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  • 1.
    Ahmad, Mohd Riduan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Esa, Mona Riza Binti Mohd
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Dutkiewicz, Eryk
    Interference from cloud-to-ground and cloud flashes in wireless communication system2014Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 113, s. 237-246Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, cloud-to-ground (CG) flash and intra-cloud (IC) flash events that interfere with the transmission of bits in wireless communication system operating at 2.4 GHz were analyzed. Bit error rate (BER) and consecutive lost datagram (CLD) measurement methods were used to evaluate BER and burst error from 3 tropical thunderstorms on November 27, 28, and 29 during 2012 northeastern monsoon in Malaysia. A total of 850 waveforms from the electric field change recording system were recorded and examined. Out of these, 94 waveforms of very fine structure were selected which matched perfectly with the timing information of the recorded BER. We found that both CG and IC flashes interfered significantly with the transmission of bits in wireless communication system. The severity of the interference depends mainly on two factors namely the number of pulses and the amplitude intensity of the flash. The interference level becomes worst when the number of pulses in a flash increases and the amplitude intensity of pulses in a flash intensifies. During thunderstorms, wireless communication system has experienced mostly intermittent interference due to burst error. Occasionally, in the presence of very intense NBP event, wireless communication system could experience total communication lost. In CG flash, it can be concluded that PBP is the major. source of interference that interfered with the bits transmission and caused the largest burst error. In IC flash, we found that the typical IC pulses interfered the bits transmission in the same way as PBP and mixed events in CG flash and produced comparable and in some cases higher amount of burst error. NBP has been observed to interfere the bits transmission more severely than typical IC and CG flashes and caused the most severe burst error to wireless communication system.

  • 2.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    The influence of lightning conductor radii on the attachment of lightning flashes2017Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 153, nr SI, s. 138-143Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of the tip radius of lightning conductors on their lightning attractive distance as predicted by the self-consistent leader inception and propagation model (SLIM) is presented. The results show that in the absence of any glow corona from the tip of the conductor a smaller tip radius gives rise to a larger attractive radius than a larger radius. It is suggested that the reason for the experimental observations which show that blunt conductors are more efficient lightning receptors than sharp ones is the presence of glow corona at the tip of the sharp ones during the time of lightning strikes. Moreover, in a given background electric field, the probability of the inception of glow corona at the conductor tip increases with increasing conductor height and decreasing conductor radius. Thus, in a given electric field, as the conductor height increases its radius has to be increased to avoid the inception of glow corona at the tip. For this reason, the conductor radius that performs best as a lightning interceptor depends on the height of the conductor and the best performance shift from smaller radii to larger ones with increasing height of the conductor.

  • 3.
    Cooray, Vernon
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Cooray, Gerald
    Karolinska Univ Hosp, Dept Clin Neurosci, Stockholm, Sweden..
    Electromagnetic fields of accelerating charges: Applications in lightning protection2017Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 145, s. 234-247Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electromagnetic fields generated by accelerating charges can be utilized to evaluate the electromagnetic fields generated by systems where moving charges and/or propagating currents are present. The technique can be used easily to evaluate the electromagnetic fields generated by systems in which propagating currents are present. This is illustrated by utilizing the equations to derive expressions for the electromagnetic fields generated by systems in which current pulses injected by lightning flashes are propagating.

  • 4.
    Cooray, Vernon
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Diendorfer, Gerhard
    OVE Serv GmbH, Vienna, Austria..
    Merging of current generation and current dissipation lightning return stroke models2017Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 153, nr SI, s. 10-18Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Current generation and current dissipation return stroke models are engineering models based on the theory associated with the propagation of current pulses along transmission lines undergoing corona. However, neither of these models incorporates the complete theory associated with the phenomenon. One can make the physical scenario complete by combining the current generation concept with the current dissipation concept. In this paper how this can be done is demonstrated by creating a return stroke model which is a combination of these two model types. The new model encompasses the full theory associated with the pulse propagation along transmission lines under corona. The paper provides a full description of the model together with a description of the spatial and temporal variation of the return stroke current and the electric and magnetic fields generated at different distances as predicted by the model.

