Breakdown Time Lag Research Articles

Underwater plasma breakdown characteristics with respect to highly pressurized drilling applications

Deep earth drilling is a key technique to extract oil, gas, and geothermal heat from the earth. Many complex energy focusing methods have been explored as an alternative approach to reach these resources but most of them require high energy. However, by utilizing short time span liquid plasma discharges, energy focusing can be achieved within traditional drilling systems. These discharges induce a rapid expansion process and a resulting shockwave. It is believed that this focused energy will lower the required cutting force to progress through the rock. Lowering the required cutting force will allow for lower drill bit wear, quicker rate of penetration, and an overall cost savings of the project. Plasma breakdown characteristics at drilling relevant pressures, ranging from 1 to 350 atm, were studied. A resistance–capacitance circuit with an air gapped spark switch was utilized to generate pulsed plasma between the pressurized electrodes. It was found that the required breakdown voltage increases as the pressure increases. It was also found that a plasma channel formation and an associated breakdown may or may not occur between the electrodes at different pressures due to variation in required breakdown voltages. Breakdown time-lag in the dielectric medium (tap water, 780 μS cm−1) increased as the pressure was increased, which indicated a higher voltage drop at higher pressures (>100 atm). The plasma generated cavitation bubble with an associated shockwave occurred as pressures were increased. However, the bubble radius and the bubble duration decreased as the pressure was increased. The plasma generated shockwave speeds fall within the expected speed of sound in water. Finally, preliminary rock cracking tests were performed on granite at high pressures (340 and 272 atm) and it was found that plasma is able to create cracks in the rock.

Impulse Breakdown Characteristics of Transformer Oil with Cellulose Particles in Quasi-Uniform Field

This study presents an experimental comparison of the breakdown characteristics of oil samples with four cellulose particle content levels in a quasi-uniform electric field under lightning impulse voltage. For the experiment to resemble the actual working conditions of transformers and meet the on-site withstand impulse voltage test requirements, both the standard lightning voltage (SLI) and oscillating lightning impulse (OLI) are considered. The experimental results show that an increase in the number of cellulose particles directly weakens the oil insulation strength. At the same particle content level, the oil breakdown voltage under OLI is higher than that under SLI, and the breakdown time lag under OLI is longer than that under SLI. The breakdown time lag is more sensitive to the effect of particle content under SLI. This work is beneficial in deepening the understanding of the impulse breakdown characteristics of transformer oil within cellulose particles and in providing references for the on-site impulse test of oil-immersed power transformers.

Breakdown characteristics of transformer oil with cellulose particles in a non-uniform field under lightning impulse voltage

This study presents experimental results on the influence of cellulose particles on the breakdown characteristics of transformer oil in a highly non-uniform field under lightning impulse voltage. The experimental results show that as the particle content increases, the breakdown voltage reduces with little change in the breakdown time lag. At the same cellulose particle content, the oil breakdown voltage under oscillating lightning impulse (OLI) is lower than that under standard lightning impulse (SLI) and the breakdown time lag under OLI is longer than that under SLI. The impulse wave oscillation has a large effect on the accumulation of particles around the high voltage electrode and cellulose particles affect the development of the streamer process. At mid to high particle content the accumulation of particles around the high voltage electrode causes a decrease in the conductivity of the surrounding oil. This work contributes to the understanding of the effect of cellulose particles in oil and breakdown and on oscillating waveforms and provides guidance for lightning impulse tests on oil-immersed power transformers in the field.

Effect of hydrostatic pressure on the polarity effect of impulse breakdown characteristics of transformer oil

The aim of this study was to clarify the hydrostatic pressure effect on the initiation and propagation process of oil streamers under the application of pulsed voltage with different polarities. The statistical characteristics of the impulse breakdown voltage and time lag in transformer oil were studied over a wide range of hydrostatic pressure, and the statistical time lag and the formative time lag were calculated by the Laue's pattern. The breakdown voltage distribution can be well fitted by 3 parameter Weibull distribution. The results show that the breakdown voltage increases with the hydrostatic pressure for both positive and negative polarity. However, the increase trend is different, linear for the negative polarity and saturated for the positive polarity. At a fixed voltage, when the pressure is increased, the breakdown time increases slightly for the negative polarity, but remarkably for the positive polarity. The statistical time lag for negative polarity is much larger than positive polarity, and the hydrostatic pressure has greater influence for negative polarity. The characteristics of formative time lag are quite different: for negative polarity, it decreases very slightly with the hydrostatic pressure, but increases remarkably for positive polarity. These differences are due to different initiation and propagation mechanisms, which are also discussed in the paper.

