Role of air bubbles in the breakdown of flowing transformer oil

Zhang, Yongze; Tao, Xiantao; Pan, Cheng; Tang, Ju

doi:10.1109/tdei.2020.008995

Cited by 22 publications

(5 citation statements)

References 24 publications

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“…35 On the other hand, the leakage current causes local heat accumulation, leading to local temperature rise and vaporization of LNG, thus generating a certain number of bubbles between the two electrodes. 36 Meanwhile, the ionization process 37 of LNG molecules could produce gas and bubbles. The bubble is charged like a capacitor.…”

Section: Experimental Results Analysis and Discussionmentioning

confidence: 99%

“…The positive charge bombardment causes the sharp temperature rise of the cathode, which will strengthen the cathode Schottky effect and generate more electrons from the cathode . On the other hand, the leakage current causes local heat accumulation, leading to local temperature rise and vaporization of LNG, thus generating a certain number of bubbles between the two electrodes . Meanwhile, the ionization process of LNG molecules could produce gas and bubbles.…”

Section: Experimental Results Analysis and Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Liquefied Natural Gas for Superconducting Energy Pipelines: A Feasibility Study on Electrical Insulation

et al. 2021

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A superconducting energy pipeline is an integrated system for fuel delivery and power transmission. In the energy pipeline, direct current (DC) power is carried by superconducting tapes with almost no loss. Moreover, liquefied natural gas (LNG) is used not only as one kind of clean energy but also as a cooling medium. However, the lack of data on the electrical insulation characteristics of LNG (especially the resistance to breakdown and flashover) restricts the development of a superconducting energy pipeline. Therefore, this paper focuses on solving a series of problems (such as gas tightness, overpressure, and high voltage) in LNG insulation testing, obtaining the electrical failure data of multicomponent LNG, and analyzing the behavior of electric breakdown and flashover in LNG. The test results show that LNG as a dielectric cooling medium has remarkable performance in withstand voltage to replace the liquid nitrogen/liquid tetrafluoromethane (LN2/LCF4) binary mixtures. The research could offer key technical support for the superconducting energy pipeline and also provide a reference for the study of electrical properties on other cryogenic fuels.

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Section: Experimental Results Analysis and Discussionmentioning

confidence: 99%

Section: Experimental Results Analysis and Discussionmentioning

confidence: 99%

Liquefied Natural Gas for Superconducting Energy Pipelines: A Feasibility Study on Electrical Insulation

et al. 2021

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“…Photographing the bubble positions over time in a horizontal oil pipeline allows one to analyze how temperature and applied voltage affect the trajectory of bubbles in horizontal oil pipelines. The results show that the movement of bubbles is divided into two phases: a rising phase and a horizontal phase [17,18]. However, these studies assume a uniform electric field when discussing bubble migration.…”

Section: Introductionmentioning

confidence: 99%

The Generation and Migration of Bubbles in Oil-Pressboard Insulation Needle-Plate System

Liu

Xue

et al. 2022

IEEE Trans. Dielect. Electr. Insul.

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Bubbles in transformer oil can easily lead to partial discharge, which can deteriorate the transformer oil and even breakdown the transformer insulation. To clarify the migration process and the characteristics of bubbles generated in an oilimmersed power transformer exposed to an extremely uneven electric field, we experimentally monitor these phenomena under an extremely nonuniform AC electric field and numerically simulate the migration distance and the migration speed of bubbles with different initial positions and sizes. The results show that the streamer discharge channel formed by a partial discharge in oil is gasified into a bubble channel. After it collides with the surface of the pressboard, its morphology is transformed into approximately spherical bubbles due to the surface tension of the gas-liquid interface. After bubbles are generated in the oil, they move away from areas with a strong electric field due to the electric-field force and gradually approach the oil surface due to the buoyancy force. The experimental results are consistent with the simulation results, which verify the rationality of the simulation model.

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“…Regarding the study of PD characteristics under bubble defects, H. Shiota et al [13] studied the behavior of bubbles in oil and found that PD can easily occur in a large bubble, which generates more bubbles. Later, Y. Zhang et al [14] investigated the relationship between the bubble dynamics and the evolution of electrical signals before the breakdown of oil medium and the oil flow rate. It was found that the breakdown of bubbles was closely related to the change in bubble shape.…”

Section: Introductionmentioning

confidence: 99%

PD characteristics and deterioration mechanism of oil-impregnated pressboard with bubble defect

Yang,

Zhao,

LIU

et al. 2023

Preprint

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The bubbles are typical defects of oil-paper insulation systems, and partial discharge (PD) initiated by them can significantly degrade the insulating performance of oil-paper insulation, which is a great threat to the insulation state of power transformers. However, the evolution process of bubble PD is less studied, and the deterioration relationship between bubble PD and pressboard insulation is still unclear. In this paper, the evolution characteristics of PD and breakdown of oil-impregnated pressboard under bubble defects are studied. The results show that bubble PD inception voltage (PDIV) and breakdown voltage (BV) are not only related to bubble size, but also affected by oil temperature. As the oil temperature increases, the bubble PDIV and BV tend to decrease and then increase. Continuous observations of the bubble radius and gas composition under the effect of PD show that the evolution of the bubble PD is attributed to the change in the gas composition inside the bubble. Then, the bubble deformation characteristics under the influence of electric field were analyzed, and it was found that the bubbles were stretched along the direction of electric field and deformed pulsatingly at a frequency of 100 Hz. Finally, the microscopic morphology, elemental content and distribution of oil-impregnated pressboard under different damage states were analyzed by scanning electron microscopy (SEM) and X-ray energy spectrometry (EDS), and the microscopic mechanisms of bubble deformation and insulation failure were discussed. This work contributes to the understanding of the mechanism of pressboard insulation failure due to bubble defects and provides a reference for risk assessment of power transformers.

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Role of air bubbles in the breakdown of flowing transformer oil

Cited by 22 publications

References 24 publications

Liquefied Natural Gas for Superconducting Energy Pipelines: A Feasibility Study on Electrical Insulation

Liquefied Natural Gas for Superconducting Energy Pipelines: A Feasibility Study on Electrical Insulation

The Generation and Migration of Bubbles in Oil-Pressboard Insulation Needle-Plate System

PD characteristics and deterioration mechanism of oil-impregnated pressboard with bubble defect

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