  • 5.
    Cooray, Vernon
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Kumar, Udaya
    Rachidi, Farhad
    Lucci, Carlo Alberto
    On the possible variation of the lightning striking distance as assumed in the IEC lightning protection standard as a function of structure height2014Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 113, s. 79-87Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of structure height on the lightning striking distance is estimated using a lightning strike model that takes into account the effect of connecting leaders. According to the results, the lightning striking distance may differ significantly from the values assumed in the IEC standard for structure heights beyond 30m. However, for structure heights smaller than about 30m, the results show that the values assumed by IEC do not differ significantly from the predictions based on a lightning attachment model taking into account the effect of connecting leaders. However, since IEC assumes a smaller striking distance than the ones predicted by the adopted model one can conclude that the safety is not compromised in adhering to the IEC standard. Results obtained from the model are also compared with Collection Volume Method (CVM) and other commonly used lightning attachment models available in the literature. The results show that in the case of CVM the calculated attractive distances are much larger than the ones obtained using the physically based lightning attachment models. This indicates the possibility of compromising the lightning protection procedures when using CVM.

  • 6.
    Diaz, Oscar
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Arevalo, Liliana
    ABB Power Syst HVDC, SE-77180 Ludvika, Sweden.
    Cooray, Vernon
    Parameter variation in leader channel models used in long air gap discharge simulation2016Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 139, s. 32-36Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Theoretical models have been developed to predict the 50% breakdown voltage of long air gaps arrangements, based on the physics of the discharge. These models are capable of estimating electric fields, leader and streamer region propagation, among others. An important parameter within this calculation is the leader model and its electric potential distribution along the discharge channel. In the present work, we compared engineering and physical leader models against experimental data recorded for a rod-to-plane electrode arrangement tested with switching-like voltage impulses. The analysis showed that the leader channel evolution depends strongly on the potential gradient assumed to sustain streamers.

  • 7.
    Ekström, Rickard
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Leijon, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Lower order grid current harmonics for a voltage-source inverter connected to a distorted grid2014Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 106, s. 226-231Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    As a result of lower order grid voltage harmonics, the grid current injected by a voltage-source inverter will also be partially distorted. In large-scale applications, active harmonic filters or notch filters are used to reduce the grid current distortion. For small-scale units, this may not be economically viable. In this article, two different grid phase tracking methods are evaluated with respect to the grid current distortion. The first method uses the zero-crossing detection (ZCD) method together with a look-up table (LUT), to generate a perfectly sinusoidal voltage synchronized with the grid. The second method uses a single-phase phase-locked loop (PLL). This method will reflect the grid harmonics in the inverter output, resulting in either cancellation or superposition of the harmonics of the grid current. A theoretical expression for the grid current as a function of the grid voltage harmonics is derived. Individual grid current harmonics as well as the total harmonic distortion (THD) are experimentally evaluated for both ZCD and PLL, and compared with theory. Results are presented for different power flows into the grid and compared with grid codes.

  • 8.
    Johari, Dalina
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Faculty of Electrical Engineering, Centre for Electrical Power Engineering Studies, Universiti Teknologi Mara, 40450 Shah Alam, Selangor, Malaysia.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Rahman, Mahbubur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Hettiarachchi, Pasan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Ismail, Mohd Muzafar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Faculty of Electronics and Computer Engineering, Telecommunication Engineering Department, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Malacca, Malaysia.
    Characteristics of leader pulses in positive ground flashes in Sweden2017Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 153, s. 3-9Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the characteristics of the electric field pulses observed during leader propagation in positive ground flashes. We analysed in detail the electric field changes occurring just before the first return stroke in 51 positive ground flashes during 2014 summer thunderstorms in Uppsala, Sweden. Pronounced leader pulses (having the same polarity as the return stroke) were observed in 22% of the cases. They were observed to occur within 1.4 ms before the first return stroke. Interpulse duration ranged from 13.3 to 50.3 μs with a mean value of 24.7 μs. The peak amplitude of the leader pulses relative to the return stroke peak ranged from 2.7 to 17.8%. The presence of these pulses shows that the leaders propagate in a stepped manner. Based on the leader pulses’ time of initiation and average speed of the leader, the distance travelled by the leader was also estimated. One case of positive ground flash preceded by opposite polarity leader pulses just before the return stroke is also reported. To the best of our knowledge, this is the first time that such a case in positive ground flashes is reported. We suggest that these opposite polarity leader pulses are due to the negatively-charged leader branch of a bi-directional leader inside the cloud that propagates towards observation point.

