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  • 1.
    Anatory, Justinian
    et al.
    University of Dar es Salaam, Tanzania.
    Theethayi, Nelson
    Uppsala University.
    Kissaka, Mussa M.
    University of Dar es Salaam, Dar es Salaam, Tanzania.
    Mvungi, Nerey H.
    University of Dar es Salaam, Dar es Salaam, Tanzania.
    Thottappillil, Rajeev
    Uppsala University.
    The effects of load impedance, line length, and branches in the BPLC transmission-lines analysis for-medium-voltage channel2007In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 22, no 4, p. 2156-2162Article in journal (Refereed)
    Abstract [en]

    This paper presents the effects of load impedance, line length and branches on the performance of medium-voltage power-line communication (PLC) network. The power-line network topology adopted here is similar to that of the system in Tanzania. Different investigation with regard to network load impedances, direct line length (from transmitter to receiver), branched line length and number of branches has been investigated. From the frequency response of the transfer function (ratio of the received and transmitted signal), it is seen that position of notches and peaks in the magnitude and phase responses are largely affected in terms of attenuation and dispersion by the above said network parameters/configuration. These are observed in the time domain responses too. The observations presented in the paper could be helpful in suitable design of the PLC systems for a better data transfer and system performance.

  • 2. 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 1937-4208, Vol. 24, no 4, p. 1883-1888Article 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.

  • 3. 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 1937-4208, Vol. 24, no 3, p. 1190-1197Article 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.

  • 4. 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 1937-4208, Vol. 24, no 4, p. 1889-1897Article 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.

  • 5.
    Anatory, Justinian
    et al.
    University of Dodoma, Tanzania.
    Theethayi, Nelson
    Uppsala University.
    Thottappillil, Rajeev
    Division for Electricity, Uppsala University.
    Power-Line Communication Channel Model for Interconnected Networks-Part I: Two-Conductor System2009In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 24, no 1, p. 118-123Article in journal (Refereed)
    Abstract [en]

    This paper presents a generalized transmission-line approach to determine the transfer function of a power-line network of a two-conductor system (two parallel conductors) with distributed branches. The channel frequency responses are derived considering different terminal loads and branches. The model's time-domain behavior is validated using commercial power system simulation software called Alternative Transients Program-Electromagnetic Transients Program (ATP-EMTP). The simulation results from the model for three different topologies considered have excellent agreement with corresponding ATP-EMTP results. Hence, the model can be considered as a tool to characterize any given power-line channel topology that involves the two-conductor system. In the companion paper (Part II), the proposed method is extended for a multiconductor power-line system.

  • 6.
    Anatory, Justinian
    et al.
    University of Dodoma, Tanzania.
    Theethayi, Nelson
    Uppsala University.
    Thottappillil, Rajeev
    Division for Electricity, Uppsala University.
    Power-Line Communication Channel Model for Interconnected Networks-Part II: Multiconductor System2009In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 24, no 1, p. 124-128Article in journal (Refereed)
    Abstract [en]

    In this paper, we present an approach to determine the transfer function for multiconductor power-line networks with distributed branches and load terminations for broadband power-line communication (BPLC) applications. The applicability of the proposed channel model is verified numerically in time domain using the finite-difference-time domain (FDTD) method for the solution of transmission lines. The channel model simulation results are in excellent agreement with the corresponding FDTD results. The model therefore could be useful in the analysis and design of BPLC systems involving multiconductor power-line topology.

  • 7.
    Anatory, Justinian
    et al.
    University of Dar es Salaam, Tanzania.
    Theethayi, Nelson
    Uppsala University.
    Thottappillil, Rajeev
    Uppsala University.
    Kissaka, M. M.
    University of Dar es Salaam, Dar es Salaam, Tanzania.
    Mvungi, N. H.
    University of Dar es Salaam, Dar es Salaam, Tanzania.
    The influence of load impedance, line length, and branches on underground cable power-line communications (PLC) systems2008In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 23, no 1, p. 180-187Article in journal (Refereed)
    Abstract [en]

    An underground cable power transmission system is widely used in urban low-voltage power distribution systems. In order to assess the performance of such distribution systems as a low-voltage broadband power-line communication (BPLC) channel, this paper investigates the effects of load impedance, tine length, and branches on such systems, with special emphasis on power-line networks found in Tanzania. From the frequency response of the transfer function (ratio of the received and transmitted signals), it is seen that the position of notches and peaks in the magnitude are largely affected (observed in time-domain responses too) by the aforementioned network configuration and parameters. Additionally, channel capacity for such PLC channels for various conditions is investigated. The observations presented in this paper could be helpful as a suitable design of the PLC systems for better data transfer and system performance.

  • 8.
    Anatory, Justinian
    et al.
    University of Dar es Salaam, Tanzania.
    Theethayi, Nelson
    Uppsala University.
    Thottappillil, Rajeev
    Uppsala University.
    Kissaka, Mussa M.
    University of Dar es Salaam, Dar es Salaam, Tanzania.
    Mvungi, Nerey H.
    University of Dar es Salaam, Dar es Salaam, Tanzania.
    An experimental validation for broadband power-line communication (BPLC) model2008In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 23, no 3, p. 1380-1383Article in journal (Refereed)
    Abstract [en]

    Recently, different models have been proposed for analyzing the broadband power-line communication (BPLC) systems based on transmission-line (TL) theory. In this paper, we make an attempt to validate one such BPLC model with laboratory experiments by comparing the channel transfer functions. A good agreement between the BPLC model based on TL theory and experiments are found for channel frequencies up to about 100 MHz. This work with controlled experiments for appropriate validation could motivate the application and extension of TL theory-based BPLC models for the analysis of either indoor or low-voltage or medium-voltage channels.

