Development Of Electrical Discharge Research Articles

Capillary discharge in the high repetition rate regime

Plasma discharge in the capillary is used to develop x-ray lasers, waveguides for high power laser pulses, and as active plasma lenses to focus high energy charged particle beams. Capillary discharges in the high repetition rate regime are of interest for applications that require large average values, such as luminosity and/or electric current of laser accelerated particles. In the present paper, we study the capillary discharge in the high repetition rate regime in connection with the ultrashort laser pulse guiding for laser electron acceleration. Using magnetohydrodynamic computer simulations and theoretical scaling, we investigate the filling of the capillary with the gas, the electric discharge development leading to outflow of the plasma from the capillary, and the recovery of gas distribution after the discharge end. In the next cycle, these processes are repeated. As a result, we found the characteristic cycle time, which determines the upper limit on the repetition rate allowed by the capillary parameters. In the case of the capillary discharges used for acceleration of sub-GeV electron beams, e.g., needed for compact free electron lasers, an upper limit on the repetition rate is approximately equal to 10 kHz. Published by the American Physical Society 2024

Analysis of the dynamics of changes in gas content in oil-filled equipment with defects of various types

The article presents the results of analysing the dynamics of changes in the values of the ratios of characteristic gases, the percentage of gases, and defect nomograms in the process of developing electrical discharges, local overheating, and combined defects in high-voltage oil-filled equipment. During the analysis, the value of gas concentrations was evaluated for compliance with different levels regulated in the current Ukrainian standard at different stages of defect development. To determine the type of defect based on the values of the ratios of characteristic gases at different points in time, the norms regulated by the IEC 60599 standard and the ETRA square were used. The dynamics of changes in the percentage of gas was analysed using the Duval triangle. The results of the analysis showed that the primary defects during the development of electric discharges can be not only electric discharges with lower intensity, but also thermal (in particular, in the temperature range of 150-300 ℃) and combined defects. At the same time, in the process of discharge development, the nature of defects may change from measurement to measurement. Thus, when assessing the possibility of further operation of transformers, in addition to the degree of danger of the defect and the rate of its development, it is necessary to take into account the possibility of transforming the defect from a less to a more “dangerous” one that develops rapidly. During the development of thermal defects, the primary defect is usually a thermal defect with a lower hot spot temperature. It was found that in equipment with overheating above 700 ℃, the change in gas content during the development of the defect has a similar character. In particular, a mirror image of the change in the percentage of methane in relation to ethylene is observed. This effect can be used to detect high-temperature overheating at an early stage of its development, even before the gas concentrations exceed the limit values, which will help to avoid the destruction of equipment insulation and extend its service life. During the development of combined defects (overheating accompanied by discharges or discharges accompanied by heating), the main defect (e.g., discharge) first appears, and in the process of development, an additional defect (e.g., heating) develops. The results obtained indicate the possibility of detecting and recognizing defects in oil-filled equipment at different stages of their development.

Developing Spiral-Conical Gears for Microsystems by Wire-Assisted Electrical Discharge Machining

The requirements of gears are increasing rapidly in the global market for applications from micro electro mechanical systems (MEMS) to aerospace. Gears of various profiles and types including spiral-conical are used for motion as well as torque transfer in microsystems. The development of such gears is a challenging task because no compromise in their quality is acceptable. It necessitates highly accurate gear manufacturing process. This article presents such a process i.e. wire-assisted electrical discharge machining (WEDM) and development of stainless-steel made spiral-conical gears of miniature size. All minute aspects of spiral-conical gear development by WEDM are reported in this paper. In order to investigate the impact of process parameters and gear quality, an experimental study has been conducted based on Taguchi’s robust design of experiment technique. The developed gears are found with good manufacturing quality characteristics.

Electrical discharge in gas bubbles in gel

The development of electrical discharge in gas bubbles immersed in a liquid or a gel depends on the combination of the conductivity and dielectric properties of the medium as well as on the composition of the gas in the bubbles. The interest in a discharge in hydrogels is strongly stimulated by its use in combination with plasma in biology and medicine. Here, we use the electrical measurements of the current waveform and fast imaging and demonstrate the correlation between the discharge propagation in the bubble and the time evolution of the discharge current. We demonstrate experimentally that, if the dielectric constant is low and the conductivity is high (short time constant), then the discharge continues to propagate and to increase in brightness and the current continues to grow until the applied voltage is removed. The quenching of the discharge typical for dielectric barrier discharge is not observed and the effects are similar in hydrogels and in water. A simple circuit model is used to explore the dependence of the current waveform on the parameters of the medium and plasma. The shape of the current pulse significantly affects the amount of energy produced by the discharge and hence is an important property for the design and monitoring of plasma sources used for water decontamination and for plasma activation of gels.

