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Streamer and breakdown behavior of transformer oil under impulse voltage are investigated with experimental observations and simulation. The optical observation by using Intensified Charge-coupled Device (ICCD) fast snapshot technique indicates that streamer channel branching is of a stochastic nature. The 2-D axially symmetric modeling based on hydrodynamic drift-diffusion model is employed to depict the streamer dynamics of transformer oil. The experimental and simulation results reveal that bushy negative streamer requires higher excitation than filamentary positive streamer. Positive streamer travels faster than negative streamer from experimental estimation. [ABSTRACT FROM PUBLISHER]

Analyses of unipolar charge transport phenomena in series, two-region composite dielectric systems are presented for planar, coaxial cylindrical, and concentric spherical electrode geometries. Space charge limited condition is applied at the charge emitting electrode for steady state and transient. Method of characteristics is used to convert the governing partial differential equations into a set of ordinary differential equations that allow analytical solutions as functions of time and space for volume and interfacial surface charge densities, charge trajectories, electric field intensity, and voltage drop across the electrodes. Solutions given in this paper can be used in design of high-voltage capacitors, pulsed-power transmission lines, and other apparatus. These solutions have also been used as a way of gaining confidence in the correctness and accuracy of our charge transport and prebreakdown models in two-phase insulation systems. [ABSTRACT FROM PUBLISHER]

Theoretical images of streamers, revealing the mechanisms behind impulse breakdown in liquid dielectrics, are presented. Streamers lead to electrical breakdown by forming paths, capable of carrying large current amplitudes between electrodes. Breakdown delays and terminal currents are calculated for various electrode geometries (40 μm needle and 6.35 mm sphere) and gap distances (up to 10 mm). Modeling results indicate that the breakdown in needle-needle electrodes requires higher impulse voltage amplitudes than in needle-sphere electrodes for the same gap distances. Streamers in needle-sphere geometries are about 50% thicker than streamers propagating in needle-needle geometries under similar impulse voltage amplitudes. [ABSTRACT FROM AUTHOR]

An electrothermal hydrodynamic model is presented to evaluate effects of the applied lightning impulse voltage parameters such as polarity, magnitude, and rise time on the initiation and propagation of the streamers formed in an IEC defined needle-sphere electrode geometry filled with transformer oil. Instantaneous velocity, column diameter, head curvature, maximum electric field, and the volume charge density have been investigated as the main characteristics of the streamer. Modeling results indicate that greater applied voltage peak amplitudes form streamers with higher velocity, greater head curvatures, and thicker columns. The bushy negative streamers usually initiate at almost twice the applied voltage magnitude and propagate slower than filamentary positive streamers. Results also show that in transformer oil at the same impulse voltage peak amplitude, shorter rise times create thicker positive and negative streamers. [ABSTRACT FROM PUBLISHER]

Subnanosecond breakdown of low-pressure gaseous spark gaps has been investigated by using a combined modeling of the volume discharge in gas and the electron emission at the electrodes. Simulation results predict minimum breakdown delays of about 400 ps for the geometries considered in this paper. These results are in good accordance with the measurements. [ABSTRACT FROM AUTHOR]