| 1. |
- Anatory, Justinian, et al.
(författare)
-
A broadband power-line communication system design scheme for typical Tanzanian low-voltage network
- 2009
-
Ingår i: IEEE Transactions on Power Delivery. - USA : IEEE. - 0885-8977 .- 1937-4208. ; 24:3, s. 1218-1224
-
Tidskriftsartikel (refereegranskat)abstract
- 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 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 10-20 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.
|
|
| 2. |
- Anatory, Justinian, et al.
(författare)
-
An experimental validation for broadband power-line communication (BPLC) model
- 2008
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 23:3, s. 1380-1383
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 3. |
- Anatory, Justinian, et al.
(författare)
-
Broadband power-line communications : The channel capacity analysis
- 2008
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 23:1, s. 164-170
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 4. |
|
|
| 5. |
- Anatory, Justinian, et al.
(författare)
-
Channel Characterization for Indoor Power-Line Networks
- 2009
-
Ingår i: IEEE Transactions on Power Delivery. - USA : IEEE. - 0885-8977 .- 1937-4208. ; 24:4, s. 1883-1888
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 6. |
- Anatory, Justinian, et al.
(författare)
-
Effects of Multipath on OFDM Systems for Indoor Broadband Power-Line Communication Networks
- 2009
-
Ingår i: IEEE Transactions on Power Delivery. - USA : IEEE. - 0885-8977 .- 1937-4208. ; 24:3, s. 1190-1197
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 7. |
- Anatory, Justinian, et al.
(författare)
-
Expressions for Current/Voltage distribution in broadband power-line communication networks involving branches
- 2008
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 23:1, s. 188-195
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 8. |
- Anatory, Justinian, et al.
(författare)
-
On the efficacy of using ground return in the broadband power-line communications : A transmission-line analysis
- 2008
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 23:1, s. 132-139
-
Tidskriftsartikel (refereegranskat)abstract
- The power-line infrastructure has been identified as an efficient system suitable for broadband power-line communication (BPLC) to connect and control various end users. However, the network is affected by stochastic attenuations due to the number of interconnected branches, their line lengths, associated terminal loads, etc. There is yet another parameter that could influence the above stated attenuations or distortions depending on the way the signals are allowed to return to the transmitting end. In this paper, we investigate whether a finitely conducting ground return could be used for BPLC and to investigate its performance over the conventional methods Where one of the adjacent power-line conductors is-used as signal return. This study could be helpful to those who are proposing the use of ground as a return conductor in BPLC systems. It will be shown that the use of ground return for the BPLC system is effective or better only when the ground conductivity is high (>50 mS/m). When ground conditions are poorer, attenuations increase with., making them unsuitable for BPLC. There are situafrequency tions where poor ground conditions can still be used but only the transmission-line lengths are shorter. The analysis presented here is based on transmission-line solutions both under lossless (without ground return) and lossy (with ground return) conditions and are applied to typical low-voltage and medium-voltage channels. Comparisons are also made based on the power spectral densities and channel capacities.
|
|
| 9. |
- Anatory, Justinian, et al.
(författare)
-
Performance of Underground Cables That Use OFDM Systems for Broadband Power-Line Communications
- 2009
-
Ingår i: IEEE Transactions on Power Delivery. - USA : IEEE. - 0885-8977 .- 1937-4208. ; 24:4, s. 1889-1897
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 10. |
- Anatory, Justinian, et al.
(författare)
-
Power-line communication channel model for interconnected networks : Part II: multiconductor system
- 2009
-
Ingår i: IEEE Transactions on Power Delivery. - USA : IEEE. - 0885-8977 .- 1937-4208. ; 24:1, s. 124-128
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 11. |
- Anatory, Justinian, et al.
(författare)
-
Power-line communication channel model for interconnected networks. Part I : two-conductor system
- 2009
-
Ingår i: IEEE Transactions on Power Delivery. - USA : IEEE. - 0885-8977 .- 1937-4208. ; 24:1, s. 118-123
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 12. |
|
|
| 13. |
- Anatory, Justinian, et al.
(författare)
-
The effects of load impedance, line length, and branches in the BPLC transmission-lines analysis for-medium-voltage channel
- 2007
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 22:4, s. 2156-2162
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 14. |
- Anatory, Justinian, et al.
(författare)
-
The Effects of Load Impedance, Line Length, and Branches in the BPLC—Transmission-Line Analysis for Indoor Voltage Channel
- 2007
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 22:4, s. 2150-2155
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 15. |
- Anatory, Justinian, et al.
