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Numerical modelling of positive electrical discharges in long air gaps
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Lightning Research Group)ORCID iD: 0000-0002-3094-4120
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This dissertation deals with research on the numerical modelling of electrical discharges in laboratory long air gaps excited with positive switching impulses. It begins with the preliminary work of several scientists during the last decades, making a detailed analysis of different approaches for modelling all the stages in a full discharge. The relations between these models are identified as well as the effect on the outcome when modifying some important input parameters.

The general concept describing the discharge phenomenon usually includes three main elements: the streamer inception, the streamer-to-leader transition and the stable leader propagation. These elements are present in many of the analysed models and the main differences between them are the assumptions and simplifications made by each author at a specific point in their methodologies. The models are usually simplified by assigning experimentally determined values to physical constants pertinent to different stages of the full discharge. These constants are the potential gradient in the leader-corona region to sustain the leader propagation, the charge per unit length along the leader channel which depends on the atmospheric conditions and the voltage impulse wave shape; and the leader propagation velocity, which is closely related to the discharge current. The dissertation includes the results of laboratory work related the study of leaders in long gap discharges, electrical parameters and optical records. By reconstructing the three-dimensional leader propagation for the rod-to-plane configuration, it was possible to study the random tortuous path followed by the leader as it propagates.

One important element included in the discharge modelling is the representation of the leader-corona region in front of the leader tip as it propagates towards the grounded electrode. For the calculation of the net charge available in the leader-corona region, two new methodologies were pro-posed based on the electrostatic potential distribution obtained from a finite element method solver. This allowed the inclusion of more elements representing different parts of the discharge in the simulation domain.

In the final part, all the analysed elements and the new proposed ones were included in a new methodology for the modelling of electrical dis-charges in long air laboratory gaps. The results obtained from this methodology were compared to experimental data. A good agreement was found between the simulation results and the experimental data.

Place, publisher, year, edition, pages
Uppsala, Sweden: Acta Universitatis Upsaliensis, 2016. , 58 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1389
Keyword [en]
high voltage techniques, numerical modeling, electrical discharge in gases, streamer mechanism, leader channel
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
URN: urn:nbn:se:uu:diva-298355ISBN: 978-91-554-9623-4OAI: oai:DiVA.org:uu-298355DiVA: diva2:945865
Public defence
2016-09-15, Polhemsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2016-08-25 Created: 2016-07-04 Last updated: 2016-09-05
List of papers
1. Leader channel models for long air positive electrical discharges
Open this publication in new window or tab >>Leader channel models for long air positive electrical discharges
2015 (English)In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 76, 208-215 p.Article in journal (Refereed) Published
Abstract [en]

The models proposed for the positive long air gap electrical discharge can be considered to be either engineering or physical in their approach. In this work, we make a general review of the available models and use two of them for a comparison with experimental data. Common underlying assumptions were found in most of the models analyzed. The comparison with the experimental data revealed that the results obtained from the models were a good representation of the physical situation when the leader potential distribution and the leader-corona region evolution were described with certain physical assumptions.

Keyword
Leader channel model, Long air gap discharge, Switching impulses
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:uu:diva-262437 (URN)10.1016/j.elstat.2015.05.026 (DOI)000359960000029 ()
Available from: 2015-09-16 Created: 2015-09-15 Last updated: 2016-09-05Bibliographically approved
2. Parameter variation in leader channel models used in long air gap discharge simulation
Open this publication in new window or tab >>Parameter variation in leader channel models used in long air gap discharge simulation
2016 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 139, 32-36 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
High voltage techniques, long gap laboratory gaps, ledaer channel model, leader-corona region
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-297871 (URN)10.1016/j.epsr.2015.11.033 (DOI)000381832800006 ()
Available from: 2016-06-28 Created: 2016-06-28 Last updated: 2016-09-19Bibliographically approved
3. Experimental study of leader tortuosity and velocity in long rod-plane air discharges
Open this publication in new window or tab >>Experimental study of leader tortuosity and velocity in long rod-plane air discharges
Show others...
2016 (English)In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 23, no 2, 806-812 p.Article in journal (Refereed) Published
Abstract [en]

Long air gap electrical discharges are of particular interest among scientists and engineers working on high voltage techniques and lightning research. In the present work we report experimental results obtained while testing a long rod-plane air gap with positive switching-like voltage impulses to study the velocity and tortuous progression of the leader discharge. Voltage and current waveforms were recorded. Two still digital cameras were used to track the leader tortuous path. By using a fast digital camera, the leader temporal evolution was recorded and its propagation velocity was estimated. Three angles were used to describe the leader tortuous progression.

Keyword
Gas discharges, EHV insulation, EHV measurements
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-297874 (URN)10.1109/TDEI.2015.005421 (DOI)000377461500024 ()
Available from: 2016-06-28 Created: 2016-06-28 Last updated: 2016-09-05Bibliographically approved
4. Methodologies for the charge estimation in the leader corona region used in modeling long air gaps underpositive voltage impulses
Open this publication in new window or tab >>Methodologies for the charge estimation in the leader corona region used in modeling long air gaps underpositive voltage impulses
2016 (English)Conference paper (Refereed)
Abstract [en]

Different methodologies have been proposed to represent the physical phenomena taking place in a laboratory electrical breakdown event. The implementation of these methodologies in numerical routines is based in several physical assumptions and a proper calculation of the electrostatic potential distribution. The whole electrical breakdown in air tested with switching-like voltage impulses can be subdivided into three main stages: first, the streamer inception (first corona), then the streamer to leader transition (second corona, leader inception) and the leader propagation. An important element in the last stage is the representation of the leader corona region (streamer region) in front of the leader tip channel as it propagates towards ground. In this paper, with the aid of a finite element method solver to determine the electric potential distribution, two new methodologies to quantify the amount of charge produced in the leader corona region were presented and compared with other ones available in the literature.

Keyword
high voltage testing, leader type discharge, leader corona region
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-297880 (URN)
External cooperation:
Conference
33rd International Conference on Lightning Protection 2016
Available from: 2016-06-28 Created: 2016-06-28 Last updated: 2016-09-05
5. Numerical modeling of long air gaps tested with positive switching impulses
Open this publication in new window or tab >>Numerical modeling of long air gaps tested with positive switching impulses
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The numerical modeling of electrical gas discharges occurring in atmospheric air have been in continuous development during the last decades in different fields like high voltage techniques and lightning protection. Different methodologies have been proposed to represent the different physical phenomena taking place at a single full discharge event, departing both from experimental and theoretical approaches. The implementation of these methodologies in numerical routines combined with the use of a finite element method solver to determine the electric potential distribution, permits creation of models whose predictions closely agree with the real situations, where electrode arrangements might include non-symmetric geometries. In this paper, we present the results obtained using a new version of a simulation methodology that have been evolving during the last years, including new elements like the three-dimensional leader tortuosity from experimental measurements and two new methods for the leader-corona charge estimation. Results from the simulation were compared with experimental records and a good agreement is found between them.

Keyword
Gas discharge, electric breakdown, EHV insulation, UHV insulation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-298356 (URN)
Available from: 2016-07-04 Created: 2016-07-04 Last updated: 2016-09-05Bibliographically approved

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