  • 9.
    Anatory, Justinian
    et al.
    University of Dar es Salaam, Tanzania.
    Theethayi, Nelson
    Uppsala University.
    Thottappillil, Rajeev
    Uppsala University.
    Kissaka, Mussa M.
    University of Dar es Salaam, Dar es Salaam, Tanzania.
    Mvungi, Nerey H.
    University of Dar es Salaam, Dar es Salaam, Tanzania.
    Broadband power-line communications: The channel capacity analysis2008In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 23, no 1, p. 164-170Article in journal (Refereed)
    Abstract [en]

    The power line has been proposed as a solution to deliver broadband services to end users. Various studies in the recent past have reported a decrease in channel capacity with an increase-in the number of branches for a given channel type whether it is an indoor or low-voltage (LV) or medium-voltage (MV) channel. Those studies, however, did not provide a clear insight as to how the channel capacity is related to the number of distributed branches along the line. This paper attempts to quantify and characterize the effects of channel capacity in relation to the number of branches and with different terminal loads for a given type of channel. It is shown that for a power spectral density (PSD) between -90 dBm/Hz to - 30 dBm/Hz, the channel capacity decreases by a 20-30 Mb/s/branch, 14-24 Mb/s/branch, and a 20-25 Mb/s/branch for an MV channel, LV channel, and indoor channel, respectively. It is also shown that the channel capacity is minimum when the load impedance is terminated in characteristic impedances for any type of channel treated here. It is shown that there could be a significant loss in channel capacity if a ground return was used instead of a conventional adjacent conductor return. The analysis presented in this paper would help in designing appropriate power-line communication equipment for better and efficient data transfer.

  • 10.
    Anatory, Justinian
    et al.
    University of Dar es Salaam, Tanzania.
    Theethayi, Nelson
    Uppsala University.
    Thottappillil, Rajeev
    Uppsala University.
    Kissaka, Mussa M.
    University of Dar es Salaam, Dar es Salaam, Tanzania.
    Mvungi, Nerey H.
    University of Dar es Salaam, Dar es Salaam, Tanzania.
    Expressions for Current/Voltage distribution in broadband power-line communication networks involving branches2008In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 23, no 1, p. 188-195Article in journal (Refereed)
    Abstract [en]

    Estimation of electromagnetic (EM)-field emissions from broadband power-line communication systems (BPLC) is necessary, because at its operating frequencies, the radiated emis sions from BPLC systems act as sources of interference/crosstalk to other radio-communication systems. Currently, the transmission-line (TL) system used for BPLC is complex, involving arbitrarily/irregularly distributed branched networks, arbitrary termination loads, varying line lengths, and line characteristic impedance. In order to study the electromagnetic-compatibility (EMC) issues associated with the radiated emissions of such complex BPLC networks, knowledge of current and voltage distributions along the length of the power-line channels is needed. This paper attempts to derive and present generalized expressions for either the current or voltage distribution along the line (whose TL parameters are known) between the transmitting and receiving ends for any line boundary condition and configuration based on the TL theory. The expressions presented in this paper could be beneficial for direct calculation of EM emissions from BPLC systems.

  • 11.
    Anatory, Justinian
    et al.
    University of Dar es Salaam, Tanzania.
    Theethayi, Nelson
    Uppsala University.
    Thottappillil, Rajeev
    Uppsala University.
    Kissaka, Mussa M.
    University of Dar es Salaam, Dar es Salaam, Tanzania.
    Mvungi, Nerey H.
    University of Dar es Salaam, Dar es Salaam, Tanzania.
    The effects of load impedance, line length, and branches in the BPLC-transmission-line analysis for indoor voltage channel2007In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 22, no 4, p. 2150-2155Article in journal (Refereed)
    Abstract [en]

    This paper presents the effects of load impedance, line length and branches on the performance of an indoor voltage broadband power line communications (BPLC) network. The power line network topology adopted here is similar to that of the system found in Tanzania. Different investigations with regard to network load impedances, direct line length from transmitter to receiver, branched line length, and number of branches has been carried out. From the frequency response of the transfer function (ratio of the received and transmitted signal), it is seen that position of notches and peaks in the magnitude and phase responses are largely affected by the above said network parameters/configuration, mainly in terms of attenuation and dispersion. These effects are observed in the time domain responses also. The observations presented in the paper could be helpful in the suitable design of the BPLC systems for a better data transfer and system performance.

  • 12.
    Anatory, Justinian
    et al.
    University of Dodoma, Tanzania.
    Theethayi, Nelson
    Uppsala University.
    Thottappillil, Rajeev
    Division for Electricity and Lightning Research, Uppsala University.
    Kissaka, Mussa
    University of Dar es Salaam, Dar es Salaam, Tanzania.
    Mvungi, Nerey
    University of Dodoma, Tanzania.
    The Effects of Load Impedance, Line Length, and Branches in Typical Low-Voltage Channels of the BPLC Systems of Developing Countries: Transmission-Line Analyses2009In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 24, no 2, p. 621-629Article in journal (Refereed)
    Abstract [en]

    This paper presents the influence of line length, number of branches (distributed and concentrated), and terminal impedances on the performance of a low-voltage broadband power-line communication channel. For analyses, the systems chosen are typical low-voltage power-line networks found in Tanzania. The parameters varied were the network's load impedances, direct line length (from transmitter to receiver), branched line lengths, and number of branches. From the frequency responses of the transfer functions (ratio of the received and transmitted signal), it is seen that the position of notches and peaks in the amplitude responses are affected by the aforementioned network parameters and topology. As a result, the time-domain responses are attenuated and distorted. Time-domain responses of power-line channels under various conditions are also investigated for a given pulse input at the transmitter. The observations presented in this;paper could be useful for suitable power-line communication system design.

  • 13. 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 1937-4208, Vol. 24, no 3, p. 1218-1224Article 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.

  • 14.
    Baba, Y.
    et al.
    Doshisha University, Kyoto, Japan..
    Rachidi, Farhad
    Swiss Federal Institute of Technology in Lausanne (EPFL), Switzerland.
    Thottappillil, Rajeev
    Uppsala University.
    Lightning to Tall Structures, in Tutorial on EMC aspects of Lightning2006Conference paper (Other academic)
  • 15.
    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.