(författare)
-
The effects of load impedance, line length, and branches in typical low-voltage channels of the BPLC systems of developing countries : transmission-line analyses
- 2009
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 24:2, s. 621-629
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 16. |
- Anatory, Justinian, et al.
(författare)
-
The Effects of Multipath on OFDM Systems for Broadband Power-Line Communications a Case of Medium Voltage Channel
- 2009
-
Ingår i: World Academy of Science, Engineering and Technology. - 2070-3724. ; 54, s. 205-208
-
Tidskriftsartikel (refereegranskat)abstract
- Power-line networks are widely used today for broadband data transmission. However, due to multipaths within the broadband power line communication (BPLC) systems owing to stochastic changes in the network load impedances, branches, etc., network or channel capacity performances are affected. This paper attempts to investigate the performance of typical medium voltage channels that uses Orthogonal Frequency Division Multiplexing (OFDM) techniques with Quadrature Amplitude Modulation (QAM) sub carriers. It has been observed that when the load impedances are different from line characteristic impedance channel performance decreases. Also as the number of branches in the link between the transmitter and receiver increases a loss of 4dB/branch is found in the signal to noise ratio (SNR). The information presented in the paper
|
|
| 17. |
- Anatory, Justinian, et al.
(författare)
-
The influence of load impedance, line length, and branches on underground cable power-line communications (PLC) systems
- 2008
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 23:1, s. 180-187
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 18. |
|
|
| 19. |
- Cooray, Vernon, et al.
(författare)
-
Pulse propagation along transmission lines in the presence of corona and their implication to lightning return strokes
- 2008
-
Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 56:7, s. 1948-1959
-
Tidskriftsartikel (refereegranskat)abstract
- Transmission line equations in air in the presence of corona are derived. The analysis shows that the corona caused by a voltage or a current pulse propagating along a transmission line can be represented by a series of corona current sources distributed along the line. Corona has two effects on the voltage or current pulses propagating along a transmission line. First, it will clamp down the pulse amplitude at the front of the pulse to the corona threshold. Second, it will cause the portion of the pulse whose amplitude is larger than the corona threshold to travel with a speed less than the speed of light. The effects of corona on the voltage or current pulses propagating along a transmission line can also be evaluated by introducing a time varying capacitance and a conductance into the transmission line. If the time varying capacitance is assumed to be proportional to the ratio between the corona charge and the applied voltage then one requires both this and the time varying conductance to represent the corona effects more accurately. Analysis of the return stroke as a current pulse propagating along a transmission line undergoing corona shows that the corona effects may explain the reason why the measured return stroke speeds are considerably less than the speed of light. Moreover, based on the effects of corona, a physical justification for the concepts used in the current generation type return stroke models is provided.
|
|
| 20. |
- Cooray, Vernon, et al.
(författare)
-
The lightning striking distance—Revisited
- 2007
-
Ingår i: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 65:5-6, s. 296-306
-
Tidskriftsartikel (refereegranskat)abstract
- First return stroke current waveforms measured by Berger [Methods and results of lightning records at Monte San Salvatore from 1963–1971 (in German), Bull. Schweiz. Elektrotech. ver. 63 (1972) 21403—21422] and Berger and Vogelsanger [Measurement and results of lightning records at Monte San Salvatore from 1955–1963 (in German), Bull. Schweiz. Elektrotech. ver. 56 (1965) 2–22] are used to estimate the charge stored in the lightning stepped leader channel. As opposed to previous charge estimates based on the entire current waveform, only the initial portion of measured current waveforms (100 μs in duration) was used in order to avoid the inclusion of any charges not involved in the effective neutralization of charges originally stored on the leader channel. The charge brought to ground by the return stroke within the first 100 μs, Qf,100 μs (in C) is related to the first return stroke peak current, Ipf (in kA), as Qf,100 μs=0.61 Ipf. From this equation the charge distribution of the stepped leader as a function of the corresponding peak return stroke current is estimated. This distribution (along with the assumed average electric field of 500 kV/m in the final gap) is used to estimate the lightning striking distance S (in meters) to a flat ground as a function of the prospective return stroke peak current I (in kA): S=1.9 Ipf0.90. For the median first stroke peak current of 30 kA one obtains S=41 m, while the traditional equation, S=10 Ipf0.65, gives S=91 m. In our view, the new equation for striking distance provides a more physically realistic basis for the electro-geometric approach widely used in estimating lightning incidence to power lines and other structures.
|
|
| 21. |
|
|
| 22. |
- Cooray, Vernon, et al.