  • 9.
    Johari, Dalina
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Univ Teknol Mara, Fac Elect Engn, Ctr Elect Power Engn Studies, Shah Alam 40450, Selangor, Malaysia.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Rahman, Mahbubur
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Hettiarachchi, Pasan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Ismail, Mohd Muzafar
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Univ Tekn Malaysia Melaka, Fac Elect & Comp Engn, Telecommun Engn Dept, Durian Tunggal 76100, Malacca, Malaysia.
    Features of the First and Subsequent Return Strokes in Positive Ground Flashes based on Electric Field Measurements2017Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 150, s. 55-62Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the characteristics of the electric fields produced by the first and the subsequent return strokes observed in positive ground flashes in Sweden. Fifty one positive ground flashes containing 60 return strokes recorded during 2014 summer thunderstorms were analyzed. In our analysis, only 12% of the cases were multiple-stroke while 88% were single-stroke. On average, the number of strokes per flash was 1.20 and the highest number of strokes per flash recorded was four. The geometric mean (GM) value of the interstroke interval was 60 ms while the distance between the first and the subsequent strokes ranged between 4.9 and 46.4km. We found that the average duration of the subsequent strokes parameters were smaller than that of the first strokes. For the first strokes, the GM values of the slow front duration, the fast transition 10-to-90% risetime, the zero crossing time, the zero-to-peak risetime and the 10-to-90% risetime were 8.7 mu s, 1.4 mu s, 29 mu s, 11 mu s and 5.7 mu s, respectively while for the subsequent strokes, the values were 4.0 mu s 0.91 mu s, 11 mu s 5.8 mu s and 3.2 mu s, respectively. Possible reasons for the shorter duration of the subsequent return strokes parameters were discussed.

  • 10.
    Kumara, L. A. Duminda
    et al.
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka..
    Edirisinghe, Mahesh
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka..
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Low voltage disk varistors under non-standard high current derivative impulse environment2016Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 139, s. 153-160Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, the behavior of low voltage disk varistors was analyzed under oscillatory type non-standard high current derivative impulses. The experiment was performed using 20 ram disk varistors with different nominal operating voltages of 14, 30, 40, 75, 150, 250, and 275 V. Non-standard current impulses were generated using a Van De Graaff generator. The current impulse is in the shape of double exponential oscillatory type wave which has the oscillation frequency of 14.53 MHz. The rise time of the impulse was found to be 8 ns with the maximum peak current rate-of-rise of 2.41 x 10(11) A/s. According to the results, under very fast non-standard current derivative impulse environment, clamping voltage could be depend on both nominal voltage of varistors and the peak current rate-of-rise of the injected impulse. Interestingly, the clamping voltages under non-standard high current derivative impulse environment for all the tested varistors were below the order of values reported for 8/20 mu s standard current impulses. It is believed that the varistor response is mainly governed by the lead's inductance whereas the influence of the varistor nonlinear resistance becomes negligible. It was found that the maximum impulse impedance values of the varistors are caused due to the increasing of its nominal voltage. Calculated current integrals were lying between 80 and 94 A(2)s whereas the maximum peak current values were lying in the range of 2070-2496A. Another important feature observed in this study was the DC offset voltage appears between terminals of varistor immediately after it is triggered due to its first oscillatory pulse of the current impulse.

  • 11.
    Silva Junior, Dalmo C.
    et al.
    Univ Fed Juiz de Fora, Elect Engn Program, Multiplatform Simulat Lab, Juiz De Fora, MG, Brazil.
    Oliveira, Janaina G.
    Univ Fed Juiz de Fora, Elect Engn Program, Multiplatform Simulat Lab, Juiz De Fora, MG, Brazil.
    de Almeida, Pedro M.
    Univ Fed Juiz de Fora, Elect Engn Program, Multiplatform Simulat Lab, Juiz De Fora, MG, Brazil.
    Boström, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Control of a multi-functional inverter in an AC microgrid - Real-time simulation with control hardware in the loop2019Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 172, s. 201-212Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper proposes the implementation of a multi-functional inverter, which was simulated with three ancillary functions. The first function is a Shunt Active Power Filter (SAPF) for harmonic content mitigation, the second is a Virtual Synchronous Machine (VSM) to show the effective regulation of voltage and frequency, and finally, power management in AC microgrids. The multi-functional converter is responsible for the integration of a PV-Battery system (distributed generation) on the AC grid. Furthermore, Real Time Digital Simulator (RTDS) and dSPACE have been used to analyze the performance and control of such multi-functional inverter when added to an AC microgrid. Results demonstrate the operation of the system and can be used as validation of the proposed control strategies through a Hardware In the Loop (HIL) simulation.