Experimental investigations of commercial gas discharge tube “Osram St 111” using time lag measuring method

The results of the breakdown time lags obtained by commercial “OSRAM St 111” gas diode are presented. The memory curves for different voltages (for 220, 250 and 300 V) are shown. The analysis of the experimentally obtained distributions (histograms and Laue distributions) for different voltages (for 220, 250 and 300 V) and different relaxation times (from 1 to 1500 ms), as well as the analysis of the randomness of the experimental results are performed. The performed statistical analysis of time lag distributions indicates two different mechanisms that lead to breakdown. First of them is characterized by the exponential distribution and the second by the Gaussian distribution.

Volume Diffuse Dielectric Barrier Discharge Plasma Produced by Nanosecond High Voltage Pulse in Airflow**supported by National Natural Science Foundation of China (No. 51437002)

Volume diffuse dielectric barrier discharge (DBD) plasma is produced in subsonic airflow by nanosecond high-voltage pulse power supply with a plate-to-plate discharge cell at 6 mm air gap length. The discharge images, optical emission spectra (OES), the applied voltage and current waveforms of the discharge at the changed airflow rates are obtained. When airflow rate is increased, the transition of the discharge mode and the variations of discharge intensity, breakdown characteristics and the temperature of the discharge plasma are investigated. The results show that the discharge becomes more diffuse, discharge intensity is decreased accompanied by the increased breakdown voltage and time lag, and the temperature of the discharge plasma reduces when airflow of small velocity is introduced into the discharge gap. These phenomena are because that the airflow changes the spatial distribution of the heat and the space charge in the discharge gap.

Spark Breakdown in Gas-Discharge-Tube Surge Arrester at Voltage Pulse

The sparkover voltage of gas discharge tubes for surge voltage protection has been found to be dependent on the rate of voltage rise. At slow voltage increase, it is close to stationary voltage conditions and is assumed to be the breakdown voltage at a given $pd$ regarding Paschen law. The deviation of stationary sparkover voltage measured on test samples is assigned to the variation of electrode conditions and illustrated as the effect of the Townsend coefficient $\gamma$ . The increase of impulse sparkover voltage at fast voltage rise depends on the time lag of the spark breakdown where the effect of statistical and formative time lag is assessed. As an origin of ion avalanche and streamer formation, the cold-field electron emission process is considered where the Poisson probability function for rare stochastic events is concerned for the evaluation of emitted electron current. Due to the absence of applicable values for relevant system parameters, the relationship between the impulse sparkover voltage and the rate of voltage rise obtained by simulation have more or less qualitative character. Values taken for the coefficients of simulation are chosen by fitting the simulated results to the measured ones. Their relevance is verified by comparing it with the typical values of discharge quantities found in the literature.

Long Time Range Breakdown Caused by Penetration of Positive Charges Packet in Low Density Polyethylene Sheets

This paper presents an experimental study on long time range breakdown of Low Density Polyethylene (LDPE) under very high dc applied fields (Emean) of 2.0 MV/cm or 3.0 MV/cm. Breakdown time lag and space charge distribution are simultaneously measured for a 200-µm-thick LDPE sheet with positive-semicon and negative-evaporated Al electrodes. A voltage is applied to the sheet until the dc breakdown occurs. 20 samples are tested for both the applied voltages. It should be remarked that 50 % survivor probability T50 , corresponding to time in which breakdown occurs for 10 samples out of 20, is 70 min for 40 kV, whereas it is 90 min for 60 kV. Results of the space charge measurement by pulsed electro acoustic (PEA) method indicates that a large number of positive charges are injected from the semicon-anode and they are accumulated in the bulk of LDPE, so that field distribution in LDPE is strongly distorted. The maximum field strength Emax(t) in LDPE after the space charge penetration for 60 kV becomes higher than that for 40 kV. However, the distortion ratio Emax(t) / Emean under 40 kV is higher than that under 60 kV. This is because the positive charges packet produced by 40 kV penetrates into deeper area of the bulk as compared with that by 60 kV.

Comprehensive evaluation of the K-factor values in the lightning impulse voltage test techniques for UHV-class electric power equipment

In the 2010 revision of IEC-60060-1 "High-voltage test techniques", the conversion of waveforms using the test voltage function (K-factor) was introduced as one of the major revisions. At present, in IEC TC42 "High-voltage and high-current test techniques," a study is conducted on the standards for the lightning impulse voltage test at WG 19 "Adaptation of TC 42 standards to UHV test requirements." The present paper comprehensively evaluates the experimental results of the K-factor values using the largest possible model assuming UHV-class electric power equipment, as well as the past experimental results of the K-factor values. Initially, these experimental results were evaluated from a view point of insulation properties to clarify the characteristics of the Kfactor values. The adaptation itself of the K-factor evaluation method to also cover UHVclass equipment is considered significant. However, for high-voltage class equipment, since the formative time lag of breakdown is longer due to the long insulation length, resulting in a longer breakdown time, the K-factor values are considered lower than the existing K-factor function. Subsequently, the experimental results of the K-factor values were comprehensively evaluated and compared with the existing K-factor function. The K-factor function may possibly have to be reviewed for UHV-class electric power equipment to take lower values than the existing K-factor function.