  • 16.
    Becerra, Marley
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Long, Mengni
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Schulz, Wolfgang
    Austrian Electrotechnical Association (OVE), Department of Austrian Lightning Detection and Information (ALDIS).
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the Estimation of the Lightning Incidence to Offshore Wind FarmsManuscript (preprint) (Other academic)
    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 off shore 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 show that only a small fraction of damages observed in the analysed parks 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 parks can generate sufficiently high thundercloud fields to self-initiate upward lightning. Furthermore, it is shown that upward flashes can betriggered 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 casestudies.

  • 17.
    Bormann, Dierk
    et al.
    ABB Corporate Research.
    Midya, Surajit
    Uppsala University.
    Thottappillil, Rajeev
    Uppsala University.
    DC components in pantograph arcing: mechanisms and influence of various parameters2007In: Electromagnetic Compatibility, 2007: EMC Zurich 2007. 18th International Zurich Symposium on, 2007, p. 369-372Conference paper (Refereed)
    Abstract [en]

    Pantograph arcing generates a net DC voltage which create interference with the track circuit signaling, saturate transformer core, generate even harmonics, create problems on control of the switching of power electronics and drives. Experiments were conducted by Bombardier Transportation and ABB as a part of the ICE project to understand the physical processes that generates this DC component, the coupling mechanisms and the distribution paths, the identification of DC vulnerable components and their response to this DC. The amplitude of the DC voltage shows a wide variation with respect to applied voltage, train speed, type of electrical load, gap between the contact wire and the pantograph and current. In this paper, the authors analyzed those experimental data to understand the typical nature of sliding arc between the pantograph and the contact wire and possible mechanisms involved with this.

  • 18.
    Bäckström, Mats
    et al.
    Combitech AB.
    Thottappillil, Rajeev
    Department of Engineering Science, Uppsala University.
    Månsson, Daniel
    Department of Engineering Science, Uppsala University.
    Montaño, Raul
    High Voltage Valley.
    Lundén, Olof
    Division of Sensor Technology, Swedish Defense Research Agency (FOI).
    Nilsson, Tony
    Combitech AB.
    Some Recent Work on Intentional EMI in Sweden2008In: European electromagnetics (EUROEM), 2008Conference paper (Refereed)
  • 19.
    Diendorfer, G.
    et al.
    Austrian Electrotechnical Association ÖVE, Vienna.
    Zhou, Helin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Pichler, H.
    Austrian Electrotechnical Association (OVE), Vienna, Austria.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Review of upward positive and bipolar lightning flashes at the Gaisberg Tower2011In: 2011 7th Asia-Pacific International Conference on Lightning (APL), 2011, p. 263-267Conference paper (Refereed)
    Abstract [en]

    First instrumentation for lightning measurements at the Gaisberg Tower (GBT) has been installed in 1998. During the 10-years period from 2000-2009 a total of 652 lightning events have been recorded. Vast majority of the lightning to the GBT was upward initiated and only one record is a candidate for a downward flash when the recorded current waveform is used for discrimination between upward and downward lightning. 3% (21/652) of the flashes were bipolar and about the same number of 4% (26/652) were positive. 73% of positive and 63% of bipolar lightning was triggered by the GBT during cold season in Austria.

  • 20.
    Flache, D.
    et al.
    University of Federal Armed Forces Munich, Neubiberg, Germany.
    Rakov, V. A.
    University of Florida, Gainesville, USA.
    Heidler, F. H.
    University of Federal Armed Forces Munich, Neubiberg, Germany.
    Zischank, W. J.
    University of Federal Armed Forces Munich, Neubiberg, Germany.
    Thottappillil, R.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the origin of two types of current pulses observed during the initial stage of upward lightning2011In: Lightning (APL), 2011 7th Asia-Pacific International Conference on, 2011, p. 235-239Conference paper (Refereed)
  • 21.
    Flache, D.
    et al.
    University of Florida, Gainesville, USA.
    Rakov, V. A.
    University of Florida, Gainesville, USA.
    Heidler, F.
    University of Federal Armed Forces Munich, Neubiberg, Germany.
    Zischank, W.
    University of Federal Armed Forces Munich, Neubiberg, Germany.
    Thottappillil, Rajeev
    Uppsala University.
    Initial-stage pulses in upward lightning: Leader/return stroke versus M-component mode of charge transfer to ground2008In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, no 13, p. L13812-Article in journal (Refereed)
    Abstract [en]

    We analyzed high-speed video images and corresponding current records for eight upward lightning flashes initiated by the Peissenberg tower (160 m) in Germany. These flashes contained a total of 33 measurable initial stage (IS) current pulses, which are superimposed on steady IS currents. Seven IS pulses had relatively short (< 8 mu s) 10-to-90% risetimes and 26 IS pulses had relatively long (> 8 mu s) risetimes. Six (86%) of seven IS current pulses with shorter risetimes each developed in a newly-illuminated branch, and 25 (96%) of 26 IS pulses with longer risetimes occurred in already luminous (current-carrying) channels. These results support the hypothesis that longer risetimes are indicative of the M-component mode of charge transfer to ground, while shorter risetimes are associated with the leader/return stroke mode. Similar results were obtained for M-component pulses that are superimposed on continuing currents following return-stroke pulses.

  • 22.
    Flache, Denis
    et al.
    Federal Armed Forces Research University, Munich, Germany.
    Rakov, Vladimir
    University of Florida, Gainesville, USA.
    Heidler, Fridolin
    Federal Armed Forces Research University, Munich, Germany.
    Zischank, Wolfgang
    Federal Armed Foprces Research University, Munich, Germany.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Different modes of charge transfer to ground in upward lightning observed at the Peissenberg tower2009Conference paper (Other academic)
    Abstract [en]

    We analyzed high-speed video images andcorresponding current records for eight upward lightningflashes initiated by the Peissenberg tower (160 m) inGermany. These flashes contained a total of 33 measurableinitial stage (IS) current pulses, which are superimposed onsteady IS currents. Seven IS pulses had relatively short (< 8μs) 10-to-90% risetimes and 26 IS pulses had relatively long(> 8 μs) risetimes. Six (86%) of seven IS current pulses withshorter risetimes each developed in a newly-illuminatedbranch, and 25 (96%) of 26 IS pulses with longer risetimesoccurred in already luminous (current-carrying) channels.These results support the hypothesis that longer risetimesare indicative of the M-component mode of charge transferto ground, while shorter risetimes are associated with theleader/return stroke mode. Similar results were obtained forM-component pulses that are superimposed on continuingcurrents following return-stroke pulses.

