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Laser Thomson scattering and Rayleigh scattering methods were applied to investigate the dynamics of laser-induced plasmas in atmospheric air. Laser-induced plasma was generated by a 1064 nm, 200 mJ Nd: YAG laser. Another nanosecond Nd: YAG laser (532 nm, 50 mJ) was used as the probe laser. The temporally and spatially resolved electron number density and temperature distributions of the laser-induced plasma were determined from the Thomson scattering spectra. From 1 μs to 21 μs after plasma generation, the electron number density around the centre of the plasma decreased from 4.96 × 1023m‐3 to approximately 1.1 × 1021m‐3, while the electron temperature dropped from approximately 51,500 K to 6900 K. The plasma images and the measured distribution of the electron number density and temperature indicated the formation of a toroidal structure approximately 18 μs after plasma generation. The Rayleigh scattering results show that the Taylor-Sedov model cannot well describe the early evolution of the shockwave in radial directions.

The pre-charged capacitor method, used in the active current injection circuit breaker in DC system, is an effective approach to realize the current injection. However, in practical applications, the performances of post-arc among different opening speed are still unknown, which have been an obstacle that blocks the design of MV DCCB. To solve this problem, high resolution measuring equipment was used to investigate the performances of vacuum circuit breaker in post-arc period. The experimental results show that the peak value of the post-arc current can be up to 6A and the post-arc current decays to zero within 10μs after current-zero. Besides, with the increase of opening speed, the fluctuation of post-arc charge increases continuously, while the average remains basically unchanged.

Carbon dioxide (CO2) is a promising alternative to sulfur hexafluoride for high-voltage circuit breaker applications. It is important to have a detailed understanding of CO2 arc properties. In this paper, radial temperature distribution of the free burning direct current arc in pure CO2 was investigated. Optical emission spectrometry was applied under different pressures (0.5 atm, 1 atm, and 1.5 atm) and at different axial positions (1 mm, 2 mm, 3 mm above the cathode). Assuming local thermodynamic equilibrium, the Fowler–Milne method was adopted for O I 715.67 nm and O I 777.19 nm in the periphery of the arc, and the single-line method was adopted for C II 657.81 nm near the center of the arc. Radial temperature profiles obtained by these two methods were combined at the position where normal temperature was assigned. The results indicate that near the center of the arc, higher pressure would lead to lower temperature; as the distance from the cathode to the position measured increases, the maximum temperature in the arc center would decrease. In addition, the temperature would decrease more sharply toward the periphery if the central temperature of the arc is higher.