Physics of dielectric surface flashover at atmospheric pressures



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Texas Tech University


The limits of the application of dc, ac, or pulsed high voltage are determined by breakdown along insulators or insulating support structures. It is of major technical importance to predict breakdown voltages for given structures, with parameters such as geometry, material, and temporal characteristics of the applied voltage. The impact of atmospheric conditions such as humidity, pressure, temperature, and types of gas present is also important. In order to determine the processes involved in surface flashover, the test setup is designed to produce and closely monitor breakdowns across various gap distances and insulator geometries at atmospheric conditions with varying humidity. Current, voltage, luminosity, and optical emission spectra are measured with nanosecond to sub-nanosecond resolution. Spatially and temporally resolved light emission data is also collected.

Results obtained from the light emission data show that a short light emission pulse is first detected at the cathode, a result of electron emission at the cathode. Approximately 100 ns later, significantly more light is detected at the anode when the electron avalanche strikes it. Finally, 50ns later, light is detected at the center of the gap, as the streamer reaches the cathode and the gap closes. The fast imaging data shows a distinct trend for the spark in air to closely follow the surface even if a strong normal electrical field component is present. This tendency is lacking in the presence of gas such as nitrogen, where the spark develops and remains away from the surface. Finally, the breakdown voltage is shown to decrease significantly with an increase in humidity.



Dielectric measurements, Electrons -- Emission, Breakdown voltage -- Measurement -- Methodology