  • 23.
    Flache, Denis
    et al.
    Federal Armed Forces Research University, Munich, Germany.
    Rakov, Vladimir
    University of Florida, Gainesville, USA.
    Heidler, Fridolin
    Federal Armed Forces Research University, Munich, Germany.
    Zischank, Wolfgang
    Federal Armed Foprces Research University, Munich, Germany.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Leader/Return Stroke versus M-Component Mode of Charge Transfer to Ground in Initial-Stage Pulses of Upward Lightning2009Conference paper (Other academic)
  • 24.
    Jia, Kelin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bohlin, G.
    Bombardier Transportation, Västerås, Sweden.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Optimal cable assembly for reducing conducted electromagnetic interference in the traction system2012In: IET Electrical Systems in Transportation, ISSN 2042-9738, Vol. 2, no 1, p. 29-37Article in journal (Refereed)
    Abstract [en]

    The present work deals with a method of modelling a traction system in PSpice with the consideration for optimal cable arrangements for reducing conducted electromagnetic interference. Multiconductor transmission line (MTL) theory is adopted to model the cable which connects the pulse-width modulation (PWM) source inverter and the motor. A simple decoupling transformation method is proposed and used to transform the MTL into several single transmission line, which can be easily modelled in PSpice. The PWM controlled voltage source and induction motor are also included in this model. Thus, the full model for a traction system is realised in PSpice. From system simulation, the voltage oscillation in the cable is observed and the conducted electromagnetic noise in the system is studied. The relationship between the frequency of the noise and the length of feeding cables are also demonstrated in this work. In order to mitigate the high-frequency noise, a cable system with a fourth parallel earth conductor is proposed and the noise level is indeed reduced by this technique. This modelling procedure for traction system can be used for any specific application like the electrified railway traction system.

  • 25.
    Jia, Kelin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bohlin, Georg
    Enohnyaket, Mathias
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Modelling an AC motor with high accuracy in a wide frequency range2013In: IET Electric Power Applications, ISSN 1751-8660, Vol. 7, no 2, p. 116-122Article in journal (Refereed)
    Abstract [en]

    This study presents a practical method to construct a high-frequency equivalent circuit model for AC motors in Spice-like simulation software. This model can be used to analyse the characteristics of the motor and predict the conducted electromagnetic noise in an adjustable speed drive system. The modelling is based on measured data of the impedance and vector fitting technique. The procedure of the modelling is elaborated in this study and verified by comparing simulated data with experimental data on a 200 kW induction motor in the frequency range from 10 kHz to 10 MHz. This modelling method can be extended to model other types of motors irrespective of the power rating of the motors. Applications of the motor modelling to study common mode voltage in the system and current oscillation in motor winding are presented.

  • 26.
    Jia, Kelin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bohlin, Georg
    Bombardier transportation, Västerås, Sweden.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Modeling the traction system in PSpice for electromagnetic noise analysis2011Conference paper (Other academic)
  • 27.
    Jia, Kelin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bohlin, George
    Enohnyaket, Mathias
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Modeling an AC Motor with High Accuracy in a Wide Frequency RangeArticle in journal (Other academic)
  • 28.
    Jia, Kelin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    EMC assessment of the railway traction system by using PSpice2010In: 2010 Asia-Pacific Symposium on Electromagnetic Compatibility, APEMC 2010, 2010, p. 598-601Conference paper (Refereed)
    Abstract [en]

    This paper describes how to analyze the EMC performance of the railway traction system by using PSpice. This analysis method is based on the accurate modelling of the IGBT and power diodes. The paper gives the analysis method as well as the modelling details of these power devices. An efficient way to predict the worst EMC performance is proposed, especially for high frequency EM noise. We have also studied the impact of the reverse-recovery time of a free wheeling diode on high frequency EM noise generation. © 2010 IEEE.

  • 29.
    Jia, Kelin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    PSpice Modeling of Electrified Railway Propulsion Drive Rectifiers for Harmonic Analysis2009In: ITST: 2009 9TH INTERNATIONAL CONFERENCE ON INTELLIGENT TRANSPORT SYSTEMS TELECOMMUNICATIONS, New York: IEEE , 2009, p. 113-116Conference paper (Refereed)
    Abstract [en]

    A method to construct the electrified railway propulsion drive rectifier in PSpice for EMC assessment is developed. The working mechanisms of a three level NPC PWM rectifier and its logical signal generator are elaborated. Besides that, the convergence problem of PSpice is explained and the proper parametric settings for simulation in this paper are given. At last, the noise spectra for two different loads are compared and the causes for this difference are discussed as well.

  • 30.
    Jia, Kelin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bohlin, G.
    Shielded cable modeling in PSpice for shielding effect analysis2012In: cccc2012 Asia-Pacific Symposium on Electromagnetic Compatibility, APEMC 2012 - Proceedings, IEEE , 2012, p. 665-668Conference paper (Refereed)
    Abstract [en]

    This paper gives a method to simulate the shielded cable in PSpice. The multiconductor transmission line theory is applied to deal with the cable system. The influence of the grounding conditions on the shielding effect is studied. Through simulations, it is observed that imperfect grounding of the shield can lead different cross-talk in the inner cable. Losing grounding at near-end or far-end of shield gives different impacts on near-end cross-talk. What is more, when one end of the shield is open the cross-talk may be severer than that when both ends of shield are open. The reasons for different cross-talk according to different kinds of imperfect grounding are discussed. By comparison the different voltage responses, advices for better shielding effect are drawn.

