality was stable during the test except some flickering effects beyond the limit.

  • 31. Arafat, Yasir
    et al.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Gustafsson, Per-Anders
    On Possibilities of Using Smart Meters for Emergency Grid Management: Analysing the Effect on Power Quality2015In: 2015 IEEE INNOVATIVE SMART GRID TECHNOLOGIES - ASIA (ISGT ASIA), 2015, 7387158Conference paper (Refereed)
    Abstract [en]

    Electricity grids worldwide are continuing to be severely constrained and stretched to capacity. Certain grid conditions e.g., peak load crisis or loss of generation may lead to severe under frequency situations. Load shedding can then be useful to prevent the national grid from being overwhelmed. Typically, load shedding is done from medium voltage substation level and all customers including emergency service providers under that substation lose power. However, it is beneficial for a society to exclude emergency service providers from load shedding. Smart Meters (SMs) are generally equipped with remotely accessible switch which gives a unique opportunity to exclude prioritized customers during emergency load shedding. Distribution System Operators (DSOs) are currently using remote SM switching typically for one customer at a time. However, the SM switching technique has not been fully investigated with regard to multiple customers. In order to fulfill the gap, this paper presents results obtained from field tests on simultaneous multiple SMs switching with a main focus on the impact of multiple SMs switching on Power Quality (PQ). The results show that impact on PQ might be negligible for small number of SMs switching. Moreover, faster SMs switching and reliable communication system is found as an important prerequisite to use SMs for emergency load shedding.

  • 32. Arifianto, I.
    et al.
    Josue, F.
    Saers, R.
    Rosenlind, Johanna
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Suwarno,
    Investigation of transformer top-oil temperature considering external factors2012In: Condition Monitoring and Diagnosis (CMD), 2012 International Conference on, IEEE , 2012, 198-201 p.Conference paper (Refereed)
    Abstract [en]

    Standard estimation of top-oil temperature uses a thermal model related to load changes and variation of ambient temperature. Attempts have been done to improve the accuracy of top-oil temperature calculations by introducing internal properties into the model i.e. oil viscosity and winding resistance. The interest of this paper is to investigate the effect of external factors on top-oil temperature by looking into the weather, i.e. wind velocity. The results are compared with measurements on a 63MVA-ONAF 55/140 kV transformer unit, which is operated in ONAN cooling mode. The unit is located in subarctic climate, and it is equipped with a monitoring system and a weather station.

  • 33.
    Ariza, David
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the inception and propagation of streamers along mineral-oil/solid interfaces2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents an experimental study of positive and negativestreamers propagating along mineral-oil/solid interfaces under square highvoltage pulses. The thesis includes the design and construction of anexperimental setup to studying the streamers in a point-plane configurationcapable to detect streamer parameters such as velocity, length, propagationtime, emitted light and charge.The first part of this experimental study is devoted to the analysis of thestreamer inception at mineral-oil/solid interfaces under negative polarity. Thestreamer inception voltage and charge recordings are reported for eachmineral-oil/solid interface. It is found that only solids with a permittivitysimilar to that of mineral oil can influence the streamer inception voltage.Solids with matched permittivity such as LDPE and PTFE increase the inceptionvoltage. The cases with solids with higher permittivity than mineral oil havesimilar inception voltage as the streamer incepted in the liquid bulk withoutsolid. The second part is devoted to studying the propagation of first mode negativestreamers along different mineral-oil/solid interfaces. A comparison of theelectrical and physical properties of the streamers (e.g. charge, length,velocity, etc.) is presented. Solid samples with different chemical compositionand different physical properties are used. The solid samples are anoil-impregnated kraft paper and an low-porosity paper referred to as kraftfibril paper made from cellulosic micro and nano fibrils. Polymeric films madeof low density polyethylene (LDPE), polyethylene terephthalate (PET),polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) are also usedas the solid. Streamers propagating along the liquid/solid interface arecompared with streamers developing in mineral oil without solid. Streamerspropagate longer and faster along solids with low surface roughness, lowporosity and higher electrical permittivity than mineral oil showing aquasi-continuous injection of charge in the early stage of propagation.The third part of the experimental study deals with second mode positivestreamers propagating along mineral-oil/solid interfaces. The inception andpropagation of the streamer are investigated using different mineral-oil/solidinterfaces. Measurements of the streamer velocity, charge, stopping length,propagation time, together with light recordings and shadowgraphs are reported.It is found that the interface can influence the streamer inception voltage,branching, stopping length, velocity, charge and current. Properties of thesolid and of the interface (i.e. surface roughness, permittivity, wettability)are parameters that influence the streamer propagation.

