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This article introduces a powerful methodology to synthesize high gain step-up dc–dc converters from differential connections of two converters. The two selected converters may be either equal or different, and they can use different kinds of gain cells. Both only have to present a common reference between the input and output voltages and the same output voltage polarity. The proposed differential connection supplies high step-up converters and mainly the method can be applied to synthesize different topologies from different well-known converters. Besides the derivation and analysis of some converters in continuous conduction mode, the article also discusses the power processing, reduction of components, addition of gain cells to further increase the gain, different kinds of modulations, and addresses a different point of view for some topologies previously published in literature. The proposed methodology is verified through thirteen prototypes derived from basic converters considering input voltage of 20 V, duty cycle of 0.75, switching frequency of 50 kHz and rated power of 100 W. Moreover, three new ultrahigh gain dc–dc converters are still derived from the insertion of gain cells in the differential converters herein proposed. These three converters are experimentally evaluated under input voltages of 20 and 30 V, rated power of 200 W and, switching frequency of 50 kHz, providing static gains from 15 up to 30, and peak efficiency of 96.78%.

Epoxy resin has been used to cast the core of the dry‐type high voltage direct current bushings and can accumulate space charge under high electric fields at high temperatures, which is believed to be a potential threat to the safe operation of dry bushings, especially under polarity reversal. In this study, results of a study of the evolution of space charge and electric field distribution in epoxy resin, under polarity reversal at 10 and 20 kV/mm, and at temperatures between 40 and 100°C, are presented. The results show that the space charge dynamics in epoxy resin during the test were different at various temperatures. At temperatures no more than 60°C, space charge accumulation within the samples was not obvious. Instead, a low‐frequency dielectric relaxation process maybe occurs during the polarity reversal, which made the charge peaks on the electrodes after the reversal were slightly smaller than those before the reversal. At temperatures no less than 80°C, considering that the applied electric field has little effect on the barrier reductions of the traps within the samples, the space charge dynamics were mainly governed by a thermally activated process, and the depths of the deepest occupied traps were obtain by analysing the transient processes.

In this study, a simulation model of surface charge accumulation has been established. The model considers three accumulation ways, i.e. electrical conduction within the gas, through insulator volume and along the insulator surface. The generation, diffusion, drift and recombination of charge carriers are also taken into account. Based on it, the influence of polarity reversal, reversal time on surface charge and electric field distribution on a basin-type insulator are studied. The polarity of the surface charges and the direction of the electric field change after the voltage polarity reversal. When the preload voltage is equal to reversal voltage, the surface charge and the electric field distributions at steady state before and after voltage polarity reversal are all the same with opposite sign, and not affected by the reversal time. However, the time to reach the steady state varies with different reversal time. The steady-state surface charge and electric field increased with the rise of reversal voltage. The transient normal and tangential electric field would not exceed the value of the steady state, which means voltage polarity reversal has no additional influence on insulation performance. This research can provide guidance to the design and manufacture of DC GIS/GIL.

In this study, the impulse breakdown of conductive water (350 μS/cm) was carried out under 25~1500 μs pulses and with a gap distance of 0.5~100 mm. The influence of pulse duration, gap distance and voltage polarity on the breakdown characteristics are shown. Martin's equation and streamer linear propagation (SLP) model for breakdown voltage calculation are compared, and their application conditions are indicated. The results show the pulse duration and the gap distance on the breakdown characteristics are opposite; however, their influence on voltage polarity are similar. Martin's equation is only appropriate for short impulse breakdown (nanosecond) while the SLP model is shown to be suitable for long impulse breakdown (microsecond or longer).

The design and operation of DC insulation systems is more complex than for AC sinusoidal supply. The most subtle issues are how the electric field in DC can vary with operation and affect the partial discharge inception voltage and partial discharge phenomenology. During operation, a DC insulation system is indeed subjected to voltage and load transients, the former due to energization and voltage polarity inversion. This paper sheds some lights on such issues, going through another fundamental problem, that is, how to carry out effective partial discharge detection under DC supply, both in steady state and during voltage transients. An algorithm that can enable automatic and unsupervised partial discharge measurements in DC electrical apparatus is presented and validated based on partial discharge monitoring performed on test objects representing defective insulation systems. Identification of the source generating partial discharges, which is the basis for diagnostic and condition maintenance, is achieved without the support of experts. The impact of voltage transients on the life and reliability of DC insulation systems is modelled in the presence and absence of partial discharges. It is shown that, depending on the repetition rate, the presence of partial discharges, even if only during voltage transients, can dramatically affect the insulation life and cause premature insulation breakdown.