  • 31.
    Jia, Kelin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wådemark, Mats
    Bohlin, George
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Overshoot problem of the output diode used in the pre-charger for the railway propulsion system2012In: IET Power Electronics, ISSN 1755-4535, E-ISSN 1755-4543, Vol. 5, no 7, p. 991-997Article in journal (Refereed)
    Abstract [en]

    Pre-charger is a specific DC-DC converter application in the railway propulsion system. This study demonstrates the possible causes for output diode failures in the pre-charger. Overshoot voltage during diode reverse-recovery is a main reason for such failure. A test set-up is proposed to study the influence of reverse bias on the overshoot voltage. The method to mitigate the contact bounce in the control circuit, in the test set-up, is also introduced. The relationship between the overshoot and reverse bias is studied by means of applying different reverse biases. The parasitic capacitance and reverse-recovery characteristic of the diode is changed by the exceeding reverse bias. Reverse-recovery time is reduced when the reverse voltage is beyond a critical level. To overcome the overshoot problem, a snubber is applied, and experimentally verified. Overvoltage is dramatically reduced by applying this snubber. Current and voltage waveforms in different branches are recorded so as to give a better understanding of the working mechanism of the snubber.

  • 32.
    Jia, Kelin
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wådemark, Mats
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Bohlin, George
    Cost-effective method for protecting MOSFET against the short circuit fault in power convertersArticle in journal (Other academic)
  • 33.
    Kande, Mallikarjun
    et al.
    KTH, School of Electrical Engineering (EES). ABB .
    Isaksson, Alf J.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Rotating Electrical Machine Condition Monitoring Automation-A Review2017In: MACHINES, ISSN 2075-1702, Vol. 5, no 4, article id 24Article, review/survey (Refereed)
    Abstract [en]

    We review existing machine condition monitoring techniques and industrial automation for plant-wide condition monitoring of rotating electrical machines. Cost and complexity of a condition monitoring system increase with the number of measurements, so extensive condition monitoring is currently mainly restricted to the situations where the consequences of poor availability, yield or quality are so severe that they clearly justify the investment in monitoring. There are challenges to obtaining plant-wide monitoring that includes even small machines and non-critical applications. One of the major inhibiting factors is the ratio of condition monitoring cost to equipment cost, which is crucial to the acceptance of using monitoring to guide maintenance for a large fleet of electrical machinery. Ongoing developments in sensing, communication and computation for industrial automation may greatly extend the set of machines for which extensive monitoring is viable.

  • 34.
    Liu, Y. Q.
    et al.
    Uppsala University.
    Theethayi, N.
    Uppsala University.
    Thottappillil, Rajeev
    Uppsala University.
    An engineering model for transient analysis of grounding system under lightning strikes: Nonuniform transmission-line approach2005In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 20, no 2, p. 722-730Article in journal (Refereed)
    Abstract [en]

    A nonuniform transmission line approach is adopted in this paper for modeling the transient behavior of different types of grounding systems under lightning strikes in time domain by solving Telegrapher's equations based on finite-difference time-domain (FDTD) technique. Electromagnetic couplings between different parts of the grounding wires are included using effective per-unit length parameters (l, c, and g), which are space and time dependent. The present model can predict both the effective length and the transient voltage of grounding electrodes accurately, while, an uniform transmission line approach with electrode length dependent per-unit length parameters [19]-[22] fails to predict the same. Unlike the circuit theory approach [1]-[4], the present model is capable of predicting accurately the surge propagation delay in the large grounding system. The simulation results for buried horizontal wires and grounding grids based on the present model are in good agreement with that of the circuit and electromagnetic field approaches [3], [9]. From an engineering point of view, the model presented in this paper is sufficiently accurate, time efficient, and easy to apply.

  • 35.
    Liu, Y. Q.
    et al.
    Uppsala University.
    Theethayi, N.
    Uppsala University.
    Thottappillil, Rajeev
    Uppsala University.
    Gonzalez, R. M.
    Uppsala University.
    Zitnik, M.
    Uppsala University.
    An improved model for soil ionization around grounding system and its application to stratified soil2004In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 60, no 2-4, p. 203-209Article in journal (Refereed)
    Abstract [en]

    An improved model for taking into account the effect of the soil ionization around grounding system under lightning strike is proposed in this paper. In this model, the soil ionization region is assumed to retain 7% of its pre-ionization resistivity, which is consistent with the experimental results on soil ionization found in literature (Trans. SA Inst. Electr. Eng. (1988) 63; AIEE Trans. 61 (1942) 349; Proc. IEE 121(2) (1974) 123) and our own laboratory experiments (Time domain modelling of the response of grounding systems subjected to lightning currents, Licenciate Thesis, Uppsala University, 2003). Compared with modelling the soil ionization as an increase in the size of the ground conductor, the model presented here will not overestimate the beneficial influence of the soil ionization in reducing the ground potential rise, especially in high resistivity soil. The model is also applied to study the transient behaviour of grounding conductors in stratified soil under lightning strike including soil ionization. It shows that making the grounding conductor to penetrate the lower resistivity soil layer could help to decrease the ground potential rise at the injection point several times.

