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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]

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]

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]

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]

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]

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]

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]

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 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]

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]

Statistical results have shown that the waveforms of impulses invading power transformers differ from those of the standard impulse voltage recommended by the IEC Standard. However, the effect of such differences on the modification effect of nano-modified transformer oil has rarely been studied. The present work therefore experimentally investigated the effects of impulse waveform parameters on the breakdown characteristics of nano-TiO 2 modified transformer oil (NMTO). We determined the breakdown characteristics of NMTO with different nano-particle concentrations, and compared the breakdown characteristics under both standard impulse voltage and non-standard impulse voltage. Specifically, the influence of the wave front time and wave tail time of the applied voltage on the breakdown characteristics of NMTO were experimentally identified. Finally, mechanisms of observed phenomena were analyzed. Test results indicate that both the waveform parameters and polarity have important effects on the modification effect of NMTO. Such effects are attributed to the migration of positive particles and charged nano-particles. [ABSTRACT FROM AUTHOR]

Switching of capacitor banks or cables leads to small breaking currents in comparison with short-circuit currents. After current interruption the circuit-breaker must withstand twice the peak value of the system voltage. Furthermore, restrikes can lead to voltage multiplication. The conjunction of relatively small breaking currents with high voltage stress must be considered in detail. This leads to a reconsideration of an appropriate design of contact speed and gap distance for capacitive switching duties. In particular the dielectric strength (DS) of the contact gap plays a major role regarding restrike performance. To simulate the capacitive switching performance of a certain contact system, the DS of a contact gap is required. A former study with a notable number of restrikes allows the calculation of the rate of rise of dielectric strength (RRDS). Taking this into consideration restrike simulations for vacuum circuit breaker for distribution and transmission voltages are presented. The evaluation of the simulations yields necessary requirements for contact speed, stroke and dielectric strength. [ABSTRACT FROM AUTHOR]

Vacuum interrupters (VI) are mainly built with ceramics as insulators. During the interruption process, the ceramics are coated with metal vapor from the contact material. In a worst case scenario, an electrical bypass is formed by the metal coating on the ceramic insulators. To avoid this, dielectric shielding is used, which provides defined surfaces for vapor coatings. Different shield arrangements offer a balance between local field stress and effective protection against impact from the metal coating. In our current work, we developed an electrostatic field simulation approach using COMSOL software. The purpose was to study the impact of the deposited layers on the performance of the VI with multiple shield arrangements. The simulations were done for three different cases, using the same VI geometry. •VI without metal coating on the ceramics; •VI with metal coating on the ceramics; •E-Field distribution between the head-shield and the metal coating on the ceramics. The identification of the effect of coatings on the electric field inside a VI during lightning impulse voltage stress can help to evaluate the breakdown voltage of the whole arrangement. Therefore, we simulated the redistribution of the electric field strength over the remaining insulated shields. [ABSTRACT FROM AUTHOR]

Two methods of output voltage adding using pulse forming lines (PFLs) have been studied and compared. Both methods use inductive energy storage (IES) instead of traditional capacitive energy storage (CES), which means that the PFLs are charged by current instead of voltage. One of the methods (Type A) used an additional transmission-line-transformer (TLT) to achieve the output voltage adding from multiple PFLs, while the other method (Type B) combined the functions of PFL and TLT into one set of transmission lines. Both methods have advantages and disadvantages over each other and both methods are believed to have certain significance in pulsed power generation. [ABSTRACT FROM AUTHOR]

A 2.6-MV field-distortion oil switch was developed and tested. Engineering design theories of this switch, including electrode areas, oil anode-cathode (A-K) gaps, insulator-surface electric field, and A-K gaps of the pre-gas switch, were described in detail. Structure designs of the switch were presented. Electric-field distributions of the oil A-K gap and insulator surface were analyzed and discussed. Also, switch breakdown processes were estimated. Finally, performances of this switch were tested on the ?JianGuang-I? facility (2.3MV/350ns). Preliminary experiment results show that with a 250kV trigger voltage, the switch-breakdown time delay is about 132ns and its jitter (the standard deviation) is less than 4.4ns. [ABSTRACT FROM AUTHOR]

