Breakdown Voltage Of Gap Research Articles

Study of Dielectric Barrier Townsend Discharge in 3-mm Air Gap at Atmospheric Pressure

Diffuse dielectric barrier discharge was first produced in 3-mm-thick air gap at atmospheric pressure using two plane parallel electrodes each covered by one specific alumina plate with a thickness of 2.3 mm. Based on the discharge photographs of 10 ns exposure time taken with an intensified CCD camera, the diffuse discharge was identified with Townsend discharge. The Townsend breakdown voltage for this 3-mm air gap is about 5.7 kV, significantly lower than 11.2 kV, the streamer breakdown voltage of the air gap. If the alumina plate is too thin, the discharge transits to filamentary discharge. If it is too thick, the discharge is too weak to observe. Thermally stimulated current experiments revealed that there exist more shallow traps in the ceramic than in quartz plate after discharge pretreatment. The uniqueness of the shallow traps in the surface of the specific alumina plate, as well as the effect of the current limitation by dielectric leads to a Townsend discharge.

Breakdown characteristics of long air gap with negative polarity switching impulse

Breakdown characteristics of air gaps under negative switching impulse are complicated. To better understand the nonlinear discharge characteristics of long air gaps, the 50% breakdown characteristics of rod-rod gaps, rod-plane gaps and rod-conductor gaps, with air gap distance ranged from 1 m to 10 m, are studied thoroughly, with two waveforms of negative switching surges. Saturating characteristics have been obtained for the above three typical gaps. For air gaps exceed 4 m, the 50% breakdown voltage appears to be lower for rod-plane gaps than that for rod-rod gaps, while the average breakdown electric field decreases with the length of air gaps. Gap factors under negative impulses tend to level off with gap spacing. Furthermore, new knowledge is obtained indicating that, the 50% breakdown voltage for rod-conductor gaps may be lower with conductor grounded than that with conductor ungrounded. Finally, it also indicates that the wave front of the applied voltage has great influence on the breakdown time of rod-rod air gaps.

Mechanism of impulse voltage breakdown in high voltage vacuum interrupters with long contact gap

The objective of this paper is to propose a breakdown mechanism of lightning impulse voltage in high voltage vacuum interrupters (VIs) with long contact gap by complementing the Cranberg "clump" hypothesis with an impulse voltage and a non-uniform field. The Cranberg "clump" hypothesis assumed that the vacuum breakdown was due to the loosely adhering microscopic particles under a DC voltage and a uniform field. The microscopic particles might be torn from an electrode surface at a critical voltage. We considered the microscopic particles located at the area with the maximum electric field had the highest possibility to be accelerated. Therefore, the transit process of the micro-particles to the opposing electrodes was under a non-uniform field distribution driven by an impulse voltage. The rise rate of the impulse voltage applied was also considered. As a result, it was found that the breakdown voltage of a vacuum gap depends upon a 0.76 power of the gap length for the plate-to-plate contacts. The diameter of the contacts was 60 mm. The contact radius of curvature was 6 mm. In the same conditions, our previous experimental results showed that the impulse breakdown voltage was in a range of 0.70 to 0.79 power of the contact gap. So the experimental results supported the Cranberg hypothesis in its extension to the impulse breakdown under non-uniform field in high-voltage VIs. Thereafter, this proposed breakdown mechanism is a complement to the Cranberg "clump" hypothesis in terms of impulse voltage breakdown under a non-uniform field in high voltage VIs.

Study on the effect of artificial radiation simulating terrestrial solar ultraviolet radiation on negative DC discharge performance of air gap

It is important to reveal the effect of terrestrial solar ultraviolet radiation (TSUVR) on discharge performance of external insulation for the design and operation of a power system in regions with strong TSUVR, especially in Tibet. However, no research was carried out in this field until now. In this study, an artificial UV lamp was used to imitate TSUVR in the relevant experiments to research on the effect of negative DC discharge. It was found that artificial radiation simulating terrestrial solar UV radiation (STSUVR) does not affect appreciably the negative DC corona characteristics and breakdown voltage of short rod-plane air gaps of several electrode materials. That is because the wavelength of the STSUVR is in the range of 290–400 nm, and its intensity is less than 200 W/m2. Thus, air, Cu and Fe cannot be photoionised by STSUVR. There is also no effect of the STSUVR on arc propagation because of energy. Although a part of the photons in the TSUVR has higher energy than the work function of Al, it is very easy for the Al to be oxidised, and the oxide film (Al2O3) can prevent Al from being ionised by TSUVR. Therefore the TSUVR does not have an obvious effect on negative DC discharge performance of air gap.

