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Supercapacitors have drawn numerous attentions in recent years since they can deliver relatively high power and energy densities. This article introduces an all-printed paper based surface mountable supercapacitor (SMS), which could withstand the reflow soldering process when integrated into microelectronic systems. The device was fabricated by screen printing and stencil printing processes, contributing to low cost and large-scale fabrication. Furthermore, building electronic devices on ubiquitous paper substrates had advantages of light weight, low cost, and eco-friendliness, etc. Based on activated carbon electrode material and ionic liquid electrolyte, the capacity of the supercapacitor could reach 14 mF at the device volume of 3.2 mm ? 2.5 mm ? 0.175 mm, besides, the specific volumetric capacity was superior than most of the commercial SMS devices. [ABSTRACT FROM PUBLISHER]

A capacitor formed of fluid-impregnated paper metalized on one side and a polymer film results in a relaxation peak caused by the much more rapid polarization of the dielectric fluid impregnated paper relative to the polymer film. This results in the capacitance being a function of frequency, with a substantial increase in capacitance at very low frequencies. A theory for such a capacitor is developed and compared with measurements on actual capacitors with relatively good agreement. The implications of the theory for discharge current and discharge efficiency are discussed. [ABSTRACT FROM AUTHOR]

Presents a study that examined the aging process of mineral oil-impregnated-high density kraft paper capacitor bushing models subjected to voltage switching surges. Effects of the removal of electrical impulse stress over a finite time period; Thickness of the insulating system of the model capacitor bushing; Implication of the partial discharged inception stress characteristics for the doubled insulation specimen.

Focuses on the recovery voltage method (RVM), a method used to estimate the polarization spectrum in composite oil/paper insulation systems. Methods for determining dielectric insulation; Mathematical description of the recovery voltage method; Identification of the equivalent circuit using a model with a single polarization capacitor.

In this paper, a novel deashing method is proposed to prepare polypropylene (PP) materials with different ash contents (60–500 ppm). Effects of the ash on dielectric and energy storage characteristics of PP in polymer film capacitors are studied. The experimental results reveal that a low content of ash will help to improve the dielectric properties. Compared to the sample with 500 ppm of ash content, the PP film with 60 ppm ash possesses a higher breakdown strength (587.1 kV/mm), a lower DC conductivity (1.12 ×10−14 S/m) and dielectric loss factor (3 ×10−4). In addition, the energy storage property also shows a remarkabe improvement, the discharge energy density can be up to 3.22 J/cm3 and the discharge efficiency remains at a high level. After the purification, the decline of the ash content in PP prevents the local electric field distortion and enhances the breakdown strength, which is beneficial for the improvement of the discharge energy density. Meanwhile, the reduction in the number of carriers ionized by the ash weakens the transport behavior and reduces the conductivity. It is concluded that the PP with high purity shows a great potential in polymer film capacitors. [ABSTRACT FROM AUTHOR]

In this paper, an advanced surface-grafting method is reported to improve the high-temperature performance of biaxially oriented polypropylene (BOPP) membranes. The leakage conductivity of the surface-grafted films decreases by 98% at 85 °C. The decline in the leakage loss contributes to the 99% charge-efficiency at 85 °C. The dielectric constant increases by 7%. The DC breakdown strength grows by 43% at 85 °C. The maximum energy storage density goes up from 1.45 to 2.77 J/cm3 at 85 °C. The surface-grafted BOPP film exhibits outstanding energy density and charge-discharge efficiency characteristics. This research provides a theoretical reference for improving the performance of capacitor film based on surface modification. [ABSTRACT FROM AUTHOR]

This paper focuses on the effects of the nano Polyhedral oligomericsilsesquioxanes (POSS) with three similar molecular structures on the thermal and electrical properties of polypropylene (PP) films, aiming to propose a comprehensive modification method. After doping with micro amount of nano POSS, the crystallinity and regularity of films are elevated. Correspondingly, PP with optimized microstructure has the lowest conductivity, due to the interaction between the nanoparticles and the matrix, as well as the strong binding force of the crystal region to the carriers. The loss of the sample is restricted, especially in the low frequency region, since the combined effect of polarization and conduction. The DC breakdown strength of the modified PP is higher than that of the PP, with an increase of above 20% at 25–85 °C. Based on quantum chemical calculations, the energy level distributions are analyzed. By selecting appropriate additives, deep trap sites can be introduced to catch carriers, preventing the breaks of polymer molecular chains. This modification of PP films shows huge potential in the improvement of dielectric properties in the field of DC capacitors. [ABSTRACT FROM AUTHOR]