  • 12.
    Song, Meng
    et al.
    Kungliga tekniska högskolan.
    Alvehag, Karin
    Kungliga tekniska högskolan.
    Widén, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Parisio, Alessandra
    Kungliga tekniska högskolan.
    Estimating the impacts of demand response by simulating household behaviours under price and CO2 signals2014Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 111, s. 103-114Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To facilitate the implementation of demand response (DR), it is necessary to establish proper methods to estimate and verify the load impacts of it. This paper develops a simulation model to investigate the joint influence of price and CO2 signals in a DR program in the ex ante evaluation. It consists of a Markov-chain load model for forecasting the power demands of residential consumers and a scheduling program for providing optimal schedules for smart appliances. A case study of the Stockholm Royal Seaport project is analysed to demonstrate how to apply the simulation model to assess a DR program by simulating consumers’ behaviour change in response to the DR signals. The results show that consumers’ attitude to the signals and willingness to change (expressed by weight λ and time preference) largely affect the load shift, bill saving and emission reduction. Moreover, by observing the load shifts over different lengths of the testing period, the model could also provide suggestions on the required testing period to get sufficient load data to distinguish the load patterns between consumers in different testing groups.

  • 13.
    Theethayi, Nelson
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära och åskforskning.
    Liu, Yaqing
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära och åskforskning.
    Montano, Raul
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära och åskforskning.
    Thottappillil, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära och åskforskning.
    On the influence of conductor heights and lossy ground in multi-conductor transmission lines for lightning interaction studies in railway overhead traction systems2004Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 71, nr 2, s. 186-193Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Railway overhead traction system is a classic example of scattered conductor configuration, where tracks and other wires form multi-conductor transmission lines (MTLs) with large variation in conductor heights above ground and they are spread across regions having different soil conditions. Lightning transient analysis in such systems has not received much attention earlier. Here we analyze the influence of conductor heights and lossy ground on the induced voltages in a two conductor MTLs for the case of a direct lightning strike. For transient analysis, modified time domain transient ground impedance expressions having better early and late time behavior was used. The dependence of transient ground impedance on conductor heights and ground resistivity are presented and discussed. The early time transient ground impedances are unaffected by ground resistivity but their decaying nature is highly dominated by ground resistivity. It is found, if one of the conductors is close to ground (a rail) and if it is at large vertical distance from struck conductor (an auxiliary power line), then with increasing ground resistivity the peak induced voltages in the conductor close to ground initially increase, then decrease and finally tend to remain constant (within 100-10,000Ωm). This phenomenon is opposite to that compared to conductors that are close to each other with minimum vertical separation (two auxiliary power lines), where the peak induced voltages increase with increasing ground resistivity. The study focuses mainly to access when a mutual coupling due to system geometry or due to ground losses becomes dominant in determining induced effects from lightning in MTLs, which could be an important contribution to the lightning interaction studies for electrified railway systems.

  • 14.
    Theethayi, Nelson
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Thottappillil, Rajeev
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Liu, Yaqing
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Montano, Raul
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Important Parameters That Influence Crosstalk in Multiconductor Transmission Lines2007Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 77, nr 8, s. 896-909Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Transient surges in one of the overhead conductors, due to direct lightning strikes, causes crosstalk [C.R. Paul, Analysis of Multiconductor Transmission Lines, John Wiley & Sons, Inc., 1994; C.R. Paul, Introduction to Electromagnetic Compatibility, John Wiley & Sons, Inc., 1992] in other adjacent conductors. It is a common electromagnetic interference (EMI) phenomenon observed in power lines, communication lines and electrified railway lines. In this paper we investigate the crosstalk in multiconductor transmission lines (MTLs) above finitely conducting ground as a function of ground conductivity, heights of the receptor conductor and the terminal loads. For receptor conductor close to the ground, compared to the emitter conductor [C.R. Paul, Analysis of Multiconductor Transmission Lines, John Wiley & Sons, Inc., 1994; C.R. Paul, Introduction to Electromagnetic Compatibility, John Wiley & Sons, Inc., 1992], the decrease in ground conductivity increases the crosstalk peak currents at near end (end near to the source in the emitter conductor) of the receptor conductor, but at the far end it could either increase or decrease depending upon the line height and ground conductivity.