A pulsed-power generator merging inductive voltage and current adders and its switch trigger application example

A pulsed-power generator using inductive adder technology is proposed for the case of a discharge gap. The merit of this generator is to merge the pulsed-voltage and pulsed-current adders via the dual secondary windings with special circuit. For the nonlinear impedance in any discharge gap, the standalone voltage-pulse and current-pulse can be outputted successively by this generator. The proposed generator is especially useful for the common resolution of implementing pulse discharge at less cost. As an application example, a compact trigger prototype was developed to compatibly use in the gas-insulated and vacuum switches. Experiments achieved good results that the triggered switches showed stable performance and long life. If the basic circuit of this proposed generator is regarded as a pulsed-generating unit, a certain number of such units connected in parallel can be expected to form a general device with generating greater breakdown-voltage and sustained-current pulses for discharge gaps.

AC breakdown performance and voltage correction of rod-plane short air gap under rain conditions

According to the operation experience and investigation in China, the insulation performance of transmission line can be reduced due to the effect of strong rain, which is not considered in the external insulation design. Meanwhile, there is no correction reference regarding the breakdown voltage of air gap under rain conditions in IEC standards. Therefore, a series of experimental tests were conducted in the artificial climate chamber and at Xuefeng Mountain Natural Site with the usage of rod-plane air gap to analyze the relationship between ac breakdown voltage and rain precipitation rate, rain conductivity and ambient temperature. It is shown that the breakdown voltage of air gap decreases with an increase of rain precipitation rate and rain conductivity, and increases with an increase of ambient temperature. In addition, according to the test results, the correction formula of ac breakdown voltage of rod-plane air gap under rain condition is proposed and verified in this paper.

Research on spark discharge of floating roof tank shunt

In order to quantitatively analyze the spark discharge risk of floating roof tank shunts, the breakdown voltage of shunt has been calculated by Townsend theory, the shunt spark discharge experiment is carried out by using 1.2/50 μs impulse voltage wave, and the relationship between breakdown voltage of shunt spark discharge and air gap is analyzed. It has been indicated by theoretical analysis and experimental study that the small gap is more easily cause spark discharge than the big gap when the contact between shunt and tank shell is poor. When air gap distance is equal to 0.1 cm, average breakdown voltage is 5280 V. When the air gap distance is less than 0.3 cm, experiment data agree well with Townsend theory. Therefore, in the condition of small gap, Townsend theory can be used to calculated breakdown voltage of shunt. Finally, based on the above conclusions, improvements for avoiding the spark discharge risk of shunt of floating roof tanks have been proposed.

DC positive discharge performance of rod-plane short air gap under rain conditions

To study the discharge performance of air gap under rain conditions and provide reference to the selection of clearance distance of external insulation in strong rain, this paper explored the influence of different environment conditions, rain intensity, rain conductivity, and ambient temperature on the dc positive breakdown voltage of rodplane air gap in the artificial climate chamber and at Xuefeng Mountain Natural Site. It is shown that the discharge voltage of rod-plane short air gap in wet condition is slightly higher than that in the dry condition; light rain has little influence on the positive dc discharge voltage of rod-plane short air gap. The relative discharge voltage of air gap decreases with an increase of rain intensity and rain conductivity with 2.2% to 0.2% / (mm/min), 1.4% to 0.1% / (100 μS/cm), respetively; and it is associated with the increase of ambient temperature with 0.3% to 0.1% / °C. In addition, several computations were carried out with different droplet sizes in rod-plane air gap. It can be indicated that the maximum electric field in the air gap increases with the increase of the radius and number of droplets.

Research on Electrical Characteristics of Dielectric Barrier Discharge and Dielectric Barrier Corona Discharge

The dielectric barrier corona discharge (DBCD) in a wire-cylinder configuration and the dielectric barrier discharge (DBD) in a coaxial cylinder configuration are studied. The discharge current in DBD has higher pulse amplitude than in DBCD. The dissipated power and the gas gap voltage are calculated by analyzing the measured Lissajous figure. DBCD has lower gas gap breakdown voltage. The average electric field is about 10–20 kV/cm in gas gap during DBCD, and is 30–40 kV/cm during DBD. In the positive half cycle the DBCD appears as continuous discharge current mode and in negative half cycle it appears as Trichel pulse mode. Under some conditions DBCD can show homogeneous diffuse discharges mode.

