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A double-arc model, which considers the differences between characteristics of AC partial arcs on top and bottom surfaces, was proposed for predicting the flashover voltage of polluted insulators in this paper. The arc constants parameters, the arc reignition criteria, as well as the radii of arc columns in the proposed model were determined by measuring partial arcs on the top and bottom wet-polluted surfaces of a triangular glass plate separately. A "Π" type glass model was made to investigate the partial arc propagation process by using an ultra-high speed camera. It has been found that the arc length increased linearly with leakage current amplitude, the ratio of arc length increments on top and bottom surface was related to salt deposit density (SDD) rather than leakage current. Based on above-mentioned researching results, the double arc calculation model was established, and the calculated results were in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The detection of gas decomposition products is widely used to diagnose the inner condition of SF6-insulated electrical equipment for its anti-interference ability and high sensitivity. A discharge chamber with Teflon coating inside was designed, with adjustable defect parameters and the volume nearly the same as real ones in gas-insulated switchgear. With the assistance of newly developed dual gas chromatography detection system, this paper investigated the influences of relatively low moisture on the discharge characteristics and gas decomposition under corona and mild spark in SF6. Considering notable hydrolysis reactions in the main gas volume and on the vessel walls, SO2F2, SO2, and S2OF10 were selected as typical gas decomposition products. The average discharge capacity and its fluctuation were found to decrease with the increase of moisture content within research scope, which is related to the electronegativity of water molecule. The concentration of typical decomposition products under various moisture conditions was observed in detail. The results show that in mild spark, O atom in S2OF10 mainly originated from oxygen rather than water vapor in SF6. To diagnose internal insulation condition by only monitoring, the magnitude of discharge capacity is proved unreliable. A new parameter, the concentration ratio of SO2/S2OF10, was proposed to group moisture content and discharge types. [ABSTRACT FROM PUBLISHER]

The capacitor stack is one of main acoustic noise sources in the high-voltage dc (HVdc) converter station. It is necessary and important to estimate the noise level of capacitor stacks before an HVdc converter station is constructed. In this paper, based on the analysis of capacitor noise generation mechanisms, the relationship between the vibration speed and sound pressure level of the capacitor is identified. The equation which can be used to calculate the noise level of capacitor stacks is derived. By applying mechanical force on the capacitor tank, the frequency-response function of the capacitor tank vibration is acquired. And then the noise level of capacitor stacks is calculated and compared with the measurement data. The results show that the noise level of the capacitor stack can be predicted effectively with the proposed calculation method. [ABSTRACT FROM AUTHOR]

In this paper, the influence of surface charges is quantitatively analyzed based on the study of surface charge distribution under DC voltage and flashover characteristics of insulators under superimposed voltage of DC and lightning impulse. It is found that when DC and impulse voltage are in the same polarity, surface charges weaken the electric field along the insulator surface and flashover voltages under superimposed voltage increases. When DC and impulse are in the opposite polarity, surface charges enhance the electric field along the insulator surface, and flashover voltages will decrease. The calculation results of the electric field along the flashover path show that the changing rate of the maximum field strength is approximately equal to the changing rate of flashover voltage, which proves that the influence of surface charges on flashover characteristics of insulators mainly depends on their distortion of the electric field. [ABSTRACT FROM AUTHOR]

Electric field is one of the key parameters to study the charge dynamics for corona discharge. To study the motion characteristics of space charge in different corona modes of ac corona, electrooptic (EO) modulation technique was used to obtain the electric field in corona space. This article focuses on the time-varying characteristics of electric field for ac corona discharge modes. The step phenomenon is observed and the evolution characteristics of electric field for corona modes, from the Trichel pulses to the stable glow, are obtained. It was found that the background field could not remove the space charge generated by the discharge completely within half a cycle, which directly proved the existence of retained charge. And it is proposed that the continuous and fast rising electric field is the characteristic of positive glow in ac corona, which may be an effective method to judge the positive glow. Additionally, electric fields at different spatial locations were studied. The electric field step at the migration zone is suppressed, and as the space charge density increases, the suppression phenomenon becomes more obvious. This article provides more information on the physical mechanisms of the ac corona modes and gives support for the research of corona plasma. [ABSTRACT FROM AUTHOR]

