| 1. |
- Nordhage, Frank, et al.
(author)
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Injection charging of polymeric capacitors
- 1976
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In: Journal of Electrostatics. - : Elsevier. - 0304-3886 .- 1873-5738. ; 2:4, s. 317-326
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Journal article (peer-reviewed)abstract
- The charging of non-polar polymer capacitors due to a step voltage is studied as a function of time. Apart from the classical charging, which is completed in nanoseconds, it is found that the current flowing into the capacitor can be described as a sum of two exponential functions of time, the time constants differing by a factor of ten. In the case of polyethylene, at least, it is clear that the shorter time constant is connected with carrier injection into the polymer from the metal surface. The longer time constant is presumable due to carrier migration within the volume of the dielectric. These findings may be correlated with our previous results on the field dependence of electrostatic charging and support the model of carrier injection to a finite depth.
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| 2. |
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| 3. |
- Nordhage, Frank, et al.
(author)
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Sliding and rolling electrification of a NaCl-metal system
- 1977
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In: Journal of Electrostatics. - : Elsevier. - 0304-3886 .- 1873-5738. ; 3:4, s. 371-383
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Journal article (peer-reviewed)abstract
- The electrification of (100)-oriented NaCl surfaces has been studied as a function of sliding velocity and normal force between an Au electrode and the insulator surface. In addition various crystallographic orientations of NaCl surfaces have been investigated with electrodes of different metals. A series of experiments comparing the sliding and rolling modes of separation has also been carried out on (100) surfaces. The results suggest that electrons are transferred from or into trapping levels in the forbidden energy range of the NaCl crystal.
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| 4. |
- Amarasinghe, Dulan, et al.
(author)
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Channel tortuosity of long laboratory sparks
- 2007
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In: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 65:8, s. 521-526
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Journal article (peer-reviewed)abstract
- Channel tortuosity of 50 cm long laboratory sparks were measured by analyzing a set of images taken by three cameras. The cameras were placed at a radial distance of 200 cm from the spark gap. The angle between any two cameras was 120 degrees. The sparks were generated between a steel rod and. a plane electrode. The distribution of the direction change of the channel was found to be Gaussian with a standard deviation of 15.3 degrees. The average tortuosity of the channel defined as the mean absolute value of the direction change was 11.8 +/- 1.4 degrees, which is smaller than the average tortuosity of natural lightning and close to the tortuosity of triggered lightning. The average tortuosity is dependent on the segment length used in calculating the direction change. A gradual increase in the average tortuosity (0.08 degrees/cm) was seen when the sparks propagated towards the plane electrode.
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| 5. |
- Amarasinghe, Dulan, et al.
(author)
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Fractal dimension of long electrical discharges
- 2015
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In: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 73, s. 33-37
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Journal article (peer-reviewed)abstract
- The fractal dimension of 500 mm long electrical discharges is presented by analyzing a set of photographic images. Three popular fractal dimension estimation techniques, box counting, sandbox and correlation function methods were used to estimate the fractal dimension of the discharge channels. To remove the apparent thickness due to varying magnitudes of current in the discharge channels, edge detection algorithms were utilized. The estimated fractal dimensions for box counting, sandbox and correlation function for long laboratory sparks were 1.20 +/- 0.06,1.66 +/- 0.05 and 1.52 +/- 0.12 respectively. Within statistical uncertainties, the estimated fractal dimensions of positive and negative polarities agreed very well. (C) 2014 Elsevier B.V. All rights reserved.
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| 6. |
- Andersson, Birgitta, et al.
(author)
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Long-term charge retention on PWBs
- 2005
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In: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 63:6-10, s. 597-602
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Journal article (peer-reviewed)abstract
- A sample of printed wiring boards, isolated from ground, has been charged tribo-electrically and the charge decay process has been studied with focus on the long-term charge decay behaviour. It was found that the time constant 1/e did not say much about the proceeding decay process. Instead a second-order approximation model for the measured decay curves has been suggested.
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| 7. |
- Arevalo, Liliana, 1978-, et al.