Generally, single-stage buck–boost inverters consist of distinct circuits operating individually in buck/boost or positive/negative modes, the latter definitely leading to crossover distortion in the output current. This paper proposes a switching strategy that changes the bimodal operation of a single-stage buck–boost topology to a single-mode inverter. This is due to the consequent voltage gain that ensures that the output voltage polarity, apart from its magnitude, is an exclusive function of the duty ratio. Operational principle and salient hardware design are explained with the help of equivalent circuits. Details about the dynamic model are presented, based on which controller design is carried out for both stand-alone and grid-connected operation. Experimental results obtained from a 300-W, 110-V laboratory prototype are presented to validate the performance of the proposed switching strategy.

In this article, the electrical tree initiation behavior in silicone rubber (SIR) under DC voltage was studied. Tests were conducted to reveal the effects of temperature (20–120 °C), defect type and voltage polarity on electrical tree initiation. In samples with an undamaged needle-tip (N samples), we find that the average tree initiation voltage (Fa«) decreases exponentially with increasing temperature by 42%. Single-branch trees and multiple-branch trees are observed. The probability of generating multiple-branch trees decreases with increasing temperature. In samples where an air gap or crack is in the needle (AN samples), Vati is 55.7% of that in N samples at 20 °C. In AN samples, Vati and tree shape do not change monotonically and Vati varies in a small range as temperature rises. Vati for N samples under negative voltage is much larger than that under positive voltage. This polarity effect is reversed in AN samples. Gas discharge theory and Frohlich's theory of dielectric breakdown explain electrical tree initiation behavior at different temperatures. Based on differential scanning calorimetry (DSC) results, we believe that partial segment relaxation of SIR at high temperature leads to Vati decreasing. Electrical trees previously generated inside the cable or an air gap created due to mechanical damage cause Vati to of a subsequently generated tree to drop to nearly half of its typical level. This information is useful for the design of HVDC cable insulation.

Investigation of space charge accumulation processes in a chemically cross-linked polyethylene for ac usage (XLPE) and a modified XLPE for dc usage (DC-XLPE) at voltage polarity reversal was carried out using pulsed electro-acoustic (PEA) measurement system. We found that a huge amount of so called packet-like charge, some of which partially increased the electric field in the material to more than twice of the average applied stress, generated in XLPE at the polarity reversal of DC stress. It enhanced the electric stress locally in the sample by almost twice of the applied average stress. On the other hand, we also found that the packet-like charge was not observed in DC-XLPE under the same experimental condition.

This research provides conclusions that can partially cover the lack of knowledge related to the effects of ambient atmospheric conditions on DC electric power transportation. Two polymer insulating materials are used for completing this research study. Inside a climate chamber, the relative humidity is controlled and adjusted from 20% to 80% RH. Then, the samples are charged with positive or negative charges by applying [inline-formula] to the corona-generating ring of needles. The surface potential is measured using an electrostatic voltmeter and is converted into surface charge density later by applying the probe response matrix method. The pre-charged samples are then stressed with high-voltage negative or positive DC values inside the climate chamber over a range of controlled values of the surrounding air humidity until flashover takes place. The space charges, which can drift in the air gap to reach the solid surface, are highly affected by the level of the relative humidity of the surrounding air. Also, increasing humidity results in a reduction of the DC flashover inception voltage and a shorter time to flashover regardless of the voltage polarity. Moreover, the positive or negative flashover inception voltage of both materials increases with pre-deposited negative charges while it decreases with pre-deposited positive charges.

DC power supply has become the driving source for some essential modern applications. Thereby, DC power conditioning has become a significant issue for engineers. Typically used rectifiers associated with a bridge structure is nonlinear in nature. Thereby, the current at input side of the rectifier contains harmonics, which also flow through the power line. The presence of harmonics causes several interruptions and reduce power quality. In this regard, a new close loop SEPIC controlled rectifier is proposed in this paper. The conventional scheme is arranged with a rectifier connected to a DC-DC converter, which is an open loop system. Consequently, such system cannot regulate voltage at load varying condition. The proposed SEPIC controlled rectifier can regulate voltage under load varying condition for a wide range. Additionally, the performance in terms of total harmonic distortion (THD) of input current and power factor at AC side are also within satisfactory range for the closed loop configuration. The controlled rectifier has four operating phases associated with switching states and input voltage polarity. The close loop configuration also incorporates a current and a voltage loop at the feedback path. The comparative studies have been performed among the proposed closed loop construction, the open-loop structure as well as the conventional construction. The effectiveness of the proposed controlled rectifier is verified in terms of THD and input power factor considering the results obtained from simulation.