For the metallized film capacitors (MFCs) designed to maximize the self-healing performance in the event of overvoltage, electrochemical corrosion is the major capacitance loss (CL) mechanism especially under high temperature and/or high humidity. In this paper, the electrode corrosion evolution is analyzed by dividing the process into anode and cathode reaction. In order to investigate the CL characteristics, three types of MFCs are stressed with 305 VAC under different temperature and humidity. Based on the corrosion mechanism and distribution analysis, a staged CL prediction method is proposed. The results indicate that the typical CL curve can be divided into 4 stages which are characterized by the reaction rate coefficient and the capacitance loss exponent derived from the experimental data. [ABSTRACT FROM AUTHOR]

The ESS Linac project, phase I, requires 12 long pulse klystron modulators with compact footprint, high pulse power and improved quality both on the output pulse waveform and on the input AC power line. Conventional long pulse modulators are typically based on HV pulse transformers and commonly exhibit poor efficiency, low power density, large footprint and cost, with still limited performance on pulse rise time, pulse flat-top accuracy and AC power line quality (flicker, current harmonic distortion, power factor). This paper presents the Stacked Multi-Level (SML) klystron modulator topology, a novel modular concept based on the association of several HV modules in series at their output, each formed by a high voltage and high-frequency transformer, a HV diode rectifier bridge and a low pass filter. Each HV module is fed from a low voltage power electronic inverter at ground potential since the transformer provides the required galvanic isolation between primary and secondary windings. This topology is believed to better suit the application and better satisfy ESS requirements, directly addressing the mentioned shortcomings of conventional topologies. The development and validation of this new concept has included the design and construction of a reduced scale prototype with the potential of delivering long (3.5 ms) and high quality pulses (0?99% rise time <120 ?s and flat top ripple <0.15%) with pulse amplitudes up to 115 kV and pulse power up to 2 MW, while maintaining excellent AC grid power quality (low flicker operation < 0.2%, sinusoidal current absorption with total harmonic distortion < 3%, and unitary power factor). The paper describes the main features of the topology and the main design aspects, presenting results both from simulation models, including parasitic elements, and from an experimental setup. [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]

Repeated impulse voltage has long been considered to affect the insulation property of power equipment, which is called accumulative effect. This phenomenon is widely studied on oil paper insulation but rarely on oil polypropylene film insulation, which is widely used in power capacitors and other equipment. Therefore, the accumulative effect of repeated impulse on oil polypropylene insulation is studied in this work. First, a repeated impulse accumulating test platform was set up and the accumulation characteristics of oil polypropylene insulation with repeated impulses were tested and analyzed. Next, the residual breakdown voltage, surface morphology and gas composition dissolved in the oil in different aging levels were tested. The results indicated that the OPF insulation residual breakdown voltage decreased and the film surface roughness increased when subjected to the repeated impulses. The dissolved gas contents changed along with the impulse accumulation aging. Lastly, the possible mechanisms of the accumulative effect in oil polypropylene insulation are discussed based on the test results. [ABSTRACT FROM AUTHOR]

In this paper, a set of performance metrics for modern biaxially oriented polypropylene (BOPP) capacitor films is established. The fundamental and applied properties of BOPP films required for application in state-of-the-art DC metallized film capacitors are reviewed, highlighting aspects related to high temperature operation, base PP properties and film processing. Commercial BOPP films — both base films and metallized films based on classic isotactic PP — are studied comprehensively, encompassing structural–morphological characterization and short- to medium-term dielectric characterization. Dielectric spectroscopy results demonstrate the negligible dielectric losses of BOPP, being in the range of 10–4 or less in the expected operation temperature regime. Thermally stimulated depolarization current (TSDC) measurements indicated a modest density of shallow traps (~0.75 eV) and a high density of deep traps (~1.08 eV) in the 5 μm and 10 μm film variants showing differences presumably arising from film processing. Such an electronic structure was found to be connected with ultra-low conductivity (in the range of 10–17–10–16 S/m), high breakdown strength (~700 V/μm) and negligible space charge accumulation up to temperatures of ~70 °C. It is shown that at current design stresses (~200 V/μm at ~60 °C) BOPP is operated close to its fundamental thermal and electrical limitations. Voltage endurance tests at higher fields revealed the onset of high-field degradation and drastically reduced insulation life, and thermal activation of deep traps in the high temperature region (~100 °C) was found to result in reduced dielectric performance. [ABSTRACT FROM AUTHOR]