For continuous or spiral windings which feature multiple continuously transposed conductors (CTC) wound in parallel, the transposition structure is commonly used to suppress circulation between conductors. This introduces a local asymmetry in transformer windings. Fault analyses have shown that building an asymmetric structure in transformers increases deformation risk in these windings. Researchers have yet to fully investigate this asymmetric structure. This study was conducted to observe the influence of transposition structure in a 110 kV transformer. The conductor’s relative position forms three patterns during the transposition process; two parameters are established to describe the position-changing process. A finite-element method (FEM) model is built to investigate the magnetic field and electromagnetic force distributions. The results indicate that the transposition structure distorts the magnetic field distribution. The maximum distortion factor of the axial component of magnetic flux density ($B_{\mathrm {z}}$) along the axial direction caused by the transposition structure is 14.6%. The transposition structure only changes the radial change slope of $B_{\mathrm {z}}$. The gap caused by the transposition process aggravates imbalance in the ampere-turns distribution, increasing the amplitude of the radial component of magnetic flux density ($B_{\mathrm {r}}$) at the middle height of the transformer low voltage (LV) winding. The maximum amplitude of $B_{\mathrm {r}}$ at the transposition structure increases by 513%. The Lorentz force over the CTCs remains constant from before to after the transposition process, though its linear density over the CTCs is unevenly distributed throughout. The axial component $F_{\mathrm {z}}$ varies from −31 to 10 kN/m, while the radial component $F_{\mathrm {r}}$ varies from −146 to −51 kN/m. The results show that the initial stage of the CTC height rising segment is a weak point and should be strengthened in the manufacturing process. [ABSTRACT FROM AUTHOR]

Nanosecond pulse discharge plasma has many prospects in industrial applications, and high-voltage repetitive nanosecond pulse generators with compact design and light weight have become one of the key issues limiting its development in some applications. This paper presents a high voltage series-connected silicon carbide (SiC) metal-oxide -semiconductor field effect transistor (MOSFETs) module which can be served as the main switch in a repetitive high-voltage nanosecond pulse generator. This kind of series-connected MOSFETs module with only single external gate driver requiring very few components is very suitable for compact assembly. By analyzing the working principle, three topologies of series-connected MOSFETs module are proposed. The switching behaviors of the three different topologies with four SiC MOSFETs series-connected are compared experimentally. The variation of switching characteristics of series-connection SiC MOSFETs module with different numbers of devices are investigated. The layout is also optimized to shorten pulse front time and improve output pulse quality. Furthermore, a 10 kV SiC MOSFETs module with a turn-on transition time ∼10 ns is developed. The double pulse test result demonstrates excellent switching performances. Finally, a compact and high-voltage pulse generator composed of three 10 kV SiC MOSFETs module is tailored, with a typical rise time ∼40 ns and peak voltage of ∼30 kV. [ABSTRACT FROM AUTHOR]

The wavefront time T f of lightning impulse plays an important role in the detection of insulation defects in metal enclosed gas insulated switchgear (GIS). Usually, a rod-plane electrode system with different geometric parameters is adopted to simulate local field enhancements in GIS. But, for GIS, the defects may occur on the high-voltage electrode which can not be properly simulated by a rod-plane electrode. To research the influence of waveform parameters on actual defects in GIS, cylinder-plane, coaxial cylinder, and basin-type insulator with a conductive protrusion, were used in this study. A generating system of double-exponential impulses with wavefront times in the range of 0.08 to 15 μs and wave tail times of approximately 50 μs was used to simulate different impulse test waveforms based on a fully enclosed oil-immersed Marx generator. The results show that for the cylinder-plane gap with a protrusion, when the gap distance of the needle tip to the plane is constant, increasing the length of the needle decreases the 50% breakdown voltage. Comparing with the insulation characteristics of rod-plane gap, the U 50 %-T f curves of the cylinder-plane electrode with needle defects thereafter no longer show a U shape as the rod-plane electrode, but increase with an increase in the wavefront time. The difference can be explained by the shielding effect of the cylinder electrode on the defect, which changes the electric field distribution of the gap. The U 50 %-T f curves of GIS bus with different voltage levels and basin-type insulator with surface conductive defect also show the similar increase trend. For V-t characteristics of GIS bus with different voltage levels, we find that the higher the voltage level, the more obvious the trend of the V-t characteristic bathtub curve. [ABSTRACT FROM AUTHOR]