  • 34.
    Ariza, David
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Beccera, Marley
    Hollertz, Rebecca
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Methling, Ralf
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Gortschakow, Sergey
    Inception of first mode negative streamers at mineral oil-solid interfacesManuscript (preprint) (Other academic)
  • 35.
    Ariza, David
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hollertz, R.
    Pitois, Claire
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Measurements of the charge of streamers propagating along transformer oil-solid interfaces2014In: Proceedings of the 2014 IEEE 18th International Conference on Dielectric Liquids, ICDL 2014, IEEE , 2014, 6893165- p.Conference paper (Refereed)
    Abstract [en]

    This paper presents an experimental study of the positive streamer charge in transformer oil and oil-solid interfaces in a point-plane gap (5mm) under impulse voltage 50ns\1800μs (maximum peak voltage 24 kV). The experiment is intended to compare the charge of streamers propagating in transformer oil with and without a solid barrier along their path. The solid barrier constricting the streamer volume consists of two parallel strips of either impregnated pressboard or a polymeric film (PA6) installed at both sides of the point electrode. The maximum cumulative charge of the streamer is found for the case when the impregnated pressboard is used and the minimum cumulative charge for the case of the polymer as a barrier.

  • 36.
    Ariza, David
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. ABB Corp Res, Stockholm, Sweden.
    Hollertz, Rebecca
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Pitois, Claire
    On the initiation of negative streamers at mineral oil-solid interfaces2015In: IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), IEEE conference proceedings, 2015, 563-565 p.Conference paper (Refereed)
    Abstract [en]

    This paper reports the probability distribution of negative streamers initiated in mineral oil with and without a solid interface. In addition, the charge injected by conduction currents prior to the streamer inception is presented. Impregnated paper and polymeric films made of PET, PTFE and PVDF are tested as solid materials. Comparison of the conduction charge for the different oil-solid interfaces is presented. It is found that the permittivity of the material used at the solid interface does not influence significantly the condition for streamer initiation in mineral oil. A nonlinear increasing of the charge readings for the impregnated paper, PET and PVDF cases are observed.

  • 37.
    Ariza, David
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. ABB Corporate Research, Sweden.
    Hollertz, Rebecca
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Pitois, Claire
    ABB Corporate research .
    Propagation of negative streamers along mineral oil-solid interfaces2015In: Proceedings of the 2015 CEIDP Conference on Electrical insulation and Dielectric phenomena, CEIDP 2015, IEEE conference proceedings, 2015, 566-569 p.Conference paper (Refereed)
    Abstract [en]

    This paper introduces an experimental study on the propagation of negative streamers along mineral oil-solid interfaces. A standard type of impregnated paper and different polymeric films (made of PET, PTFE and PVDF) are selected as solid materials immersed in mineral oil. The effect of the solid material on the streamer propagation along the interface formed with transformer oil is studied. Streamer velocities classified as first mode propagation point cathode are reported. Voltage gradient of the streamer channel and its stopping voltage are calculated for all the cases. Comparison of streamer charge and stopping length propagation are reported.  