The Development of Electrical Tree Discharge in Epoxy Resin Impregnated Paper Insulation

An electrical tree discharge model of multilayer insulation paper was prepared, and a voltage of 20 kV was used for electrical tree cultivation and initiation tests. Based on the microscopic image information and partial discharge (PD) information during the aging of the electrical tree, the development of electrical tree discharges between layers of paper comprising epoxy resin-impregnated paper insulation was studied. The results show that, by analysing PD information such as the discharge volume phase spectrum and the discharge repetition rate phase spectrum, the development of the electrical tree branch progresses in four stages: initial, growth, stagnation, and bursting. During the growth and stagnation stages, the main discharge paths of the electrical tree are mainly formed, and there are many filamentous fibres on the path edge. During the burst stage, more branches will be formed on the electrical tree, which will cause the greatest damage to the insulation. With the extension of the electrical tree path, the discharge magnitude and discharge times also increase. There are specific discharge patterns in different growth stages of the electrical tree, and the number of discharge events in each positive half-cycle is significantly greater than that in a negative half-cycle. Combining the microscopic image information and PD information during the aging of such an electrical tree, a theoretical basis for evaluating insulation state by PD monitoring is realised. The long-chain molecules of cellulose and epoxy resin break bonds and oxidise, which decompose into a large number of free radicals, monosaccharides, and other low-molecular-weight products.

Characteristics of the Development of Electric Discharge between the Jet Electrolyte Cathode and the Metal Anode at Atmospheric Pressure

The article presents the results of an experimental study of the electrical discharge between a jet electrolyte cathode and a metal anode in electrolysis and plasma-electrolyte modes at atmospheric pressure. The current-voltage discharge characteristics in the treatment of M1 copper and AISI 304 stainless-steel specimens have been studied with a hollow current lead with an electrolyte feeding rate of w = 3.34–13.36 m/s within the voltage range of 20–565 V. The patterns of discharge development have been demonstrated in electrolysis mode in the form of a hemisphere and in the electrolyte plasma mode in the form of cyclically repeating shapes: drop, cylinder, cones, ellipsoid, spheres, and superimposed shapes. The discharge characteristics for rotation, destruction, localization, electric breakdowns, and glowing are determined. The condition of the existence of the ellipsoid electrolyte-plasma discharge is described. The characteristics of discharge development have been registered at an interelectrode spacing of 2–8 mm in the stationary mode and with its movement relative to the metal anode surface. The influence of the discharge shape on the noise level, specimen mass, and surface roughness is considered.

Transitional regimes of pulsed electrical discharge in medium-conductivity water

New regimes of pulsed electrical discharge development have been observed during experiments in water with conductivity 90 μS/cm. Two new transitional regimes between common thermal and streamer–leader discharge mechanisms were observed in the voltage range (2.8–3)Ubr, where breakdown voltage is Ubr = 9 kV. The first transitional regime initiates on anode as fast discharge: leader-like structure with strong self-glowing shoots into the gap by 2 mm in first 10 µs at half voltage drop and transforms then into regular thermal mechanism finishing the gap breakdown in about 1 ms. The second transitional regime initiates on anode as a thin, 0.3 mm length single streamer-like channel in first 10-μs which disappears rapidly at half voltage drop and the plasma channel develops only after long time period (about 2 ms) from cathode at the speed of 30–50 m/s.

Characteristics of the Development of Electric Discharge between Jet Anode and Liquid Cathode

We present experimental results on the behavior of the burning of electrical discharge between a nonuniform jet anode and liquid cathode and of the discharge voltage and current pulsations for various voltages of the power supply. We determine the frequency spectrum of the discharge voltage oscillations, as well as the temperatures on the electrolyte cathode surface, by means of infrared thermography and pyrometer.

Breakdown in short rod-plane air gaps under positive lightning impulse stress

Prediction of withstand voltages in air-insulated systems are made on the basis of empirical models that are not sufficiently accurate for complex geometries. Better understanding of the spatiotemporal development of electrical discharges is necessary to improve the present models. Discharges in lightning impulse stressed 20–100 mm rod-plane gaps are examined using a highspeed camera, photo-multiplier tubes (PMTs) and a highbandwidth current measurement system. The images and measurements of gaps larger than 20mm show a fast initial streamer discharge with a current rise time of some tens of ns, followed by a dark period of a few μs and a propagation of a slower leader-type channel leading to breakdown. The breakdown mechanisms in the shortest gaps are faster and geometry dependent, probably occuring by heating of initial streamer channels. Different light filters used with the PMTs indicate that all parts of the leader-type discharge development emit light over a spectrum from UV to IR. The initial discharges emit low amounts of warm light and IR compared to the leader-type channel. Finally, it is suggested that empirical breakdown voltage prediction models should be interpreted in light of the leader-type breakdown mechanism.

