Journal ArticleDOI
Thermal bubble breakdown in liquid nitrogen under nonuniform fields
M. Hara,Zhen-chao Wang,H. Saito +2 more
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In this article, the electrical forces acting on thermally induced bubbles in nonuniform field gaps with/without fins and the correlation between bubble behavior and dielectric characteristics in liquid nitrogen are studied.Abstract:
The electrical forces acting on thermally induced bubbles in nonuniform field gaps with/without fins and the correlation between bubble behavior and dielectric characteristics in liquid nitrogen are studied. The results show that the gradient force and Maxwell stress strongly affect the bubble dynamics and bubble shape in the gap. Especially the pronounced gradient force near the fin tip reduces the growth of bubble there. These electrical forces acting on the bubble result in a lesser effect of thermal bubble on the breakdown voltage if the fins are formed to guide a bubble trapped in the groove from a higher field region to a lower one. >read more
Citations
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Journal ArticleDOI
Electrical insulation characteristics of superconducting power apparatus
M. Hara,Hitoshi Okubo +1 more
TL;DR: In this article, electrical pre-breakdown phenomena and electrical insulating performance of vacuum, gas, solid, and composite insulators under cryogenic operating conditions of superconducting apparatus including the quenching phenomena are discussed.
Journal ArticleDOI
Effect of inhomogeneities on streamer propagation: II. Streamer dynamics in high pressure humid air with bubbles
TL;DR: In this paper, the authors investigated the consequences of random inhomogeneities in the form of low pressure bubbles on the propagation of streamers in high pressure humid air and found that bubbles have larger E/N (electric field/gas number density) than the ambient gas with larger rates of ionization.
Journal ArticleDOI
Thermal bubble motion in liquid nitrogen under nonuniform electric fields
TL;DR: In this paper, the electric field effect on bubble motion as it rises due to buoyancy within applied dc electric fields is quantitatively investigated using a rod-plane gap, and the experimental results show that dc non-uniform electric fields have an obvious effect in bubble behavior; bubbles move closer to the plane electrode away from a higher field region to a lower one, irrespective of electric field direction.
Journal ArticleDOI
Experimental Study on Breakdown Characteristics of Transformer Oil Influenced by Bubbles
TL;DR: In this paper, the breakdown voltage of transformer oil and oil-impregnated pressboard under alternating current (AC) and direct current (DC) voltages were measured in both no bubbles and bubbles.
Journal ArticleDOI
Influence of Bubbles in Pressurized Liquid Nitrogen on the Discharge Behavior in a Homogeneous Electric Field
M. Blaz,Michael Kurrat +1 more
TL;DR: In this paper, the influence of gaseous nitrogen on the discharge behavior in liquid nitrogen is investigated, and the experiments were conducted in pressurized liquid nitrogen with an ambient pressure of 3 and 5 barabs.
References
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Journal ArticleDOI
Thermal-bubble initiated breakdown characteristics of liquid helium and nitrogen at atmospheric pressure
Masanori Hara,T. Kaneko,K. Honda +2 more
TL;DR: In this paper, an experimental study on the DC breakdown characteristics of liquid helium and nitrogen in the presence of thermally created bubbles is presented, and the results show that the bubble shape is affected significantly by the application of an electric field, and that the breakdown voltage depends closely on bubble shape.
Proceedings Article
Thermal-buble initiated breakdown characteristics of liquid helium and nitrogen at atmospheric pressure
Masanori Hara,T. Kaneko,K. Honda +2 more
TL;DR: Experiments show that electric field promotes to form a vapor locking in a gap with a hot spot and in turn the formation of locked vapor produces the serious reduction of breakdown voltage.
Journal ArticleDOI
Breakdown behavior of cryogenic liquids in the presence of thermal bubbles under ramped voltage
TL;DR: In this article, the breakdown process of liquid coolants in the presence of thermal bubbles was classified into three categories depending on the voltage slope: (1) breakdown through a composite insulation system of undeformed bubbles and surrounding cryogenic liquid with fast rising voltage such as the standard lightning impulse voltage; (2) break through a strongly elongated bubble by an electric field with the rise time of milliseconds; and (3) breakdown in a vapor bridge of the gap, formed by growth of a bubble fixed on an electrode with a hot spot, by electric fields rising in approximately 100 ms.
Journal ArticleDOI
Effect of thermally induced bubbles on the electrical breakdown characteristics of liquid nitrogen
TL;DR: In this article, the authors investigated the electrical breakdown characteristics of liquid nitrogen under a simulated quenching condition, i.e. in the presence of thermally induced bubbles and an electrical field with a rise time of 1-30 ms.
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Thermal bubble breakdown in cryogenic liquids under non-uniform fields
M. Hara,Zhen-chao Wang,H. Saito +2 more