On the measurement of the conductivity of highly insulating liquids

Tobazéon, R.; Filippini, J.C.; Marteau, C.

doi:10.1109/94.368663

Cited by 46 publications

(14 citation statements)

References 2 publications

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“…The nature of streamers has been investigated for decades [1][2][3][4][5][6][7][8][9][10][11][12][13][14], but is still not well understood. For positive streamers in non-polar liquids, it is common to define four distinct modes of propagation, mainly characterized by their speed [2,15].…”

Section: Introduction To Streamersmentioning

confidence: 99%

Simulation model for the propagation of second mode streamers in dielectric liquids using the Townsend-Meek criterion

et al. 2018

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A simulation model for second mode positive streamers in dielectric liquids is presented. Initiation and propagation is modeled by an electron-avalanche mechanism and the Townsend-Meek criterion. The electric breakdown is simulated in a point-plane gap, using cyclohexane as a model liquid. Electrons move in a Laplacian electric field arising from the electrodes and streamer structure, and turn into electron avalanches in high-field regions. The Townsend-Meek criterion determines when an avalanche is regarded as a part of the streamer structure. The results show that an avalanche-driven breakdown is possible, however, the inception voltage is relatively high. Parameter variations are included to investigate how the parameter values affect the model. visible light [3], re-illuminations, from one or more of its branches. Above the breakdown voltage, streamers may change between the 2nd, the 3rd, and the 4th mode during propagation. There are usually more reilluminations in the 3rd mode than the 2nd mode. The inception of the 4th mode is associated with a drastic increase in speed and fewer, more luminous, branches [2].There are numerous mechanisms that can be involved in the streamer phenomena, the challenge is identifying their importance during initiation and propagation. Applying a potential to a needle can cause charge injection, giving a space-charge limited current [16] causing Joule heating [16], which in turn can cause bubble nucleation [17]. A breakdown in the gas bubble can then propagate the needle potential, and the process may repeat. This is one way to explain 1st mode propagation. Electric fields can also cause electrohydrodynamic flow, which could cause streamer formation through cavitation [18]. Electrostatic cracking has also been proposed as a cavitation mechanism [19]. A main topic of discussion is whether a lowering of the liquid density is needed before charge generation can occur. Electron avalanches are important in gas discharge, but their importance in liquid breakdown is still disputed. In water, strong scattering could prevent electrons from forming avalanches in the liquid phase [20]. Therefore, discharges in micro-bubbles can be important for charge generation [10,14,20]. The same mechanism was also proposed for non-polar liquids [19], however, the relative permittivity is about 80 in water and about 2 in a typical oil, and this difference can prove important since the field enhancement within a bubble in oil is much lower than in water. Contrary to water, there are indications of electron avalanches in non-polar liquids [16,21,22], furthermore, while the initiation and the propagation length of 2nd mode streamers are dependent on the pressure, their propagation velocity is not pressure dependent [16,23]. This implies that the mechanism responsible for propagation occurs in the liquid phase and that the gaseous channel follows as a consequence. In very high electric fields, field-ionization can occur [24,25], and this mechanism has been proposed for the fast 3rd and 4th propagation mode...

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Section: Introduction To Streamersmentioning

confidence: 99%

Simulation model for the propagation of second mode streamers in dielectric liquids using the Townsend-Meek criterion

et al. 2018

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“…The measurement platform is shown in FIGURE 1. The test of oil ion mobility is always measured by DC polarity reversal current [15].…”

Section: A Experimental Setupmentioning

confidence: 99%

“…Equations (13)(14)(15) contain the Poisson's equation and current continuity theorem. The Poisson's equation (13) is used to calculate the electric field of space charges.…”

Section: Charge Transformation Model Under the Electric Fieldmentioning

confidence: 99%

Space Charge Transport Characteristic Considering the Non-Uniform Electric Effect of Ion Mobility

et al. 2020

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Oil-paper insulation is the main insulating medium of converter transformers. Space charge can result in the distortion of electric field in oil-paper insulation, hence it's necessary to analyze the space charge transport characteristic and its influence on the oil-paper insulation. In the paper, the space charge transport characteristic considering the electric field is investigated, and an upstream finite element method is presented to calculate the space charge distribution in oil insulation of converter transformer considering the influence of injection barrier, ion mobility, trapped coefficient and carrier recombination coefficient. Finally, the insulation state of tortuous oil-path is evaluated. Experiments were conducted to analyze the relationship between ion mobility and electric field intensity, the results indicate that the influence of space charge on the electric field intensity in the tortuous oil-path can not be ignored for the design of converter transformer. INDEX TERMS Electric field, ion mobility, space charge, converter transformer, upstream finite element.

