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dc.contributor.author
Pachin, Juriy
dc.contributor.supervisor
Franck, Christian
dc.contributor.supervisor
Koch, Myriam
dc.date.accessioned
2022-08-10T07:20:10Z
dc.date.available
2022-08-10T06:03:59Z
dc.date.available
2022-08-10T07:20:10Z
dc.date.issued
2022
dc.identifier.uri
http://hdl.handle.net/20.500.11850/562762
dc.identifier.doi
10.3929/ethz-b-000562762
dc.description.abstract
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.
en_US
dc.format
application/pdf
en_US
dc.language.iso
en
en_US
dc.publisher
ETH Zurich
en_US
dc.rights.uri
http://rightsstatements.org/page/InC-NC/1.0/
dc.subject
GASEOUS INSULATING MATERIALS (ELECTRICAL ENGINEERING)
en_US
dc.subject
SF6 alternatives
en_US
dc.subject
uniform electric strength
en_US
dc.subject
Statistical time lag
en_US
dc.subject
Breakdown development
en_US
dc.subject
Protrusion
en_US
dc.subject
Novel Environmentally Friendly Insulating Gas Mixtures
en_US
dc.title
Novel Environmentally Friendly Insulating Gas Mixtures: Uniform Electric Field Strength and Breakdown Development
en_US
dc.type
Doctoral Thesis
dc.rights.license
In Copyright - Non-Commercial Use Permitted
dc.date.published
2022-08-10
ethz.size
321 p.
en_US
ethz.code.ddc
DDC - DDC::6 - Technology, medicine and applied sciences::621.3 - Electric engineering
en_US
ethz.identifier.diss
28230
en_US
ethz.publication.place
Zurich
en_US
ethz.publication.status
published
en_US
ethz.leitzahl
ETH Zürich::00002 - ETH Zürich::00012 - Lehre und Forschung::00007 - Departemente::02140 - Dep. Inf.technologie und Elektrotechnik / Dep. of Inform.Technol. Electrical Eng.::02632 - Inst. f. El. Energieübertragung u. Hoch. / Power Systems and High Voltage Lab.::03869 - Franck, Christian / Franck, Christian
en_US
ethz.leitzahl.certified
ETH Zürich::00002 - ETH Zürich::00012 - Lehre und Forschung::00007 - Departemente::02140 - Dep. Inf.technologie und Elektrotechnik / Dep. of Inform.Technol. Electrical Eng.::02632 - Inst. f. El. Energieübertragung u. Hoch. / Power Systems and High Voltage Lab.::03869 - Franck, Christian / Franck, Christian
en_US
ethz.date.deposited
2022-08-10T06:04:06Z
ethz.source
FORM
ethz.eth
yes
en_US
ethz.availability
Open access
en_US
ethz.rosetta.installDate
2022-08-10T07:20:20Z
ethz.rosetta.lastUpdated
2022-08-10T07:20:20Z
ethz.rosetta.exportRequired
true
ethz.rosetta.versionExported
true
ethz.COinS
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