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This article discusses an advanced method for estimating dc conductivity of oil using parameters evaluated under switching impulse voltage application. Firstly, the effectiveness of switching impulse application for assessing the condition of oil–paper insulation is investigated. Thereafter, the evaluated parameters under switching impulse voltage are fitted by Havriliak and Negami (HN) model for estimating the oil conductivity. The method is applied on oil-impregnated pressboards containing different moistures and a distribution transformer for experimental investigation. Moreover, the limitations of the proposed method are also discussed in this article. [ABSTRACT FROM AUTHOR]

This paper presents an advanced technique for calculating activation energy of oil-impregnated pressboard through dielectric response current measurement under switching impulse voltage at different temperatures. The proposed technique analyzes the measured impulse voltage and current signals to formulate its equivalent circuit at different temperatures. The equivalent circuit parameters are utilized to determine the shifting of ac conductivity curve along frequency axis with variations in temperatures. Based on the shifted ac conductivity curves at different temperatures, the corresponding activation energy of the insulation is estimated. The effectiveness of the proposed technique is investigated through a few laboratory prepared test samples. [ABSTRACT FROM AUTHOR]

The demand for DC gas-insulated switchgear/gas-insulated transmission line (GIS/GIL) becomes more and more urgent in recent years owing to the rapid development of high voltage direct current (HVDC) transmission systems. Insulators in DC GIS/GIL could easily accumulate a large number of charges on its surface during long-term operation, which might lead to overstressing of polymeric insulation or surface flashover. Therefore, it is of great significance to propose an effective method for dissipating extra surface charges. However, achieving charge dissipation without opening the tank is still a great challenge to SFC6-insulated equipment for a long time. In this paper, a novel method, which is named X-ray based non-contact charge dissipation method (XNCDM) for insulators in SF6-insulated equipment, is proposed. The effects of X-ray irradiation on the charges dissipation and the influences of irradiation dose were experimentally investigated in SF6. The mechanisms underlying are discussed in detail. Results show that surface charges on the insulator can be almost completely dissipated after short-time X-ray irradiation with enough dose, owing to the significant enhancement of electric conduction along the insulator surface and charge neutralization by gas ions near the gas-solid interface. This paper provides a novel technique for realizing rapid surface charge dissipation on the insulator, which is of great significance for a variety of engineering applications of DC GIS/GIL. [ABSTRACT FROM AUTHOR]

Triggered vacuum switch (TVS) is significant in the field of pulse power technologies, especially in high power application. Particularly, the rise-time of trigger pulse is important for paralleled TVSs which are frequently used to increase peak current. Trigger source based on pulse transformer and solid state switch has good reliability and low jitter, thus, the design of a fast-rise-time trigger source based on solid-state switch and pulse transformer is crucial for the parallel connected TVS. The work presented here extends the state of the art in the area of high power pulse generator. This paper introduces the design procedure of a pulse transformer based on closed magnetic core and a discharging circuit based on solid-state switches in detail. The influence of leakage inductance and distributed capacitance of the pulse transformer on the output pulse waveform are analyzed. PSPICE simulations are studied to optimize the design of the pulse transformer. Based on the theoretical calculations and simulations, special winding structures, suitable material of magnetic core, and proper width of copper strip are carried out to obtain faster rise-time. Four parallel connected MOSFETs are used in the trigger source because of their anti-paralleled diodes and high switching-speed. The experimental results show that, the pulse transformer can generate a rectangular pulse with an adjustable amplitude of 0?5 kV, a pulse width of 0?5 ?s, and the rise-time is about 160 ns. Lastly, the pulse transformer has a compact structure and can be used to trigger the TVS reliably. [ABSTRACT FROM AUTHOR]

Water plays a pivotal role in pulse switches, owing to its fast recovery characteristic and high dielectric strength. In this paper, we empirically studied the effect of behavior of vapor bubbles on the dielectric recovery characteristics of water during the post-breakdown. The experimental medium is distilled water, and highly pressurized CO 2 in its supercritical phase is used as a comparative medium to test the voltage recovery ratio. The dielectric recovery characteristics of water was explained by alternating expansion-contraction bubble behaviors, including bubble density variation in the second oscillation stage. The experimental results showed that water showed a shorter recovery time (2 ms), and it could be regarded as a promising medium for high-repetition-rate switch. The motion of second oscillating bubbles resulted in a considerably short recovery time. [ABSTRACT FROM AUTHOR]

In this paper, a self-triggering linear transformer driver (LTD) technology based on the principle of electromagnetic induction is presented. A detailed circuit model of the self-triggering LTD module is established in PSPICE to explore the feasibility of the self-triggering method. Through simulation and analysis, an original design of a prototype self-triggering LTD is established. Some factors, which influence the performance of the self-triggering LTD are demonstrated and analyzed thoroughly in this paper, such as peaks of induced trigger voltages and pre-magnetizing. Simulation results indicate that all induction cavities in the self-triggering LTD module can be triggered with an easier external trigger method and the cavity triggering sequence is acceptable. The peak current at the output of self-trigger LTD module is in the range of 0.96 MA to 1.01 MA and the 10-90% rise time is about 31ns in the simulation. [ABSTRACT FROM PUBLISHER]

The objective of this paper is to investigate the effect of a high-frequency high-voltage impulse conditioning technique on the inrush current interruption phenomena. In this paper, the inrush current interruption phenomena referred to the actual interruption and the currentless period following interruption. First, Six 7.2 kV vacuum interrupters (VIs) were conditioned by 400 batches of voltage impulses. The duration of each batch were set to 0.1 s. The peak value of each impulse could reach up to 100 kV. The repetition frequency of the impulse was set to 1000 Hz. The contact gap was 0.8 mm. The VIs were tested for the inrush current interruption performance with inrush current set to 2 kA and 5 kA, with a frequency of about 3800 Hz. The experimental results showed that there were two different types of inrush current interruption depending on high-frequency high-voltage impulse conditioning. The inrush current interruption type I referred to the inrush current interruption during the prestrike process before the contacts touched. This type inrush current interruption could be caused by the erosion of prestrike arc. Moreover, the high frequency voltage impulse conditioning influenced the occurrence frequency, the number of interruptions and the duration of the inrush current interruption type I. The inrush current interruption type II referred to the inrush current interruption during the contact bouncing process after the contacts touched. The inrush current interruption type II occurred only in the case of the VIs after conditioning. Furthermore, the occurrence frequency of the inrush current type II decreased with increasing inrush current. [ABSTRACT FROM AUTHOR]

