Influence of vapor bubbles initiated by steady heating on the breakdown of liquid nitrogen

Study on dynamics of the bubble in transformer oil under non‐uniform electric field

“…The forces on a bubble in liquid are described in literatures [5][6][7][8]25]. Under the non-uniform field, for the incompressible fluid, there are three main forces acting on a spherical bubble, which are electrodynamic force, drag force and buoyancy, respectively.…”

“…Later, the thermal bubble deformation is observed by Hara et al [4] in liquid nitrogen and helium with pulse voltages of a rise time from 1 μs to 300 ms. Their experiments show that under the pulse voltages of different rise time, the bubble in the gap may exhibit spherical, cylindrical or elongated bubbles to form a bubble bridge. Then numerous studies have been devoted to the motion of a bubble immersed in the bulk of the liquid nitrogen submitted to a uniform or non-uniform electric field [5][6][7][8], and the results reveal that different voltages and electrodes impact the characteristics of bubble motion. In [9], it deals with the dynamics of a bubble initiated in the vicinity of a sharp electrode in a dielectric liquid gap submitted to an electric field and to the conditions leading to the generation of a streamer at the gas-liquid interface.…”

AC breakdown voltage of thermal bubble induced two-phase flow condition of inflammable fluorocarbon by self-heating electrode

“…T.P.Hong found a divergence between the BDV test result and the predicted value of liquid nitrogen. However, an estimated increase of gas temperature could explain the reduction of the measured value if taking into account the heat power in the electrode [6].…”

“…However, the bubbles in the experimental models in previous literatures are all generated by auxiliary heater and then introduced into the electrode gap, instead of the electrode heating the liquid by itself [1][2][3][4][5][6]. Hence It is doubted that if the test methods above displayed the actual working condition precisely because the electrodes don't generate bubbles by self-heating, which is not the exactly situation occurring in the windings of transformers or superconducting apparatuses.…”

Study of Turn-to-Turn Electrical Breakdown for Superconducting Fault Current Limiter Applications

“…Although breakdown phenomena in LN2 have been studied for a long time [4] - [6], their specificities are not all well known. In particular, the breakdown voltage of LN2 is expected to be severely reduced during a quench, due to the intense heating leading to the appearance of vapor bubbles in LN2 [7] - [9] . The experimental setup is designed to reproduce the particular thermal and insulating features of a r-SCFCL occurring during a quench.…”