(author)
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A new static calculation of the streamer region for long spark gaps
- 2012
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In: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 70:1, s. 15-19
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Journal article (peer-reviewed)abstract
- Different electrostatic approximations have been proposed to calculate the streamer region without going in deep details of the behavior of density of particles under the effect of high electric fields; this kind of approximations have been used in numerical calculations of long spark gaps and lightning attachment. The simplifications of the streamer region are achieved by considering it to be a geometrical region with a constant geometrical shape. Different geometrical shapes have been used, such as cones or several parallel filaments. Afterward, to simplify the procedures, the streamer region was approximated by two constants, one denoted K-Q, called the geometrical constant and in other cases K named as geometrical factor. However, when a voltage that varies with time is applied to an arrangement of electrodes (high voltage and grounded electrodes), the background electric field will change with time. Thus, if the background electric field is modified, the streamer zone could cover a larger or smaller area. With the aim of reducing the number of assumptions required in the calculation of long gap discharges, a new electrostatic model to calculate the streamer region is presented. This model considers a variable streamer zone that changes with the electric field variations. The three-dimensional region that fulfills the minimum electric field to sustain a streamer is identified for each time step, and the charge accumulated in that region is then calculated. The only parameter that is being used in the calculation is the minimum electric field necessary for the propagation of streamers.
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| 8. |
- Arevalo, Liliana, et al.
(author)
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Numerical simulation of long laboratory sparks generated by positive switching impulses
- 2009
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In: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 67:2-3, s. 228-234
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Journal article (peer-reviewed)abstract
- A numerical methodology using two different leader channel criteria has been implemented. The methodology is based on Bondiou and Gallimberti's proposition [A. Bondiou, I. Gallimberti, Theoretical modelling of the development of the positive spark in long spark, J. Phys. D: Appl. Phys. 27 (1994) 1252-1266]. The leader channel criteria used are Rizk engineering criterion [Rizk, A model for switching impulse leader inception and breakdown of long air gaps, IEEE Trans. Power Deliv., 4(1) (1989)] and Local thermodynamic - L.T.E. - physical concept [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7-193]. The methodology was tested in three different cases; a deterministic case, a statistical variation and a typical constant level test. Deterministic calculation considered corona inception using stabilization corona electric field criterion of Gallimberti [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7-193] and the leader moving as segments. The statistical simulation has two different statistical delays, one at inception and the other due to the tortuous characteristics of the leader channel. The constant level test consists of 200 positive switching impulses with the same characteristics such as maximum applied voltage, time to crest and time to fall. Time to breakdown and breakdown voltage were found based on the results obtained from the constant level test characteristics. All the numerical results presented are based on experimental conditions reported in [Les Renardières Group, Research on long gap discharges at Les Renardières, Electra N 35 (1973)] from the world class research group namely Les Renardieres Group.
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| 9. |
- Arevalo, Liliana, et al.
(author)
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On the interception of lightning flashes by power transmission lines
- 2011
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In: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 69:3, s. 220-227
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Journal article (peer-reviewed)abstract
- The design of the lightning protection system LPS of transmission lines is based on the well knownelectro-geometrical model. The electro-geometrical model assumes that the first point on a powertransmission line that will come within striking distance of the tip of a down-coming stepped leaderchannel is the strike point of the lightning flash. The model neglects almost all of the physics associatedwith the lightning attachment.Nowadays, as it is possible to use modern hardware and software tools and several different numericalmethods, it is feasible to apply the physics of the discharge process to the study of lightning attachment.Such models take into account the movement of the downward and the resulting upward leaders fromdifferent points on the structures under consideration.In this paper, a procedure based on lightning physics was used to analyze the lightning attachmentphenomena in EHV transmission lines of 230 kV and 500 kV and the results were compared with thepredictions of the electro-geometrical method.
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| 10. |
- Arevalo, Liliana, et al.
(author)
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'The mesh method' in lightning protection standards - Revisited
- 2010
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In: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 68:4, s. 311-314
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Journal article (peer-reviewed)abstract
- At present the design of the Lightning protection systems (LPS) for structures as stipulated in standards is based on the electro - geometrical method, which was initially used to protect power lines from lightning. A derivative of the electro-geometrical method is the rolling sphere method. This method together, with the protection angle method and mesh method are used almost in all lightning standards as the measure in installing the lightning protection systems of grounded structures. In the mesh method, the dimension of the cell size in different levels of protection is determined using the rolling sphere method. Since the rolling sphere method does not take into account the physics of the lightning attachment process there is a need to evaluate the validity of the stipulated value in standards of the minimum lightning current that can penetrate through the mesh in different levels of protection. In this paper, meshes of different sizes as stipulated in the lightning protection standards were tested for their ability to intercept lightning flashes using a lightning attachment model that takes into account the physics of connecting leaders on. The results are in reasonable agreement with the specifications given in the lightning protection standards.
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