Streamer characteristic and breakdown in synthetic and natural ester transformer liquids with pressboard interface under lightning impulse voltage

This paper presents experimental studies on streamer and breakdown of synthetic and natural ester liquids with the presence of pressboard interface in a divergent point-plane field under lightning impulse voltage. Based on the current, light signals and streamer images, characteristics of both positive and negative streamers on pressboard surface were described, which resemble the features of streamers in open liquid gaps. Introducing pressboard in parallel does not influence the streamer stopping length and thus not weaken the oil gap breakdown voltage, under both positive and negative polarities at gap distances up to 75 mm. However, presence of parallel pressboard significantly reduces the acceleration voltage in mineral oil but seems have no influence on ester liquids under positive polarity, while it tends to accelerate the streamer velocity at larger gap distance and under higher voltage in both ester liquids and mineral oil under negative polarity. Generally, streamer on ester/pressboard interface propagates further than on mineral oil/pressboard interface at the same voltage level; both breakdown voltage and acceleration voltage on ester/pressboard interface are lower than those on mineral oil/pressboard interface at the investigated gap distances up to 75 mm.

Experimental Study on the Breakdown of Gaps in Fire

Some flashover incidents of high-voltage transmission lines are reported to be induced by fire. Though the mechanism of fire induced flashover is not well understood, it is deemed that fire could reduce the insulation strength of air. This paper has compared the breakdown characteristics of gaps in normal air conditions and those in fire. The results show that the breakdown voltage or electric field strength of gaps in fire decreases greatly. The value of breakdown electric field strength in alcohol flame is about 1.454 KV/cm, which is only about 28.8% of that in air. The value of breakdown electric field strength in wood crib fire is about 0.300KV/cm, corresponding to 19.9% of that in air. This study demonstrates that flame and soot particle of fire are responsible for fire induce flashover of high-voltage transmission lines.

Weibull Statistical Analysis of Pulsed Breakdown Voltages in High-Pressure Carbon Dioxide Including Supercritical Phase

Pulsed discharge plasma in supercritical fluids (SCFs) has attracted a great deal of attention in the field of plasma application for chemical processing. Characteristics of electrical breakdown are one of the important concerns for dielectric reliability of a plasma reactor with SCFs. In this paper, the pulsed breakdown voltages of quasi-uniform gaps were measured by changing the CO2 medium from gas to supercritical phase at a given temperature, and Weibull statistical analysis was applied to the measured breakdown voltages. The area effect on breakdown voltage, which is known to give an equivalent effective constant to Weibull shape parameter m, was examined with three sphere-to-sphere gaps. The experimental results indicate that the dispersion in the pulsed breakdown voltage in pressurized carbon dioxide obeys Weibull distribution, and the Weibull shape parameter m depends on the state of the CO2 medium. The dependence of m on the medium density that was obtained from direct analysis of breakdown voltages for a given electrode system indicated a similar tendency to that of the effective constant by area effect analysis.

A Way for High-Voltage $\mu\hbox{s}$ -Range Square Pulse Generation

In this paper, a new way for high-voltage μs -range quasi-square pulse generation based on a ns source pulser and a chopping spark gap is introduced. The source pulser delivered high-voltage source pulse with front edge at ns range to the chopping gap, and the chopping gap chopped the long flat back edge of the source pulse, so that a quasi-square pulse was formed on a high-impedance load. The breakdown-delay characteristics of the chopping gap, which was the most important, were studied in detail. Results of the experiments showed that when the pulse voltage peaked by the first peaking gap was a little lower than or approximate to the breakdown voltage of the chopping gap, the chopping gap broke down at the back edge of the peaked pulse so that the breakdown-delay time can increase from 30 ns to several μs. The breakdown-delay time of chopping gap is confined to the flat top of the peaked pulse. By using this mechanism of breakdown delay, a quasi-square pulse with pulse width of 1.95 μs, amplitude of 55 kV, and front edge of 22 ns was produced on a 1.15-kΩ load. Repetitive chopping pulses at 0.2 Hz were provided to demonstrate the feasibility of the chopping gap. By contrast to the conventional chopping, four essential conditions were concluded. Based on these results, a controllable trigatron-type chopping gap system is introduced to ensure chopping stability. It provides an important new way for μs-range high-voltage square pulse generation.

Dimensional Analysis to Ozone Generation by Pulsed Streamer Discharge in Dry Air

The generation of ozone is efficient by using short high-voltage combined with a dielectric layer placed adjacent to the outer electrode in dry air. Ozone concontration depend on the peak pulsed voltage, pulse repetition rate, gas flow rate, reactor length and so on. For ozone generation by pulsed streamer discharge in dry air, a mathematical model, which describes the relation between ozone concentration and these parameters that are of importance in its design, is developed according to dimensional analysis theory. The presence of nitrogen on ozone formation in dry air cannot only consume high energy electron but also form nitrogen oxides (NOx) in discharge plasma. Nitrogen oxides (NOx) play an important role in the process of ozone generation in air discharge, where the catalytic cycle for ozone destruction takes place. So the nitrogen influencing factor should be considered. Formula is derived for predicting the characteristics of the ozone generation, within the corona inception voltage to the gap breakdown voltage. The predicted results are shown to be in good agreement with experimental findings.

