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Reference: ISH2015_466

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Time-resolved measurements on thermal parameters of leader discharges using a Mach-Zehnder interferometer



Leader discharge is a main phase of long gap breakdown, characterized by high gas temperature (generally accepted to be above 1500 K). To evaluate the thermal parameters of leader channel, a Mach-Zehnder interferometer was established in our previous work. The diameter, radial distribution of gas density and gas temperature of leader channels can be derived from the interference fringe images. However, only one fringe image was obtained every impulse discharge before. In this paper, improved time-resolved interferometry was applied to the investigation of positive leader discharge produced by IEC standard switching impulse voltages. Thermal expansion process of leader channel was observed and quantitatively studied. Resolving of fringe patterns shows that the typical value of leader diameter is 1 mm to 2.2 mm with an expansion velocity around 11 m/s in the first 50 µs and around 2 m/s or less after 100 µs. Typical gas density at the channel centre is from 8% to 15% of the ambient air, and gas temperature varies from 2000 K to 3500 K. The diameter of the region with temperature higher than 1500 K is around 1 mm. Besides, a one-dimensional thermo-hydrodynamic model was adopted to simulate the parameters evolution of leader discharge. The simulation results show satisfactory consistence with experimental data, which illustrates the validity of the measurements. The time-resolved interferometry presented in this paper provides an experimental approach to quantitative investigation of leader discharge.

File Size: 858,9 KB

Year: 2015

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