(författare)
-
The striking distance of lightning flashes and the early streamer emission (ESE) hypothesis
- 2007
-
Ingår i: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 65:5-6, s. 336-341
-
Tidskriftsartikel (refereegranskat)abstract
- The attachment of a lightning flash to a lightning conductor (or to any other structure) takes place through a connecting leader that rises from the structure towards the descending stepped leader of a lightning flash. The spatial separation between the tip of the stepped leader and the lightning conductor (or the grounded structure) at the initiation of the connecting leader is known as the striking distance. In this paper the striking distance of stepped leaders is derived as a function of conductor height, conductor radii and the prospective return stroke current. Based on these results the validity of the early streamer emission (ESE) hypothesis is discussed. According to the ESE hypothesis, the striking distance of a lightning conductor can be increased by the artificial initiation of streamers from a lightning conductor. The results cast doubt on the validity of the ESE hypothesis. This in turn calls for more experimental data and field validations before using the ESE hypothesis in standard lightning protection practice.
|
|
| 23. |
- De Conti, Alberto, et al.
(författare)
-
A comparison of different approaches to simulate a nonlinear channel resistance in lightning return stroke models
- 2008
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113:D14, s. D14129-
-
Tidskriftsartikel (refereegranskat)abstract
- Different physical models that describe the time variation of the channel resistance are investigated in a lightning return stroke model. Such models consider one of the three following hypotheses: (1) the channel resistance decays exponentially with time, (2) the channel resistance decays with the radial expansion of the channel core, which is assumed to be described by the strong-shock approximation, or (3) the channel resistance varies with time according to three different arc resistance models (defined by Toepler, Barannik and Kushner et al.). Analyses illustrate the effect of a time-varying channel resistance on channel currents and corresponding electromagnetic fields. It is shown that the strong-shock approximation is able to predict typical features of experimentally observed lightning electromagnetic fields and return stroke speed profiles. It is also shown that results predicted by the strong-shock approximation can be qualitatively reproduced by either using simplified arc resistance equations (such as Toepler's and Barannik's ones) or considering an exponential decay of the channel resistance with attenuation constants linearly increasing with height.
|
|
| 24. |
|
|
| 25. |
- Li, Bing
(författare)
-
Impact Evaluation of Intentional Electromagnetic Interference (IEMI) on Targeted Loads in Complex Networks Using Analytical Investigations
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the proliferation of various electronic and electrical devices, IEMI has become a critical issue that may severely threaten the modern society. For practical protection considerations, it is crucial to comprehensively evaluate the potential damages resulted by IEMI. The major objective of this thesis is to study the impacts of IEMI on the targeted load in complex networks. More exactly, with respect to certain IEMI, the characteristics of the resulting frequency response on the targeted load are studied, and the effects of network configurations, i.e., the attribute of load impedances, lengths of lines, parameters of disturbance source, location of source and network structures, are also investigated.First, we developed a novel efficient method to solve the frequency response, which is applicable for arbitrary networks. The key idea is decomposing the whole complex network into multiple equivalent units, and performing a recursive approach to efficiently compute the frequency response without losing the precision.Subsequently, we studied the periodicity of the load response in the frequency domain. Starting with a simple network, we derived and verified the period of the frequency response. During the study, the periodicity with respect to load and media was discussed.Furthermore, with respect to five important time-domain norms, i.e., time-domain peak, total signal energy, peak signal power, peak time rate of change, and peak time integral of the pulse, we considered a parameterized ultra-wideband (UWB) transient as the disturbance source, and thoroughly studied its impacts on the targeted load regarding network configurations, which include load impedance, the lengths of lines and parameters of the UWB transient.Finally, we adopted a statistical approach to investigate the receptivity at the targeted load in a network. Via complementary cumulative distribution function, the stochastic IEMI and its effects on the targeted load were studied. Moreover, by statistical approach, we also investigated how the network structure affects the frequency response of the targeted load. The results give suggestions on how to protect the targeted load by varying network structures.
|
|
| 26. |
- Lindeberg, Per-Anders, et al.