Insulation Behavior of Small-air-gap for the Molded-insulation System

Insulation behavior of small-air-gap for the molded insulation system has been investigated by comparing the well-known Paschen curve. Three electrode systems Metal-Gap-Metal (MGM), Metal-Gap-Insulator (MGI) and Insulator-Gap-Insulator (IGI) were employed as the test samples. It was found that Vs (breakdown voltage of the air gap) of the MGM were higher than the conventional Paschen curve, which can be attributed to the lacked initiating electron for Vs. This behavior was also obtained for MGI and IGI system. However, X-ray irradiation gives the remarkable effect on these Vs resulting in the coincidence to the Paschen data. According to the references' data-review and some experimental data for Paschen minimum region, new fundamental and universal Paschen curve for the solid insulation system was proposed.

Physical mechanisms for reduction of the breakdown voltage in the circuit of a rod lightning protector with an opening microswitch

The effect of air gap breakdown voltage reduction in the circuit with an opening microswitch is substantiated from the physical point of view. This effect can be used to increase the efficiency of lightning protection system with a rod lightning protector. The processes which take place in the electric circuit of a lightning protector with a microswitch during a voltage breakdown are investigated. Openings of the microswitch are shown to lead to resonance overvoltages in the dc circuit and, as a result, efficient reduction in the breakdown voltage in a lightning protector-thundercloud air gap.

Barrier effect on the corona discharge form and structure in the air

A barrier discharge is a high voltage nonstationary discharge that appears in an interelectrode gap where there is at least one solid (or liquid) dielectric barrier in the path of the discharge. Dielectric barriers are used to raise the breakdown voltage in different high voltage devices. Thus, the barrier effect demands versatile research: for direct, alternating, and impulse voltages. This article is devoted to the study of the action of a barrier placed parallel to the plane electrode on the corona discharge forms and the gap breakdown voltage in a needle-plane electrode system, to the investigation of the dependence of the discharge processes for different distances from the needle to the barrier, and to the research of the barrier insulation effect on the development of the processes in the discharge glow region. The latter includes a detailed study of the charge distribution on the dielectric surface.

Analysis of Space Charge Generating Devices for Lightning Protection: Performance in Slow Varying Fields

This paper starts with a review of anode corona modes with particularly streamer-free glow known as ultra-corona, with the view of exploring its application in lightning protection. Due to the inherent intensification of the ambient electric field atop a tall structure, strict conditions have to be imposed on the streamer-free space charge generation and the stability of that mode of corona when exposed to rapid field variations due to remote lightning. A novel ultra-corona electrode satisfying the above conditions is introduced. High voltage test results on such electrodes are presented including corona current, charge and laboratory air gap breakdown voltage. By applying dimensional analysis, a generalized formula for corona currents from such a device atop a tall structure is presented which includes the effects of the ambient ground field, structure height, ambient electric field at the top of the structure, electrode dimensions, and wind speed.

The influence of the sand-dust environment on air-gap breakdown discharge characteristics of the plate-to-plate electrode

The experiments of plane-plane gap discharge was carried out in an environment of artificial sandstorm. By comparing and analyzing the differences in gap breakdown voltage between the sand & dust environment and clean air, some problems were investigated, such as effects of wind speed and particle concentration on the breakdown voltage, differences of gap discharge characteristics between the dust & sand medium and the clean air medium. The results showed that compared with the clean air environment, the dust & sand environment had a decreased gap breakdown voltage. The longer the gap distance, the greater the voltage drop; the breakdown voltage decreased with the increase of particle concentration in flow. With the increase of wind speed, the breakdown voltage decreased at the beginning and rose afterwards. The results of the paper may helpful for further research regarding the unidentified flashover and external insulation characteristics of the HV power grid in the dust & sand environment.

Determination of the breakdown voltage of an aqueous interelectrode gap

The characteristics of the prebreakdown and leading stages of the high-voltage breakdown of an interelectrode gap are studied. It is shown that the level of the breakdown voltage is determined either by the value of the discharge ignition voltage or by the value of the flashover voltage of the interelectrode gap, while considering for which of the values the requirements are maximum in each particular case.