The gas-solid interface is generally considered to be the weakest part in gas-insulated systems. The flashover voltage of a gas-solid interface is difficult to predict because it involves an extremely complex physical process affected by multiple factors. In this paper, we employ the support vector regression (SVR) method based on mass data on the features of the electric field that are indicators of the flashover voltage. We cast 48 kinds of epoxy resin post insulators as samples, and 61 features are extracted to characterize the surface electric field distribution and the flashover voltage under standard lightning impulse voltage. Four indicators that may be useful in predicting the flashover voltage were obtained; the maximum electric field along the surface of the insulator (E max), the normal electric field components of E max (E n_Emax), the maximum gradient of the surface tangential electric field component (E t_gm), and the integral of the area in which the E value exceeds x% of E max along the insulator surface (V t60). We establish an SVR flashover voltage prediction model with these four features, whose average deviation is 7% in 10,000 predictions. It is expected that this study may provide a reference for the continued study of the gas-solid surface flashover mechanism. [ABSTRACT FROM AUTHOR]

Prefire is the unexpected breakdown of gas switch at triggered mode and have to be limited at extremely low level in fast linear transformer driver (FLTD). In this paper, the dispersion of breakdown voltage as well as prefire characteristics of high pressure gas spark switches under typical working conditions of FLTD was investigated and reported. Tested switches included a three-electrode field-distortion gas switch (TFGS) and a six-stage multichannel gas switch (SMGS), which had compact structure and low inductance. The results showed that the self-breakdown voltage of both TFGS and SMGS obeyed three parameter well-bull distribution and the dispersion of Ub at ±90 kV could reach 4% of TFGS and 14% of SMGS, respectively. The dispersion of Ub was remarkably influenced by the floating potential of middle electrode. By grounding the triggering electrode via a kilohm resistor, the dispersion of Ub decreased to 2% in TFGS and 6.5% in SMGS, respectively. When a voltage equalization method by cascade resistors was introduced, the dispersion of Ub in SMGS dramatically decreased to 4.4%. In repetitive operation at triggered mode, the prefire rate of TFGS reached 0.9% at $\gamma = 80{\%}$ working coefficient and decreases with the decrease of $\gamma $ , being 0.3% at $\gamma = 72{\%}$ and 0.2% at $\gamma = 65{\%}$ , respectively. The prefire rate of SMGS was much higher, reaching 1.7% at $\gamma = 72{\%}$ and 0.7% at $\gamma = 65{\%}$ , and decreased to 0.6% and 0.3%, respectively, after applying the equalizing resistors. Generally, the prefire rate of SMGS was somewhat higher than that of TFGS with the same working coefficient and the floating potential limiting was imperative for prefire inhibition. [ABSTRACT FROM AUTHOR]

Lightning impulse withstand test is extremely important to the insulation examination of oil-immersed equipment, but the increase of the entrance capacitance of ultrahigh voltage equipment usually makes the front time T 1 of test impulses exceed the upper limit regulated by IEC 60060-1. In order to evaluate the equivalency between the withstand tests under standard lightning impulses and impulses with longer front time (T 1 < 6 μs), as well as to explore the effect of wavefront on dielectric strength of transformer oil, the breakdown characteristics of transformer oil under impulses with different front time in quasi-uniform and non-uniform field were studied. The results show that, in quasi-uniform field, the 50% breakdown voltages U 50 % are almost independent of the front time, but the minimum breakdown voltages slightly increase as the front time increases. In a highly inhomogeneous field, the front time has remarkable effects on the 50% breakdown voltages under positive impulses, contrary to the weak influences under negative impulses. Light signals and shadow images of streamers were recorded to analyze the influence of wavefront on the initiation and propagation characteristics. It is found that an increase in front time would increase the initiation voltages of both positive and negative streamers, but their shapes do not change much as front time varies. The dependence of light signals of streamers on front time was only observed under positive impulses. The mechanism underlying the differences between the front time related breakdown characteristics of transformer oil under positive and negative impulses is discussed, as well as the waveform equivalency for impulse withstand tests of oil-immersed equipment. [ABSTRACT FROM AUTHOR]

