Electrical breakdown in dielectric liquids-a short overview

Wedin, Pär

doi:10.1109/mei.2014.6943430

Cited by 54 publications

(39 citation statements)

References 27 publications

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“…Dielectric liquids are widely used for insulation of high power equipment, such as transformers, since liquid insulation has good cooling properties, high electrical withstand strength, and recovers from an electrical discharge within short time [1]. Electric breakdown in liquids is preceded by the formation of a prebreakdown channel called a streamer [2].…”

Section: Introduction To Streamersmentioning

confidence: 99%

“…A partial discharge, a local electric breakdown, changes the electric field distribution, which could cause another local breakdown, and in this way, a streamer may propagate through a liquid. A streamer bridging the gap between two electrodes, for instance an energized part and a grounded part, lowers the electrical withstand strength and may cause a complete electric breakdown, possibly destroying the equipment [1].…”

Section: Introduction To Streamersmentioning

confidence: 99%

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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%

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 molecules comprising the dielectric act as sources of electrons and the electronic properties of the molecules play an important role in streamer initiation and propagation. Many studies have investigated streamer propagation and breakdown in natural esters under high-voltage conditions [10][11][12][13][14][15][16][17]. Propagation tests have shown that streamers propagate faster and further in natural ester than in mineral oil under an equivalent applied electric field.…”

Section: Introductionmentioning

confidence: 99%

Molecular Structure and Electronic Properties of Triolein Molecule under an External Electric Field Related to Streamer Initiation and Propagation

Wang

et al. 2017

Energies

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Natural ester has been widely studied as an alternative dielectric liquid to mineral oil in recent years. Unsaturated triacylglycerol molecules are the main components of natural ester; therefore, in this paper, we investigate the molecular structure and electronic properties of the triolein molecule, an oleic-type triacylglycerol molecule, as a representative component of natural ester oils. The effects of external electric fields at the electric field intensity related to streamer initiation and propagation on the bond lengths, dipole moment, total energy, infrared spectra, and orbital energy of the triolein molecule are investigated using density functional theory (DFT). In addition, the excitation energies, transition wavelengths, and oscillator strengths of the first eight excited states of the triolein molecule under external electric fields are calculated by time-dependent DFT. The results show that the bond lengths, dipole moments, total energy, and infrared spectra change obviously under external electric fields. With increasing external electric field intensity, the energy of the highest occupied molecular orbital increases, and the gap between that and the energy of the lowest unoccupied molecular orbital decreases, which make the molecule susceptible to excitation. The calculations contribute to an understanding of the causes behind the degradation of the insulation properties of natural ester oils.

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“…The mechanism of the breakdown in fluid is different under positive and negative polarities. Under a negative polarity, electrons are injected into the fluid if there is a high electrical field to initiate the streamer (Wedin, 2014;Denat et al, 1988). The interaction between the electrons and the molecules in the fluid will cause joule heating and create gas bubbles.…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, under positive polarity, the source of the electrons is obtained from the ionisation of the fluid molecules themselves (Holtzhausen and Vosloo, 2011). These electrons will accelerate toward the positive electrode and further ionisation of the induced positive charge in the gas channel will cause an electron avalanche and streamer propagation (Holtzhausen and Vosloo, 2011;Wedin, 2014;Chadband, 1980).…”

Section: Introductionmentioning

confidence: 99%

The effect of polarity on the lightning breakdown voltages of palm oil and coconut oil under a non-uniform field for transformers application

Thien

Azis

Jasni

et al. 2016

Industrial Crops and Products

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a b s t r a c tThis paper presents a study of the lightning breakdown voltages of Palm Oil (PO) and Coconut Oil (CO) under a non-uniform field with consideration on the polarity effect at various gap distances. All tests were carried based on a needle-sphere electrode configuration and various gap distances ranging from 2 to 25 mm under positive and negative voltage polarities. Three different testing techniques were used in this study including rising-voltage, up-and-down and multiple-voltage methods. The PO used in this study was Refined, Bleached and Deodorised Palm Oil (RBDPO) Olein. Three different samples of RBDPO and one sample of CO were tested. The Weibull distribution was used as a statistical approach to determine the withstand voltages of all samples at 1% and 50% probabilities for each type of oil. Under positive voltage polarity, it was found that the 50% breakdown voltages of RBDPO and CO were comparable with Mineral Oil (MO) whereby the highest percentage of difference among all gap distances was less than 15%. RBDPO and CO have lower 50% breakdown voltages than MO under a negative lightning impulse for which the highest percentage of difference can be up to 40%.

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Electrical breakdown in dielectric liquids-a short overview

Abstract: The article presents a summary of the current state of knowledge and research related to electrical breakdown in organic dielectric liquids.

Cited by 54 publications

References 27 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

Molecular Structure and Electronic Properties of Triolein Molecule under an External Electric Field Related to Streamer Initiation and Propagation

The effect of polarity on the lightning breakdown voltages of palm oil and coconut oil under a non-uniform field for transformers application

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