As large as 4607 cm−1 gain coefficient in two beam coupling experiment was obtained by introducing PVK:C60 film to ZnSe assisted liquid crystal system. As short as 5.0 ms holographic recording time was reached when probing the grating formation process, showing great potential in real time applications. Systematical two beam coupling and grating probing experiments were performed in studying the mechanism behind the high photorefractive (PR) performance. Unusual energy transfer direction change and gain coefficient fluctuation were observed when the voltage polarity and incidence side were altered in the related two wave coupling experiments.

This paper concerns the studies on streamer propagation in mineral oil, synthetic ester and natural ester at standard lightning impulse inception voltage in small point-plane gaps. The inception voltages of both polarities were measured using step method and then analysed statistically. Simultaneously, streamer characteristics such as shape, emitted light and propagation velocity were compared between the liquids tested. The obtained results showed that the inception voltages were close to each other for all the three liquids tested. Concerning streamer characteristics, it was seen that the spatial shapes of the streamers were similar taking into consideration the given voltage polarity. The same may be said about the propagation velocities, indicating that the velocities of the positive streamers were twice as high as the negative ones. In the case of registered time courses of emitted light, the frequencies of the light pulses corresponding to the propagation of the streamers in both esters were a little bit higher than the pulses emitted by the streamers, which developed in mineral oil. In general, in all three liquids the streamers at inception voltages developed as so-called `stopping length' streamers.

This paper describes experimental studies on streamer propagation in synthetic ester and mineral oil under lightning impulse voltage. These studies are concentrated around the small electrode gaps (15 and 20 mm) of the point-plane electrode arrangement. The spatial shapes of the developing streamers, oscillograms of light emitted and propagation velocities were analyzed and compared. Two streamer propagation modes were observed during the studies performed. Slow 2nd mode streamers developed below the so-called acceleration voltage while fast 3rd mode streamers developed at acceleration voltage and above. Independently of the liquid used the registered streamers shapes corresponding to a given voltage polarity were identical. Concerning the light oscillograms, higher frequencies of light pulses were observed in the case of synthetic ester. A significant difference between both the considered liquids was however noticed in the threshold value of the testing voltage at which the 3rd mode streamers appeared. Fast positive streamers started to develop in synthetic ester at lower testing voltage (of about 26 kV for 20 mm gap and 20 kV for 15 mm gap) than in the case of mineral oil. For negative polarity of lightning impulse, within the applied testing voltages, 3rd mode streamers were observed only in synthetic ester. For both electrode gaps acceleration voltage for negative polarity was 2.2 of estimated inception voltage. This allowed forming the conclusion that synthetic esters have a lower ability of preventing the development of fast and energetic streamers, even at small (15 and 20 mm) electrode gaps.

In this study, investigation of the unipolar resistive switching (RS) of InGaZnO film indicates that the reset voltage polarity can strongly affect the RS region. The dependence of the RS characteristics on the top electrode (Pt, Al, or Cu) was investigated. Asymmetrical electrodes (Cu/InGaZnO/Al) were chosen and the dependence of the RS parameters (e.g., high and low resistance states, set and reset voltages) on these two diverse electrodes can provide two indicators to trace the location of the RS region. The RS region is usually located near the anode when the applied set and reset voltages have the same polarity. In comparison, when the reset voltage has the opposite polarity to the set voltage, the RS region prefers to be located near the anode of the reset process rather than the cathode (which is used as the anode in the set process), indicating the movement of the RS region during the reset process. With the aid of joule heating, oxygen ions can overcome the energy barrier during the reset process under small voltage, resulting in the CFs restructuring and having the inverse shape, which is responsible for the drift mechanism of the RS region.

The active-forced-commutated (AFC) bridge employs a symmetrical thyristor-bridge with auxiliary self-commutated full-bridge chain-link (FB-CL) circuit to assist its soft transition and forced commutation. This combination can form a thyristor based voltage source converter (VSC) with significantly reduced on-state losses and dc-fault blocking capability. Due to the full topological symmetry of the AFC-bridge, either current direction or dc-link voltage polarity can be reversed for power flow reversal as for the full-bridge modular multilevel converter (FB-MMC). Thus, the AFC-bridge is compatible with both line-commutated-converter (LCC) and VSC terminals in a multi-terminal high voltage direct current (MT-HVDC) network. This paper investigates its front-to-front (F2F) dc-dc application for matching the regional dc grids in a LCC and VSC hybrid HVDC network. Simulation studies are carried out to demonstrate its potentials as a high efficiency multi-functional solution for dc-dc conversion.