Frequency Domain Spectroscopy (FDS) is mainly used to determine the moisture in the paper-oil insulation systems in power transformers and Oil-Impregnated-Paper (OIP) bushings. Another application of this method is detection of puncture developing in the paper layer between the adjacent conductive foils in the condenser core. The paper presents theoretical calculations of tan? frequency response in the case of short circuit of conductive layers in bushing's condenser core and their experimental verification, with the help of paper-oil insulation capacitor. Furthermore, examples of measurements of real bushings in operation that agree with the proposed idea are described. [ABSTRACT FROM AUTHOR]

In this paper, the design method of dc capacitor bushing core has been studied. According to the derived epoxy/paper composite life model, the bushing core design methods are proposed based on the life of materials, which can make a more reasonable electric field distribution within bushing core. By adjusting the size of plates, the insulation life of innermost and outermost of the bushing core is made to be equivalent, resulting in more efficiency in usage of insulation material. Taking 800 kV dry bushing for example, the optimization size is designed. An iterative algorithm is used to optimize the design of the bushing core to minimize the volume of bushing core, while meeting the maximum designed withstand field strength under the ac and dc voltage. [ABSTRACT FROM AUTHOR]

Although vacuum technology is commonly used in power systems, challenges still remain for vacuum circuit breakers (VCBs) to cope with the requirements of capacitor bank switching duties as the insulation performance can deteriorate by inrush current. In order to reduce the restrike probability, vacuum interrupters (VIs) in series are recommended. The objective of this paper is to investigate the field emission current I e characteristics and voltage distribution in series vacuum gaps after making inrush current. The results show that I e of the VI pre-stressed by inrush current is much higher than that of the new one and I e has a conditioning effect. It is found that the insulation performance of two pre-stressed VIs in series is not significantly improved compared to a single VI. But the insulation performance of a new VI and a pre-stressed VI in series is significantly improved. Moreover, the voltage distribution of two VIs in series can be estimated by I e. It is found that each VI only withstands about 50% of the applied voltage when two pre-stressed VIs are in series. However, the new VI can withstand >70% of the applied voltage when a new and a pre-stressed VI are in series. [ABSTRACT FROM AUTHOR]

A comparative study of biaxial-orientated polypropylene (BOPP) films extracted from one failed HVDC filter capacitor (serving for 10 years) and one fresh capacitor (spare capacitor from the same batch) is reported in this paper. Experimental results show that the 10-year online operation does not bring about molecular changes; however, molecule reorganization and recrystallization was detected using differential scanning calorimetry and dynamic mechanical analysis tests. Electrical measurements including dielectric spectra, DC conductivity measurement, DC breakdown strength and were also performed. The experimental results show that the aging process causes an increase in dielectric constant, dissipation factor, DC conductivity, and the DC breakdown strength. Thermal stimulated current measurements indicate that traps were introduced by aging and are responsible for such abnormal changes. The nano-cavitivies generated by molecule reorganization could possibly act as charge traps. Therefore, homo-charges can accumulate in the vicinity of the electrodes, leading to the degradation of long-term withstand strength but an enhancement of short-term breakdown strength. [ABSTRACT FROM AUTHOR]

The insulation problem of converter transformers has become one of the core issues in HVDC system, which is receiving more and more attention. A converter transformer has complex structures and requires high insulation level. The voltage waveform which the converter transformer insulation withstands is different from AC transformers. In the valve side of the converter transformer, the insulation endures a mixed voltage of AC voltage, DC voltage, harmonics and the pulsating component etc. Partial discharge (PD) occurring in oil-pressboard insulation is the one of the main causes of insulation breakdown, and it is the main factor of electrical aging of materials. Even though PD characteristics under pure AC or DC voltage waveform have been studied by many researchers, little research has been done with the mixed voltage. In this paper, the AC + DC mixed voltage experiment system is set up to study the PD characteristics under mixed voltage waveforms. The study results indicate that the pressboard withstands most of the DC component and void withstands most of the AC component when applied mixed voltage. For PD inception voltage, it is decided by both the AC component and DC component. For PD development, AC component has more significant influence than DC component. However, the DC component is found to promote PD activity under AC half cycle with the same DC polarity and inhibit PD activity under AC half cycle with the opposite DC polarity. The results in this paper provide an experimental foundation for the converter transformer insulation breakdown mechanism and analysis. [ABSTRACT FROM PUBLISHER]

