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1. Effects of waveform parameters on the breakdown characteristics of OIP subjected to impulse voltages and evaluation method for waveform equivalence.

Author

Sima, Wenxia, Ye, Lian, Sun, Potao, Chen, Qiulin, Zhang, Huangjing, and Chen, Jiaqi

Abstract

The impulse voltage wave invading a transformer is not the double exponential impulse wave (DEIW) specified by the IEC but a non‐standard waveform with oscillation attenuation characteristics, and this fact leads to doubts about the scientificity and optimality of insulation coordination. A key solution for this issue is the establishment of an equivalent relationship between the measured non‐standard impulse voltage wave and the DEIW. In this study, a test platform of multiparameter impulse voltage was set up. Then, the authors obtained the 50% breakdown voltage (U50%) of the oil‐impregnated paper (OIP) for transformer under the bipolar oscillatory attenuated impulse wave (BOAIW) and the DEIW with different waveform parameters. The effects of waveform parameters on the breakdown characteristics of the OIP were finally revealed. On the basis of experimental data and several mathematical methods, the authors established the U50% prediction mathematical models for the OIP under the BOAIW and DEIW. Based on the prediction models and the microfluctuation characteristics of measured overvoltage's waveform parameters, the authors proposed a method for evaluating the waveform equivalence. The characteristics of voltage amplitude and change rate were regarded as the two key factors for the waveform equivalence of this method. [ABSTRACT FROM AUTHOR]

Published
2019
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2. Comparison of AC breakdown characteristics on insulation paper (pressboard) immersed by three‐element mixed insulation oil and mineral oil

Author

Yang Lijun, Chen Xin, Li Jian, Hao Jian, Liao Ruijin, and Feng Dawei

Subjects
Materials science, oil-immersed insulation paper, lcsh:QC501-721, Energy Engineering and Power Technology, Relative permittivity, Field strength, Dielectric, three-element mixed insulation oil, Stack (abstract data type), mixed oil-immersed paper, lcsh:Electricity, medicine, Breakdown voltage, Electrical and Electronic Engineering, Composite material, Mineral oil, oil-gap structure, mineral oil-immersed paper, Water content, moisture content, Pressboard, paper, dielectric thickness, temperature 25.0 degc, breakdown strength, insulation paper, thin insulation paper, breakdown field strength, insulating oils, ac breakdown voltage, oil-immersed pressboard, electric breakdown, thin multilayer insulation paper, ac breakdown characteristics, lcsh:Electrical engineering. Electronics. Nuclear engineering, naphthenic mineral oil, lcsh:TK1-9971, medicine.drug
Abstract

Insulation oil is an important dielectric in power devices, and many studies on mixed insulation oil have been conducted in recent years to improve the performance of insulation oils. To replace mineral oil directly, the authors previously developed a novel three-element mixed insulation oil successfully; the main parameters of which satisfy the IEC 60296-2012 standard for mineral oil. In the present study, the AC breakdown properties of insulation paper (pressboard) immersed by the new mixed oil and naphthenic mineral oil were compared. For both insulation oils, the increase in temperature cannot significantly reduce the breakdown strength of oil-immersed insulation paper (pressboard) at a low moisture content, and the increment of moisture content cannot reduce the breakdown voltage at a low temperature (25°C). The breakdown voltage decreases only when the two factors increase simultaneously. For the mixed and mineral oils, the AC breakdown voltage of oil-immersed paper (pressboard) with different thicknesses has significant difference. The mineral oil has a high breakdown voltage for the thin insulation paper, whereas the mixed oil has a high breakdown voltage when the thickness of the insulation paper (pressboard) exceeds 0.2 mm. This phenomenon is mainly caused by the breakdown field strength that varies with the increase of dielectric thickness and the different change trends of paper (pressboard) immersed with the mixed and the mineral oils. Moreover, the stack of thin multilayer insulation paper enables the mixed oil-immersed paper to have a higher breakdown strength than the mineral oil-immersed paper. For the AC breakdown voltage of oil-immersed pressboard with an oil-gap structure, the mixed oil is comprehensively superior to the mineral oil due to its larger relative permittivity.

Published
2020
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3. The Effect of Fe

Author

Bin, Du, Qian, Liu, Yu, Shi, and Yushun, Zhao

Subjects
Paper, impregnated paper, dielectric loss, Electric Conductivity, Nanotechnology, Particle Size, Magnetite Nanoparticles, relative permittivity, trap depth, Article, breakdown voltage
Abstract

This paper systematically studies the effect of Fe3O4 nanoparticle size on the insulation performance of nanofluid impregnated paper. Three kinds of Fe3O4 nanoparticles with different sizes and their nanofluid impregnated papers were prepared. Environmental scanning electron microscopy (ESEM) and infrared spectroscopy were used to analyze the combination of Fe3O4 nanoparticles and nanofluid impregnated paper. The effect of nanoparticle size on breakdown voltage and several dielectric characteristics, e.g., permittivity, dielectric loss, of the nanofluid impregnated paper were comparatively investigated. Studies show that the Fe3O4 nanoparticles were bound to impregnated paper fibers by O–H bonds, while the relative permittivity and dielectric loss of the nanofluid impregnated papers were increased. Meanwhile, the increase of trap depth, caused by the nanoparticles, can trap the electric charge and improve the breakdown strength. The test results show that the direct current (DC) and alternating current (AC) breakdown voltages of nanofluid impregnated paper increased by 9.1% and 10.0% compared to FR3 nanofluid impregnated paper, respectively.

Published
2020