    It is found that the ground impedance [J.R. Carson, Wave propagation in overhead wires with ground return, Bell. Sys. Tech. J. 5 (1926) 539–554; Y.J. Wang, S.J. Liu, A review of methods for calculation of frequency dependant impedance of overhead power transmission lines, Proc. Natl. Sci. Conc. ROC (A), 25 (6), (2001) 329–338; E.D. Sunde, Earth conduction effects in transmission systems, 1st ed., Dover Publications Inc., New York, 1968; A. Deri, G. Tevan, A. Semlyen, A. Castanheira, The complex ground return plane a simplified model for homogenous & multilayer earth return, IEEE Trans. PAS 100 (8) (1981) 3686–3693; K.C. Chen, K.M. Damrau, Accuracy of approximate transmission line formulas for overhead wires, IEEE Trans. EMC 31 (4) (1989) 396–397; A. Semlyen, Ground return parameters of transmission lines an asymptotic analysis for very high frequencies, IEEE Trans. PAS 100 (3) (1981) 1031–1038; E.F. Vance, Coupling to Cable Shields, Wiley Interscience, New York, 1978; J.R. Wait, Theory of wave propagation along a thin wire parallel to an interface, Radio Sci. 7 (6) (1972) 675–679; R.G. Olsen, J.L. Young, D.C. Chang, Electromagnetic wave propagation on a thin wire above earth, IEEE Trans. Anten. Propag. 48 (9) (2000) 1413–1418; M. D’Amore, M.S. Sarto, Simulation models of a dissipative transmission line above a lossy ground for a wide-frequency range. I. Single conductor configuration, IEEE Trans. EMC 38 (2) (1996) 127–138; M. D’Amore, M.S. Sarto, Simulation models of a dissipative transmission line above a lossy ground for a wide-frequency range. II. Multiconductor configuration, IEEE Trans. EMC 38 (2) (1996) 139–149; F. Rachidi, C.A. Nucci, M. Ianoz, C. Mazzetti, Influence of lossy ground on lightning induced voltages on overhead lines, IEEE Trans. EMC 38 (3) (1996) 250–264; F. Rachidi, C.A. Nucci, M. Ianoz, Transient analysis of multiconductor lines above a lossy ground, IEEE Trans. Power Deliv. 14 (1) (1999) 294–302; F.M. Tesche, M.V. Ianoz, T. Karlsson, EMC Analysis Methods and Computational Models, John Wiley and Sons Inc., 1997; A.K. Agrawal, H.J. Price, S.H. Gurbaxani, Transient response of multiconductor transmission lines excited by a nonuniform electromagnetic field, IEEE Trans. EMC 22 (2) (1980) 119–129] has profound influence in all the crosstalk cases studied here. Hence, a brief review and comparison of different closed form ground impedance expressions under the limits of transmission line approximation [F.M. Tesche, M.V. Ianoz, T. Karlsson, EMC Analysis Methods and Computational Models, John Wiley and Sons Inc., 1997] and its behavior at both high and low frequencies is presented. It is shown that low frequency approximation of ground impedance is not sufficient for lightning transient studies involving ground conductivities lower than 10 mS/m. The observations presented in the paper have important implications in EMI studies of large distributed outdoor systems, such as the railway network, subjected to lightning strikes.

  • 15.
    Widén, Joakim
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Paatero, Jukka
    Helsinki University of Technology.
    Lund, Peter
    Helsinki University of Technology.
    Impacts of distributed photovoltaics on network voltages: Stochastic simulations of three Swedish low-voltage distribution grids2010Inngår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 80, nr 12, s. 1562-1571Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The continuously increasing application of distributed photovoltaics (PV-DG) in residential areas around the world calls for detailed assessment of distribution grid impacts. Both photovoltaic generation and domestic electricity demand exhibit characteristic variations on short and long time scales and are to a large extent negatively correlated, especially at high latitudes. This paper presents a stochastic methodology for simulation of PV-DG impacts on low-voltage (LV) distribution grids, using detailed generation and demand models. The methodology is applied to case studies of power flow in three existing Swedish LV grids to determine load matching, voltage levels and network losses at different PV-DG penetration levels. All studied LV grids can handle significant amounts of PV-DG, up to the highest studied level of 5 kWp PV per household. However, the benefits of PV-DG in terms of relative improvement of on-site reduction of demand, mitigated voltage drops and reduced losses were most significant at a penetration level of 1 kWp PV per household.

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