(författare)
-
Blitzeinwirkungen auf Oberleitungs- und Signalanlagen in Schweden
- 2007
-
Ingår i: Elektrische Bahnen. ; :1-2, s. 67-80
-
Tidskriftsartikel (refereegranskat)abstract
- Für ältere elektrotechnische Bahnanlagen waren die Aspekte der elektromagnetischen Verträglichkeit von geringerer Bedeutung als für heutige Anlagen. Vor allem für neuere Signal- und Zugerkennungsanlagen mit kleineren Abmessungen sanken die erlaubten Höchstwerte für Ströme und Spannungen. Dies hat die Störungsempfindlichkeit erhöht. Eine wichtige, wenn nicht die wichtigste Störungsquelle sind atmosphärische Entladungen, also Blitze. Ihre Einwirkung auf elektrifizierte Bahnstrecken in Schweden wurde theoretisch durch Simulationen untersucht. Die Empfindlichkeit der Komponenten wurde experimentell geprüft. Bei Bahnanlagen reicht die Ableitung von Blitzen nicht aus, um Schäden durch Blitzentladungen zu vermeiden. Gefährdete Komponenten sollten durch angemessene Maßnahmen gegenüber elektromagnetischen Störungen besser geschützt werden.
|
|
| 27. |
|
|
| 28. |
|
|
| 29. |
|
|
| 30. |
- Liu, Yaqing, et al.
(författare)
-
Investigating the validity of existing definitions and empirical equations of effective length/area of grounding wire/grid for transient studies
- 2007
-
Ingår i: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 65:5-6, s. 329-335
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 31. |
|
|
| 32. |
- Liu, Yaqing, et al.
(författare)
-
The Residual Resistivity in Soil Ionization Region Around Grounding System for Different Experimental Results
- 2003
-
Ingår i: IEEE Symposium on Electromagnetic Compatibility. Symposium Record. - 0780378350 ; , s. 794-799
-
Konferensbidrag (refereegranskat)abstract
- The residual soil resistivity at peak of injection current with lightning current wave shape in soil ionization region around the grounding system is analyzed based on different experimental results in the literature by E.E. Oettle (1988), P.L. Bellaschi et al. (1942) and A.C. Liew and M. Darveniza (1974) and the recent experimental results in the high voltage laboratory at Uppsala University. The results show that the residual resistivity in soil ionization region is changing largely versus different soil resistivity ranging from 50 /spl Omega/m to 827 /spl Omega/m. Combining all the data, the geometric mean of the residual soil resistivity in ionization region is approximately 7% of the original soil resistivity. This value of 7% can be used in modeling of the transient behavior of grounding system under the lightning strike including non-linear soil ionization phenomenon.
|
|
| 33. |
|
|
| 34. |
- Mazloom, Ziya, et al.
(författare)
-
A Method for Interfacing Lumped-Circuit Models and Transmission-Line System Models With Application to Railways
- 2009
-
Ingår i: IEEE transactions on electromagnetic compatibility (Print). - 0018-9375 .- 1558-187X. ; 51:3, s. 833-841
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 35. |
- Mazloom, Ziya, et al.
(författare)
-
Indirect Lightning-Induced Voltages Along a Railway Catenary-Track Multiconductor Transmission-Line System With Lumped Components
- 2011
-
Ingår i: IEEE transactions on electromagnetic compatibility (Print). - 0018-9375 .- 1558-187X. ; 53:2, s. 537-539
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 36. |
- Mazloom, Ziya, et al.
(författare)
-
Influence of Discrete Series Devices on Crosstalk Phenomena in Multiconductor Transmission Lines
- 2007
-
Ingår i: EMC ZURICH-MUNICH 2007, SYMPOSIUM DIGEST. ; , s. 245-248
-
Konferensbidrag (refereegranskat)abstract
- 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.
|
|
| 37. |
|
|
| 38. |
- Mazloom, Ziya, et al.
(författare)
-
Method to Include Lumped Devices in Multi-conductor Transmission Line System Models
- 2009
-
Ingår i: 2009 IEEE POWER & ENERGY SOCIETY GENERAL MEETING, VOLS 1-8.
-
Konferensbidrag (refereegranskat)abstract
- 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.
|
|
| 39. |
- Mazloom, Ziya, et al.
(författare)
-
Modeling of Passive Series Devices on Multiconductor Transmission Lines for Transient Analysis in Power and Railway Systems
- 2008
-
Ingår i: EuroEM Conference 2008.