In the linear transformer driver system, the capacitor needs to satisfy the requirement of long life time and low inherent inductance. The inherent inductance of the capacitor plays an important role in limiting the rise time and peak current of the LTD output pulse, therefore, the volume of the capacitor should be as small as possible to reduce the inductance. Since the paper?s permittivity is larger than the film?s and the breakdown strength of film is larger than that of the paper, we adopt oil immersed paper-film mixed dielectric as the capacitor dielectric structure to take advantage of the combined properties of the two different dielectric films. In this paper, based on the result of the simulation, the electrode structure was optimized and a capacitor was designed with a capacitance of 100 nF and an inherent inductance of less than 140 nH. According to results of the experiment, the capacitor inherent inductance satisfies the expected requirement. The typical failure can be classified into two main modes: (1) insulation erosion at the pressure-contact taps and (2) foil edge breakdown, both resulting in short circuit failure. Based on the typical failure modes found from the dissection of failed capacitors, an improved design is presented. [ABSTRACT FROM AUTHOR]

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]

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]

The ?1100 kV UHVDC wall bushing is the important power equipment in the ?1100 kV DC power transmission project of China. However, the reported literatures rarely mention its design method and the optimization of its insulation structure. In this paper, two specific designing schemes including the resin impregnated paper (RIP) condenser and the metalshielded core have been both adopted in the design of the wall bushing. Moreover, the actual operating environment and the rated parameters of the ?1100 kV UHVDC wall bushing have been analyzed in detail. Then, the nonlinear finite element method (FEM) analysis has been applied in the three-dimensional electric stress simulation of the UHVDC wall bushing. The electric field and temperature dependencies of the composite insulation used in the wall bushing have been taken into account. The E-field simulation results indicate that with the RIP condenser, the potential and electric field distribution can be much more uniform along the composite insulator of the bushing. Therefore, the compact design of the wall bushing can be obtained by this designing scheme. On the other hand, with the type of the metal-shielded core, the high E-field strength areas are mainly concentrated on the metal shield and the outer grading ring of the wall bushing. Therefore, the nonlinear FEM was applied in the structure optimization of the internal metal-shielded system used in the wall bushing. Finally, the maximum E-field strength of the wall bushing can meet the control requirement. Based on the simulation results and the optimization structure, the ?660 kV scaled prototype of the UHVDC wall bushing has been produced and passed through all the type tests according to the IEC 62199. The feasibility of the design of the ?1100 kV UHVDC wall bushing has been verified. This paper can provide the theoretical guidelines for the design, manufacture and operation of the UHVDC wall bushing. [ABSTRACT FROM AUTHOR]

The surface charges that accumulate on polypropylene (PP) film can induce electrical field distortion and surface flashover, which accelerate the electrical aging of a capacitor. This paper investigated the effect of combined voltage on the surface charge behaviors and flashover voltage and a modification method to inhibit the accumulation of surface charge. The carrier mobility in different conditions was calculated using a surface potential decay process to analyze the transportation of surface charges. Samples that were fluorinated for 15, 30, 45 and 60 min and unfluorinated samples were prepared prior to experiments. The samples were corona charged with a pair of needle-plate electrodes by DC voltage and a combination of DC voltage and pulse voltage. The flashover experiments were performed under DC voltage, pulse voltage and superimposed voltage in atmospheric air. The results indicate that the maximum carrier mobility and maximum flashover voltage can be obtained when the samples are surface modified for 45 min. The surface charge density decreases with an increase in the carrier mobility under DC voltage. Under a combination of DC voltage and pulse voltage, the initial surface charge density is influenced by both the carrier mobility and the pulse voltage. The results suggest that surface modification for a certain time can significantly inhibit the surface charge accumulation, improve the carrier mobility and increase the flashover voltage. [ABSTRACT FROM AUTHOR]

The indoor DC yard of the ±1100 kV UHVDC transmission project is preferred to the outdoor solution, and the rational design of shielding electrodes for the ±1100 kV apparatus becomes the key to system security. In this paper, the design requirements of indoor DC yards were described and the preliminary designs of the indoor shielding electrodes for the key ±1100 kV DC apparatus were proposed. The whole 3-D FEM model of one ±1100 kV indoor DC yard was established. An empirical formula of the critical E-field strength for the evaluation of relatively large shielding electrodes was proposed based on the corona tests of typical ball and ring electrodes. The electric field distribution of the whole indoor DC yard was calculated and the surface electric field strength of all the shielding electrodes for the key ±1100 kV apparatus was evaluated. The results show that after optimization, the maximum surface field strength on the shielding electrode of ±1100 kV DC filter capacitor decreased from 1507 V/mm to 1335 V/mm, lower than the critical value for evaluation, then the corona free design of all the ±1100 kV indoor shielding electrode could be predicted. The method of electric field evaluation and optimization could provide important references for the development of shielding electrodes in the ±1100 kV or other UHV indoor DC yards. [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]