Recently, the pulsed power systems have found wide applications. For this reason, using the pulsed power generators that in addition to responding to the needs of the user, are providing the advantages of compactness, high flexibility, high repetition rate and cost efficiency is inevitable. This paper proposes a converter which is a combination of Marx topologies and solid state voltage multipliers. It is capable of producing high voltage pulses with varying amplitudes at different frequencies where is modular and flexible. The resonant circuit used in this structure can reduce the stress on switching element and increase the output voltage while providing a zero current switching for the full bridge converter. Its analytical design is described and its verification is proved by the simulation results in MATLAB\SIMULINK. As a proof of concept, the measurement results taken from the experimental prototype, are presented as well. [ABSTRACT FROM AUTHOR]

In this paper, a study concerning self-breakdown voltage characteristics, electrode erosion, and degradation of the insulator, of a two-electrode spark-gap switch has been presented based on experiments. A 6 ?F pulse capacitor and a DC high voltage source (set at ?40 kV) were utilized to achieve ?0.1 pulses per second repetitive arc discharge between two fixed Cu-W (Cu30/W70) alloy electrodes in the 1.2 L airtight chamber of the switch. With average transfer charge of 2.2 C per shot, this switch was tested for 5800 shots altogether. The results demonstrated the electrode erosion rate of the cathode was 6.3434?10?6 cm3/C whereas that of anode was 5.4691?10?6 cm3/C. Besides, by analyzing electrode surfaces' morphology and PTFE insulator surfaces' compositions after 5800 shots with the help of a scanning electron microscope, a dynamic 3D aspheric metrology instrument, an X-ray photoelectron spectrometer, a metallographic microscope, and a Mettler-Toledo analytical balance, some evidence of physical processes and chemical reactions between plasma channel, electrode materials, and insulation materials could be observed. Moreover, the chamber was opened and inspected for 10 times during the whole procedure, thus providing an overall description of the variation of the switch. It should also be pointed out that owing to complex mechanisms during the aging process, the self-breakdown voltage followed a mixed Normal distribution other than any other simple distributions. [ABSTRACT FROM AUTHOR]

Generally, for pulsed power applications with low jitter and high repetition rates, the use of semiconductor switches have replaced the traditional gap switches and thyratron circuits due to the limited lifetime of the thyratron and gap switches under such operating conditions. However, the limited ratings of these semiconductor switches require series and/or parallel stacking in order to handle high voltages and current levels associated with the discharge energy. Described in this paper is the design of a high voltage switch that uses a simple and reliable gate driver circuit for pulsed power application. In this design, the switch module is made up of insulated-gate bipolar transistor (IGBTs) and their gate driver circuits compactly fitted onto a single module. The ease by which the switch modules can be configured (series stacking and/or parallel stacking) to meet future load variations allows for flexible operation of this design. In addition, the detailed implementation of the gate driver circuit for reliable and easier synchronization of the switches, the simultaneous transfer of both signal and power for current boost are also described in this paper. A 120 nF capacitor bank energy was discharged using a configuration of the developed high voltage switch and a developed 15 kV, 1.5 kJ/s peak power capacitor charger, and by experimental results, the operation of the proposed circuit was verified to be effectively used as a switch for pulse discharging. [ABSTRACT FROM AUTHOR]

Positive leader current spikes were observed in long air gap discharge. However, there has been no explanation on this phenomenon so far, and some leader advancement models can only produce the current without spikes. Therefore, it is necessary to figure out this phenomenon in order to deepen the understanding of leader discharge. In this paper, experiments of leader development were carried out in a 10 m rod-plane gap under positive switching impulse. The discharge current and high speed photographs of discharge process were recorded synchronously. Then the high speed photographs during the period when the leader current fluctuated were carefully analyzed. The experimental results showed that the leader current spikes were with leader branching. Finally, the effect of branching on the spikes of positive current was explained qualitatively and a hypothesis on leader branching was proposed. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) in gas insulated switchgear (GIS) has been studied extensively under AC voltage or transient voltage applied alone. However, the transient voltage in an actual system is superimposed on the AC operating voltage, which has rarely been studied. In this paper, the effect of AC and switching impulse superimposed voltage on PD characteristics was studied in SF6 gas. A test platform of generating superimposed voltage with controllable phase was used to study free particle and floating potential defect models. When the AC voltage was 90 and 110% of PD inception voltage (PDIV), the standard switching impulse with amplitude of about twice the PDIV was superimposed on different phases of the AC voltage. When the AC voltage is below the PDIV, results show that PDs of free particle defect model can be initiated when switching impulse is superimposed on 45 and 90° of AC. The PDs in the subsequent cycles of AC reignited into a self-sustaining discharge. For the floating potential defect, PDs have a marked difference duration, which is initiated by switching impulse in different phase. However, there is no change in PDs in each model when the AC voltage is above the PDIV. [ABSTRACT FROM AUTHOR]

In this paper, sulphur hexafluoride (SF₆) insulated vacuum interrupter circuit breakers have been used to explore replacing SF₆ gas with a trifluoroiodomethane and carbon dioxide (CF₃I-CO2) gas mixture. The search for an alternative insulation gas is driven by the well known extreme global warming potential of SF₆. For this purpose, the circuit breaker gas compartment of a piece of gas insulated switchgear (GIS) was filled with a CF₃I gas mixture and then tested using lightning impulses up to the rated withstand strength. The tested ring main unit was initially designed to be insulated with SF₆ gas. The unit is a three-phase switchgear containing two switches per phase; a selector interlock and a vacuum bottle circuit breaker per phase. The test programme performed in this investigation demonstrated the breakdown performance and insulation strength of the new gas mixture as well as the vacuum circuit breakers behavior when insulated with a new insulation medium. Data on the dielectric properties of the proposed gas mixture is presented, and the performance of the tested vacuum circuit breaker is discussed. Promising results are obtained which indicate the suitability of this more-environmentally friendly gas for high voltage insulation purposes. [ABSTRACT FROM PUBLISHER]