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“…voltage dependence conductivity [200,201]. Therefore, the applied voltage should be low enough to avoid charge carrier injection and field enhancement dissociation (<0.1 kV/mm).…”

Section: Selection Of Measurement Voltagementioning

confidence: 99%

“…Therefore, the applied voltage should be low enough to avoid charge carrier injection and field enhancement dissociation (<0.1 kV/mm). Moreover, in order to avoid electrohydrodynamic motion and electroconvection effects, the measuring voltage should be less than 300 V. However, the voltage should be high enough to elude electrochemical polarisation (>1 V) [201]. In addition, when a high field stress is applied for a longer time compared to ion transit time (time taken by an ion to cross the electrode gap), swept out of ionic particles from the bulk may result in lower conductivity.…”

Section: Selection Of Measurement Voltagementioning

confidence: 99%

Condition monitoring of biodegradable oil filled transformer

Mudiyanselage¹,

Bandara²

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Natural and synthetic ester insulating oils have higher fire points and excellent biodegradable characteristics. Therefore, in order to reduce the adverse environmental impact and to improve the fire safety of transformers, there is an increasing demand for natural and synthetic ester insulating liquids as a transformer insulating oil. However, present understanding on ageing behaviour of ester oil-paper composite insulation system and knowledge on application of existing condition monitoring tools for ester based insulation systems are inadequate. This impedes the cost effective and reliable field applications of ester insulating oils, particularly application of natural esters. To reduce this knowledge gap, series of controlled ageing experiments are performed in this research project to provide a better and comprehensive understanding on ageing behaviour of ester oil-paper insulation systems. Furthermore, applicability of existing chemical and electrical based condition monitoring techniques for ester oil-paper insulation systems is systematically investigated in this research project.In this thesis, ageing behaviour of dry pressboard insulation in mineral and three different ester insulating oils under simulated transformer operating environment is investigated. Moreover, the ageing behaviour of natural ester-pressboard composite insulation in moisture rich environment is also compared with that of mineral oil-pressboard system. Degree of polymerisation of pressboard samples measured at different ageing interval is used in this research to determine the ageing condition of pressboard. Moreover, applicability of oil related diagnostic parameters such as concentration of dissolved furanic compounds, acidity value, Dielectric Dissipation Factor (DDF), viscosity and colour to assess the degree of degradation of both ester and mineral insulating oils is thoroughly investigated in this research project. The potential of FTIR (Fourier Transform Infrared spectroscopy) techniques for characterising the degree of degradation of paper insulation is also discussed in this thesis. In addition, this thesis concentrates on characterisation of the charge dynamic in insulating oil through modelling of their dielectric responses.The comparison of gassing behaviour of ester and mineral insulating oils under two different low temperature faults and low energy electric discharge condition is also presented in this thesis.Dissolved Gas Analysis (DGA) results presented in this thesis depicts that faults gases detected in ester and mineral oil samples subjected to a similar fault are akin in type but quantitatively different. The quantity of fault gases produced in two different natural ester oils is also dissimilar.For example, soy-based natural ester produces a large quantity of ethane (C2H6) under low temperature overheating condition than sunflower oil based natural ester. Therefore, this research project investigates the applicability of well-established DGA interpretation schemes namely Duval II | P a g e triangle, IE...

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On the measurement of the conductivity of highly insulating liquids

Cited by 46 publications

References 2 publications

Simulation model for the propagation of second mode streamers in dielectric liquids using the Townsend-Meek criterion

Simulation model for the propagation of second mode streamers in dielectric liquids using the Townsend-Meek criterion

Space Charge Transport Characteristic Considering the Non-Uniform Electric Effect of Ion Mobility

Condition monitoring of biodegradable oil filled transformer

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