Breakdown Phenomena in Nitrogen Due to Repetitive Nanosecond-pulses

Nanosecond-pulse breakdown indicates special characteristics depending on the pulse rise-time and duration. Based on a repetitive nanosecond-pulse generator, breakdown phenomena of parallel-plane gaps in nitrogen were investigated with single pulse and repetitive bursts under different gap conditions. The relationships between applied voltage, pulse repetition frequency, breakdown time lag, repetitive pulse stress time and the number of applied pulses are presented. The curves regarding E-field strength, breakdown time lag and gas pressure are also obtained. The experimental results show that breakdown characteristics with repetitive nanosecond-pulses are different from that with single pulse. Repetitive nanosecond-pulse breakdown is concerned with the accumulation effect that is attributed to residual ions and metastable species survived from previous pulses. In addition, a modified empirical formula about E-field strength, breakdown time lag and gas density is given for the breakdown data.

Experimental study of polarity dependence in repetitive nanosecond-pulse breakdown

Pulsed breakdown of dry air at ambient pressure has been investigated in the point-plane geometry, using repetitive nanosecond pulses with 10 ns risetime, 20–30 ns duration, and up to 100 kV amplitude. A major concern in this paper is to study the dependence of breakdown strength on the point-electrode polarity. Applied voltage, breakdown current and repetitive stressing time are measured under the experimental conditions of some variables including pulse voltage peak, gap spacing and repetition rate. The results show that increasing the E-field strength can decrease breakdown time lag, repetitive stressing time and the number of applied pulses as expected. However, compared with the traditional polarity dependence it is weakened and not significant in the repetitive nanosecond-pulse breakdown. The ambiguous polarity dependence in the experimental study is involved with an accumulation effect of residual charges and metastable states. Moreover, it is suggested that the reactions associated with the detachment of negative ions and impact deactivation of metastable species could provide a source of primary initiating electrons for breakdown.

Experimental Study of Similarity Laws in Gas Breakdown with Repetitive Nanosecond Pulses

It has been known that breakdown voltage has a functional dependence on the product of gas pressure and gap distance. Furthermore, the product of gas pressure and breakdown time lag is related to electric field divided by gas pressure. In this paper, both these similarity laws were investigated in repetitive nanosecond-pulse breakdown of dry air and nitrogen. The experimental results indicated that breakdown voltage was close to DC value when repetition rate was up to 1 kHz, and the product of gas pressure and breakdown time lag is unambiguously associated with E-field strength divided by gas pressure under repetitive nanosecond-pulse conditions.

Repetitive Nanosecond-Pulse Breakdown in Tip–Plane Gaps of Air

Repetitive pulsed power is becoming an important area of high-power technology. Dielectric failure data concerning electrical insulation play a basic role, but breakdown has been inadequately studied for the repetitive nanosecond-pulse conditions. This paper is concerned with the breakdown characteristics of tip–plane gas gaps under repetitive burst conditions at variant repetition rates (rep-rates) and diverse gap distances. The relationship among applied voltage, breakdown time lag, number of applied pulses to breakdown, repetitive pulse stress time, and rep-rates is presented. The experimental results presented show that breakdown polarity dependence is not distinct. The data also indicate that significant concentrations of excited particles and residual charges would be formed during the consecutive nanosecond pulses and would present a memory effect that affects the development of gas breakdown. In addition, the detachment of negative ions, cathode collision of positive ions, and deexcitation of metastable species can provide the source of avalanche-initiating electrons.

An experimental investigation of repetitive nanosecond-pulse breakdown in air

A compact, repetitive pulsed power system has many applications, but some basic aspects of the breakdown characteristics need further investigation. The purpose of this paper is to investigate the breakdown characteristics of dry air with repetitive nanosecond pulses. The variables affecting the discharge conditions, including the applied pulse voltage, pulse repetition frequency, gap distance and gas pressure, are investigated. The relationship between the breakdown time lag, the repetitive stressing time, and the number of applied pulses to breakdown with pulse repetition rate, E-field strength and pressure are obtained, and the breakdown characteristics and mechanism are also discussed. It is suggested that activated neutral species and residual ions should be taken into account, and repetitive nanosecond-pulse breakdown is characterized by the accumulation effect.