Conventional Modular Multilevel Converter (MMC) with Half-Bridge Sub-Modules (HB-SMs) can be used effectively as a solid-state high-voltage pulse generator to chop a high-voltage dc input into a bipolar pulsed output voltage without employing neither high-voltage semiconductor switches nor series-connected switches. Nonetheless, its boosting capability is constrained. In this paper, a hybrid boost MMC-based bipolar high-voltage pulse generator is proposed where each arm contains a combination of Full-Bridge SMs (FB-SMs) and HB-SMs. The HB-SMs and FB-SMs have the same rated voltage. The proposed approach is able to generate bipolar pulses, and operates with a wide range of boosting capability. Detailed illustration of the proposed configuration and its operational concept are presented. Simulation models for the proposed approach are built, for different FB-SMs to HB-SMs ratios, using Matlab/Simulink platform. Experimental results for a scaled-down prototype are presented to validate the concept. [ABSTRACT FROM PUBLISHER]

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]

The conventional unipolar Marx generator can be employed for bipolar pulsed electric field by adding a high-voltage H-bridge at the load side which necessitates stacked switches. Alternatively, bipolar Marx generator with low-voltage switches can be employed. The existing bipolar Marx generators are typically fed from dc supplies, where polarized capacitors are employed. The capacitance of involved capacitors is selected such that the total energy stored in the generator's capacitors is higher than the bipolar pulse energy. As a result, polarized capacitors with relatively high capacitances are required. In addition, a high number of controlled switches per stage are required (at least four switches per stage). In this paper, a new solid-state bipolar Marx pulse generator with only three controlled switches per stage is proposed. The proposed generator is fed from sinusoidal/square ac voltage and non-polarized capacitors with low capacitance are employed. The proposed bipolar Marx-generator can be used effectively with resistive loads for exponential pulse generation. A detailed illustration of the proposed approach is presented and a discussion, to elucidate the differences between the proposed pulse generator and the other existing ones, are presented. Simulation results for the proposed pulse generator are presented to validate the concept. Finally, experimental results have been obtained from a low-voltage model of the proposed generator. [ABSTRACT FROM AUTHOR]

Plasma synthetic jet (PSJ) has a wide application prospect in flow separation suppression and boundary layer control. Comparing with traditional control methods, synchronous discharges of PSJ with high repetition frequency and high energy could achieve a better flow control effect because it can meet multi-angle, wide-range and long-time flow control requirements. In this paper, a microsecond-pulse power supply for synchronous discharges of three plasma synthetic jet actuators (PSJA) is developed. Parameters of output pulses are as follows: the maximum voltage pulse is 10 kV, the pulse repetition rate is 1000 Hz and the full width is 15 ?s. The generator can withstand a discharge current with an amplitude of 320 A and a discharge energy of 150 mJ. The electrical characteristics of the synchronous discharges of PSJAs including the voltage-current waveforms, discharge images and Schlieren images are investigated. The experimental result shows that the microsecond-pulse generator could sustain three discharge channels in PSJAs when the output voltage is 10 kV. These discharge channels have preferable performance in synchronicity when the repetition frequency is 1000 Hz. Furthermore, the Schlieren images show that the power supply can sustain three PSJAs with a maximum jet velocity of up to 150 m/s. [ABSTRACT FROM AUTHOR]

The lifetime tests for High Voltage Ceramic Capacitors (HVCC) were investigated under repetitive frequency operation at 25 Hz and three kinds of failure modes were summarized. The significant innovation of this paper is testing HVCC, made in the laboratory, under repetitive pulses and proposing several effective improvement methods. The results show that the lifetime of HVCC meets inverse power-law with the applied voltage and the voltage acceleration factor is about 5.8. Failure modes of HVCC are inner breakdown of ceramic dielectric, interface breakdown of ceramic-epoxy and abscission of brass terminals. The inner breakdown is in connection with abrupt destructive discharge under much higher stress while the interface breakdown is related to interface delamination and development of electrical trees in relatively low strength. The third failure mode is always caused by high current density. Based on the failure modes, several methods were taken to improve the performance of HVCC, which included coating semiconductor at the edge of silver layers, adding coupling agent to ceramic-epoxy interface and improving the structure of brass terminals. The lifetime of HVCC under repetitive frequency operation has been extended greatly from 103 shots to more than 105 shots after the investigation and improvement. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) cable field tests require the use of high frequency sensors coupled to the cable for PD apparent charge evaluation. PD sensors can be coupled to the cable by magnetic field, like high frequency current transformers, or by electric field, like capacitive couplers. If high sensitivity and high bandwidth are required, then capacitive couplers need to be employed since high frequency current transformers exhibit a limitation concerning bandwidth and gain. This paper summarizes some capacitive couplers topologies, their drawbacks and their benefits, and finally proposes a topology based on high voltage capacitors and operational amplifiers. The topology described in this paper allows obtaining a capacitive coupler with a low cutoff frequency in the range of a few kHz and a high cutoff frequency in the range of tens of MHz. The bandwidth achieved with this topology makes possible a reliable PD pulse wave shape record, useful for mathematical post processing, and exhibits a good sensitivity, improving PD field test measures, in both off-line and on-line tests. [ABSTRACT FROM PUBLISHER]