High-Voltage pulse generators are commonly used in biotechnology, medicine, industrial applications, food processing and drinking water purification. The dc-dc boost converter has been used before in pulsed applications for its ability to amplify a relatively low input dc voltage to a high-voltage output. A high-voltage solid-state chopping switch is then used to chop the generated high output voltage. In this work, a boost-converter based ringing circuit with high voltage gain is proposed for water treatment applications. The basic concept of the proposed approach depends on operating the boost converter under discontinuous current conduction. With the proposed approach, the chopping high-voltage switch at the output stage is eliminated, which positively affects the system cost and efficiency. A full-design of the circuit and passive components is presented to ensure that the desired pulse specifications are achieved. The proposed approach has been validated using simulation and experimental results. [ABSTRACT FROM AUTHOR]

Partial discharges (PDs) induced by artificial fixed protrusions inside an SF6 gasinsulated switchgear (GIS) test object under oscillating switching and lightning impulse voltages (OIVs) were investigated experimentally. The features of PD current and light pulses (sequences) under impulses were analyzed. The characteristics of PD behaviors under oscillating lightning impulse (OLI), oscillating switching impulse (OSI) and 50 Hz AC voltages were studied according to their statistical distributions. The experimental data were quantitatively analyzed to compare the effectiveness of AC and OIV voltages in exciting the PDs in terms of PD inception and PD activity. Most PDs occurred successively around the peaks of the oscillation period of OIVs and periodical PD sequences were formed. Compared to positive point PDs, negatives occurred more frequently, but with smaller magnitudes. The positive OSI was found to have relative high efficiency in exciting PDs from fixed protrusion comparing to other types of voltage investigated. The occurrence frequency of PD under negative OLI was one or more orders of magnitude greater than that under AC voltage. The average PD magnitudes under positive OIVs were much greater than the others. Both the average PD magnitude and the occurrence frequency were greater at 0.2 MPa, than at 0.4 MPa. This indicates that the AC PD test is not very sensitive to local enhanced field defects, such as fixed protrusions on conductors, because of the limited PD measurement sensitivity and the corona stabilization under AC voltage. [ABSTRACT FROM AUTHOR]

In actual operation, the shielding failure rate of UHV transmission line is much higher than that in simulation, so it is crucial to study the lightning shielding performance by experimental research. The testing UHV transmission line model is scaled down in the ratio of 12.5 which is relatively large comparing to other testing models. Two kinds of negative switching impulse waveform were applied to HV rod to simulate the lightning descending leader. The probability of transmission line being stroked was calculated statistically by recording more than two thousand discharges and the factors that affecting the discharge probability were studied through contrast tests. The results show that the grounding condition, DC bias, the protection angle, the switching impulse voltages have an influence on the discharge probability, breakdown voltage and breakdown time. The spatial boundary of shielding failure area was determined in the middle of the span. The upper and lower spatial boundary and the distance between them increased with the increasing of the lateral distance between HV rod tip and transmission line model simultaneously. [ABSTRACT FROM AUTHOR]

Cross-linked polyethylene (XLPE) and Ethylene Propylene Rubber (EPR) are the common polymeric materials used for power cable insulation in the USA. While in service, the main threats to the cable insulation include electrical stress, thermal stress, and mechanical stress. The electrical stress, from either operation voltages or abnormal over-voltages during transients, has negative impacts to the power cables insulation. The excessive electrical stress will trigger the aging of insulation materials, which will lead to the failures of cables, resulting in outages of power systems. The aging phenomena of polymeric power cables have been extensively studied during the past decades. Although the study of aging mechanisms was done on molded samples, little is known about the aging phenomena of the XLPE and EPR cables by switching impulses. In this experiment, the 15 kV XLPE and EPR cable samples were aged up to 10,000 switching impulses. The study helped to assess the reliability of the XLPE and EPR cables serving in electrical power systems. [ABSTRACT FROM AUTHOR]

Forward pumping current is required for current interruption operation of a semiconductor opening switch (SOS). In this study, the influence of the forward pumping current on current interruption of the reverse current has been investigated experimentally. The duration and the peak value of the forward current were varied and the reverse current obtained under different conditions has been compared. As a result, it has been found that a short forward current can lead to high peak value of the reverse current. It is considered from the results that the density of the minority carriers is increased by the forward current of shorter duration because recombination consumes fewer carriers. Furthermore, when the duration of the forward current shortens with a lower peak value and depletion the peak value of the reverse current increases, the interruption of reverse current quickens. This can be explained by the fact that the time during which minority carriers are turned around by the reverse current is shorter in case of less accumulation and faster removal of minority carriers. With these investigations, it has been understood that relatively short and low forward current and high reverse current is needed for high efficiency inductive energy storage circuit using the SOS. [ABSTRACT FROM PUBLISHER]