The switch mode power conversion circuits buck, boost, and buck-boost incorporate a power inductor as an energy storage device. If the power inductor in these fundamental circuits is replaced with a transmission line, new power conversion circuits will emerge. By introducing microwave properties, such as propagation delay and characteristic impedance, new functions may be feasible in the area of power conversion. Examples of such functions could be inverting and noninverting voltage polarity abilities or circuits, which share switch components between multiple output voltages reducing the number of semiconductors needed. Alternatively, the buck-boost power converter circuit may give rise to new high-efficiency radio circuits in the area of microwave technology.

This paper explores the influence of air pressure, temperature and humidity on the switching impulse (SI) flashover performance of different types of clean and dry insulators at different high altitude sites of 2820 m to 5050 m along the Qinghai-Tibet Railway, the highest elevation railway in the world. Seven types of insulators are used in the flashover tests: one is a composite insulator, two are glass insulators and four are porcelain insulators. At the test sites, the ambient temperature varies between 6.7 degC to 28.5 degC and the absolute humidity is between 4.11 g/m3 to 9.69 g/m3. The test results show that the 50% switching impulse flashover voltage of different types of insulators at high altitude sites is independent of the materials and sheds of insulators but has a multi-factor non-linear relation with the shortest arc distance, the dry air pressure, the absolute humidity and the ambient temperature. The relative flashover voltage decreased with the ambient temperature is dependent on the voltage polarity, with 0.152% to 0.165% /degC for negative SI and 0.099% to 0.108% /degC for positive SI at the ambient temperature of from 6.7 degC to 28.5 degC. The relative flashover voltage increased with the absolute humidity and is dependent on the air pressure. The higher the altitude is, the more the influence is of the absolute humidity on the flashover voltage of insulators.

Breakdown and corona are investigated in clean and dust-polluted rod-rod air gaps varying gap length, rod radius and voltage polarity. It is shown that similar to previous results under impulse voltages, dust pollution can significantly reduce the DC breakdown voltage values of such gaps which depends upon electrode radius, gap length and voltage polarity. These factors should therefore be considered prior to the design and application of air insulation in desert regions, where sand and dust storms can occur frequently. Possible mechanisms which control the observed behaviour are explained in detail.

Curvature of Selemion, C, exhibited a quite definite relationship to the charge, Q. There was an almost perfect linear relationship between them, as long as the applied voltage to Selemion was higher than Vth, which was a threshold voltage in need for the induction of redox reaction 2Ag + 1 2 O2 ↔ Ag2O. At Vth or above, a larger quantity of charge was given to the Selemion owing to the reaction. Although such a linear relationship slightly worsened, once the voltage polarity was reversed, Q versus C still maintained a certain definite relationship. Therefore, it was speculated that the Selemion bending curvature was still controllable through the control of charge (or current). Besides charge (or current), the existence of water inside Selemion was an essential factor for the induction of its bending. Because Selemion is an electrically insulating material, quite indifferently to the applied voltage, and the water contained in Selemion created ions, and Selemion must have been converted into a semi-conductive material that could respond to the applied voltage.

Nanopore fabrication by controlled breakdown (CBD) overcomes many of the challenges of traditional nanofabrication techniques, by reliably forming solid-state nanopores sub-2 nm in size in a low-cost and scalable way for nucleic acid analysis applications. Herein, the breakdown kinetics of thin dielectric membranes immersed in a liquid environment are investigated in order to gain deeper insights into the mechanism of solid-state nanopore formation by high electric fields. For various fabrication conditions, we demonstrate that nanopore fabrication time is Weibull-distributed, in support of the hypothesis that the fabrication mechanism is a stochastic process governed by the probability of forming a connected path across the membrane (i.e. a weakest-link problem). Additionally, we explore the roles that various ions and solvents play in breakdown kinetics, revealing that asymmetric pH conditions across the membrane can significantly affect nanopore fabrication time for a given voltage polarity. These results, characterizing the stochasticity of the nanopore fabrication process and highlighting the parameters affecting it, should assist researchers interested in exploiting the potential of CBD for nanofluidic channel fabrication, while also offering guidance towards the conceivable manufacturing of solid-state nanopore-based technologies for DNA sequencing applications.

