| 1. |
- Anatory, Justinian, et al.
(författare)
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A broadband power-line communication system design scheme for typical Tanzanian low-voltage network
- 2009
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Ingår i: IEEE Transactions on Power Delivery. - USA : IEEE. - 0885-8977 .- 1937-4208. ; 24:3, s. 1218-1224
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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.
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| 2. |
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| 3. |
- Anatory, Justinian, et al.
(författare)
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The Effects of Multipath on OFDM Systems for Broadband Power-Line Communications a Case of Medium Voltage Channel
- 2009
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Ingår i: World Academy of Science, Engineering and Technology. - 2070-3724. ; 54, s. 205-208
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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
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| 4. |
- Anatory, Justinian, et al.
(författare)
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The influence of load impedance, line length, and branches on underground cable power-line communications (PLC) systems
- 2008
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Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 23:1, s. 180-187
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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.
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| 5. |
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| 6. |
- Liu, Y. Q., et al.
(författare)
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An engineering model for transient analysis of grounding system under lightning strikes : Nonuniform transmission-line approach
- 2005
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Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 20:2, s. 722-730
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Liu, Y. Q., et al.
(författare)
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An improved model for soil ionization around grounding system and its application to stratified soil
- 2004
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Ingår i: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 60:2-4, s. 203-209
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Mazloom, Z., et al.
(författare)
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Modeling Indirect Lightning Strikes for Railway Systems With Lumped Components and Nonlinear Effects
- 2011
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Ingår i: IEEE transactions on electromagnetic compatibility (Print). - 0018-9375 .- 1558-187X. ; 53:1, s. 249-252
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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