An all solid-state high-voltage rectangular pulse generator is proposed in this paper. This generator broadly consists of a Marx generator, a pulse forming line (PFL) and a magnetic switch (MS). As the power supply, the Marx generator discharges to the PFL through an inductor. The inductor should cooperate with MS since it influences the discharging process directly and determines the volt-second product of the MS and the pre-pulse over the load. The MS saturates at exactly the moment the discharging process ends. Then PFL discharges to the matched resistor load through the saturated MS and a high voltage rectangular pulse is obtained over the load. The design of Marx generator and MS are introduced in this paper. Experiments under a single shot and repetitive frequency of 5 kHz were carried out. PSPICE simulations with a simplified model of MS were carried out to verify the experimental results. The experimental result matches well with the results of the simulation. A rectangular pulse with 12.5 kV voltage amplitude, 46-ns rise-time, 220 ns pulse-width was obtained over the 50 Ω resistor load. [ABSTRACT FROM PUBLISHER]

This paper presents a capacitor charging power supply (CCPS) using high-voltage dc/dc converter for pulsed power applications. For the main converter, it used full-bridge phase-shifted (FBPS) pulse-width modulation (PWM) converter. The proposed CCPS has modularity concept, and the output voltage was boosted by a high-voltage high-frequency (HVHF) transformer included in FBPS PWM converter. The control method is used a phase-shifted PWM to reduce the losses caused by switching. To solve the voltage unbalancing problem of the output capacitors, synchronization algorithm is selected. Also Thermal characteristics are analyzed by theoretical calculation and simulation. Experimental results of the single module and CCPS are provided to validate the effectiveness of the proposed system and it was carried out the 20-kV 160-kW prototype. [ABSTRACT FROM PUBLISHER]

In this paper, we propose and design a novel generator for the high voltage square pulses with the changeable polarities in order to reach the requirements and the needs for the intended experiments on sterilization of microorganism. The major component of our circuits is a non-trivial combination between a half bridge Marx generator and an H bridge in series, combining with the DSP control unit, which can adjust the voltages, frequencies, pulse widths and polarities, and also tolerate various loads. More precisely, we illustrate the design and operation principles for each module in the constructed circuit and analyze the system performance with various loads. The effectiveness and correctness of our proposed circuit and methodologies have been verified and demonstrated by both PSIM simulation results and our own prototype. In this paper, we also show the stability and reliability of the pulse generator we proposed in terms of various load conditions and operation safety respectively. Furthermore, we also observe that the key parameters based on our constructed pulse generator can be easily adjusted which include voltages, frequencies, pulse widths and polarities. We hope that our work will stimulate the further investigations on design and analysis of pulse generators with a focus on modularization and miniaturization. [ABSTRACT FROM PUBLISHER]

Electrical breakdown in air in a point-plane topology involves complex processes that are still not fully understood. Unlike uniform-field topologies, the highly-divergent fields produced by point-plane topologies create pre-breakdown corona with volumetric space charge. It is known that space charges developed by corona discharge have significant impacts on the breakdown voltage in non-uniform electrode topologies. With large inter-electrode gaps (>cm) the breakdown voltage for a HV point cathode in air at atmospheric pressure is noticeably larger than a HV point anode. However, this paper shows that in shorter point-plane gaps in air (less than ~10 mm), in the air pressure range 0.1-0.35 MPa, an HV point anode has a similar breakdown voltage which eventually is surpassed by the HV point cathode as the inter-electrode gap is increased. The inter-electrode gap at which the HV cathode has a higher hold-off voltage is found to be dependent on the gas pressure and radius of the point electrode. [ABSTRACT FROM PUBLISHER]

With the fast development of multi-terminal high-voltage direct-current (HVDC) transmission technology, there is an urgent demand for the HVDC interruption technique. In this paper, an interruption scheme for HVDC based on artificial current zero is proposed with its main circuit breaker consisting of modularized vacuum switch in series. A triggered sphere gap is adopted as the commutation switch to achieve bidirectional DC interruption. The interruption process, particularly, the most important two commutation processes, is simulated based on a circuit model. The residual current and its influence after current commutation, which might exist due to the weak arc extinguishing capacity of the sphere gap, are analyzed. It is proposed to use back-up circuit breakers to interrupt the residual current. Furthermore, the influence of the frequency of the countercurrent on the interruption process, particularly, on the integral of i2t in the triggered sphere gap due to the residual current, is discussed. [ABSTRACT FROM AUTHOR]

Recent studies suggest that fluoronitriles compound Novec 4710 possesses a dielectric strength two times higher than that of SF6, while with a low global warming potential of only 2400. Mixed with CO2 buffer gas, the Novec 4710 mixtures offer excellent dielectric properties and the possibility to be used as an eco-friendly alternative to SF6 for medium voltage switchgears. This paper focuses on the comparative study of the breakdown strength and partial discharge (PD) characteristics between the fluoronitrile/CO2 mixtures and SF6 under AC voltages. Breakdown tests are conducted under different electrode configurations, i.e., planeplane, sphere-plane, rod-plane, and needle-plane, at different pressures and electrode gaps. In the uniform field, equivalent dielectric strength to SF6 at 100 kPa can be reached by a mixture containing 15% fluoronitrile at identical total pressure; while in non-uniform and highly non-uniform fields, SF6 exhibits higher dielectric strength than 20% mixture. The PD analysis suggests that SF6 has much more PDs with lower magnitude and the 20% fluoronitrile/CO2 mixture has less PDs but with higher magnitude. Due to the different PD characteristics, the corona stabilization effect may be responsible for the higher breakdown strength of SF6 under highly non-uniform field. [ABSTRACT FROM AUTHOR]

Vacuum circuit breakers are widely used in medium-voltage class. In vacuum circuit breakers, restrikes and non-sustained disruptive discharges sometimes occur after current interruptions. It is said that these late breakdowns are triggered by the microparticles. This paper aims to investigate the relationship between the motion of microparticles and subsequent late breakdown phenomena. It does by artificially injecting microparticles into the vacuum gap and observing their motion using a highspeed video camera. We focused on the sputtering of the electrode material during the current interruption and the mechanical stress of the switching operation as being the origin of these microparticles. We found that the motion of microparticles can be grouped into two distinct patterns: bouncing and attaching. Bouncing microparticles seem to be made of metal, while most of the attaching microparticles attached themselves to the cathode, and their charge was about five times greater than that of the bouncing microparticles. The attaching microparticles seem to be positively charged by secondary electron emissions from the surface under electron bombardment due to the field emission current from the cathode. From these results, we believe that the surfaces of the attaching particles are covered with an insulating layer. From our observations of the production of microparticles by mechanical stress, we have found that the breakdown voltage of the gap drastically drops after a mechanical switching operation where microparticles are produced. The breakdown voltage is restored with repetitive mechanical switching operations and subsequent voltage application. However, the breakdown voltage drops again when the operating speed of the electrode is increased. We also found that microparticles are scattered from the cathode spots on electrodes that have not been current-conditioned, and they are hardly produced from electrodes that are current-conditioned. From these results, we believe that controlling the speed of the mechanical switching operation and the current conditioning are effective ways to prevent the microparticles from being produced. [ABSTRACT FROM AUTHOR]

