Increase In Electric Strength Research Articles

Streamers and partial discharges in water

Several types of streamers are considered in the paper, usual streamers, nonelectrode and postbreakdown streamers. Attempts of pulse electrical strength increase with the help of conductive layers and the reasons for unusual streamers appearance are discussed.

A new potential barrier model in epoxy resin nanodielectrics

The dielectric constant and the conductivity of epoxy resin nanocomposites exhibit a lower value at slight filler loading compared with the host epoxy resin. The electrical strength has an increase and presents an optimal value at filler loading of 1 wt%. The interaction zone between the nanoparticles and the polymeric matrix is considered as an independent region. Accordingly, a new potential barrier model is proposed. Based on the model, carriers are restrained in the interaction zone when nanoparticle is in an isolated dispersion, leading to a decrease in both mobility and density of carriers. As a result, the conductivity decrease and the electrical strength increase. The restriction of dipole movement in the interaction zone and the increase of free volume are collectively contributed to the reduction of the dielectric constant. With increasing filler loading, the thickness of the interaction zone extends due to the overlap of the interaction zone, even a conductive path occurs when filler loading exceeds the percolation threshold, leading to a great increase in both mobility and density of carriers. Consequently, the conductivity increase and the electrical strength decrease. The increase of the dielectric constant is chiefly ascribed to the particles.

Problems of Creation of High-Efficient Magnetocumulative Generators. Electric Strength of Helical Magnetocumulative Generators

Helical MCGs have a wide range of output characteristics, and they are frequently used in pulsed-power experiments. The absence of electric breakdowns at compression of a magnetic flux in the generator volume is one of the important factors of stable and efficient operation of fast helical MCGs. This paper considers the problems associated with both a decrease of maximum voltages in the MCG circuit and an increase of electric strength of the generator elements. The direction of possible electric breakdowns, i.e., their localization, is shown experimentally. The influence of shock-compressed air on the electric strength of the device is also presented. The use of solid (film) insulation on the stator windings is important. A value of the magnetic flux losses in the winding insulation is determined experimentally.

Electron-beam sustained CO2 laser operating on CO2 : N2 : H2O mix

Users of high power CO2 lasers may be interested in finding a substitute for expensive He which would provide sufficient efficiency and specific power of laser radiation. In the present work, operating modes of the electron-beam sustained discharge CO2 pulse-periodic laser operating on CO2:N2:H2O mixes were investigated. The research has revealed that at equal energies of radiations the efficiency for CO2:N2:H2O mixes are approximately 25% lower than those for CO2:N2:He mixes. The decrease in efficiency is compensated for by an increase in electric strength of the mixes containing H2O, both in pulse and in pulse-periodic modes.

The influence of coatings and the surface state on the electric strength of vacuum insulated electrodes used with a 50 Hz supply

The electric strength of the vacuum insulation of plane electrodes not subject to surface conditioning was studied with a 50 Hz sinusoidal wave in the range up to 100 kV (peak). The electrodes with rounded-off edges of Rogowski’s profile were made of OFHC copper or aluminium and were of 50 mm diameter. The paper shows the influence of fundamental factors defining the conditions of a vacuum insulation system on its electric strength, such as: the presence of a cobalt–tungsten layer coating the surfaces of copper electrodes, the presence of aluminium oxide layer coating the surfaces of aluminium electrodes, the method of preparing the electrodes surfaces (mechanical polishing or electropolishing), the value of air pressure (within the range of 2 mPa–0.2 Pa) and at a constant value pressure of 0.2 mPa, the length of vacuum gap. Experiments showed an insignificant electric strength increase of unconditioned vacuum insulation systems could be obtained by means of electropolishing copper electrode surfaces instead of mechanical polishing. When copper electrode surfaces were coated with a layer of cobalt–tungsten or cobalt–tungsten–molybdenum deposited by electroplating, the investigated systems showed a 30% increase of electric strength at a pressure of 2 mPa. Aluminium electrodes coated with aluminium oxide showed a 100% increase of electric strength of unconditioned vacuum insulation systems at the same pressure.

