| 1. |
- Anatory, Justinian, et al.
(author)
-
The effects of load impedance, line length, and branches in the BPLC transmission-lines analysis for-medium-voltage channel
- 2007
-
In: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 22:4, s. 2156-2162
-
Journal article (peer-reviewed)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.
|
|
| 2. |
- Flache, Denis, et al.
(author)
-
Different modes of charge transfer to ground in upward lightning observed at the Peissenberg tower
- 2009
-
Conference paper (other academic/artistic)abstract
- 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.
|
|
| 3. |
- Flache, D., et al.
(author)
-
Initial-stage pulses in upward lightning : Leader/return stroke versus M-component mode of charge transfer to ground
- 2008
-
In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 35:13, s. L13812-
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 4. |
|
|
| 5. |
- Liu, Yaqing, et al.
(author)
-
Investigating the validity of existing definitions and empirical equations of effective length/area of grounding wire/grid for transient studies
- 2007
-
In: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 65:5-6, s. 329-335
-
Journal article (peer-reviewed)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.
|
|
| 6. |
- Liu, Y. Q., et al.
(author)
-
An engineering model for transient analysis of grounding system under lightning strikes : Nonuniform transmission-line approach
- 2005
-
In: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 20:2, s. 722-730
-
Journal article (peer-reviewed)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.
|
|
| 7. |
- Manyahi, M. J., et al.
(author)
-
Simplified model for estimation of lightning induced transient transfer through distribution transformer
- 2005
-
In: International Journal of Electrical Power & Energy Systems. - : Elsevier BV. - 0142-0615 .- 1879-3517. ; 27:4, s. 241-253
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 8. |
- Manyahi, M. J., et al.
(author)
-
Transient response of transformer with XLPE insulation cable winding design
- 2005
-
In: International Journal of Electrical Power & Energy Systems. - : Elsevier BV. - 0142-0615 .- 1879-3517. ; 27:1, s. 69-80
-
Journal article (peer-reviewed)abstract
- 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.
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
|
|
| 12. |
- Thottappillil, Rajeev, 1958-, et al.
(author)
-
Comment on ‘’Radio frequency radiation beam pattern of lightning return strokes : A revisit to theoretical analysis” by Xuan-Min Shao, Abram R. Jacobson, and T. Joseph Fitzgerald
- 2005
-
In: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202. ; 110:D24
-
Journal article (peer-reviewed)abstract
- In summary, SJF present a new approach to deriving a radiation electric field equation for the TL model when there is no current discontinuity at the return stroke front. This approach (see their equation (11)) is identical, except for the SJF sign error, to that found in the literature (e.g., equation (47) of TUR). However, their electric field equation (10), asserted to be general, is incapable of handling models with current discontinuity (intrinsic in some models) at the return stroke front, and their electric field equation (12) for the TCS model is incomplete. The correct equation for the TCS model is given by TUR (see their equation (49)). A truly general electric field equation that is valid for any model and for any distance to the field point is equation (7) of Thottappillil and Rakov [2001b].
|
|
| 13. |
- Thottappillil, Rajeev, 1958-, et al.
(author)
-
Protection against lightning surges
- 2009
-
In: Lightning Protection. - London : Institution of Engineering and Technology. - 9780863417443 - 9781849191067 ; , s. 269-305
-
Book chapter (other academic/artistic)
|
|
| 14. |
- Zhou, Helin, et al.
(author)
-
A New Approach To Estimation Of Effective Height Of Towers On Mountain Tops For Lightning Incidence Studies : Sensitivity Analysis
- 2009
-
Conference paper (other academic/artistic)abstract
- In this paper, we review and evaluate the definitions and methods that could be used to estimate the effective height of a given tower on mountaintop based on the statistical observations . We derive the effective heights based on Rizk’s lightning attachement model, which are less than those predicted by the earlier methods based on statistical observations. Then we perform sensitivity analysis to evaluate the effect of uncertainties in model parameters that influence the effective height. Variations in the effective height as a function of model parameters, including the final quasi-stationary leader gradient, minimum positive streamer gradient, upward connecting positive leader speed, and mountain base radius, are presented, with Gaisberg tower as the example. It’s found that the effective height depends primarily on the structre height, mountain shape and upward positive leader speed. This new approach presented here can be employed to estimate the effective height for towers for which no lightning incidence data needed for the earlier methods are available. And the information could be also used in designing lightning protection of communication/transmission line towers and masts on mountain tops.
|
|
| 15. |
|
|