-
Konferensbidrag (refereegranskat)abstract
- Usually the crosstalk or field to wire coupling mechanisms in multiconductor transmission lines (MTL) are studied considering lumped loads or devices connected at the line terminations (at source and load ends) or as shunt load to ground along the lines, as seen in conventional power system networks e.g. [1-3]. However there are practical systems, e.g. in typical Swedish railway systems, wherein discrete devices exist in series with the line (booster transformers) or in shunt between the lines (auto transformers and track circuits). With lightning transients various parameters that influence crosstalk in MTL systems, such as the ground conductivity, have been analyzed e.g. in [1]. We shall present various cases of crosstalk mechanisms when the devices are connected either in series with the line or in shunt between the lines. The method used for simulating the voltage and current pulse propagation along the MTL systems is the FDTD method [4] in conjunction with the recursive convolution proposed in [5] for inclusion of ground losses. The passive series components connected along the MTL are simulated by the circuit solver ATP/EMTP [6, 7]. Emphasis will be given to present the model that connects the FDTD routine with the circuit solver in a more efficient way. The currents entering or leaving a given type of component at a given position along the lines are modeled as time dependant current sources in the circuit solver and the terminal voltages appearing in the circuit are returned to the FDTD routine as node voltages. We shall also present the efficacy of the proposed method and mathematically discuss the validity of the present work. The influence of finitely conducting ground on the current pulse propagation is also included in the analysis. From the crosstalk analysis it is also shown that the series connected passive devices cannot be disregarded as they largely influence pulses propagating on the lines in the event of transient phenomena due to lightning or switching. This study could be beneficial for future practical studies of surge protection and insulation coordination.
|
|
| 40. |
|
|
| 41. |
- Montano, Raul, et al.
(författare)
-
An Efficient Implementation of the Agrawal et al. Model for Lightning-Induced Voltage Calculations Using Circuit Simulation Software
- 2008
-
Ingår i: IEEE Transactions on Circuits and Systems Part I: Regular Papers. - 1549-8328. ; 55:9, s. 2959-2965
-
Tidskriftsartikel (refereegranskat)abstract
- One of the popular, simple, and accurate field-to-wire coupling models for studying transmission-line lightning interaction is the Agrawal et al model [1]. In this model, the coupling mechanisms are represented by distributed sources along the line, wherein each distributed source is due to the horizontal component of the illuminating electric field at that point on the line. These sources give rise to the propagating scattered voltage along the line, while the total voltage at any instant at a given point along the line is the sum of scattered voltage and the voltage at that point due to the illuminating vertical component of the electric field. There is a difficulty in applying the Agrawal et al. model with the built-in transmission-line models of various circuit simulation software such as the Alternate Transients Program-Electromagnetic Transients Program [2]-[5], PSpice [6], Simpow [7], PSS/E [71, etc., as the voltage source due to the horizontal component of the electric field in the Agrawal el al. model is in series with the line impedance [1], [8] and not in between two transmission-line segments. In this paper, a simple circuit approach for efficient implementation of the Agrawal et al. model using any circuit simulation software that has built-in transmission-line models is proposed.
|
|
| 42. |
|
|
| 43. |
|
|
| 44. |
- Nag, Amitabh, et al.
(författare)
-
First versus subsequent return-stroke current and field peaks in negative cloud-to-ground lightning discharges
- 2008
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113:D19, s. D19112-
-
Tidskriftsartikel (refereegranskat)abstract
- We examine relative magnitudes of electric field peaks of first and subsequent return strokes in negative cloud-to-ground lightning flashes recorded in Florida, Austria, Brazil, and Sweden. On average, the electric field peak of the first stroke is appreciably, 1.7 to 2.4 times, larger than the field peak of the subsequent stroke ( except for studies in Austria where the ratio varies from 1.0 to 2.3, depending on methodology and instrumentation). Similar results were previously reported from electric field studies in Florida, Sweden, and Sri Lanka. For comparison, directly measured peak currents for first strokes are, on average, a factor of 2.3 to 2.5 larger than those for subsequent strokes. There are some discrepancies between first versus subsequent stroke intensities reported from different studies based on data reported by lightning locating systems (LLS). The ratio of LLS-reported peak currents for first and subsequent strokes confirmed by video records is 1.7 to 2.1 in Brazil, while in the United States ( Arizona, Texas, Oklahoma, and the Great Plains) it varies from 1.1 to 1.6, depending on methodology used. The smaller ratios derived from the LLS studies are likely to be due to poor detection of relatively small subsequent strokes. The smaller values in Austria are possibly related ( at least in part) to the higher percentage ( about 50% versus 24-38% in other studies) of flashes with at least one subsequent stroke greater than the first. The effects of excluding single-stroke flashes or subsequent strokes in newly formed channels appear to be relatively small.
|
|
| 45. |
|
|
| 46. |
|
|
| 47. |
- Theethayi, Nelson, et al.