Nowadays the phase controlled switching is a preferred method for capacitive switching. Thus the prestrike characteristic is an important issue for the control strategy. The objective of this paper is to understand the prestrike characteristics of vacuum interrupters (VIs) in the capacitive making operations of 40.5 kV vacuum circuit breakers (VCBs). In the experiment, three VIs with CuCr50 (50 wt% of Cr) contact material and three VIs with CuCr40 (40 wt% of Cr) contact material with contact diameter of 50 millimeters were prepared. The CuCr50 and CuCr40 contact materials are made by using infiltration and arc-melted technology, respectively. An L-C oscillating circuit generated an inrush current with a frequency of 207 Hz and with a peak of 6.48 kA, while the applied voltage was 46.3 kV which is equivalent to the peak voltage for a 35 kV three-phase network whose capacitive voltage factor is 1.4. The experimental results show that the complementary cumulative distribution function (CCDF) of the prestrike gaps dpre follows a 3-parameter Weibull distribution. The prestrike gap below which prestrike would always occur is similar for all six test VIs which is 2.4–3.1 mm. However, the average values of d\0, ¿50 and ¿90 for infiltration CuCr50 contact material are 57.5%, 45.3% and 28.9% higher than the ones in arc-melted CuCr40 contact material, respectively. During the inrush current flowing, at each zero-crossing of the inrush current the prestrike arc tries to extinguish with the occurrence of three types of contact gap breakdowns. Furthermore, if the contact gap breakdowns are withstood at the inrush current zero-crossing, inrush current interruption phenomenon happens, which proves a common phenomenon in capacitive making operation. The inrush current interruption phenomenon is mainly determined by the prestrike distance and not by the material quality. The experimental results imply that the field emission dominated breakdown and the micro-particle induced breakdown both take effect in the prestriking and contact gap breakdown process. [ABSTRACT FROM AUTHOR]

Researchers and designers of insulation systems are facing new challenges due to the ubiquitous presence of power electronics devices in power conversion applications across various voltage levels. The stresses applied to insulation systems by power electronic devices require new approaches for evaluating the intensity and frequency content of working electric field strength and degradation processes. Typically these parameters are assessed through the analysis of partial discharges. Multilevel converters are increasingly being implemented in industrial applications due to the advantages they offer for example in efficiency, harmonic distortion and filtering strategies. This paper presents an analysis of partial discharges in a magnet twisted-pair wires subjected to high voltage pulse-width-modulated pulses obtained from a multilevel converter. A comparison between the number of levels and modulation frequencies on partial discharge inception and intensity are presented. As an assessment criterion, the voltage-time product above partial discharge inception level was compared. [ABSTRACT FROM AUTHOR]

In the paper a new partial discharge (PD) location technique based on acoustic emission and conventional partial discharge detection method is presented. Synergetic combination of two methods allows obtaining a high accuracy of the insulation fault location and reducing the time of measurement procedure. Several cases of practical application of the new technique for PD location in the power transformers tested in an HV laboratory and in a substation are discussed. [ABSTRACT FROM PUBLISHER]

According to the IEC standards, test objects in back-to-back capacitor bank switching tests are subjected to inrush currents of 20 kA peak and 4250 Hz frequency during making operations. For vacuum interrupters (VIs), the contact surfaces may be seriously damaged by the high-energy arc of the inrush current. The field emission current characteristics reflect the surface microscopic conditions after undergoing the inrush current. The objective of this paper is to investigate the impact of the inrush current during back-to-back capacitor bank making operations on the field emission current characteristics of vacuum interrupters under AC power frequency voltage. The amplitudes of the inrush current were set as 10 and 20 kA, respectively. The sample VIs underwent the inrush current at each amplitude twice. After each inrush current, the field emission current of the VI was measured by applying a power frequency voltage upon the contacts with a fixed gap of 1 mm. By applying an AC power frequency voltage, an unsymmetrical field emission current was measured. In addition, according to the Fowler-Nordheim (F-N) theory, the field enhancement factor β and the effective emission area Ae were calculated. The experimental results show that there is a significant unsymmetrical field emission current at each polarity of the power frequency voltage. Moreover, during the voltage rising phase, the field enhancement factor β is higher and the effective emission area Ae is smaller than that during the voltage falling phase for both positive and negative voltage polarities. A heating-cooling hysteresis effect of the emission sites could explain the phenomena. [ABSTRACT FROM PUBLISHER]

A modular double gap pseudospark discharge based switch has been recently designed and developed for various pulsed power applications. The modular pseudospark geometry has two gaps that are separated by a cavity drift space region. It employs a single trigger unit in the cathode region to initiate discharge for the rapid breakdown of both the gaps. Successful experiments for the double gap pseudospark with typical coaxial arrangement of multichannel discharges were performed. The peak discharge currents at breakdown voltage of about 40 kV were 5 and 10 kA through resistive loads of 5.25 and 2.7 Ω, respectively. The design of the double gap pseudospark along with switching results is presented in this paper. [ABSTRACT FROM AUTHOR]

Pulsed electric field (PEF) can be used effectively in water treatment applications by passing infected water through two electrodes excited from a high voltage pulsed power supply which guarantees killing the harmful germs. In this paper, a new high-voltage pulse-generator with closed loop control of its output voltage is presented for treating water via underwater pulsed streamer corona discharge. The proposed generator is fed from a low AC voltage source (utility mains 220 V, 50 Hz) which makes it suitable for domestic applications. The proposed topology provides transformer-less operation which reduces the system size and enhances the overall efficiency. The proposed topology is based on capacitor-diode voltage multiplier (CDVM) circuits in conjunction with DC-DC converters (Boost and Buck-Boost converters). The simulation and experimental results elucidate the proposed configuration. [ABSTRACT FROM AUTHOR]