By using 1 MV Marx generator and a 220 kV GIS bus, an experiment platform has been established, and a stainless steel needle is applied to simulate spike defect, so as to study the influence of pressure, wave front time and electric field on 50 % breakdown voltage (U50) and voltage-time (V-t) characteristics of SF6 gas gap with existence of a spike defect on the bus of GIS under double exponential impulse voltage. When wave front time is short, 50% breakdown voltage of the SF6 gap hardly changes with various pressures, and U50%-P curve turns to be a hump shape when wave front time increases. However, pressure has no significant effect on V-t characteristics. The slope of V-t characteristics curve is negative when wave front time of applied voltage is short (0.08~0.9μs), and it will turn to be positive when wave front time becomes longer (several ~15μs). A new method to fit these V-t characteristics curves under impulse voltage with longer wave front times is proposed. It is found that 50 % breakdown voltage decreases almost linearly with the increase of electric field non-uniformity factors (f), and V-t characteristics cluster with valley-like profile have been drawn at different f. Dispersion of V-t characteristics cluster reduces and the flat region expands with the increase of f, and minimum value of breakdown voltage of SF6 gap with spike defect under impulse voltage, which is of guiding significance for engineering, can be obtained. [ABSTRACT FROM AUTHOR]

This paper reports the experimental results from the appearance of three discharge modes in a special geometry as a function of applied negative voltage pulses. The geometry is a four-gap pseudospark one with a gap distance of 4 mm, a metallic hollow cathode, and an anode. The applied pulsed voltage Up varies from −20 to −80 kV. The pulse shape is a rectangular one with a pulsewidth of 50 ns and a rise time of 4 ns. There is no breakdown at Up < 27 kV, and at Up > 27 kV, a pseudospark discharge starts, which transforms at Up > 45 kV into a surface discharge. The working gas is dry air at a constant pressure of 13 Pa. Using these parameters, electric field simulations of the triple point junctions are conducted and time-integrated pictures of the different discharge modes are presented. When the gas pressure is increased from 13 to 35 Pa, the voltage range of the pseudospark discharge mode grows from 13 to 65 kV. [ABSTRACT FROM PUBLISHER]

The reverse recovery characteristics of high power thyristor are important device physical properties influencing the reliable operation of HVDC thyristor valve. In this paper, the reverse recovery characteristics of high power thyristor are investigated from the aspects of both external circuit and internal device physics. By analyzing the depletion of carrier during the reverse recovery of thyristors, a determination method of minority carrier lifetime is proposed to construct a connection between the macroscopic reverse recovery characteristics and the microscopic device physical parameter such as minority carrier lifetime. Meanwhile, the influence of the current with a power frequency on the characteristics of reverse recovery especially on the reverse recovery time is investigated experimentally, and the relationship between external circuit and internal physical property is discussed. The results show that thyristor reverse recovery storage time is independent of sinusoidal currents under power frequency, which is approximately equal to its minority carrier lifetime in the base region of high power thyristors; Finally, the influences of reverse recovery characteristics on the protection strategy of thyristor unit are analyzed, and the related methods of thyristor unit routine test are also discussed. This work will be beneficial to the operational maintenance of thyristor valve in power system. [ABSTRACT FROM AUTHOR]

In this paper, a dual-electrode gas switch triggered by ejected plasma is proposed to ensure the switch to be triggered reliably under extremely low switching coefficient. The switch has the configuration of dual electrodes, in one of which a microincentive chamber is embedded to develop ejected plasma into the switch gap, leading to the breakdown of the switch. Both the features of ejected plasma and the triggering discharge characteristics of the switch are studied with different types of gas, gas pressures, voltage polarities, gap distances, triggering pulse energies, and so on. The results show that the switch can be triggered reliably in a much wide working voltage range, as the minimum switching coefficient is low to 9% with the delay time of about 10 \mu \texts . With the decrease of gas pressure and the increase of triggering pulse energy, the height of ejected plasma increases while the delay time of the switch reduces. The polarities of charging voltage and triggering voltage both have obvious influence on the delay time of the switch, and the effect of the former is greater. Under the same gas pressure and triggering pulse energy, the delay time in SF6 is much bigger than that in N2. [ABSTRACT FROM PUBLISHER]