Electric strength of vacuum systems with Co-Mo alloy coated Cu electrodes

The paper presents the results of investigations of the electric strength at 50 Hz AC voltage of vacuum insulation systems that were not subjected to conditioning. The experiments have shown that a Co-Mo alloy coating electrolytically deposited on the surface of copper electrodes causes, at the pressure 2 mPa, >25% increase of electric strength of unconditioned vacuum insulation systems. This breakdown strength decreases with increasing gap spacing between the electrodes, and amounts /spl sim/17 kV/mm for systems with Cu electrodes at the electrode gap of 1 mm, and /spl sim/9 kV/mm at a gap of 6 mm. Plane electrodes with rounded-off edges of Rogowski's profile were used in the investigations. The electrodes with 50 mm diameter, were made of OFHC Cu. The paper shows the influence of the value of pressure from /spl sim/1 mPa to 1 Pa and at constant pressure of /spl sim/1 mPa, the length of vacuum gap, and the presence of a Co-Mo alloy layer coating the electrodes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-field conduction and carrier traps in polyethylene copolymerized with various monomers

The electrical breakdown and electrical conduction of ethylene copolymers have been studied. The electric strength of ethylene copolymers containing an optimum content of halogen moieties such as bromophenyl and fluoroethylene groups was found to be higher than that of LDPE over the wide temperature range from −196°C to 90°C. Also, conduction currents in the copolymers were suppressed at high electric fields. X-ray-induced thermally stimulated currents (TSC) revealed that halogen comonomers act as carrier traps with a depth of about 0.4 eV. Consequently, the introduction of comonomer-containing halogen groups into polyethylene suppresses electron acceleration as a result of an increase in trapping and scattering of conduction electrons. This leads to an increase in electric strength which is determined by the electron avalanche breakdown.

ハロゲン含有ポリエチレン共重合体の高電界電気伝導およびキャリヤトラップと絶縁破壊

The electrical breakdown and electrical conduction of ethylene copolymers have been studied. The electric strength of ethylene copolymers containing an optimum content of halogen moieties such as bromophenyl and fluoroethylene groups was found to be higher than that of LDPE over the wide temperature range from −196°C to 90°C. Also, conduction currents in the copolymers were suppressed at high electric fields. X-ray-induced thermally stimulated currents (TSC) revealed that halogen comonomers act as carrier traps with a depth of about 0.4 eV. Consequently, the introduction of comonomer-containing halogen groups into polyethylene suppresses electron acceleration as a result of an increase in trapping and scattering of conduction electrons. This leads to an increase in electric strength which is determined by the electron avalanche breakdown.

Electric strength of moving electrodes in a still and in a moving gas

The influence on the sparking voltage across uniform field electrodes moving in a still gas, air, is considered quantitatively by the development of the effective-gap concept, assuming laminar flow. When the electrodes move in the direction of the ionising electron stream, the d.c. electric strength is reduced, and, when the electrodes move in the opposite direction, the d.c. electric strength increases, provided, in both cases, that the velocity of electrode movement is comparable in magnitude with the electron-drift velocity (under a.c. conditions, a reduction in strength always occurs). The argument is then extended to take into account the case of moving electrodes in a moving gas, and a similar effect is found to be superimposed on that obtained previously for a moving gas. Possible relevance to electrically stressed aerials moving at speed through the atmosphere is briefly considered.

Effects of temperature and techniques of measurement on the intrinsic electric strength of polythene

The electric strength of polythene has been measured under intrinsic conditions in the temperature range 20–85°C. Values are obtained using a new type of specimen, developed by McKeown, and also with the conventional recessed specimen. The McKeown specimen gives results which are greater at all temperatures than conventional values, and for these specimens, the temperature dependence of the intrinsic electric strength agrees with Frohlich's ‘amorphous’ or high-temperature theory of breakdown.Experiments are described which show that this increase of electric strength achieved with the McKeown specimens at room temperature is attributable to the presence of the solid epoxide resin in which the polythene and spherical electrodes are set, though the reason for the increase is, as yet, unknown.