Many research fields need special high-voltage pulses in pulsed power applications, which are different from typical rectangular pulses. In this paper, a high-voltage waveform modulator of two methods using a solid-state Marx generator has been developed and tested. Instead of manufacturing a generator with a specialized structure, the modulator can control a general Marx generator by low-voltage programmable logic devices to produce an irregular but controllable high-voltage triangular pulse with pulse length of ~4.5 μs and peak voltage of ~123 kV. [ABSTRACT FROM PUBLISHER]

This paper presents the design of IGBT-based switching modules for a nitrogen gas laser. First, the CC-topology, which drives the laser, is discussed and simulated. Simple models of the laser tube and the switch are presented. The comparison of the simulation with experimental data shows good accuracy. The results are used to discuss the influence of the parasitic inductance and the capacitances on the laser tube behavior. Cascades with an 11-cell series connection based on different IGBT-chips (1700 V and 1200 V) have been built up and measured. The focus of the design is the high speed synchronous switching of all switching cells. Therefore, the design of a pulse transformer-based gate drive and a symmetrization network is presented. The module equipped with the four parallel 1200 V/35 A-IGBTs per cell produces the highest switching power. Among the variants, the switch peak current is up to 700 A at blocking voltages of up to 13.2 kV in the real environment of the nitrogen laser. The switch current slope reaches up to 30 A/ns and the laser tube current up to 1.8 kA. The variant with 1200 V/35 A-IGBTs produces an output energy which is about 15 % higher compared to the former MCT-based switch. Furthermore, a modified CCtopology for lower blocking voltage is investigated. The IGBT-based switches are able to replace the MCT-switches in this application. Between the different switches a tradeoff has to be done between high output energy and the effort for the assembly. [ABSTRACT FROM PUBLISHER]

The electromagnetic radiation effect of high-voltage, subnanosecond pulsed electric fields attracts strong interest from researchers because of its significant development potential in biological treatments, particularly in noninvasive diagnosis and treatment. But up to now, high-voltage subnanosecond pulse generators are widely used for national defense and military, and they are difficult to implement successfully in the civil medical field. A compact, self-contained, repetitive frequency, high-voltage subnanosecond pulsed power source is proposed in this paper. It was designed, built, and tested successfully. Based on a four-stage, low-inductance Marx generator, the pulsed source produces subnanosecond rise-time pulses. A chopping switch was designed to cut off unformed signals and generate subnanosecond pulses. A measurement device, based on the principle of a capacitive voltage divider, was also constructed to determine both the amplitude and the rise-time of the pulse delivered by the source. Preliminary tests show that the source can produce repetitive frequency pulses with a peak value that exceeds 30 kV, as well as rise-time and pulse width (full wave at half maximum) within 1 ns under atmospheric pressure conditions. The pulse amplitude may be extended to hundreds of kilovolts by filling the switch system with an inert gas. The rise-time would be shortened as well. The pulsed power source shows optimistic prospects in the biological fields. [ABSTRACT FROM PUBLISHER]

In this paper, the design, installation, and performance of a ?100 kV gas switch for linear-transformer-driver (LTD) are presented. LTD demands require gas switches that can be operated at a 200 kV DC voltage, and require trigger jitter and inductance as small as possible. A field distortion switch has been designed based on the L3 switch, the design criteria of switch electric field and trigger system are explained in detail. A two dimensional plasma model is developed to analyze the contribution of trigger system to the closing of gas switch. An experimental platform was built to test the self breakdown and triggered breakdown characteristics of the switch. When the switch is charged to ?100 kV and is triggered by a -120 kV pulse with a 30 ns rise time, the delay time is 78 ns and the jitter is 1.6 ns. A comparative test was done to research the function of UV preionization gap, the test results shown that the UV preionization gap can reduce the switch delay time and jitter, it can effectively improve the trigger performance of the switch. Meanwhile, using the short-circuit discharge, the inductance and impedance were measured, the switch inductance is about 30 nH, and the impedance is varied from 50mΩ to 30mΩ. [ABSTRACT FROM AUTHOR]

The past and recent investigations show that front time of switching overvoltage waveforms in Ultra High Voltage (UHV) system of long distance transmission are mostly in long wave front time exceeding 1000μs. The long front time of switching impulse voltage has been deviated from the critical front time. This paper is involved with breakdown characteristics and external insulation design under long front switching impulse voltage in UHV system. All the Tests were performed on an outdoor UHV test site at altitude of 2100 m, China Southern Power Grid Co. Ltd. (CSG). Breakdown characteristics of rod-plane and actual size tower-conductor in /spl l.chemo/800 kV UHV DC transmission line are obtained under wide front time switching impulse voltages from 100 to 2350 μs. From the comprehensive studies of such tests, it is proposed that U50 of front time exceeding 1000 μs increases 20% compared with the results of standard switching impulse (250/2500 μs) tests and standard deviations of U50 is 6% in UHV transmission system. Finally, an air gap insulation design procedure in conductor-tower of UHV transmission line at altitude of 0-2000 m is presented. Long front time switching impulse strength of conductor-tower gap is proposed into selection by reference in UHV transmission line insulation design. [ABSTRACT FROM AUTHOR]

Along with rapid advancement of power semiconductors, voltage multipliers have introduced new series of pulsed power generators. In this paper, based on conventional voltage multiplier and by using power electronics switches a new topology in high voltage pulsed power application is proposed. This topology is a modular circuit that can generate a high output voltage from a relatively low input voltage with fast rise time and adjustable frequency, pulse width, and voltage levels using a series connection of switched capacitor cells. A comparative analysis is carried out to show the advantages of proposed topology. Experimental and simulation results are presented to confirm the analysis. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate an impact of the inrush current on the prestrike and restrike characteristics of vacuum interrupters (VIs) during capacitive current switching duty. Eleven 7.2 kV VIs are used. Their contact parameters are contact gap 4 mm and contact material CuCr25 (25%weight of Cr). A series of 80 CO operations are executed for each test VI. The amplitude of inrush current Iinrush (3800 Hz) is set to 0 kA, 2 kA, 5 kA and 10 kA, respectively. The switching current is less than 1 A rms. The (1-cosωt) shape of the recovery voltage with a peak of 15 kV is applied to the test VI. The experimental results show that the prestrike and restrike phenomena are significantly influenced by the contact surface conditions damaged by the inrush current. The cumulative probability of the prestrike gap dpre follows a 3- parameter Weibull distribution. When Iinrush increases from 2 kA to 5 kA, the prestrike gap increases accordingly. The 10% dpre increases from 0.5 mm to 0.7 mm. The 50% dpre increases from 0.7 mm to 1.0 mm. The 90% dpre increases from 1.0 mm to 1.5 mm. The scale in the Weibull distribution, which can describe the scattering of dpre, is 0.2 mm and 0.6 mm in the case of Iinrush = 2 kA and Iinrush = 5 kA, respectively. It is found that the occurrence frequency of the inrush current interruption increases from 37.9% to 68.3% with the increase of Iinrush from 2 kA to 5 kA. Moreover, the inrush current also has an impact on the restrike types, which are classified into three types according to the waveform features. The average restrike probability increases from 4.6% to 17.9% and further to 30.4% with the increase of the inrush current from 0 kA to 2 kA and 5 kA, respectively. In addition, the higher the inrush current, the restrike tends to occur earlier during the recovery voltage period. [ABSTRACT FROM AUTHOR]