  • 38.
    Ariza, David
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hollertz, Rebecca
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Inception of first mode negative streamers at liquid/solid interfacesIn: Journal of Physics D: Applied PhysicsArticle in journal (Refereed)
    Abstract [en]

    This paper presents an experimental study on the inception of first mode negative streamers at different mineral-oil/solid interfaces. This study is performed with a point-plane configuration immersed in mineral oil (point cathode). The mineral-oil/solid interface is done by assembling a solid in an inclined position into the point-plane gap. The solid is in contact (or in the proximity) with the point electrode tip. The tested solids are a kraft paper, a paper made from cellulosic micro and nano fibrils and different polymeric films (low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF)). These solids have different relative permittivity and structural composition. It is found that the streamer inception voltage is statistically similar for the cases with solids with higher permittivity than mineral oil. The streamer inception voltage for the case without any solid barrier is also statistically similar to the cases with solids with higher permittivity than mineral oil. It is also found that the inception voltage is higher for streamers initiated at permittivity-matched interfaces (cases with LDPE and PTFE). Additionally, the influence of the spatial limitation with the solid surface to the volume where the streamer initiation process takes is performed with PTFE by varying the distance between the point electrode and the solid surface. It is shown that the streamer inception voltage depends on the distance between the point electrode and the solid surface. Furthermore, It is observed that the streamer inception voltage is also influenced when the distance between the point electrode and the surface of the PTFE is several micrometers (twenty times longer than the penetration depth of the avalanche responsible of streamer initiation). Additionally, it is also shown that a recently-proposed streamer inception criterion is unsuitable to predict the streamer inception conditions close to permittivity matched and mismatched liquid/solid interfaces.

  • 39.
    Ariza, David
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hollertz, Rebecca
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Second Mode Positive Streamers Propagating Along Mineral-oil/solid InterfacesManuscript (preprint) (Other academic)
    Abstract [en]

    This paper presents an experimental study on second mode positive streamers propagating along mineral-oil/solid interfaces. The inception and propagation of these streamers is investigated with different impregnated solids (low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) polyvinylidene fluoride (PVDF), two papers referred to as kraft paper and a kraft fibril paper, made from cellulosic micro and nano fibrils, a lignin-free paper and a paper with high lignin content referred to as k107 kraft paper). Streamers are initiated in a point-plane configuration under step voltages with 35 ns rise time. The radius of the tip is 2.9 μm and the solid is installed in an inclined position in close contact to the point electrode. Shadowgraphs, charge and light recording of the streamers are reported for each case. Furthermore, estimations of the streamer stopping length, velocity, current and average charge are reported. It is found that the streamer inception is influenced by the solid interface indicating that the inception process is not only conditioned by the field at the tip but also by the interface. A time delay is observed before the initiation of the streamer and probably correlated with the initiation process and formation of the gaseous phase. Additionally, the threshold propagation voltage of the second mode streamers at mineral-oil/solid interfaces is shown to be independent of the interface. It is also shown that the different characteristics of streamers propagating along the tested interfaces cannot be fully explained by the capacitive coupling effect due to permittivity mismatch. Thus, it is suggested that the characteristics of streamers propagating near interfaces is affected by other properties of the solid such as chemical composition, wettability and surface roughness.

  • 40.
    Ariza, David
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hollertz, Rebecca
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Pitois, Claire
    ABB AB Corporate Research.
    First Mode Negative Streamers along Mineral Oil-solid Interfaces2017In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 24, no 4Article in journal (Refereed)
    Abstract [en]

    This document presents an experimental study on the propagation of first mode negative streamers along mineral oil-solid interfaces. Samples made of an oil impregnated kraft paper and a low-porosity paper made from cellulosic micro and nano fibrils, as well as different polymeric films (low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF)) are used as the solid. A comparison of the length, charge and velocity of streamers for all different mineral oil-solid interfaces is reported. It is shown that streamers propagate longer and faster along mineral oil-solid interfaces with low surface roughness, low porosity and higher electrical permittivity than mineral oil. Those streamers show a quasi-continuous injection of charge in the early stage of their propagation. This quasi-continuous charge injection consists of a sequence of small charge steps separated by few tens of nanoseconds in between. In comparison, the streamers that propagate along surfaces with similar permittivity to the mineral oil have lower injection of charge and higher stopping voltage conditions than streamers propagating free in the liquid without any solid barrier.

