Koch, Myriam (2015)
Prediction of Breakdown Voltages in Novel Gases for High Voltage Insulation.
ETH Zürich
doi: 10.3929/ethz-a-010411940
Dissertation, Bibliographie
Kurzbeschreibung (Abstract)
Sulphur hexafluoride (SF6) is an important insulation medium for high voltage equipment due to its superior insulation properties. SF6 is widely used in gas insulated switchgear. However, the gas also has a very high global warming potential and the content of SF6 in the atmosphere is constantly increasing. Further, due to the worldwide increasing demand for electric power the number of installations containing SF6 as insulation medium is expected to grow. Therefore, an alternative insulation gas with similar electric properties but substantially less environmental impact would be preferable to substitute SF6. The traditional search for new insulation gases is done with classical breakdown experiments. They have to be carefully executed for different field configurations over a wide pressure range and for all standard voltage waveforms. This is a time consuming procedure. As an alternative for the investigation of a large group of candidate gases within a reasonable time horizon, recently a three step approach was developed. This approach comprises a quantumchemical screening of interesting molecules, an investigation of the swarm parameters of selected gases and the prediction of the breakdown behaviour for technical relevant geometries of the best candidates. The aim of the thesis at hand is to provide a prediction method for the latter step. In the literature a model for SF6 is described to calculate the breakdown voltages in arbitrary electrode configurations and under standard voltage waveforms based on the stepped leader model. As input parameters, results from swarm experiments, i.e. the critical field strength and the effective ionization coefficient, thermodynamic properties and results from time lag measurements in a principal setup are sufficient. Those parameters can be accessed more easily than e.g. a full set of collisional cross sections which is required for most of the other available simulation models. Before the investigation of different gases the model was crosschecked with own measurements in SF6. For the application to other electron attaching gases than SF6, it was necessary to develop a method to calculate the thermodynamic parameters of the gases and to derive the temperature dependence of those parameters. Experiments in a principal setup provide an estimation of the initial streamer radius and parameters for the description of the lower limit of the statistical time lags. Furthermore, a new method for the exact determination of the partial discharge inception voltage, providing start electrons by short X-ray pulses, was developed. The strongly attaching gas octafluoropropane (C3F8) and the less attaching gas tetrafluoromethane (CF4) were chosen for the validation of the prediction method. Both gases are well investigated and therefore in the literature many contributions are available for comparison. The investigations of C3F8 show that with the model it is possible to describe the partial discharge behaviour, the lowest breakdown voltages and the upper voltage limit for delayed breakdowns of the gas. For CF4 additionally the breakdown voltages for homogeneous, weakly inhomogeneous and strongly inhomogeneous field configurations were calculated which showed good agreement with literature data. These results give strong evidence that the model can be used for the prediction of the breakdown behaviour of attaching gases. Based on these findings the hydrofluoroolefin HFO1234ze was investigated which is only very recently discussed for high voltage insulation purposes. From swarm parameter measurements it is known that the gas is strongly attaching but exhibits a very pronounced pressure dependence of the critical field strength. Nevertheless, the partial discharge behaviour and the breakdown limits of the measurements in the principal setup can be well modelled. The breakdown voltages were predicted for a homogeneous field with substantial surface roughness and for a strongly inhomogeneous field for alternating and lightning impulse voltages. Classical breakdown measurements were performed for comparison. For this novel gas a very good agreement was achieved as well. Thus, the thesis provides a method for the prediction of breakdown voltages of arbitrary field configurations under standard voltage waveforms for gases with electron attaching properties. With this further gases can be characterized for the usage as high voltage insulation media.