Electrical explosion of aluminum wire is a very promising method for aluminum nanoparticle production. The exploding wire plasma has significant influence on the formation of the nanoparticles. In this paper, the electron temperatures and the electron densities in the plasma are estimated through Boltzmann plot and Stark broadening effect. The aluminum particle densities, charge state distributions, and the energy relaxation in the plasma are estimated accordingly. The diffusion of the plasma into protective argon gas is studied through its spatial distribution. The electron temperatures of the electrical explosion of wire (EEW) plasma with an aluminum wire in argon gas are 1~2 eV, and the electron densities are of the order of magnitude ~1019/cm3, which decrease rapidly over time after the EEW occurs. The diffusion of the EEW plasma of aluminum wire into ambient argon gas can be divided into two main phases, namely, the previous fast diffusion phase and the subsequent slow diffusion phase. The plasma is with quite different diffusion features due to the differences of the corresponding relative number density of the plasma to argon gas. For plasma with relative density much higher than 1, the diffusion velocity in the fast diffusion phase is significantly higher than that with relative density near 1, and in the slow diffusion phase, the distribution radius of the plasma can continue to increase significantly due to the considerable energy coupled from the circuit to the aluminum particles. Dependence of the plasma radii on the deposited energies are derived from the experimental data. For plasma with relative density near 1, due to the much longer relaxation time during the slow diffusion phase, very little energy can be transferred from the circuit to the aluminum particles and the plasma radii only increase slightly during this phase after the aluminum particles spent most of their kinetic energy in the previous fast diffusion phase. [ABSTRACT FROM PUBLISHER]

A positive streamer in a strong electric field in air at 1-atm pressure is investigated with particle-in-cell/Monte Carlo collision method including a photoionization model. The simulation results of streamer discharge in parallel plate air gap with and without the photoionization model are compared. It is shown that the seed electrons produced by photoionization generate secondary avalanches which lead to the formation of the streamer. No streamer is observed without photoionization model. [ABSTRACT FROM AUTHOR]

The non-standard lightning impulse waveforms (N-SLIWs) including oscillating lightning impulses, very fast transient voltages (VFTOs) and steep waveforms in the power system gravely endanger the inner insulation of power transformer. To prevent insulation failure and provide guidance for robust transformer design, in this paper, two typical insulation models of oil-immersed transformer were established and their breakdown characteristics under N-SLIWs were investigated. The research mainly focused on the influence of front time and oscillation frequency of N-SLIWs on the breakdown characteristics. The experimental results showed that the breakdown voltage increased with the decrease of front time. For low frequency-oscillating lightning impulse waveforms (LF-OLIWs), breakdown voltage increased with the increase of oscillation frequency and was up to 30% higher than that under standard lightning impulse waveform (SLIW). For VFTOs, with the increase of frequency, breakdown voltages presented a law of inverted "U" type. Insulation model could withstand the highest value of VFTO when the oscillation frequency was around 2.4 MHz. But when the frequency was as high as 9 MHz, breakdown voltage was close to that under SLIW. A very high frequency oscillation was the main reason for the reduction of breakdown voltage as its steepness dV/dt assisted the effective transmission of the sphere?s potential to the head of the streamer channel. [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) illumination can effectively shorten the statistical lag and jitter in gas breakdown processes. The spark gap discharge can produce abundant spectrum including UV waveband. In this paper, a simple but reliable spark gap operating with N2 at atmospheric pressure is used to test optical radiation characteristics, such as spectrum intensity, rise time, fall time, and duration of optical pulse, which are adjusted by changing the circuit or configuration parameters. Three UV-illuminated switches with different UV spark gap configurations have been tested. The experimental results approve our assumption. With a uniform electric field UV spark gap, the breakdown voltage standard deviation percentage of the switch is 0.74%. [ABSTRACT FROM PUBLISHER]

