Juriy Pachin


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Pachin

First Name

Juriy

ORCID

0000-0002-4429-2725

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2018 - 201952020 - 202310
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Publications 1 - 10 of 15
  • A proposal of new environmental friendly gases for the use in electrical insulation application, II
    Item type: Other Publication
    Egüz, Eda; Hösl, Andreas; Pachin, Juriy; et al. (2019)
  • Novel Environmentally Friendly Insulating Gas Mixtures: Uniform Electric Field Strength and Breakdown Development
    Item type: Doctoral Thesis
    Pachin, Juriy (2022)
    The dominance of sulfur hexafluoride (SF6) in gas insulated switchgear (GIS) is based on the combination of its beneficial physical and chemical properties. However, due to its very high global warming potential (GWP), its replacement with alternative environmental friendly insulating gases is supported in a lot of countries and regions by legislative organs. Consequently first SF6-free solutions are commercially available and in service. However, there is still a discussion about the best candidate as the environmental friendly alternative to replace SF6. In the high voltage laboratory (HVL) of ETH Zurich, a structured investigation is performed to identify potential candidates for SF6-replacement. In a first step, semi-empirical screening methods are used to identify the most interesting molecules. If these substances are available, their swarm parameters describing the initial stage of an electrical discharge in almost ideal experimental conditions are investigated in pulsed Townsend experiments. The influence of more complex physical phenomena in technically relevant application environments, including higher pressures, higher voltages and surface imperfections is investigated in breakdown experiments. These breakdown experiments are performed in uniform electric fields influenced by electrode surface imperfections. Finally, partial discharge phenomena and breakdown development are investigated in the most promising gases by electrical current measurements through an embedded tip. The obtained parameters will provide a basis for further breakdown behavior modeling, significantly reducing testing efforts in research and development for future GIS. The systematic search for potential replacement candidates for SF6 was the subject of various theoretical and practical studies and research topics during the last decade. No candidate was identified as a single substance to replace SF6. As a consequence, the focus shifted to gas mixtures of strongly attaching gases with buffer gases, such as N2, CO2 or air. Accordingly, the testing effort is increasing today, as not only pure substances but also its mixtures have to be investigated, which makes the quantitative prediction methods even more important. Currently, the HVL team is adapting its structured investigation methods to predict the electric strength of gas mixtures. The current thesis contributes to it with the definition of ideal experimental conditions and corresponding breakdown voltages as well as the identification and evaluation of phenomena leading to deviations. These deviations can depend on voltage application methods, electrode surface imperfections, gas properties and mixing ratios, electric field uniformity, statistical nature of the mechanisms involved in breakdown development. To achieve this, the present thesis focuses on the three topics listed below. For each topic, experiments are performed, the results evaluated and conclusions and correlations drawn. First, an experimental frame was defined including setup and method, to perform breakdown voltage measurements based on literature, parameter optimization study in air and SF6, and practical considerations. The influence of the experimental parameters and their definitions were also validated in collaboration with other laboratories to obtain reproducible measurement results. In particular, the availability of seed electrons and the electrode surface structure have a significant influence on the experimental results. In the next step, breakdown voltage measurements were performed with the defined experimental parameters in gas mixtures of C4-FN, C5-FK, and CF3I with CO2, as well as in SF6 and CF3I gas mixtures with HFO1234ze(E). Comparison of breakdown fields with swarm data showed a good agreement. Small deviations in the calculated breakdown fields according to the streamer criterion from the measured breakdown fields were mostly related to experimental conditions such as gas pressure and gas properties leading for example to deposits on the electrode surface. Finally, the breakdown development process in gases subject to a voltage step, starting from a needle tip embedded in a uniform electric field, was investigated. This process based on streamer and streamer to leader transition was observed by current and light signals. The experiments were performed in SF6 mixtures with N2 and CO2 for reference, and in both mixtures of C4-FN/CO2/O2 5 %/90 %/5 % and C5-FK/CO2/O2 5 %/84 %/11 % considered for application. Observations showed that the breakdown mechanism is affected already by a small fraction – a few percent – of a strongly attaching gas at high voltage operational pressure levels. In this case, the breakdown mechanism changes from streamer to leader. Based on these findings, it is expected that the basic design criteria of a GIS will remain unchanged for gases other than SF6.
  • Electrical Breakdown Study in CO2 and CO2-O2 Mixtures in AC, DC and Pulsed Electric Fields at 0.1-1 MPa Pressure
    Item type: Journal Article
    Kumar, Siddharth; Huiskamp, Tom; Pemen, A.J.M.; et al. (2021)
    IEEE Transactions on Dielectrics and Electrical Insulation
    In this paper, the results of the experiments performed on electrical breakdown in CO2 and CO2-O2 mixtures in weakly and strongly non-uniform fields generated with impulse (2/160) µs, AC and DC waveforms are presented. In weakly non-uniform fields, the electrical breakdown field approximately follows 11 kV/(cm bar) when stressed with both AC and DC (positive and negative) waveforms. For positive impulse, the breakdown voltage is higher and the time lag to breakdown is scattered, indicating a lack of starting electrons from CO2 gas. Furthermore, the breakdown strength of CO2 - O2 (10-30)% mixtures is investigated. On application of negative polarity impulse, the breakdown strength is significantly higher than positive impulse in the measured pressure range of 0.3-0.7 MPa in strongly non-uniform fields, contrary to that seen during breakdown in weakly non-uniform fields. Breakdown voltage for negative impulse is further enhanced in a mixture of CO2-O2 (80-20)%.