  • 41.
    Ariza, David
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Methling, Ralf
    INP - Leibniz Institute for Plasma Science and Technology.
    Gortchakow, Sergey
    INP Leibniz Institute for Plasma Science and Technology.
    Hollertz, Rebecca
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Influence of Paper Properties on Streamers Creepingin Mineral Oil2017In: Proceedings of IEEE International Conference on Dielectric Liquids, ISSN 2153-3725, E-ISSN 2153-3733Article in journal (Refereed)
    Abstract [en]

    This work presents an experimental study ofsecond mode positive streamers propagating along mineral oilpaperinterfaces. A point-plane arrangement immersed inmineral oil with the paper inclined 60 degrees to the planeelectrode is used to create the liquid-solid interface. Kraft paperand a kraft fibril paper, made from cellulosic micro and nanofibrils, with higher density and lower surface roughness are usedas the solid materials. High speed shadowgraphy and chargerecordings are used to compare the propagation of second modepositive streamers along the mineral oil-kraft paper and mineraloil-kraft fibril paper. Streamers creeping along the mineral oilkraftpaper interface propagate mainly into the liquid, with oneor two main filaments. In comparison, the streamers propagatingalong the kraft fibril paper show a strong reduction of thebranching; these streamers consist of a single filament thatpropagates exactly on the solid surface. Streamers along the kraftfibril paper also have longer propagation time than for the casewith kraft paper. Mutual electrostatic shielding betweenfilaments is observed for the streamers creeping on the kraftpaper. An electrostatic analysis of the influence of permittivity,density and surface roughness of the solid in the electricalproperties of the streamer filaments is also performed.

  • 42.
    Ariza, David
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hollertz, Rebecca
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Beccera, Marley
    Pitois, Claire
    KTH.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    First mode negative streamers at mineral oil-solid interfacesManuscript (preprint) (Other academic)
  • 43.
    Ariza, David
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hollertz, Rebecca
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Methling, Ralf
    Gortschakow, Sergey
    Influence of paper properties on streamers creeping in mineral oilManuscript (preprint) (Other academic)
  • 44. Austrin, L.
    et al.
    Figueroa-Karlström, E.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Evaluation of switching losses in magnetic amplifiers as an alternative to IGBT switching technologies2008In: International Conference on Power Electronics, Machines and Drives, 2008, no 538 CP, 250-254 p.Conference paper (Refereed)
    Abstract [en]

    In future more electric aircraft (MEA) applications increased requirements of power levels stress the importance of low losses in converters and switching elements. In this work the losses of transistor switches are analysed and compared with the losses in magnetic amplifiers (Magamp) where amorphous alloy properties allows design of competitive devices. More Electric Aircraft technology can take advantage of this to accomplish compact, robust and reliable systems with low losses. Magamps are already used in the power supply of the Electronic Flight Control System in the Swedish "Gripen" fighter-aircraft. This paper presents a comparison between Magamp technology and an alternative Insulated Gate Bi-polar Transistor (IGBT) design. The study is concentrated on the power losses in a proposed 10 kW converter with ± 270 VDC (540 VDC) regulated output, where the fundamental difference between the switching elements is that the magnetic switch handles AC and the IGBT handles DC. To allow comparison, the copper and magnetic losses in the magnetic switch of the magnetic amplifier are considered as equivalent to the switching and conduction losses in the IGBT. The comparison is based on the sum of losses in power converters comprising six switching elements.

  • 45. Austrin, L.
    et al.
    Ribbenfjärd, David
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Simulation of a magnetic amplifier circuit including hysteresis2005Conference paper (Refereed)
    Abstract [en]

    The purpose of this paper is to demonstrate the feasibility. of using a dynamic hysteresis model in simulating a magnetic amplifier (mag amp). The presented model includes static hysteresis, classical eddy currents, and excess losses. The proposed modeling approach is shown to be a feasible tool for designing mag amps.