The Effect of Electrode Construction in Breakdown Time Lag of Impulse Breakdown in Mineral Oil

A breakdown time lag of uniform and nonuniform electric fields using point-plane and sphere-sphere electrodes in mineral oil was measured. The stainless-steel spherical electrode was 12.5 mm in diameter. The needle electrode was made of iron and its tip was electrolytically polished. The copper plate electrode measured 10 mm×20 mm×1 mm. The effect on breakdown time lag wielded of differences in the distance between electrodes and applied impulse voltage revealed that the time lag was proportional to the applied voltage and the breakdown time lag of a nonuniform electric field was shorter than that of a uniform electric field. It was found that the breakdown phenomena in point-plane and sphere-sphere electrodes were respectively similar to a streamer-type breakdown and a streamer breakdown structure.

Creeping Discharge Characteristics under Rectangular Pulse Voltage in SF6 Gas

The effect of a barrier set up between a needle and a plate in SF6 gas was investigated under pulse voltage. It was found that inserting a barrier resulted in unusual bending of the creeping discharge path and extension of the equivalent length between electrodes. Consequently, a long time lag of breakdown and high breakdown voltage were obtained.

Size effect and statistical characteristics of dc and pulsed breakdown of liquid helium

Breakdown time lag in liquid helium is measured over a wide range of electrode sizes and pulsed electric field strengths. The breakdown time lag and dc breakdown strength are statistically analyzed by using the Weibull distribution function and weak link theory. It is found that the time lag depends on both electrical stress and the electrode surface area stressed above a critical level. It is supposed that breakdown triggering electrons are generated by field emission phenomena at small protrusion tips on the cathode surface. In higher external electric fields, a less sharper protrusion emits initial electrons with a shorter time lag and may become responsible for liquid breakdown. A theoretical equation is proposed to predict the electrode size and electrical stress dependency of the breakdown time lag, based on Fowler and Nordheim theory. It is shown that the equation is consistent with the Weibull distribution function under multiple stress of electric field and stressing time.

Pulsed dielectric breakdown of pressurized water and salt solutions

The dielectric breakdown of pressurized water and salt solutions subjected to high amplitude electric fields of submicrosecond duration has been investigated. Well-defined pulses (80 kV, 3 ns rise time, 100 ns duration) have been applied to a gap (0.04–0.21 cm), between Rogowski profile electrodes, containing de-ionized, nondistilled water; de-ionized, distilled water; sodium chloride solutions (0.001–1.0 M); or magnesium sulfate solutions (0.01–0.1 M). Breakdown in these liquids has been studied at pressures up to 400 atm. Calibrated voltage dividers situated on the source and load sides of the test gap permitted measurement of the interelectrode potential and the current response. From these measurements, the time lag to breakdown, breakdown voltage, power input to the liquid, and temporal characteristics of the breakdown process have been determined. The breakdown time lag increases with increasing pressure and gap width, and decreases with increasing field. Moreover, it is weakly dependent on the conductivity of the liquid. A dynamical model has been developed to explain these results. In this model, field emission currents heat the liquid and create a region with density below the critical density for the formation of electron avalanches. An ionizing wave front subsequently develops and propagates via a sequence of processes occurring in the region ahead of the front; namely, heating by electron injection, lowering of the liquid density, and avalanche growth and retardation. The time for nucleation of the low density region has been experimentally determined and is in good agreement with theory.

大気中直流準平等電界ギャップのXeClレーザ誘導破壊遅れ

大気中直流準平等電界ギャップのXeClレーザ誘導破壊遅れ

A nanosecond acoustic source: Experimental investigation of pulsed dielectric breakdown of water and its dependence on pressure and conductivity

Spark gaps are finding use as underwater acoustic sources in sonar and prospecting applications. It is thus important to determine the influence of pressure and conductivity on the dielectric breakdown of water. Well defined rectangular pulses (80-kV, 3-ns rise time, 100-ns duration) have been applied to a gap (0.04–0.21 cm), between Rogowski profile electrodes, containing de-ionized, nondistilled water, de-ionized, distilled water, or sodium chloride solutions (0.001–1.0 M). Breakdown in these liquids has been studied at pressures up to 400 atm. Calibrated voltage dividers situated on the source and load sides of the test gap permitted measurement of the interelectrode potential and the current response. From these measurements, the time lag to breakdown, breakdown voltage, power input to the liquid, and temporal characteristics of the breakdown process have been determined. The breakdown time lag increases with increasing pressure and gap width, and decreases with increasing field. Moreover, it is weakly dependent on the conductivity of the liquid. An Ohmic current-voltage relation has been observed during the prebreakdown stage. A dynamical model has been developed to explain these results and is also presented at this meeting. [Work supported by ONR.]