As a key influence factor on the lifetime of pulsed capacitors, the repetitive frequency (fR) of charge/discharge is studied in this paper based on the method of TSDC measurement. When fR ranges from 0.1 Hz to 10 Hz, the lifetime of capacitors increases. The TSDC measurement is conducted, which is used to study the parameters of space charge induced by charge/discharge at various frequencies. The measurement result indicates that compared with capacitors which have experienced no charge/discharge, for capacitors that have experienced charge/discharge at 0.1, 1, 8 and 10 Hz for 3000 times, the trap density within the dielectric respectively increases by 66.1, 62.1, 54.8 and 31.5%. For pulsed capacitors which have experienced charge/discharge at 10 Hz, the peak current (IM) is 22.2 pA, meanwhile, for pulsed capacitors which have experienced charge/discharge at 0.1 Hz, the Im is 29.4 pA. For pulsed capacitors which have experienced charge/discharge at 10 Hz, the depth of deep traps is 0.94 eV, and the temperature corresponding to Im is 97 °C, meanwhile, for pulsed capacitors which have experienced charge/discharge at 0.1 Hz, the depth of deep traps is 1.83 eV, and the temperature corresponding to Im is 110°C. The parameters reflecting the characteristic of space charge can reasonably explain why the lifetime of capacitors tested at 10 Hz is three times of that at 0.1 Hz. [ABSTRACT FROM PUBLISHER]

The fracture behavior of metallized electrode (ME) under pulsed current with current density of 1011∼1012 A/m2 and pulse with width of microseconds is studied in this paper. High-speed camera is applied to record the surface state of metallized electrode. Based on photos of the surface state and waveforms of the current and voltage, the fracture behavior under the stages of melting, liquefaction, vaporization and plasma are acquired. The process of the exploding phenomenon is discussed in detail. The photos show that the fracture direction is perpendicular to the current. Joule heating and electromagnetic force is the reason for the development direction of the fracture. The influencing factors of electric explosion are experimentally analyzed. Results indicate that the specific action integral (h) can not be considered as a constant. The specific action integral (h) and energy transfer efficiency (?) will decrease with the increasing of di/dt (ratio of peak current value to peak time) and current density (j). The energy transfer efficiency (?) increases from 36% to 71% when the current density ranges from 2.3?1011 A/m2 to 1.1?1011 A/m2, which means the threshold value of electric explosion of 5 nm ME is closely to 1?1011 A/m2. The research results indicate that the high current density (1011~1012 A/m2) and high di/dt may lead to the electrode fracture in the metallized film capacitor. The safe-use current density of capacitors must be below 1?1011 A/m2. [ABSTRACT FROM AUTHOR]

As a key influence factor on the lifetime of pulsed capacitors, the repetitive frequency (fR) of charge/discharge is studied in this paper based on the theory of space charge. A fact that in the absence of heat accumulation, from 0.1 to 10 Hz, the lifetime of capacitors increases with the fR is found. The measurement of space charge induced by charge/discharge at various frequencies is conducted. The measurement result indicates that the amount of space charge in capacitors experienced charge/discharge at 0.1 Hz is 29% higher than that of 10 Hz, which can reasonably explain why the lifetime of capacitors tested at 10 Hz is twice of that at 0.1Hz. Besides, a simplified TSDC is carried out to qualitatively measure the trap density of capacitors experienced lifetime tests, and found that the traps formed during charge/discharge tests at 0.1 Hz is more than 7x that of 10 Hz. The dielectric loss angle tangent (tan?) of capacitors which have experienced charge/discharge at various frequencies is also tested, and from the tan? tested at 0.001 Hz, (3.7 when fR is 0.1 Hz and 2.4 when fR is 10 Hz), it is revealed that the aging of pulsed capacitors can be slowed by enhancing the fR of charge/discharge, which matches well with the results of lifetime test. [ABSTRACT FROM AUTHOR]