Ultra high voltage (UHV) systems are increasingly being planned and constructed, hence studies are promoted on the standard for high-voltage test techniques for UHV-class equipment, the scope of which includes the switching impulse voltage test waveform. Influences that must be considered to study this test waveform are those of actual switching overvoltage waveforms generated in the UHV system and applied to equipment and the change in the breakdown characteristics associated with a longer insulation length such as an air gap clearance. In the present paper, to determine the switching impulse test waveform, switching overvoltage waveforms applied to the UHV equipment were initially investigated. As a result, it emerged that the time to peak Tp was long, ranging from 700 μs to 1000 μs, for closing overvoltage which is relatively high switching overvoltage. When other types of overvoltage in the switching surge range were considered, the Tp varied widely from 100 μs to 1000 μs. Subsequently, the insulation characteristics of UHV-class long air gaps for switching impulse waveforms were investigated. It emerged that, for the fundamental model, namely rod-plane electrodes, the Tp of switching impulse waveforms with the lowest breakdown voltage (critical time to peak, Tcr) ranged from 350 μs to 550 μs whereas it shifted to a shorter time of 200 ??s to 350 ??s when environmental conditions, such as humidity and precipitation, were taken into consideration. For basic structure models assuming actual facilities and real scale structure models, the Tcr ranged from 100 μs to 300 μs. Furthermore, the internal insulation characteristics for switching impulse waveforms, such as SF6 gas and oil-paper insulation, were also investigated. Consequently, in the case of the internal insulation of equipment such as gas insulated switchgears (GIS) and transformers, the Tp of switching impulse waveforms had a minor influence on the insulation characteristics, even if it varied from 100 μs to 1000 μs. Following comprehensive evaluation of these characteristics, it was concluded that, in the switching impulse test for UHV-class equipment, it is reasonable to apply a waveform of 250/2500 μs, which is the same as that for equipment of 800 kV or less. [ABSTRACT FROM PUBLISHER]

Capacitor charging power supply (CCPS) is one of the most important components of a pulsed power system. The CCPS studied in this paper is used in power conditioning systems for Laser Nuclear Fusion. With a view to enabling multiple CCPSs to work concurrently in an environment of high voltage, high power and strong electromagnetism, this paper carries out a profound and systematic research into the characteristics of a capacitor charging power supply, including charging rate, harmonic features, efficiency and voltage precision, etc. Furthermore, some measures to improve the characteristics of CCPS are put forward. The advantages of high charging rate, low harmonic, high efficiency and accurate charging voltage are proved by the results of experiments and the performance in practical operation on a 23.5 kV, 50 kW, 4400 μF CCPS. [ABSTRACT FROM AUTHOR]

The ferroelectric and fatigue properties of spray deposited K ? substituted cesium nitrate: poly (vinyl alcohol) composite films have been studied. The XRD pattern confirms the presence of ferroelectric phase of CsNO3 in the composite films upto doping concentration of 7.5%. The elemental analysis has been studied using EDX measurements. It is observed the remanent polarization (Pr) increases linearly that with doping concentration and optimum value of Pr = 9.2 ?C/cm2 was found. The fatigue measurements also show improvement in K - substituted composite films. The switching time has been found to reduce four times in the K ? substituted films. The C ? V characteristics of the composite films show the butterfly feature and also confirm presence of ferroelectricity in the composite films. [ABSTRACT FROM AUTHOR]

When two-electrode spark gap switches are applied to main discharging circuit of pulsed power conditioning system, trigger generators will be needed. To guarantee triggering reliability and protect other key components in the pulsed power conditioning system, such as pre-ionization branch and xenon lamp, magnetic switch is needed to insulate the high triggering voltage in the main discharging circuit. In this paper, starting from the analysis of the working principle of the discharging circuit, we present the solution of Fe-based nanocrystalline alloy switch. Specifically, we provide the basis of theoretical calculation and the method of material selection for the design and realization of this magnetic switch. Via the performance tests in pulsed power conditioning system, the validity of material selection and parameter design is proved. This paper provides a reference for the engineering design and application of magnetic switches in huge pulsed power systems. [ABSTRACT FROM AUTHOR]

A collaborative effort at Texas Tech University on high power RF transmitters has directly translated to the development of phased array pulsed ring down sources (PRDS). By operating an array of PRDS, peak radiating power on target can theoretically be increased to the squared of N sources. The primary limitation on the application of the array concept is the jitter with which the individual sources can be fired. An ideal jitter of a small fraction of the risetime is required to accurately synchronize the array to steer and preserve the amplitude of the radiated pulse. This paper describes in detail the implementation of a GPS based timing system that will synchronize the operation of each of the elements of a geospatially distributed phased array to maximize the peak power delivered to a single position. Theoretical array performance is shown through Monte Carlo simulations, accounting for switch jitter and a range of GPS timing jitter. Each module will include a control unit, low jitter pulser, low jitter spark gap, antenna element, as well as a GPS receiver. The location of each module is transmitted to a central controller, which calculates and dictates when each element is fired. Low jitter in the timing of the GPS reference signal is essential in synchronizing each element to deliver the maximum power. Testing using a preliminary setup using GPS technology is conducted with both 1 pps and 100 pps outputs. Jitter results between modules are recorded to ~10 ns without any correction factors and 1-2 ns with simple averaging. With the timing and geospatial errors taken into account, the proposed concept will show usable gains at phased array operating frequencies up to several hundred MHz. [ABSTRACT FROM AUTHOR]