Breakdown in short rod-plane air gaps under positive lightning impulse stress

<p>Prediction of withstand voltages in air-insulated systems are made on the basis of empirical models that are not sufficiently accurate for complex geometries. Better understanding of the spatiotemporal development of electrical discharges is necessary to improve the present models. Discharges in lightning impulse stressed 20–100mm rod-plane gaps are examined using a highspeed camera, photo-multiplier tubes (PMTs) and a highbandwidth current measurement system. The images and measurements of gaps larger than 20mm show a fast initial streamer discharge with a current rise time of some tens of ns, followed by a dark period of a few μs and a propagation of a slower leader-type channel leading to breakdown. The breakdown mechanisms in the shortest gaps are faster and geometry dependent, probably occuring by heating of initial streamer channels. Different light filters used with the PMTs indicate that all parts of the leader-type discharge development emit light over a spectrum from UV to IR. The initial discharges emit low amounts of warm light and IR compared to the leader-type channel. Finally, it is suggested that empirical breakdown voltage prediction models should be interpreted in light of the leader-type breakdown mechanism.</p>

Time‐resolved imaging of electrical discharge development in multiple bubbles immersed in water

The formation and development of plasma in multiple air bubbles submerged in water was investigated using a pin‐pin electrode system. The discharge dynamics with different bubble‐bubble and bubble‐electrode distance was investigated using a 300 000 frame per second high‐speed charge‐coupled device (CCD) camera. It was observed that the proximity of bubbles and electrodes is crucial for the breakdown process. Depending on the position of the bubbles and electrodes, the breakdown could be categorized into three modes: (1) the axial mode, where the streamer propagates along the axis of the bubbles; (2) the surface mode, where the streamer propagates along the inner curved surface of the bubbles; and (3) the hybrid mode, where the streamer propagates both along the axis and the inner surface simultaneously. For larger electrode gap, the discharge only initiates at the tip of the electrode, and does not propagate into the bubble.

Investigations of the development of thunderstorm with hail. Part 1. Cloud development and formation of electric discharges

The results of synchronous radar, radiometric, and lightning-detection measurements are analyzed to reveal interrelations between the parameters of electric discharges and the parameters of cumulonimbus clouds developing in the North Caucasus. The dependences of electric activity of the cloud on radar parameiers as well as on the parameiers reirieved from Meteosat SEVIRI radiometer measurements are considered. Electric discharges (intracloud discharges and lightnings) were registered for 1 hour 40 minutes (the maximum frequency was equal to 448 discharges per minute). The relation ships are identified that connect the parameters of electric discharges with the precipitation rate and with the field of cloud top temperaiure. It was found that the frequency of eleciric discharges increases as the precipitation rate increases. The maximum frequency is reached at the precipitation rate equal to 70 mm/hour. Normalized autocorrelation functions ofthe field ofcloud top temperature retrieved from the satellite data are constructed. The high correlation is revealed between the scale of inhomogeneity of the field of cloud top temperature and the frequency of electrical discharges.

Using the light emission measurement in assessment of electrical discharge development in different liquid dielectrics under lightning impulse voltage

This article presents the results of studies concerning the assessment of propagation modes of electrical discharges developing in different liquid dielectrics. This assessment was performed on the basis of measurements of light emitted during discharge development. For liquid dielectrics such as natural ester, synthetic ester and mineral oil tested under standard lightning impulse voltage of both polarities, two propagation modes of discharges were identified: slow developing discharges of propagation velocities of few mm/μs and fast developing discharges of velocities of tens mm/μs. Comparing the results concerning the liquids tested in synthetic ester and natural ester fast discharges appeared at much lower testing voltage than in the case of mineral oil. Simultaneously, at the same voltage level, the frequency of light pulses corresponding with the discharges developing in esters was higher than frequency of pulses observed when discharges developed in mineral oil. Thus the results showed that both esters are less resistant to the appearance of fast and energetic discharges, which means that esters may have a lower ability to protect against the lightning impulses in real insulation systems. It is suggested that this disadvantage of the ester liquids should be necessarily taken into account during the design process of transformers filled by them.

The behaviour of water droplets on the silicone rubber surface in an electric field

This paper describes the influence of a water droplet placed on flat samples of silicone rubber for enhancement the local electric field and generate electrical discharges. Studies have shown a significant influence of the droplet geometry on the electric strength of the samples. For non-symmetrical arrangement of the three droplets in the inter-electrode space electrohydrodynamic phenomena was observed: a stable change in the droplets shape placed near the electrodes and stretching and tearing down of the water droplets placed far from the electrodes. Captured photos and films of the water droplets behavior placed on the surface of the samples provided data to perform the simulation of the distribution of electric field and an estimate the value of the electric field, which was followed by the development of electric surface discharges.