  • 36.
    Liu, Yaqing
    et al.
    Uppsala University.
    Theethayi, Nelson
    Uppsala University.
    Thottappillil, Rajeev
    Uppsala University.
    Investigating the validity of existing definitions and empirical equations of effective length/area of grounding wire/grid for transient studies2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 5-6, p. 329-335Article in journal (Refereed)
    Abstract [en]

    There are various definitions for effective length/area of grounding wire/grid for lightning transients [A.S. Farag, T.C. Cheng, D. Penn, Grounding terminations of lightning protective systems, IEEE Trans. Dielectics, Elect. Insul 5(6) (1998) 869-877; B.R. Gupta, B. Thapar, Impulse impedance of grounding grid, IEEE Trans. Power Apparatus Syayem PAS-99(6) (1980) 2357-2362; Y. Liu, N. Theethayi, R. Thottappillil, An engineering model for transient analysis of grounding system under lightning strikes: non-uniform transmission line approach. IEEE Trans. Power Delivery 20 (2) (2005) 722-730; M.I. Lorentzou, N.D. Hatziargriou, Modelling of long grounding conductors using EMTP, in: IPST'99, International Conference on Power System Transients, Budapest, 20-24 June, 1999; L.D. Grcev, M. Heimbach, Frequency dependent and transient characteristics of substation grounding system, IEEE Trans. Power Delivery 12 (1997) 172-178.]. The present work investigates and discusses the validity of those existing definitions. Further, practical methods for estimating the effective length/area of different grounding structures are proposed for engineering applications. The calculations for effective length/area based on non-uniform transmission line approach (Liu et al., 2005) show that, for a single grounding wire, the empirical equation for effective length in Farag et al. (1998) is not valid when the injection current has very fast rise time. Also, the empirical equation for effective length of grid edge in Gupta and Thapar (1980) is not applicable for grids with large inner mesh size.

  • 37.
    Long, Mengni
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra Garcia, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Modeling the Attachment of Lightning Dart and Dart-Stepped Leaders to Grounded ObjectsIn: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187XArticle in journal (Refereed)
    Abstract [en]

    Attachment of downward subsequent dart leadershas been recently proposed as a possible mechanism of lightningdamage of wind turbine blades. Since subsequent dart and dart-stepped leaders propagating after the first lightning discharge are one-to-two orders of magnitude faster than downward stepped leaders, the direct evaluation of the dart leader interception by upwardconnecting leaders from the turbine has not been attempted before. In this paper, the self-consistent leader inception and propagation model SLIM is used to evaluate the lightning attachmentprocess of subsequent dart leaders by accounting the rapid changingelectric fields produced by their fast descent toward the ground. For this, an improved evaluation of the charge per unit length requiredto thermalize the upward connecting leader is derived. The analysis considers upward connecting leaders propagating along the preheated channel of a prior discharge. Three study cases oflightning attachment of dart leaders and dart-stepped leader reported in rocket-triggered lightning experiments are evaluated. It is shown that reasonable predictions of the length, duration, andvelocity of positive upward connecting leaders can be obtainedwith SLIM in agreement with the experimental results. Furtherresearch on upward leader discharges necessary to improve themodeling of attachment of dart lightning leaders is discussed.

  • 38.
    Long, Mengni
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra Garcia, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the Attachment of Dart Lightning Leaders to Wind TurbinesIn: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046Article in journal (Other academic)
    Abstract [en]

    Wind turbines are prone to damages due to lightning strikes and the blades are one of the most vulnerable components. Even though the blade tip is usually protected in standard designs,lightning damages several meters away from it have also beenobserved in field studies. However, these damages inboard fromthe tip cannot be explained by the attachment of downwardstepped leaders or the initiation of upward lightning alone. In this paper, the attachment of dart leaders in an upward lightning flashis investigated as a mechanism of strikes to inboard sections of the blade and the nacelle. Dart leaders in an upward lightning flashuse the channel previously ionized by the preceding stroke or thecontinuous current. The analysis is performed with the self-consistent leader inception and propagation model SLIM. A commercial wind turbine with 45 m long blades and hub height of 80 m is analysed as a case study. The impact of the prospective return stroke peak current, the rotation angle of the blade and the wind on the location of lightning strikes on this mechanism is analysed. The probability of lightning attachment of dart leaders along the blade for the case study is also calculated. It is shown that the dart leader attachment is a mechanism that can explain lightning strikes to the nacelle and to the inboard region several meters away from the blade tip. However, this mechanism cannot explain the lightning strikes observed in the close vicinity of theblade tip (in the region between 1.5 and 6 m from it). The modelling study here also shows that for the turbine under consideration, nacelle receptors intercept most of dart leaders,around 73%, even if the initial continuous currents flow to the blade tip. Overall, it is estimated that around 80% of strikes inupward lightning flashes attach to the tip receptor of the blade.

  • 39.
    Long, Mengni
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra Garcia, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the attachment of dart lightning leaders to wind turbines2017In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 151, p. 432-439Article in journal (Refereed)
    Abstract [en]

    Wind turbines are prone to damages due to lightning strikes and the blades are one of the most vulnerable components. Even though the blade tip is usually protected in standard designs, lightning damages several meters away from it have also been observed in some field studies. However, these damages inboard from the tip cannot be explained by the attachment of downward stepped leaders or the initiation of upward lightning alone. In this paper, the attachment of dart leaders in an upward lightning flash is investigated as a mechanism of strikes to inboard sections of the blade and the nacelle of large wind turbines. Dart leaders in an upward lightning flash use the channel previously ionized by the preceding stroke or the continuous current. The analysis is performed with the self-consistent leader inception and propagation model (SLIM). A commercial large wind turbine with 45 m long blades and hub height of 80 m is analysed as a case study. The impact of the prospective return stroke peak current, the rotation angle of the blade and the wind on the location of lightning strikes on this mechanism is analysed. The probability of lightning attachment of dart leaders along the blade for the case study is also calculated. It is shown that this damage mechanism could create a new strike point only when the blade of a wind turbine rotates sufficiently from its initial position (at the inception of the initial upward leader) until the start of the dart leader approach. Thus, dart leader attachment is a mechanism that can explain lightning strikes to the nacelle and to the inboard region several meters away from the blade tip in large wind turbines. However, dart leader attachment cannot explain the lightning strikes observed in the close vicinity of the blade tip (in the region between 1.5 and 6 m from it).