As the deregulation of the electric power industry moves forward, there is an increasing need for cost cutting and it is becoming exceedingly important to keep track of the residual life and identify the timing of replacement for power transmission equipment that has aged for several tens of years in the field. This paper, taking up the theme of "insulation degradation phenomena and lifetime evaluation for power transmission equipment", conducted cross-sectional comparison of different types of equipment although this kind of evaluation was made independently for these equipment types so far. This paper covered six types of equipment: gas insulated switchgear (GIS), gas insulated transformers, oil filled (OF) transformers, OF cables, crosslinked polyethylene (XLPE) cables, and power capacitors. As a result of examining the characteristics such as electric, thermal, mechanical, and hygroscopic degradations, each of these equipment types was found to have distinctive Voltage-time (V-t) and Voltage-number (V-N) characteristics, which sometimes greatly varied from those of others. Since thermal degradation is dominant for gas insulated transformers and oil filled transformers, their lifetimes depend on the reduction of mechanical strengths of Polyethylene Terephthalate (PET) or insulating paper. Therefore, it is effective to diagnose decomposition products such as CO, CO2 and furfural generated in the thermal degradation mechanism. On the other hand, the influence of electric degradation has more significant impact on the other equipment types except OF cables. Such GIS components as epoxy spacers, XLPE cables, and power capacitors for which long-term ac voltages are dominant, are commonly characterized by the long-term V-t characteristics with a large gradient (small n-value). In terms of insulation structures, there is a possibility of reducing the degree of degradation by improving solids or the interface between solids and electrodes. [ABSTRACT FROM AUTHOR]

This paper presents the derivation of the three dimensional scaling law for liquid insulators. The case of the parallel plate capacitor geometry was investigated, and it was assumed that the "breakdown voltage" random variable follows Weibull distribution. The deduced scaling law was experimentally verified for fresh and used mineral transformer oil. Good agreement of the obtained results with theoretical expectations confirms validity and applicability of the three dimensional scaling law in the investigated case. Results obtained in this paper indicate that application of the scaling law is more convenient in the case of oil insulators compared to other insulator types, due to mutual independence of discharge processes. [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]

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]

On-line partial discharge (PD) monitoring is widely used to detect stator winding insulation deterioration. The most common type of on-line PD sensor for turbine generators is the 80 pF capacitive coupler installed at the machine terminals which detects the PD in the very high frequency (VHF) range. More recently, ultra high frequency (UHF) antennae have also been used to detect stator winding PD in large turbine generators. Both types of sensors have been installed in 16 turbine generators. This paper discusses the results from near simultaneous measurements from both types of sensors on the same machines. It was expected that the UHF sensors would have stronger discrimination of the electrical disturbances internal to the machine compared to the VHF sensors, but the VHF sensors would be more sensitive to PD. As expected, the VHF sensors were generally more corrupted by electrical disturbances. However, in about half of the machines investigated here, the UHF sensors were significantly more sensitive than the VHF sensors. Many examples of phase-resolved PD patterns that illustrate these findings are presented. [ABSTRACT FROM AUTHOR]

This paper proposes a novel topological solution for pulsed power converters based on capacitor-discharge topologies, integrating a Fast Voltage Compensator which allows an operation at constant power consumption from the utility grid. This solution has been retained as a possible candidate for the CLIC project under study at CERN, which requires more than a thousand synchronously-operated klystron modulators producing a total pulsed power of almost 40 GW. The proposed Fast Voltage Compensator is integrated in the modulator such that it only has to treat the capacitor charger current and a fraction of the charging voltage, meaning that its dimensioning power and cost are minimized. This topology can be used to improve the AC power quality of any pulsed converters based on capacitor-discharge concept. A prototype has been built and exploited to validate the operating principle and demonstrate the benefits of the proposed solution. [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]

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 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]