The sparkover behaviour of sphere-rod gaps under standard impulse voltages is investigated by assessing the influence of gap spacing, impulse voltage waveshape and polarity, and atmospheric conditions on the distribution of the sparkover voltage. At sparkover the growth of streamers of both polarities can be estimated since a value of 2 MV/m is found to be characteristic for the average negative streamer gradient. The IEC atmospheric conditions correction is discussed and compared with a new optimised correction procedure. The feasibility of using the sphere-rod gap as substandard for measuring impulse voltages, replacing the conventional more expensive sphere gap, is examined.

The basic characteristics of reset discharges related to a wall voltage and a priming effect were investigated under a conventional ramp driving scheme. The reset discharges could be minimized by controlling the wall voltage which is determined by pre-reset conditions. Accordingly, the current study presents a simple pre-reset condition for minimizing the reset discharge. Essentially, it is not only to reduce the duration of reset discharges but also to reduce the intensity of light emissions when the wall voltage polarity is opposite to the external voltage polarity.

Evaluation of insulation strength for lightning surge that actually enters into substations is important in estimating insulation reliability of gas-insulated equipment. The standard lightning impulse voltage (1.2/50 µs) is used for factory tests. However, the actual lightning surge waveforms in substations are complex and are usually superimposed with various oscillations. Insulation characteristics of SF6 gas as a function of such complex voltages have not been sufficiently clarified. This paper deals with gap breakdown characteristics in SF6 gas under submicrosecond pulses. Breakdown voltages are lower under a polarity reversal condition than under a monopolarity condition. The cause of this difference is discussed while observing discharge propagation using an image converter camera. The electrode size effect is also discussed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 146(4): 18–25, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10246

We investigate translocation of linear and circular double-stranded DNA molecules through solid state nanopores where each molecule is recaptured and re-translocated many times. Single molecules can be recaptured by switching voltage polarity for hundreds or even thousands of times. The large number of recapture events allows statistics on the translocation of individual molecules. Surprisingly, we observe that recaptured DNA molecules do not translocate in a linear head-to-tail fashion, but instead translocate as a folded blob where multiple parts of the DNA molecule simultaneously translocate through the pore in parallel. This folding is observed through the presence of up to 13 DNA double strands from the same molecule simultaneously inside the pore, as well as many smaller fold numbers occurring during the course of a translocation event. The strong folding is particularly prominent when the molecule is recaptured at short time scales, i.e. shorter than its characteristic time to relax to its equilibrium configuration. At longer recapture times, both the amount of folding and the mean duration of translocation approach the values observed in non-recapture experiments. The data shows that the translocation time of a molecule depends on the molecule’s conformation at the start of the translocation process, with extended molecules having a longer translocation time. The observations can be attributed to a high-density non-equilibrium DNA configuration that arises in the close vicinity of the nanopore immediately after translocation, which dissipates on a time scale given by the Zimm relaxation time.

Responsivity and thermionic dark current are studied in asymmetric stepped GaAs/AlGaAs multiquantum well infrared detectors with a single bound state. Although attributed to different transport properties, both the photoexcited and the thermally emitted carriers exhibit asymmetric transport properties with respect to the voltage polarity. The experimental characteristics are explained by the minibands-quasi continuum energy structure above the barrier.

This paper illustrates a new model that enables the estimation of life of polymeric insulation subjected to DC stress, both in the presence and in the absence of voltage polarity inversions. The derivation of the model parameters is based on the results of space charge measurements and accelerated life tests realized at constant DC stress, which allows the characterization of the performance of insulating materials under DC electrical stress to be carried out in short times. The expected life of a cable in service can be evaluated by means of this model, provided that the rate of voltage inversions expected during its life is known or estimated. The model is applied here to results of tests carried out on polyethylene-based materials for cable insulation, and model parameters are calculated resorting to two different approaches. A satisfactory fitting of life test results is achieved, thus confirming the validity of the proposed model.

The current–voltage characteristics (CVC) for nonstationary Josephson I 1 , interference I 2 , and quasiparticle J currents through tunnel junctions involving partially dielectrized superconductors with charge-density waves were calculated. The CVC peculiarities depend on combinations of superconducting, Δ , and dielectric, Σ , order parameters for both electrodes. Symmetrical (s) and nonsymmetrical (ns) junctions, when one of the electrodes is an ordinary (BCS) superconductor, are considered in detail. The current J ns depends on the voltage polarity, which is not inherent to the ns-junctions involving only BCS superconductors. In the s-case, both symmetrical and nonsymmetrical CVC for J s are possibly depending on the Σ equality (including their signs) for electrodes. The theory describes the properties of NbSe 3 and high- T c oxides.