  • 40.
    Long, Mengni
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra Garcia, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the interception of dart lightning leaders from wind turbine blades2014In: Lightning Protection (ICLP), 2014 International Conference on, IEEE conference proceedings, 2014, p. 1376-1381Conference paper (Refereed)
    Abstract [en]

    Wind farms are an important part of renewable energy system but they are frequently damaged by lightning strikes, especially to the blades of the turbine. Recent field observations have shown lightning damages several meters inboard away from the blade tip, which cannot be explained fully by the interception of stepped leaders or swept strokes. This paper proposes a possible additional mechanism to explain the lightning attachment points in inboard area of blade due to dart lightning leaders. This mechanism is verified through the Self-consistent Leader Inception and Propagation Model -SLIM-which is used here to dynamically evaluate the upward connecting leader propagation under the influence of both stepped and dart leaders.

  • 41.
    Long, Mengni
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Modeling the Attachment of Lightning Dart and Dart-Stepped Leaders to Grounded Objects2017In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 59, no 1, p. 128-136Article in journal (Refereed)
    Abstract [en]

    Attachment of downward subsequent dart leaders has been recently proposed as a possible mechanism of lightning damage of wind turbine blades. Since subsequent dart and dart-stepped leaders propagating after the first lightning discharge are one-to-two orders of magnitude faster than downward stepped leaders, the direct evaluation of the dart leader interception by upward connecting leaders from the turbine has not been attempted before. In this paper, the self-consistent leader inception and propagation model SLIM is used to evaluate the lightning attachment process of subsequent dart leaders by accounting the rapid changing electric fields produced by their fast descent toward the ground. For this, an improved evaluation of the charge per unit length required to thermalize the upward connecting leader is derived. The analysis considers upward connecting leaders propagating along the preheated channel of a prior discharge. Three study cases of lightning attachment of dart leaders and dart-stepped leader reported in rocket-triggered lightning experiments are evaluated. It is shown that reasonable predictions of the length, duration, and velocity of positive upward connecting leaders can be obtained with SLIM in agreement with the experimental results. Further research on upward leader discharges necessary to improve the modeling of attachment of dart lightning leaders is discussed.

  • 42.
    Long, Mengni
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the lightning incidence to wind Farms2016Conference paper (Refereed)
  • 43.
    Long, Mengni
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Becerra, Marley
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On the Simulation of the Interception of Lightning Dart Leaders2015In: Lightning Protection (XIII SIPDA), 2015 International Symposium on, IEEE conference proceedings, 2015, p. 288-292Conference paper (Refereed)
    Abstract [en]

    This paper presents the numerical evaluation of the propagation of positive upward connecting leaders under the influence of lightning dart leaders. The simulation is performed with the self-consistent leader inception and propagation model - SLIM-. An analytical expression is derived for calculating the charge per unit length required to thermalize a new upward leader segment. The simulation is validated with two dart leader attachment events in a lightning triggering experiment reported in the literature. Good agreement between the estimations and the measurements of dart leader interception in length, duration and velocity of upward leader propagation has been found. Further analysis is carried out on dart lightning leader interception.

  • 44.
    Manyahi, M. J.
    et al.
    University of Dar es Salaam, Tanzania.
    Leijon, M.
    Uppsala University.
    Thottappillil, Rajeev
    Uppsala University.
    Transient response of transformer with XLPE insulation cable winding design2005In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 27, no 1, p. 69-80Article in journal (Refereed)
    Abstract [en]

    Significant advances in XLPE insulation cables that have higher electric field strength withstand capability have made it possible to apply these high voltage (HV) cables as windings in generators and transformers. Therefore, the recent advent of HV generator (Powerformer) that can be connected directly to the power transmission line has motivated the design of HV transformer (Dryformer) that performs one step transformation from transmission to distribution voltage levels. Since the dryformer will be connected directly to transmission lines, they will be subjected to transients resulting from direct and indirect lightning strikes as well as fast switching surges from Gas insulated circuit breakers. This paper presents the results of experimental studies on the cable winding power transformer (Dryformer) to study its response to various transients. Experimental investigations have been carried to obtain the transformer model parameters based on terminal measurement of admittance functions using Network Analyser, and hence for comparing the model predictions with experimentally obtained responses. The model has been successfully used in estimating the dryformer transient responses at its terminals due to surge application of various front times and peak amplitudes that are representative of lightning and switching caused transients. Experiment and simulation results show that there are considerable differences in the transient response characteristics of dryformer windings as compared to that of transformers with traditional winding design. These differences on transient responses are discussed in perspective of their basic difference in winding design features.

  • 45.
    Manyahi, M. J.
    et al.
    University of Dar es Salaam, Tanzania.
    Thottappillil, Rajeev
    Uppsala University.
    Simplified model for estimation of lightning induced transient transfer through distribution transformer2005In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 27, no 4, p. 241-253Article in journal (Refereed)
    Abstract [en]

    In this work a simplified procedure for the formulation of distribution transformer model for studying its response to lightning caused transients is presented. Simplification is achieved by the way with which the model formulation is realised. That is, by consolidating various steps for model formulation that is based on terminal measurements of driving point and transfer short circuit admittance parameters. Sequence of steps in the model formulation procedure begins with the determination of nodal admittance matrix of the transformer by network analyser measurements at the transformer terminals. Thereafter, the elements of nodal admittance matrix are simultaneously approximated in the form of rational functions consisting of real as well as complex conjugate poles and zeros, for realisation of admittance functions in the form of RLCG networks. Finally, the equivalent terminal model of the transformer is created as a pi-network consisting of the above RLCG networks for each of its branches. The model can be used in electromagnetic transient or circuit simulation programs in either time or frequency domain for estimating the transfer of common mode transients, such as that caused by lightning, across distribution class transformer. The validity of the model is verified by comparing the model predictions with experimentally measured outputs for different types of common-mode surge waveform as inputs, including a chopped waveform that simulate the operation of surge arresters. Besides it has been verified that the directly measured admittance functions by the network analyser closely matches the derived admittance functions from the time domain impulse measurements up to 3 MHz, higher than achieved in previous models, which improves the resulting model capability of simulating fast transients. The model can be used in power quality studies, to estimate the transient voltages appearing at the low voltage customer installation due to the induced lightning surges on the high voltage side of the transformer. The procedure is general enough to be adapted for any two-port devices that behaves linearly in the frequency range of interest.