Research efforts at Texas Tech University on impulse antenna phased array has resulted in the development of a dependable high voltage, high repetition rate switch that can minimize jitter into the ps range. To accurately synchronize a phased array to steer and preserve the risetime of a radiated pulse, the jitter can only be a fraction of this risetime. Initial testing with a similar system in [1] produced sub-ns jitter results for operations in different gases and gas mixtures. This paper discusses in detail 50 kV, 100 Hz switch operations using different testing parameters. The switch jitter as a function of triggering conditions is discussed, including a comprehensive evaluation of jitter as a function of operation pressure as well as trigger magnitude. Several phenomenon were observed and discussed to quantify the switch jitter with respect to operation pressure and trigger magnitude. The temperature of gas and its effects on switch jitter is also documented in this paper, with a jitter improvement of ~25% recorded. An empirical formula was determined as a function of the gas density, electric field of the main gap, and electric field for the trigger for the experiments conducted in this manuscript. A 50 Ω, 1 nF pulse forming line is charged to 50 kV and provides the low inductance voltage source to test the switch. The hermetically sealed spark gap, with a modular design composed of copper tungsten electrodes, gas feeds, Kel-F lining, as a well as a G-10 shell is used to house the high pressure gases for the experiments. Trigatron-type triggering is provided by a solid state opening switch voltage source that supplies 75-150 kV, 10 ns risetime pulses at a rep rate up to 100 Hz in burst mode. [ABSTRACT FROM AUTHOR]

This study investigates the characteristics of electrical trees in silicone rubber (SiR) samples after soaking in silicone grease (SG) for various times and exposed to switching impulses. The results show that the tree initiation probability increases from 60 to 100 % after SG soaking for 340 h when the impulse amplitude is 38 kV and the tree fractal dimension increases from 1.16 to 1.45. A similar trend is observed under negative impulse. It is suggested that SG soaking leads to a higher tree initiation probability and a larger tree fractal dimension. In addition, isothermal surface potential decay measurements are employed to obtain the trap parameters of SiR samples. Equilibrium swelling procedures are used to test the crosslinking density. The energy level and density of deep trap both decrease with SG soaking time, which is beneficial for the transport of charge carriers injected from the needle tip and further results in more severe scission of SiR molecular chains. Moreover, the expansion of free volume originating from the broken physical crosslinking structure allows more violent impact ionization of charges to occur, which can also aggravate the scission of SiR molecular chains. Therefore, the decreased tree resistance can be found in SiR after SG soaking. Furthermore, the polarity effects can be observed during the tree initiation and propagation process, which are mainly rooted in the different distribution of hole­type and electron-type traps. [ABSTRACT FROM AUTHOR]

When driving capacitive loads, pulses with steep falling edges are difficult to obtain using conventional pulsed power modulators, which also makes them unsuitable for operating at higher frequencies. In this paper, a repetitive high voltage pulse adder is described, which can generate nearly rectangular pulses even with capacitive loads. This pulse adder is based on solid-state switches, and each power stage contains two Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs): one set which outputs high voltage pulses and the other set which is used to dissipate charges stored in the load and distributed capacitors. Testing the proposed pulse adder with dielectric barrier discharge (DBD) loads, nearly rectangular pulses are obtained. In our present work, a 40-stage modulator has been built and successfully operates at an output voltage of 30 kV and a repetitive frequency of 20 kHz. The rise and fall times are less than 200 ns, and a minimum pulse width of 6 μs was obtained. This prototype has been applied in DBD experiment research. [ABSTRACT FROM AUTHOR]

This paper describes a novel MOSFET gate driver circuit design for pulsed power application. It is shown that MOSFET switching speed can be enhanced by using an energised inductor as a high current source in series with the gate terminal of a power MOSFET. This topology demonstrates switching speeds of less than 10ns for MOSFETs with high input gate capacitance. It is also shown that by increasing the current in the gate drive and with an optimised layout, a single gate driver can be used to drive multiple parallel connected MOSFETs synchronously without compromising their performance. The circuit design is analysed and experimental results presented when operating at an instantaneous power of 25 kW. [ABSTRACT FROM AUTHOR]

This paper describes the design of a 48 kJ/s high-voltage capacitor charging power supply (CCPS), focusing on its efficiency, power density, and reliability. On the basis of a series-parallel resonant converter (SPRC) that provides high efficiency and high power density owing to its soft-switching, the design of the CCPS is explained in detail, including its input filter, resonant tank parameters, high-voltage transformer and rectifier, as well as its protection circuit. By using two resonances per switching cycle, which provides a trapezoidal instead of a sinusoidal waveform of the resonant current, the proposed CCPS can take advantage of the lower conduction loss and reduced switching loss by improving the crest factor and allowing a higher value of the snubber capacitor, respectively. In addition, the compact design of an input filter without bulky components such as a DC reactor and an electrolytic capacitor allows for high power density, a high power factor, and low cost. In addition, the control loops for the voltage and current were optimized with a fast response time in order to compensate for the low frequency ripple of the input voltage, which results from the reduced filter component. Experiments on the developed charger were carried out with both resistor and capacitor loads in order to measure not only its efficiency and power factor with respect to the output power but also its charging time, in order to estimate the average charging current. The experimental results obtained with a resistor load showed a maximum efficiency of 96% and a power factor of 0.96 for a full-load condition. For the measured charging time of a 4 mF capacitor, with 9.68 s for 10 kV charging, the average charging current was estimated as 4.13 A. Moreover, to verify the reliability of the developed CCPS, a variety of tests, including opening and shorting of the output terminal as well as misfiring of the discharge switch during the charging operation, were performed with a 200 kJ pulsed power system. Finally, it was experimentally confirmed that the developed CCPS shows high performance in terms of efficiency (96 %), power factor (0.96), and reliability with a high power density (820 W/L). [ABSTRACT FROM AUTHOR]

