Breakdown of liquid dielectrics

Abstract

A study was made of electrical breakdown of a liquid (hexachlorodiphenyl) the viscosity of which is very dependent on temperature. It is shown that in uniform fields breakdown results from formation and growth of a vapour bubble in the liquid. This was established by direct microscopic observations of the ‘breakdown event’ at room temperature and by measurements of times to breakdown as the viscosity was changed by five orders of magnitude between room temperature and 56.5 °C. When the time of voltage application is too short for the vapour bubble to grow to its critical size then the breakdown strength is higher than that obtained under direct voltages. Under 10/50 μs impulses the breakdown strength of hexachlorodiphenyl at room temperature was 5 MV/cm. It is suggested that vaporization was initiated by development of points of zero pressure in the liquid. Assuming that, in an electric field, development of points of zero pressure resulted from the presence of submicroscopic particle impurities in the liquid, a simple expression was derived for the onset of vaporization. It is shown that this expression gives good predictions for the known dependences of breakdown strength of n -hexane on both temperature and pressure and for the variation of breakdown strength of aliphatic hydrocarbons with molecular weight. It is further shown that the time required for a vapour bubble in n -hexane to grow to the size at which breakdown occurs is comparable with the experimentally measured formative time lag.

Effects of Concentration of Nanoscale Tin-Doped Indium Oxide on Electrical Breakdown of High-Resistance Liquid Crystal

“…Since it is considered that the viscosity of LC is usually on the order of 100 mP, 12) the time lag of breakdown for the doped LC is considered to be within a few msec. 13) Let us consider nano-ITO spherical particles of radius r and high permittivity " suspended in dielectric LC of permittivity " 0 under an external electric field E. The impurity particles will become polarized, and it has been shown that the force acting on them in a nonuniform field is given by 9,10)…”

Can a Century Old Experiment Reveal Hidden Properties of Water?

“…Pohl [100] as well as Parmar and Jalaluddin [101] assumed that the dielectrophoretic forces result in electrohydrodynamic motion producing non-uniformity in the applied electric field. The pumping action of strong divergent electric fields [102] and the electroconvection effects [103] have been explained as due to strong electric stresses on liquids in non-uniform fields. According to Maxwell's treatise on the theory of electricity and magnetism [104] and to the theory of liquid hydrodynamics under electric fields by Landau and Lifshitz [105], there are pressure forces perpendicular and tension forces parallel to the electric field lines.…”

Breakdown Characteristics of Electrical Discharges in High-Density Helium Near the Critical Point

“…We also assume that the gas-like breakdown mechanisms follow the general Townsend theory, and that the liquid-like breakdown can be modeled by a discharge forming a vapor bubble. 22,32) The BV based on these two mechanisms, V N , can be expressed as…”

“…Here, V N1 is the BV based on the Townsend theory, 17) d is the gap length, is the mean free path of electrons, È is the ionization potential, is the secondary Townsend coefficient, A is a coefficient related to the electrode geometry, and B is the coefficient associated with Lorentz's internal field and is expressed by 33) with the relative permittivity " r . V N2 is the BV based on the bubble model, 22,32) C 1 is a fitting coefficient, " 0 is the vacuum permittivity, and s b and r b are the surface tension and the radius of the ''bubble'', respectively. We employed r b ¼ 5 nm, which is a typical radius of a bubble generated due to the negative electron affinity in liquid He, 22) and it was found that V N2 did not change substantially for r b > 0:1 nm.…”

“…In the bubble model, bubbles are formed by local heating due to the applied electric field. 32) In contrast, near the CP, no energy may be required for bubble formation, because low-density regions, which are intrinsic in the structure of density-fluctuating fluids, may act as bubbles. Therefore, we conclude that the BV near the CP becomes relatively low due to such intrinsic bubbles.…”