Using a triangular ice sample, the characteristics of the DC arc appearing on ice surfaces was investigated. Based on the results obtained, a model for predicting the 50% flashover voltage of ice-covered insulators energised with DC was presented. The model takes into account the ice surface conductivity, voltage polarity, and arc root radius. Moreover, to validate the model, the 50% flashover voltage of a short string of five IEEE standard insulators covered with artificial ice under both DC– and DC+ was measured. There was an excellent concordance between the experimental results and those calculated from the mathematical model.

Acoustic emission (AE) characteristics have been investigated during electrical tree growth from a needle tip in a plastic insulating material. Alternating voltages (50 Hz) of 16, 20, and 24 kV rms were applied. Various patterns of tree growth, branch-like, bush-like, and filamentary trees, and formation of voids were observed. The amplitude of AE from the branch-like and filamentary trees was relatively small, and the amplitude distribution exhibited a sharp peak at small amplitude. On the other hand, the amplitude of AE from the bush-like tree and at void formation was large, and the amplitude distribution covered a wide range. The number and the amplitude of AE events were studied in relation to the phase of alternating voltage. The largest number of events was observed at the peak of the applied voltage for the branch-like and filamentary trees, and before the voltage peak for the bush-like trees. Most AE signals were detected when the absolute value of the voltage increased for the branch-like, bush-like, and filamentary trees but were detected in all voltage phases when voids formed. During tree activity, the AE amplitude was tended to be largest at the voltage peaks, but during void formation, was largest just after the change of voltage polarity.

An injected round bore railgun (77 cm long by 1 cm diameter bore) was designed and built for testing insulator materials. The firing parameters were held fixed and the rail to rail resistance of various insulators was measured versus shot number. The insulators studied include a variety of glass filled polymers, and filled and unfilled thermoplastics. Insulator, projectile, and rail mass losses were also measured. A voltage polarity dependence of the rail mass loss was clearly demonstrated. The surface conduction of the insulators was measured as a function of distance from the breech. The tests indicate that a significant improvement in performance over filled epoxy materials is possible with certain polymers.

The surface potential decay characteristics of corona-charged stretched and unstretched PVDF films have been investigated as a function of time, thickness, initial surface potential, and voltage polarity. An attempt is made to explain the results on the basis of trapping of charges in the bulk of the material. It is assumed that the charge deposited from corona is trapped in the surface states and is subsequently thermally injected into the bulk.

The surface potential decay characteristics of corona charged cellulose acetate films have been investigated as a function of charging time, initial surface potential, thickness and voltage polarity. Some of these studies have also been performed on iodine doped (2% wt/wt) cellulose acetate films. The carrier mobility has been calculated from these measurements and comes out to be 1.96 × 10−9 cm2 V−1 s−1 for pure cellulose acetate films. It has been found that the carrier mobility increases to 6.0 × 10−6 cm2 V−1 s−1 by iodination.

The static field discharge behavior of rod-plane gaps filled with SF6 is discussed in the pressure range of 100-500 kPa for applied voltages of positive and negative polarities. Discharge characteristics were determined using hemispherically capped rod electrodes of various radii up to 6.3 mm. Electrode gap spacings from 10 to 40 mm were studied. It is shown that the corona stabilization processes in SF6 are affected by gas pressure, the polarity of the applied voltage, gap length, and the radius of curvature of the rod electrode.

This paper is devoted to a comparison study of the breakdown voltage of CO2, N2, and SF6 gases, and CO2–SF6 and N2–SF6 mixtures under different voltage waveforms, namely AC, DC, and lightning impulse voltages, in point–plane and sphere–sphere electrode arrangements. The influence of pressure, voltage polarity, and percentage of SF6 in CO2 and N2 were studied, and equivalencies between the breakdown voltage of SF6 and those of the considered mixtures were analyzed. It is shown that the breakdown voltage of SF6 is the highest, whatever the applied voltage waveforms. Similarly, for a given voltage waveform, the breakdown voltage of SF6 is the highest. The AC breakdown voltage is the lowest for all gases. The addition of small amounts of SF6 to CO2 and N2 significantly improved the breakdown voltages of both natural gases. For a given breakdown voltage, the ratio between the pressure of CO2 to that of SF6 was generally lower than the pressure of N2 to SF6, whatever the voltage waveforms.