Capacitor charging power supply (CCPS) is a developed technology that utilizes resonant converters topology for high power applications. This paper proposes new a capacitor charging power supply using leg-rotation control method within a phase-shifted PWM full-bridge dc/dc converter. The capacitor charging power supply was connected in series to increase output voltage. Also, the proposed system is designed with soft switching techniques in order to achieve high efficiency, and a leg-rotation control method was used to reduce the heat generated from the IGBTs. The operation of the converter and design methodology will be described. A simplified model of a high-voltage high-frequency transformer is given and the structure is designed to decrease high-voltage stress. The validity of the proposed system is then verified by experimental results. The performance test of the capacitor charging power supply was carried out with a 2 μF capacitive load with a 20 kV output voltage. [ABSTRACT FROM AUTHOR]

An approach to high field control, particularly in the areas near the high voltage (HV) and ground terminals of an outdoor insulator, is proposed using a nonlinear grading material; Zinc Oxide (ZnO) microvaristors compounded with other polymeric materials to obtain the required properties and allow easy application. The electrical properties of the microvaristor compounds are characterised by a nonlinear fielddependent conductivity. This paper describes the principles of the proposed fieldcontrol solution and demonstrates the effectiveness of the proposed approach in controlling the electric field along insulator profiles. A case study is carried out for a typical 11 kV polymeric insulator design to highlight the merits of the grading approach. Analysis of electric potential and field distributions on the insulator surface is described under dry clean and uniformly contaminated surface conditions for both standard and microvaristor-graded insulators. The grading and optimisation principles to allow better performance are investigated to improve the performance of the insulator both under steady state operation and under surge conditions. Furthermore, the dissipated power and associated heat are derived to examine surface heating and losses in the grading regions and for the complete insulator. Preliminary tests on inhouse prototype insulators have confirmed better flashover performance of the proposed graded insulator with a 21 % increase in flashover voltage. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the di/dt capability and the turn-on action of conventional thyristors (including common thyristor and GTO) under short pulse conditions. Although the common thyristor is proven to be not adequate for pulse application, the GTO behaves excellently and it exhibits the potential of being operated in the case of much higher di/dt and pulse current than its rated values. Multi-cell PSpice simulation model of GTO was developed to evaluate influence factors of current distribution in thousands units of the GTO. It was found that forward transport time (TF) of excess carriers flowing through base region in each unit mainly determines the current distribution. If some unit has smaller TF, it will bear larger current compared with others in the turn-on process and thus has the risk of overheating. The use of magnetic switch in series with GTO can greatly reduce the power dissipation in the process and guarantee the GTO?s safe operation. Our tests have originally resulted in a maximum di/dt of 6 kA/μs for a 10-μs half-sine wave current pulse of 17.3 kA amplitude by using a GTO, whose rated RMS on-state current is 1500 A and di/dt capability is 800 A/μs. The measurements show that turn-on losses and conduction losses are less than 0.5 J. [ABSTRACT FROM AUTHOR]

The objective of this paper is to gain insight into free recovery processes in vacuum interrupters after diffused vacuum arcs extinction. A sub-microsecond voltage impulse, which peaked at 90 kV with a rising time of 150 ns) (rate of rise 480 kV/?s), were electronically controlled to apply upon a switching gap of a vacuum interrupter at a predetermined interval after a power frequency current zero. Based on the breakdown voltages at different intervals after arc extinction, we can obtain the free recovery behavior of the vacuum interrupter. The contact materials under study included Cu, CuCr25 and CuCr50. The contacts were butttype, and the contact diameters were 12 and 25 mm, respectively. The arc current peaked at 2.1 kA with a frequency of 50 Hz and the arcing time was ~9 ms. The results show the free recovery behavior stepped from ~28 kV to ~70 kV at ~4 ?s after arc extinction for the three kinds of contact materials with the two contact diameters given. By calculation of the dissipation of metal vapor density and ion density, we conclude that the decay of ions, rather than metal vapor, may be the main reason for the stepwise behavior of the free recovery process after diffused vacuum arcs extinction. [ABSTRACT FROM AUTHOR]

In this paper athree-stage pulse generator architecture capable of generating high voltage, high current pulses is reported and system issues are presented. Design choices and system dynamics are explained both qualitatively and quantitatively with discussion sections followed by the presentation of closed-form expressions and numerical analysis that provide insight into the system?s operation. Analysis targeted at optimizing performance focuses on diode opening switch pumping, energy efficiency, and compensation of parasitic reactances. A compact system based on these design guidelines has been built to output 8 kV, 5 ns pulses into 50 ?. Output risetimes below 1 ns have been achieved using two different compression techniques. At only 1.5 kg, this light and compact system shows promise for a variety of pulsed power applications requiring the long lifetime, low jitter performance of a solid state pulse generator that can produce fast, high voltage pulses at high repetition rates. [ABSTRACT FROM AUTHOR]

This paper describes the design of a compact and highly repetitive pulsed power modulator based on semiconductor switches. Output specifications of the proposed modulator are as follows: variable output pulse voltage, 1-10 kV; width, 1-10 μs; pulse repetition rate (PRR), 1-50,000 pps; and average output power, 10 kW. The proposed solid-state pulsed power modulator has two main parts: an IGBT stack that hasa gate drive circuit for the pulse output with a variable pulse width and repetition rate, and a capacitor charger that has a controllable output voltage. To connect all the storage capacitors in a series for high voltage pulses, a simple and reliable IGBT stack structure was proposed based on the Marx generator. In addition, the gate driver circuit, which supplies power and signals to all the IGBTs simultaneously, was introduced. This providesa superior protection function against the arc and the short. To charge the storage capacitors, a novel 10 kW (10 kV, 1 A) high voltage capacitor charger with the combined advantageof a series-loaded resonant converter and a ZVS (zero-voltage-switching) full-bridge pulse width modulation (PWM) converter was proposed and designed especially for the solid-state pulsed power modulator. Theexperiment results verified that the proposed scheme and structure can be used effectively for a high voltage pulsed power modulator that requires variable voltage, repetition rate, and pulse width, depending on the process of the applications. [ABSTRACT FROM AUTHOR]

In this paper, a compact repetitive nanosecond pulsed power generator based on transmission line transformer (TLT) is developed for non-thermal plasma generation. The high voltage capacitor, the spark gap switch and the input side of the TLT are built into a compact structure to obtain a fast high-power pulse. The properly designed magnetic cores placed around the coaxial cables of the TLT have been chosen to obtain a higher voltage gain. The layout of TLT is optimized to make the generator more compact. Experiment test shows that voltage pulses of 30 kV with rise time of about 25 ns, pulse duration of about 100 ns, pulse repetition rate of 500 pps have been achieved. [ABSTRACT FROM AUTHOR]