Measuring picosecond flashover in pressurized sulfur hexafluoride (SF6)

Abstract

The exceedingly fast speed of breakdown in gas presents numerous challenges for measurement systems. Data integrity and analysis of recorded results are considerably affected by the measurement setup. In efforts to remove the effect of the measuring system and verify observations pertaining to the physical phenomenon of breakdown, two systems are compared. In addition, issues concerning the design, manufacturing and operation of high voltage pressurized spark gaps are discussed. Risetime of voltage collapse is measured in a pressurized SF6 spark gap using D-dot sensors and oscilloscopes with analogue bandwidth ranging from 6 to 30 GHz. Results from a 50 GHz series sampling oscilloscope are also presented. Inter-electrode distance is varied between 0.1 and 0.9 mm and pressure is increased from 1 to 19 bar. Breakdown voltages are measured ranging from c. 10 to 180 kV. Risetime values ranging from 50 to 800 ps and distinct variations in the voltage collapse waveform are observed. Measurements are documented and significant variables affecting the breakdown process and risetime analysis are identified. Risetime dependency to pressure, gap distance and electric field strength are presented using several analysis methods and compared to known theory. Methods to overcome or compensate the identified variables are discussed. Finally, optimal solutions for measurement systems and future research are presented.