  • Measurements of the electron swarm parameters of R1225ye(Z) (C3HF5) and its mixtures with N2 and CO2
    Item type: Journal Article
    Pachin, Juriy; Hösl, Andreas; Franck, Christian (2019)
    Journal of Physics D: Applied Physics
  • A proposal of new environmental friendly gases for the use in electrical insulation application
    Item type: Other Publication
    Hösl, Andreas; Pachin, Juriy; Chachereau, Alise; et al. (2018)
  • SF6-Free Gas-Insulated Switchgear: Current Status and Future Trends
    Item type: Journal Article
    Franck, Christian; Chachereau, Alise; Pachin, Juriy (2021)
    IEEE Electrical Insulation Magazine
    This article provides an overview of research on SF6 replacement gases for electric power equipment, of existing SF6-free technologies, and of worldwide developments in legislation to support these new technologies.
  • Discussion on the mechanism leading to positive synergism in SF6 mixtures with HFO1234ze(E)
    Item type: Journal Article
    Egüz, Eda; Pachin, Juriy; Franck, Christian (2022)
    Journal of Physics D: Applied Physics
    The electric strength in HFO1234ze(E)/SF6 mixtures is investigated with swarm and breakdown experiments. The density-reduced critical electric field as well as the breakdown voltage measured with both techniques, are found to be higher than that of the pure gases in mixtures with more than 10% SF6. The underlying mechanism for the observed positive synergy is investigated and the explanation proposed by Hunter and Christophorou (1985 J. Appl. Phys. 57 4377-85) is discussed for this mixture. The pressure-dependent attachment rate is found to increase with SF6 ratio thus satisfying the main requirement of the proposed mechanism in Hunter and Christophorou's study. It appears nevertheless that due to the fast saturation with pressure and low rates in the mixtures, the three-body attachment processes account only for a small increase in the electric strength. An alternative hypothesis is proposed which considers the strong reduction of electron energies via inelastic processes in HFO1234ze(E), and is qualitatively demonstrated based on measurements and simulations.
  • Perfluoro-1,3-dioxolane and Perfluoro-oxetane: promising gases for electrical insulation
    Item type: Journal Article
    Hösl, Andreas; Pachin, Juriy; Chachereau, Alise; et al. (2018)
    Journal of Physics D: Applied Physics
    Perfluorinated cyclic ethers represent an interesting class of molecules to use as dielectric gases for electrical insulation. Measurements of the two compounds 4,4,5,5-Tetrachloro-2,2-difluoro-1,3-dioxolane (c-C3Cl4F2O2, CAS 87075-01-2) and Octafluoro-1,4-dioxane (c-C4F8O2, CAS 32981-22-9) in a Pulsed Townsend Experiment are presented, their ionization and attachment rate coefficients are obtained and their electron attachment cross sections are estimated. Both gases have a high critical electric field strength of about 3.5 and 1.3 times the strength of SF6, respectively, which is presumably due to very high electron attachment cross sections in the range from 2-4 eV. In particular, for c-C3Cl4F2O2 the values appear to be very close to the S-wave scattering limit around 3 eV. Based on these results, we recommend the two analogous compounds Perfluoro-1,3-dioxolane (c-C3F6O2, CAS 21297-65-4) and Perfluoro-oxetane (c-C3F6O, CAS 425-82-1) for further research for the use as insulation and refrigerant gases, since they are chemically comparable and have high vapor pressures.
  • Improved Estimation of Uniform AC Electric Breakdown Field Strength of HFO1234ze(E)
    Item type: Journal Article
    Basu, Devayan; Pachin, Juriy; Egüz, Eda; et al. (2023)
    IEEE Transactions on Dielectrics and Electrical Insulation
    The gas number-density reduced ac electric breakdown field strength (E/N)bd in pure HFO1234ze(E) is investigated from 0.45 to 4 bar with a variable electrode gap distance of 4.88, 10 and 13.32 mm. The aim of the present contribution is to clarify two aspects that are contradictorily reported in the literature. First, the pressure dependence of (E/N)bd and secondly the fact that the first breakdown value in HFO1234ze(E) can be significantly different from subsequent breakdowns in the same arrangement. To clarify these two aspects, particular attention is paid to improving the experimental procedure and considering the role of electrode surface roughness and solid dissociation products caused by the breakdowns. The methodology of experimentation has been improved, compared to standard breakdown experiments: a freshly polished set of electrodes is used for every breakdown measurement and the electrode surface is preconditioned with low-energy breakdowns in CO2 to reduce the possibility of micro-protrusions. Quantitative analysis confirms the improved and reproducible surface characteristics due to the preconditioning. The (E/N)bd values measured this way, show an increase with pressure up to 3 bar in 4.88 mm gap distance. In addition, it is confirmed that HFO1234ze(E) is a non-self-restoring gas. Subsequent breakdowns can be significantly lower than the first one across the measured pressure range and this decrease in breakdown strength increases, as energy input to the breakdown becomes higher.
  • Breakdown Measurement of N2O Mixtures with CO2, N2, 02 in Uniform Electric Fields
    Item type: Journal Article
    Pachin, Juriy; Hösl, Andreas; Franck, Christian; et al. (2021)
    IEEE Transactions on Dielectrics and Electrical Insulation
    Breakdown strength in uniform electric fields of N2O mixtures with CO2, N2, and O2 is measured under AC voltage stress, 300 kPa pressure, and electrode separation of 5 mm. The obtained results show the best synergism of 115% for N2O/CO2 30/70 mixture. For high electric strength of mixtures, a high fraction of N2O is beneficial, but is limited by the oxidizing power. Considering this limit, a N2O/CO249.1/50.9 mixture can be used with the electric strength 135% of synthetic air and 45% of SF6, respectively.
Publications 1 - 10 of 15