Alumina filled epoxy resin is important insulating material, which discharge characteristics are greatly determined by its material properties. In this paper, the surface flashover characteristics of the epoxy resin with various alumina contents (250- 400 phr) in 0.4 MPa SF6 are studied. The short-term and long-term withstand voltages and the application times are measured, and then the V-T characteristics are compared accordingly. The withstand voltage of the epoxy resin with certain alumina content decreases exponentially with time and the long-term withstand voltage is about 20-30% lower than the short-term withstand voltage. The discharge damages to alumina filled epoxy resin material are also studied through the carbonization traces and the microcosmic damage patterns. It is found that the epoxy resin with 350 phr alumina has the lowest short-term and long-term withstand voltages and most serious carbonizations according to the experimental results. The ?wormholes? formation in the discharge and its effect in the flashover process are analyzed and discussed based on the carbonation traces and the microcosmic patterns. It is found that the flashover paths shift from creeping-discharge-based to bulk-breakdown-based due to wormholes effect with the increase of alumina content and the critical alumina content is about 300-350 phr. [ABSTRACT FROM PUBLISHER]

Electrode erosion is a notable issue influencing the performance and restricting the lifetime of gas switches. In the erosion process, electrode materials heated by spark channel will melt or evaporate and be driven to depart from electrode surface, contaminating the gas switch insulator, and potentially inducing flashover accidents. In this paper, sputtering spots are observed near the erosion crater in a two-electrode gas switch, which indicates the existence of molten droplet ejection. In addition, a set of polymethyl methacrylate rings are inserted in the gas switch to detect the ejection of molten droplet as well as to simulate the switch insulator for investigating the degradation of surface insulation strength. The results show that the ejection of molten droplet is along the tangent surface of electrode with a small divergent angle. After repeated discharges, the insulator surface is bombarded by the droplet ejection and forms dense cracks and embedded metal particles in a narrow band. The spatial varied droplet ejection causes a decrease in both flashover electric field and surface resistance. It also leads to different surface resistances in different regions, which can result in an uneven electric field distribution. Thus, droplet ejection increases the probability of surface flashover accidents in gas switches. [ABSTRACT FROM PUBLISHER]

We described the fabrication and testing of a multi-plasma-jet triggered gas switch(MPJTGS). The MPTJGS consists of two high-voltage electrodes and a trigger electrode, in which a novel six-channel annular microplasma gun is embedded to generate multichannel plasma jets as seed electron sources when a nanosecond trigger pulse arrives. The multiple discharge channels were induced by the multichannel plasma jets. We investigated the multichannel discharge performance of the MPJTGS in two working modes with charging voltage of ±25 kV, trigger voltage of +40 kV (25-ns rise time), and trigger energy of 2, 32, and 240 J at different working coefficients. Results showed that the average number of discharge channels increased as the trigger energy increased, and decreased as the working coefficient decreased. The MPJTGS operated in Mode II had better multichannel discharge characteristics than in Mode I at the same condition. At trigger energy of 240 J and working coefficient of 87.1%, the average number of discharge channels could reach 7 in Mode II. [ABSTRACT FROM PUBLISHER]

In order to clarify the features of the pre-flashover and predict ice flashover more accurately, the entire evolution of leakage current during the pre-flashover process of both AC long and short suspension insulator strings covered with ice were recorded and analyzed in this paper. It is found that the pre-flashover processes of both ice-covered long and short insulator strings could be divided into four stages based on the time domain characteristics of leakage current. Two significant parameters were proposed as characteristic parameters for the analysis of pre-flashover characteristics, namely the characteristic current (IW) which was the quasi-constant value in Stage III, and the critical current (IFT) which was the leakage current amplitude value in the last cycle before flashover in Stage IV. The relationships between these two characteristic parameters and the influencing factors including ice build-up severity, the contamination degree, and the conductivity of the freezing water were also studied. It was believed that the characteristic parameter IW could be adopted as early-warning value of pre-flashover along the ice-covered suspension insulator, and IFT as the criterion of the critical flashover. [ABSTRACT FROM AUTHOR]

From field experience and laboratory experiments, it was indicated that the flashover performance of contaminated insulators was significantly influenced by the insulator geometry. In the paper, insulators with three different profiles including seven types of deep under-ribs disc insulator, three types of two-shed disc insulator and three types of three-shed disc insulator were tested in an artificial climate chamber to investigate the influences of insulator profile parameters on the flashover performance of large tonnage disc insulators. The artificial contamination test results indicated that 50% flashover voltage stress (E50%) decreased with the increasing insulator diameter and creepage distance. The influence of salt deposit density (SDD) was also investigated, and it was found that E50% of alternating-shed insulator decreased more rapidly than that of deep under-ribs insulator with the increase of SDD. An empirical expression was proposed, by employing the least-square method, to describe the relationships between E50% and insulator configuration parameters as well as SDD. Through analyzing the generalized fitting coefficients (r) of the equation and the standard error of estimate (s), it can be concluded that the calculated results are in good agreement with the experimental data. Moreover, special attentions were also paid to the influence of the under-ribs and the ratio of shed overhang distance to the shed spacing on flashover performance respectively. This work can enrich the investigation of insulators parameters and may provide useful reference for performance evaluation and selection of insulators in EHV and UHV transmission lines. [ABSTRACT FROM PUBLISHER]

