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Purpose – A model for streamers based on charge transport has been developed by MIT and ABB. The purpose of this paper is to investigate the consequences of changing numerical method from the finite element method (FEM) to the finite volume method (FVM) for simulations using the streamer model. The new solver is also used to extend the simulations to 3D. Design/methodology/approach – The equations from the MIT-ABB streamer model are implemented in OpenFOAM which uses the FVM. Checks of the results are performed including verification of convergence. The solver is then applied to some of the key simulations from the FEM model and results presented. Findings – The results for second mode streamers are confirmed, whereas the results for third mode streamers differ significantly leading to questioning of one hypothesis proposed based on the FEM results. The 3D simulations give consistent results and show a way forward for future simulations. Originality/value – The FVM has not been applied to the model before and led to more confidence in second mode result and revising of third mode results. In addition the new simulation method makes it possible to extend the results to 3D.

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., ABB Corporate Research Center (Vasteras, Sweden)

Flashover formation and expansion mechanisms on the surfaces of different dielectrics immersed in transformer oil have been numerically analyzed. Streamers emanating from a needle electrode tend to transform to surface flashovers if the immersed dielectric permittivity is higher than the liquid permittivity and/or the dielectric interfacial surface cuts the path of the streamer. Perpendicular interface of the immersed dielectric impedes the breakdown by deflecting the streamer and slowing down the surface flashover. The parallel dielectric interface, however, assists the breakdown by regulating the surface flashover velocity to an approximately constant value (∼10 km/s)., IEEE Dielectrics and Electrical Insulation Society

Streamer branching in liquid dielectrics is driven by stochastic and deterministic factors. The presence of stochastic causes of streamer branching such as inhomogeneities inherited from noisy initial states, impurities, or charge carrier density fluctuations is inevitable in any dielectric. A fully three-dimensional streamer model presented in this paper indicates that deterministic origins of branching are intrinsic attributes of streamers, which in some cases make the branching inevitable depending on shape and velocity of the volume charge at the streamer frontier. Specifically, any given inhomogeneous perturbation can result in streamer branching if the volume charge layer at the original streamer head is relatively thin and slow enough. Furthermore, discrete nature of electrons at the leading edge of an ionization front always guarantees the existence of a non-zero inhomogeneous perturbation ahead of the streamer head propagating even in perfectly homogeneous dielectric. Based on the modeling results for streamers propagating in a liquid dielectric, a gauge on the streamer head geometry is introduced that determines whether the branching occurs under particular inhomogeneous circumstances. Estimated number, diameter, and velocity of the born branches agree qualitatively with experimental images of the streamer branching., IEEE Dielectrics and Electrical Insulation Society, IEEE Nuclear and Plasma Sciences Society