(författare)
-
A theoretical study on the consequence of a direct lightning strike to electrified railway system in Sweden
- 2005
-
Ingår i: Electric Power System Research. - : Elsevier BV. ; 74:2, s. 267-280
-
Tidskriftsartikel (refereegranskat)abstract
- Direct lightning strike to a single-track electrified railway system in Sweden is modeled in this paper. Using this model, the induced voltages in each of the nine conductors at heights varying from 0.5 m (tracks) to 10 m above the ground are estimated. The effect of the finitely conducting ground is included using a time domain expression for the transient ground impedance that has better early time and late time behavior. The main interconnection between the conductors and the flashover strength of the supporting insulators is included in the simulations. A simple model for the arc channel during flashover of the insulators and the ionization of the soil around the pole foundations is also included in the model to assess the possible realistic surge voltage distribution in the system. It is shown in the paper that finite ground conductivity, interconnections between the conductors, arcing phenomena of insulation flashover and grounding of the poles decide the voltage/current distribution in the conductors. Simulations have been also carried out to determine the voltages on the lines and across the rails as function of distance from the point of strike as it could be a necessary data for deciding the possible future protection schemes. It was found that for a lightning stroke of 31 kA peak, large common mode and differential mode surges exist on the lines which could create excessive voltages between the line and neutral of the transformer and might pose a threat to the various low voltage equipments used for telecommunication, signaling and control.
|
|
| 48. |
|
|
| 49. |
- Theethayi, Nelson, et al.
(författare)
-
Currents in buried grounding strips connected to communication tower legs during lightning strikes
- 2008
-
Ingår i: IEEE transactions on dielectrics and electrical insulation. - 1070-9878 .- 1558-4135. ; 15:4, s. 1153-1161
-
Tidskriftsartikel (refereegranskat)abstract
- During a lightning strike to communication tower stroke currents are shared by the tower and by the shields of the cables along the tower. The currents in the tower proceed towards the grounding system (possibly a combination of counterpoises or ring conductors or ground rods or grounding grids) connected to tower legs' foundation. In this paper, lightning strike to communication tower on mount Gaisberg in Austria is considered and measured currents at the tower top and those shared by an instrumented grounding strip connected to one of the tower leg's are presented. The measured currents at different locations on the 70-m long ground strip are compared with the predictions of a frequency dependant lossy transmission line (TL) model and reasonably good agreement was found. From this validation it is claimed that the TL models are appropriate for lightning transient analysis of grounding systems.
|
|
| 50. |
- Theethayi, Nelson, 1975-
(författare)
-
Electromagnetic Interference in Distributed Outdoor Electrical Systems, with an Emphasis on Lightning Interaction with Electrified Railway Network
- 2005
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the electromagnetic compatibility (EMC) problems of distributed electrical networks, especially that caused by lightning to electrified railway. Lightning transients were found to damage important devices that control train movements, causing traffic stoppage and delays. This thesis attempts to develop computational models for identification of parameters influencing the coupling phenomena between those devices and lightning. Some supporting experimental investigations are also carried out. This thesis forms the groundwork on the subject of lightning interaction with the electrified railway networks.Lightning induces transient overvoltages in railway conductor systems such as tracks, overhead wires, and underground cables, either due to direct lightning strike to the system or due to the coupling of electromagnetic fields from remote strikes. Models based on multiconductor transmission line theory were developed for calculating the induced voltages and currents. A transmission line return stroke model, that can predict the remote electromagnetic fields comparable to experimental observations, is also developed.Earlier works on modeling earth return impedances for transient studies in power distribution systems are not readily applicable for railways for lightning transients, in cases of low earth conductivities found in Sweden and for large variation in conductor heights. For the wires above ground, the ground impedance models were modified for wide range of frequencies, soil conductivities and wide spread of conductor heights. Influences of pole insulator flashovers, pole-footing soil ionizations and interconnections between the conductors on the lightning surge propagation are studied. Wave propagation in buried shielded and unshielded cables with ground return is studied. Simplified, valid and computationally efficient ground impedance expressions for buried and on-ground wires are proposed. A model for the coupling phenomena (transfer impedance) through multiple cable shields with multiconductor core is also proposed. Besides, experimental studies on lightning induced transients entering a railway technical house, failure modes of relay and rectifier units used in the train position/signaling applications for lightning transients are performed. A high frequency circuit model for the booster transformer for lightning interaction studies is developed. The simulation models are being converted to user-friendly software for the practicing engineers of the railway industry.
|
|
