Analysis of the Emitted Frequency Spectra of Breakdowns in SF6 Gas as well as in Alternative Insulating Gases for Gas Insulated Systems

Due to their high current steepness, dielectric breakdowns in gaseous insulation emit electromagnetic interferences, which may disturb or even destroy electronic measuring equipment when performing breakdown tests in a laboratory. In order to analyze the emitted frequency spectra of electric breakdowns in SF6 gas as well as in alternative insulating gas mixtures, a large number of single gas breakdown tests was performed in a test vessel, and the emitted frequency spectra were measured with an antenna and a signal and spectrum analyzer. Several parameters were examined, such as gas pressure, breakdown voltage, gap distance, homogeneity and the distance between the antenna and the test vessel. With regard to the insulating gas mixture, there was no visible impact on the emitted frequency spectra. However, it could be observed that a smaller gap distance and a higher breakdown voltage, thus a higher electric field strength, lead to both higher signal amplitudes and higher maximum frequencies. Likewise, a slightly inhomogeneous electrode arrangement results in higher maximum electric field strengths and, therefore, to higher amplitudes and higher maximum frequencies than a homogeneous electrode arrangement of the same parameters.