Typ des Eintrags: | Dissertation | ||||
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Erschienen: | 2015 | ||||
Autor(en): | Koch, Myriam | ||||
Art des Eintrags: | Bibliographie | ||||
Titel: | Prediction of Breakdown Voltages in Novel Gases for High Voltage Insulation | ||||
Sprache: | Englisch | ||||
Referenten: | Franck, Prof. Christian M. ; Kindersberger, Prof. Josef | ||||
Publikationsjahr: | 2015 | ||||
Ort: | Switzerland | ||||
Reihe: | Dissertationen ETH | ||||
Band einer Reihe: | 22558 | ||||
DOI: | 10.3929/ethz-a-010411940 | ||||
Kurzbeschreibung (Abstract): | Sulphur hexafluoride (SF6) is an important insulation medium for high voltage equipment due to its superior insulation properties. SF6 is widely used in gas insulated switchgear. However, the gas also has a very high global warming potential and the content of SF6 in the atmosphere is constantly increasing. Further, due to the worldwide increasing demand for electric power the number of installations containing SF6 as insulation medium is expected to grow. Therefore, an alternative insulation gas with similar electric properties but substantially less environmental impact would be preferable to substitute SF6. The traditional search for new insulation gases is done with classical breakdown experiments. They have to be carefully executed for different field configurations over a wide pressure range and for all standard voltage waveforms. This is a time consuming procedure. As an alternative for the investigation of a large group of candidate gases within a reasonable time horizon, recently a three step approach was developed. This approach comprises a quantumchemical screening of interesting molecules, an investigation of the swarm parameters of selected gases and the prediction of the breakdown behaviour for technical relevant geometries of the best candidates. The aim of the thesis at hand is to provide a prediction method for the latter step. In the literature a model for SF6 is described to calculate the breakdown voltages in arbitrary electrode configurations and under standard voltage waveforms based on the stepped leader model. As input parameters, results from swarm experiments, i.e. the critical field strength and the effective ionization coefficient, thermodynamic properties and results from time lag measurements in a principal setup are sufficient. Those parameters can be accessed more easily than e.g. a full set of collisional cross sections which is required for most of the other available simulation models. Before the investigation of different gases the model was crosschecked with own measurements in SF6. For the application to other electron attaching gases than SF6, it was necessary to develop a method to calculate the thermodynamic parameters of the gases and to derive the temperature dependence of those parameters. Experiments in a principal setup provide an estimation of the initial streamer radius and parameters for the description of the lower limit of the statistical time lags. Furthermore, a new method for the exact determination of the partial discharge inception voltage, providing start electrons by short X-ray pulses, was developed. The strongly attaching gas octafluoropropane (C3F8) and the less attaching gas tetrafluoromethane (CF4) were chosen for the validation of the prediction method. Both gases are well investigated and therefore in the literature many contributions are available for comparison. The investigations of C3F8 show that with the model it is possible to describe the partial discharge behaviour, the lowest breakdown voltages and the upper voltage limit for delayed breakdowns of the gas. For CF4 additionally the breakdown voltages for homogeneous, weakly inhomogeneous and strongly inhomogeneous field configurations were calculated which showed good agreement with literature data. These results give strong evidence that the model can be used for the prediction of the breakdown behaviour of attaching gases. Based on these findings the hydrofluoroolefin HFO1234ze was investigated which is only very recently discussed for high voltage insulation purposes. From swarm parameter measurements it is known that the gas is strongly attaching but exhibits a very pronounced pressure dependence of the critical field strength. Nevertheless, the partial discharge behaviour and the breakdown limits of the measurements in the principal setup can be well modelled. The breakdown voltages were predicted for a homogeneous field with substantial surface roughness and for a strongly inhomogeneous field for alternating and lightning impulse voltages. Classical breakdown measurements were performed for comparison. For this novel gas a very good agreement was achieved as well. Thus, the thesis provides a method for the prediction of breakdown voltages of arbitrary field configurations under standard voltage waveforms for gases with electron attaching properties. With this further gases can be characterized for the usage as high voltage insulation media. |
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Fachbereich(e)/-gebiet(e): | 18 Fachbereich Elektrotechnik und Informationstechnik 18 Fachbereich Elektrotechnik und Informationstechnik > Institut für Elektrische Energiesysteme > Hochspannungstechnik 18 Fachbereich Elektrotechnik und Informationstechnik > Institut für Elektrische Energiesysteme |
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Hinterlegungsdatum: | 05 Mär 2024 14:39 | ||||
Letzte Änderung: | 05 Mär 2024 14:39 | ||||
PPN: | |||||
Referenten: | Franck, Prof. Christian M. ; Kindersberger, Prof. Josef | ||||
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