  • 46. Mazloom, Z.
    et al.
    Theethayi, N.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Modeling Indirect Lightning Strikes for Railway Systems With Lumped Components and Nonlinear Effects2011In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 53, no 1, p. 249-252Article in journal (Refereed)
    Abstract [en]

    Induced voltages due to lightning strikes along multiconductor transmission line (MTL) systems terminated with different loads at line ends have been widely studied by solving telegraphers' equations using the finite-difference time-domain method. However, MTL systems with lumped series and shunt-connected devices/components along the lines have not attracted much attention. There are methods available for introducing lumped components along MTL systems. In this paper, a method previously developed by the authors will be used to determine induced voltages across transformers connected to the catenary wire and track-circuit relay units along the MTL system representative of a Swedish single-track railway system for the case of indirect lightning strikes. Nonlinearities like soil ionization and insulator flashovers are also considered. It is found that both the nonlinearities and lumped components together dominate the induced-voltage amplitude and wave shapes across devices/components.

  • 47.
    Mazloom, Ziya
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Theethayi, Nelson
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    A Method for Interfacing Lumped-Circuit Models and Transmission-Line System Models With Application to Railways2009In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 51, no 3, p. 833-841Article in journal (Refereed)
    Abstract [en]

    Transient analysis of lossy multiconductor transmission lines (MTL) have been studied using the finite difference time domain (FDTD) method with lumped loads/devices connected at line terminations. In electrified railway networks series and shunt devices (whose circuit models derived either from experiments/borrowed off the shelf), e.g., transformers, converters, switchgear, signal equipments, etc., are found distributed along the MTL system. To simulate such railway systems involving both transmission lines (TL) and lumped circuits, an interface technique between TL system solved using FDTD and all the lumped circuits solved using ATP/EMTP software (circuit solver) is proposed. This sufficiently accurate method is simple to apply as only instantaneous voltages and currents are transmitted between standalone FDTD routine and circuit solver. Moreover, the user avoids coding complex circuit models within the FDTD, while at the same time efficiently uses the potential of accurate frequency dependant loss models (nonexistent in circuit software) coded in FDTD. The technique is applied on typical electrified railway systems to demonstrate how traction transformers, track circuits, and line interconnections affect the propagating voltages and currents. The method could be beneficial for transient protection and insulation coordination studies in electrified railway systems.

  • 48. Mazloom, Ziya
    et al.
    Theethayi, Nelson
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Indirect Lightning-Induced Voltages Along a Railway Catenary-Track Multiconductor Transmission-Line System With Lumped Components2011In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 53, no 2, p. 537-539Article in journal (Refereed)
    Abstract [en]

    Transients caused by field-to-wire coupling due to lightning strikes in the vicinity of multiconductor transmission lines (TL) have been widely studied. In those studies, the lines represent single overhead lines, power lines, and the like with lumped loads/devices at line terminations. In electrified railway power systems, series or shunt devices, such as transformers, converters, switchgear, and signal equipments, are distributed along the TL system. In this paper, the indirect lightning effects on a typical railway catenary-track multiconductor TL system with lumped components, namely, booster and auto transformers (BT and AT systems), and track circuits, are studied. It is found that the induced voltage wave shapes and amplitudes at any point along the line are dominated by BT or AT system type, and that the voltages appearing across AT windings are higher than for the corresponding BT windings. However, the induced voltages across the track circuits are less dependent on system type and most affected by the introduction of components.

  • 49.
    Mazloom, Ziya
    et al.
    Division for electricity and lightning research, Uppsala University.
    Theethayi, Nelson
    Division for electricity and lightning research, Uppsala University.
    Thottappillil, Rajeev
    Division for electricity and lightning research, Uppsala University.
    Influence of Discrete Series Devices on Crosstalk Phenomena in Multiconductor Transmission Lines2007In: EMC ZURICH-MUNICH 2007, SYMPOSIUM DIGEST, 2007, p. 245-248Conference paper (Refereed)
    Abstract [en]

    Usually the crosstalk mechanisms in multiconductor transmission lines (MTL) are studied considering lumped loads or devices connected at the line terminations (either at source or load ends) or as shunt load to ground along the lines, as seen in conventional power and railway system networks. However there are practical systems, e.g. like in typical Swedish railway systems, wherein discrete lumped devices like the booster transformer (BT) exist in series with the line. With lightning transients various parameters that influence crosstalk in MTL systems, such as the ground conductivity, have been analyzed e.g. in [1]. For realistic crosstalk analysis we conclude that inclusion of discrete devices like BT should be accounted. The study could be beneficial in better understanding of the crosstalk mechanism in the electrified railway systems.

  • 50. Mazloom, Ziya
    et al.
    Theethayi, Nelson
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Method to Include Lumped Devices in Multi-conductor Transmission Line System Models2009In: 2009 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, VOLS 1-8, 2009Conference paper (Refereed)
    Abstract [en]

    Transient analysis and crosstalk in multiconductor transmission line (MTL) systems with internal and external losses has been widely studied by solving telegrapher’s equation using the finite difference time domain (FDTD) method. Most of those studies are carried out with lumped loads/devices connected at the line terminations (at source and load ends). However, in practical systems such as typical railway and power systems, lumped devices, like, transformers, rotary converter stations, line interconnections and insulators, substation and switchgear equipments (grounding systems, insulators, surge protectors, circuit breakers, etc.) and signaling equipments exist either in series or in shunt with the MTL systems, but not necessarily at the ends. Detailed/complex circuit models (linear or nonlinear) for all those devices either exist in the literature or can be developed from experiments. In this paper a more general method based on Kirchoff’s current law (nodal analysis) is proposed to interface the FDTD code with Alternative Transients Program/Electromagnetic Transients Program (ATP/EMTP) circuit simulation software for transient analysis with any complex circuit model along the MTL system. The method is efficient and simple and it could be beneficial for accurate and realistic transient protection, mitigation and insulation coordination studies in large distributed electrical systems. A case study is made for an electrified railway with booster transformer traction system.

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