There are no nanodroplets of water in wet oil-impregnated pressboard

Kosmulski, Marek

doi:10.1007/s10570-021-03855-1

Cited by 2 publications

(3 citation statements)

References 6 publications

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“…The variations in the activation energies of the DC conductivity of the pressboardinsulating oil-water composite with the values for UPW and with UPW+ NaCl exclude the possibility of conductivity through liquid water containing high contents of inorganic salt ions in the composite, a model of which was proposed in [44].…”

Section: Dielectric Permittivity and Dielectric Relaxation Of Moist P...mentioning

confidence: 99%

“…The constant current conductivity model proposed in [44] assumes that the conductivity of the pressboard-insulating oil-water composite is determined by that of liquid water with high concentrations of inorganic salt ions. Hence, the model completely contradicts the experimental results of conductivity, permittivity and dielectric relaxation of the composite.…”

Section: Dielectric Permittivity and Dielectric Relaxation Of Moist P...mentioning

confidence: 99%

“…Recently, it has been reported [44] that the DC conductivity of the composite was caused by the presence of liquid water containing high concentrations of inorganic salt ions.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of the Influence of Insulation Moisture during Long-Term Exploitation of Transformers on Their Reliability as Determined by Alternating Current Electrical Parameters

Zukowski,

Kierczynski,

Rogalski

et al. 2024

Energies

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This paper presents the results of the study of the direct current (DC) and alternating current (AC) electrical properties of an electrical pressboard–bio-insulating oil–water composite in a wide range of water content and temperatures used in electric power transformers. These parameters allow the level of insulation reliability to be determined after many years of operation of power transformers. To analyse the experimental results, a model of the DC and AC conductivities of nanocomposites based on the quantum-mechanical phenomenon of electron tunnelling was used. It was found that in a low-frequency region, the conductivities of AC and DC and their activation energy are equal. The relaxation times of AC conductivity and permittivity are also equal. It was found that the dependence of the DC conductivity on the distance between water molecules is an exponential function. On the basis of the model of conductivity by electron tunnelling between potential wells, the average number of water molecules in a nanodroplet, located in a composite of electrical pressboard–bio-insulating oil–moisture was determined to be (126 ± 20). It was found that the measured dependencies of DC and AC conductivity, permeability and dielectric relaxation times are consistent with the results of computer simulations performed on the basis of the model. This study showed that the composite of pressboard impregnated with bio-oil spontaneously transforms through water absorption into a pressboard–bio-oil–water nanocomposite. These will serve as the basis for the application of actual conductivity and dielectric relaxation mechanisms to improve the accuracy of moisture estimation in the solid component of power transformer insulation carried out on the basis of measurements of DC and AC properties. This will improve the operational safety of the transformers, minimise the occurrence of transformer failure and the associated environmental pollution.

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Section: Dielectric Permittivity and Dielectric Relaxation Of Moist P...mentioning

confidence: 99%

Section: Dielectric Permittivity and Dielectric Relaxation Of Moist P...mentioning

confidence: 99%

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Analysis of the Influence of Insulation Moisture during Long-Term Exploitation of Transformers on Their Reliability as Determined by Alternating Current Electrical Parameters

Zukowski,

Kierczynski,

Rogalski

et al. 2024

Energies

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DC and AC Tests of Moisture Electrical Pressboard Impregnated with Mineral Oil or Synthetic Ester—Determination of Water Status in Power Transformer Insulation

et al. 2022

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In this study, the conductivity and permittivity of electrical pressboard—insulating liquid—water composites were investigated, and the electrical properties of the composites and water were analysed comparatively. Mineral oil and synthetic ester were used as insulating liquids. It was found that the presence of water caused an increase in the permeability of the composite in the frequency range below 100 Hz. The value of static permittivity determined by water in the content of 5 wt. % was approximately 15. To obtain this value caused by liquid water, its volume should be approximately five (oil) and four times (ester) higher than its actual content, respectively. The determined values of the activation energy of the DC conductivity of the composites were several times higher than the values of the activation energy of the conductivity of the liquid water. The experimental values of the dielectric relaxation times were many orders of magnitude higher than the dielectric relaxation times of water. This means that the experimental results obtained for the dielectric permittivity, the activation energy of conductivity and the dielectric relaxation times for moisture electrical pressboard impregnated by mineral oil or synthetic ester exclude the possibility of the presence of liquid water in the composites. It was found that the conductivity of the composites increased exponentially with increasing water content. Such dependencies are characteristic of hopping conductivity, caused by the quantum phenomenon of electron tunnelling between nanometre-sized potential wells. As the increase in conductivity is determined by the presence of water in the composites, therefore, the nanometre potential wells were single-water molecules or nanodrops.

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There are no nanodroplets of water in wet oil-impregnated pressboard

Cited by 2 publications

References 6 publications

Analysis of the Influence of Insulation Moisture during Long-Term Exploitation of Transformers on Their Reliability as Determined by Alternating Current Electrical Parameters

Analysis of the Influence of Insulation Moisture during Long-Term Exploitation of Transformers on Their Reliability as Determined by Alternating Current Electrical Parameters

DC and AC Tests of Moisture Electrical Pressboard Impregnated with Mineral Oil or Synthetic Ester—Determination of Water Status in Power Transformer Insulation

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