  • 46. Austrin, L.
    et al.
    Torabzadeh Tari, Mohsen
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Larsson, A.
    Analysis of a feasible pulsed-power supply system for an Unmanned Aerial Vehicle2006In: ICAS-Secretariat, 2006, 3605-3612 p.Conference paper (Refereed)
    Abstract [en]

    More Electric Aircraft technology enables the power supply of electric energy weapons such as high-power microwave and laser weapons. Aspects of electric power generation, energy storage, distribution and pulse-conditioning systems for the power supply of directed energy weapons in Unmanned Aerial Vehicle are addressed in this paper. A trend in aircraft design is to electrify more parts of the aircraft via the concept of More Electric Aircraft (MEA) and its technology which allows for increased electric power consumption. Thus, MEA technology enables the power supply of weapons and protection systems that are using electric energy. Among these devices directed energy weapons such as high-power microwave (HPM) and laser weapons are feasible. Such systems require high power pulsed electric energy with, thus imposing new requirements of on-board power supplies. In the demonstrated concept it is important to analyze power losses and efficiency as well as weight and volume in order to evaluate the possibility to adapt the system in an UAV.

  • 47.
    Austrin, Lars
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On magnetic amplifiers in aircraft applications2007Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    In the process of designing an electric power supply system for an aircraft, parameters like low weight and low losses are important. Reliability, robustness and low cost are other important factors. In the Saab Gripen aircraft, the design of the primary power supply of the electric flight control system was updated by exchanging a switching transistor regulator to a magnetic amplifier (magamp). By introducing a magamp design, weight was saved and a more reliable power supply system at a lower cost was achieved.

    In this particular case, with the power supply of the electric flight control system in the Saab Gripen fighter, advantage could be taken of a specific permanent magnet generator (PM-generator). The frequency of the generator offered the perfect conditions for a magamp controller. A key parameter in designing magnetic amplifiers (magamps) is low losses. New amorphous alloys offer new possibilities of the technique in designing magnetic amplifiers, because of their extremely low losses.

    The core losses are evaluated by studying the equations and diagrams specifying the power losses. The core losses are evaluated and compared with the copper losses in the process of optimizing low weight and low losses. For this an engineering tool is developed and demonstrated.

    Evaluations of the hysteresis characteristics for the magnetic alloys, as well as modeling and simulation of the core losses, are presented in this work. The modeling of the core losses includes hysteresis losses, eddy current losses and excess losses as well as copper losses. The losses are studied dynamically during realistic operational conditions. The model can be used for any generic analysis of hysteresis in magnetic circuits. Applications of magnetic amplifiers in aircrafts have been demonstrated to be a feasible alternative

  • 48. Austrin, Lars
    et al.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Modeling of a Three-phase Magnetic Amplifier2004In: Proceedings of the 24th Congress of the International Council of the Aeronatical Science, Yokohama, Japan, 2004Conference paper (Refereed)
  • 49. Austrin, Lars
    et al.
    Torabzadeh-Tari, Mohsen
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A new high power density generation system2006In: ICAS-Secretariat, 25th Congress of the International Council of the Aeronautical Sciences 2006, 2006, 3600-3604 p.Conference paper (Refereed)
    Abstract [en]

    A trend of increased Electric Power in Aircraft stresses the need of robust, low weight systems with low losses. New hard and soft magnetic materials have made it feasible to work with high speed and high frequency. Applications of new soft magnetic materials and hard magnetic materials like NeFeB magnets have enabled high density power generation systems. A new concept comprising a high speed PM-generator system and a magnetic amplifier control is presented. Magnetic amplifiers are used in the power supply of the Electronic Flight Control System in the Swedish "Gripen" fighter-aircraft. This technology is attractive in More Electric Aircraft (MEA) systems due to the possibility to achieve a compact, robust and a highly reliable system with low losses. Applications of new soft magnetic materials, such as amorphous magnetic alloys, have enabled the use of magnetic amplifier (magamp) technology in the design of competitive electric power converters. This paper presents a studied design on a 20-40 kW generator system including a +/- 270V controlled output, performed by magnetic amplifier technology. This work addresses the power generator, and the power converter. High speed PM-generators are offering high power density. The impact of operating a generation system with higher frequency and an increasing number of poles as well as the advantages with new soft magnetic materials is studied. The iron losses and the copper losses are analyzed for the generator, and the power converter.

  • 50. Autrin, Lars
    et al.
    Ribbenfjärd, David
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Simulation of a mangietc amplifier circuit including hysteresis2005In: Intermag Asia 2005, 2005, 225-226 p.Conference paper (Refereed)
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