Field distortion gas switches are extensively used in pulsed power systems. Switch performance typically degrades because of electrode erosion, which directly influences the output parameters, stability, and reliability of pulsed power systems. With the same value of $pd$ , different pressure and gap lengths in gas switches can affect electrode erosion property and thus, the subsequent performance degradation, but few results have been published. In this paper, repetitive discharges have been undertaken in a three-electrode field distortion gas switch with fixed pd$ to study the influence of pressure and gap length on electrode erosion and switch performance. The morphology of electrode surface and time histories of both trigger jitter and the probability of prefire have been investigated during the whole life cycle of the gas switch. The results show that when pd$ is fixed, high pressure and a short gap make for low trigger jitter at the start of the switch life cycle but lead to more severe electrode erosion, expediting the degradation of performance in field-distortion gas switches. Meanwhile, the probability of prefire increases rapidly with the increase of pressure. [ABSTRACT FROM PUBLISHER]

In the use of spark gaps as switching devices in pulsed power systems, spark resistance is a crucial factor influencing the voltage rise time and the efficiency of energy delivered to the load. However, current oscillations make it difficult to accurately measure the spark resistance. Therefore, we present a spectrographic method to measure the spark radius and the conductivity of spark channel according to its emission spectrums. A series of experiments has been carried out to investigate the time-dependent properties of spark resistance under oscillatory damped current pulses. The current and voltage waveforms have been recorded to calculate the energy deposited in the spark channel. Furthermore, the influences of gas pressure and gap length on spark resistance and the deposited energy have been discussed. The results indicate that lower resistance, and energy deposition is obtained with shorter gap lengths operating at higher pressures. [ABSTRACT FROM PUBLISHER]

Reducing the working coefficient of gas switch can effectively lower the prefires probability. This paper discusses in detail the discharge characteristics of a three-electrode plasma-jet triggered gas switch (PJTGS), especially at low working coefficients. The triggered discharge process of the PJTGS is analyzed. Plasma jets are observed and discussed with respect to trigger voltage, trigger energy, and gas pressure. In addition, the switch jitters at different conditions are investigated, including ground resistor, charging voltage, trigger energy, trigger voltage, and working coefficient. The results indicate that the height of the plasma jet increases with the increase of trigger voltage and energy, and decreases with the increase of gas pressure. At working coefficients higher than 75%, trigger voltage of +80 kV, and ground resistor of 100 \(\Omega \) , reliable subnanosecond jitters can be obtained with the charging voltages of ±25, ±30, ±40, and ±50 kV. When the working coefficients are between 50% and 28.1%, the switch jitters range from 1.6 to 3.5 ns. Even at the working coefficient of 28.1%, the PJTGS can still be triggered reliably with a switch jitter of 3.5 ns. [ABSTRACT FROM AUTHOR]

The triggering discharge behavior of the rail gap influences the jitter of discharge delay and inductance of the spark switch due to the formation of multiple spark channels in the rail-gap switch, which is related with the development of avalanche in the discharge process under the nanosecond triggering pulses. In this paper, the PIC/MCC method is used to investigate the avalanche development under a triggering pulse. A model of intershielding is proposed in the PIC/MCC method considering the effect of the space charges. From the simulation and experimental results, it has been clarified that the avalanche process can be controlled by the statistical delay time of the effective primary electrons. The intershielding model can also explain the effect of the rise time of a triggering pulse on the avalanche development. [ABSTRACT FROM PUBLISHER]

By introducing a compensated Monte Carlo collision (MCC) model into the particle-in-cell/MCC method, the streamer initiation process in a laser-triggered gas switch is simulated with a large time step. The spatial distributions of electron density at various pressures and voltages are obtained. [ABSTRACT FROM AUTHOR]