Time-resolved imaging of electrical discharge development in underwater bubbles

The formation and development of plasma in single air bubbles submerged in water were investigated. The difference in the discharge dynamics and the after-effects on the bubble were investigated using a 900 000 frame per second high-speed charge-coupled device camera. It was observed that depending on the position of the electrodes, the breakdown could be categorized into two modes: (1) direct discharge mode, where the high voltage and ground electrodes were in contact with the bubble, and the streamer would follow the shortest path and propagate along the axis of the bubble and (2) dielectric barrier mode, where the ground electrode was not in touch with the bubble surface, and the streamer would form along the inner surface of the bubble. The oscillation of the bubble and the development of instabilities on the bubble surface were also discussed.

Prebreakdown air ionization in the atmosphere

This chapter is devoted to the analysis of electron-ionization and -elimination processes at early stages of electric-discharge development in air at altitudes of mainly 0–90 km. In this chapter, ionization processes in an external electric field, as well as background ionization by fast particles and electron attachment and detachment with participation of atomic and molecular oxygen, are considered. Temperature and concentration dependences of rate constants are described. Analysis of ionization models allowing simplified approaches to detailed computation models is undertaken. It is shown that the electric breakdown process in air, under the influence of an external electric field, comprises several stages that are different with respect to different altitudes over the Earth. Numerical modeling on the basis of a detailed plasma chemical model, taking into account the heating of gas by the discharge, has shown that the relaxation processes leading to gas heating also lead to the appearance of a nonlinear stage of electric breakdown. The considered phenomena can be convenient in the consideration of a high-altitude origination of natural discharges in fields of thunderstorm clouds.

Effect of the development of electrical parallel discharges on performance of polluted insulators under DC voltage

Our work consists of studying the development of parallel discharges on a broad insulating surface simultaneously under uniform pollution’s conditions and DC voltage. This phenomenon plays a very important role on the electric performance of this insulation. The parameters of influence considered in this paper are the following: the width of the polluted material, the degree of its contamination and the polarity of the applied voltage. The tests were performed on a rectangular surface of a glass with various dimensions, and various types of electrodes (rods, planes) were used. The visualization of the parallel discharges was performed by a fast camera. The experimental results emanated from this study show that there is a limiting band width of pollution from which two consecutive electric arcs can develop independently until the insulation’s flashover with a minimal voltage. The value of this limiting width is approximately 12 cm in positive polarity and 20 cm in negative polarity. It was noted that this limiting effective width is not influenced at all by the variation of the wet layer’s volume conductivity. In this paper, two methods and empirical equation were used to confirm these results. In addition, the results indicate that any plane–plane system of electrodes can be associated with multiple rods-rods configurations, which have the same performance.

Numerical simulation of sprites halo

In the framework of C. Wilson’s hypothesis substantiating a possibility of electric discharge development in the Earth’s atmosphere at high altitudes above thunderclouds, numerical simulations were executed of the discharge exciting the sprite halo with realistic variations of thundercloud dipole moment transferred to the ground by positive lightning discharge. For various values of time and altitude, at which the avalanche-to-streamer transition occurs, optical radiation was calculated in the 1P, 2P, and 1N bands of the nitrogen molecule and Meinel’s band of the N2+ ion. The calculated brightness and space-time evolution of the luminescence are consistent with the data of the field observations of the halo luminescence.

Measurement Techniques Used for Study of Electrical Discharge Mechanisms in Insulating Ester Fluids under Lightning Impulse

This article describes the measurement techniques used for the study of mechanisms of electrical discharge development in ester fluids under lightning impulse voltage. These techniques ...

Modes of underwater discharge propagation in a series of nanosecond successive pulses

Initiation and development of nanosecond electric discharges in deionized water was studied by time-resolved shadowgraphy and emission imaging. Pulses of 4–10 kV in amplitude, 5 ns rise time and 30 ns duration were applied to a high-voltage (HV) pin-like electrode with the diameter of the pin tip about 2 µm. Two distinct bush-like and tree-like modes of the discharge propagation were observed in the same conditions already at the rising slope of HV pulse. Both the modes are supersonic. The probability of finding one of them depends on applied voltage. Bush-mode propagates at 4 km s−1 at the initial stage; the deposited energy is less than 0.05 mJ. For the tree-like mode, propagation velocity, number of branches and deposited energy show well-prononced dependence on applied voltage. It is suggested that the bush-like discharge ignites in the gaseous cavity, whereas the tree-like discharge propagates in bulk liquid. The role of electrostriciton in the initiation and propagation of two modes is discussed, and comparison with microsecond discharges is given. Transition from bush-like discharge to tree-like mode may occur in successive positive pulse coming 500 ns after initial pulse.