This paper describes the implementation of a load voltage observer into the control algorithms of a Rapid Capacitor Charger controlled by a digital signal controller (DSC) with a fast DSP core. A hybrid peak current mode control algorithm with digital control of the PWM signal and high speed analog current sensing is used to control the inverter of the charger. The DSC controller keeps the current loop stable using adaptive slope compensation. In addition to providing fast adaptive digital control of the current loop, the DSC can perform additional functions such as estimation of the voltage level of the load capacitor. This avoids the cost, bandwidth limitations and insulation challenges of a conventional HV-sensor. To evaluate the performance of the load voltage observer, we measured the output voltage with a laboratory grade HV probe to establish a reference to test the results of the digital algorithm. [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 series compensation stations of the UHV AC demonstration project in China, capacitive voltage transformers (CVTs) failed several times during the operation of disconnecting switches (DSs). The reasons for this failure are analyzed in this paper. The stray inductor, the stray capacitor between the platform and ground and the capacitor of the CVT forms a resonant circuit in series compensation stations, causing repeated oscillating overvoltage and impulse current acting on the CVTs during DS operation. A full-scale experiment indicates that the oscillating frequency is approximately 200 Hz and the repeating frequency is approximately 0.5 MHz. The simulation experiment in the laboratory indicates that the partial welding mode and the partial high electric field are the main causes of damage to the CVT element insulation. A mechanism of the insulation damage is proposed, and some suggestions are given based on our results. [ABSTRACT FROM AUTHOR]

When the metallized polypropylene film capacitor (MPPFC) is used under high electric field in pulsed power systems, an obvious voltage decay phenomenon will occur. The voltage decay is mainly resulted from the relaxation polarization in dielectric applied under high electric field. This paper focuses on the relaxation polarization in metallized biaxially oriented polypropylene (BOPP) film capacitors. The extended Debye model of relaxation polarization is discussed and the parameters of each RC branch are obtained. Meanwhile, the relationship between the increasing proportion of polarization charge (ΔQa/Qh) and temperature is investigated. The experimental results show that under 1kV, ΔQa/Qh varies from 0.018 to 6.868 with the temperature varing from 10 to 70 /spl deg. Moreover, the equivalent capacitance of capacitors in frequency domain is analyzed with consideration of slow polarization. The analysis shows that both a lower frequency and a higher temperature can accelerate the relaxation polarization and increase the voltage decay. Based on the extended Debye model developed from the polarization charge test, the voltage drop is calculated and the results can match well with those of the voltage maintaining test. [ABSTRACT FROM AUTHOR]

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]

Studies of circuit breakers are of interest to high voltage direct current (HVDC) power system. The method for investigation of the switching arc characteristics of a 500 kV metallic return transfer breaker (MRTB) is presented in this paper, by coupling magneto-hydro-dynamics (MHD) arc model with the resonant circuit equations. 2-D MHD arc model taking account of important physical processes of mass flow, Ohmic heating, radiation energy transfer, momentum exchange, Lorentz force and current flow is developed, and then the influence of stray resistor is analyzed under the interrupting current of DC 4 kA. Calculation results of the distribution of temperature and gas pressure in the nozzle region are presented, where the shock wave and negative voltage-current characteristic of arc are discussed. The calculated arc current and voltage are in agreement with the experimental results to some extent, which could verify the validity of the calculation method partially. [ABSTRACT FROM AUTHOR]

In this paper, electrical properties of nanocomposites made of epoxy resin filled with oxide coated aluminum particles are investigated. Nanocomposite samples were prepared and experiments were performed to measure the dielectric properties including breakdown strength with respect to different filler concentrations. Material characteristics were analyzed using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD) and Thermogravimetric (TGA) techniques. Maximum electric energy density in the epoxy nanocomposite dielectric material was evaluated for different filler concentrations and compared with that of pure epoxy. Both large permittivity and high breakdown strength are required for large electric energy storage. The addition of nanoparticles enhanced the permittivity and resulted in potential gain in electric energy density even if there is slight reduction in breakdown strength. Experimental results show that permittivity increased by factor 7 and electric energy density enhanced by factor 4 as that of pure epoxy at a relatively low filler concentration of 18 wt%. Theoretical modeling of the nanocomposite was done and influence of filler loading on the permittivity, breakdown strength and electric energy density of the nanocomposites were evaluated. From the results, it is seen that theoretical model approximates the experimental values at low filler concentrations. [ABSTRACT FROM AUTHOR]

Metallized polypropylene film capacitors (MPPFCs) are the key components in pulsed power systems. The self-healing property guarantees MPPFCs? application under high electric fields. This paper mainly concentrates on the effect of the pulsed discharge current on the lifetime performance. The end connection peak current density (Id) and reversal coefficient (?) are two critical parameters which affect the lifetime. Experiments are designed to investigate the lifetime under different Id and ?. The results indicate that the lifetime is sensitive to ?. Empirically derived lifetime-scaling equation is given to predict the lifetime under different ?. When Id is higher than 13 A/m, the electrode fracture might occur in the MPPFCs and the probability of the sudden capacitance drop will increase. Therefore, this phenomenon results in lifetime reduction. [ABSTRACT FROM AUTHOR]