Breakdown Voltage Distribution Research Articles

2.1 kV (001)- β -Ga2O3 vertical Schottky barrier diode with high-k oxide field plate

We report a vertical β-Ga2O3 Schottky barrier diode (SBD) with BaTiO3 as field plate oxide on a low doped thick epitaxial layer exhibiting 2.1 kV breakdown voltage. A thick drift layer of 11 μm with a low effective doping concentration of 8 × 1015 cm–3 is used to achieve high breakdown voltage. Using the high-k dielectric with a dielectric constant of 248, the breakdown voltage increases from 816 V for the non-field-plated SBD to 2152 V (>2× improvement) for the field-plated SBD without compromising the on-state performance. The diode dimensions are varied to analyze the effect of edge high-field related leakage with reverse bias and also the effect of current spreading during forward operation. Very uniform distribution of breakdown voltages of 2152 ± 20 V are observed for the diode diameters from 50 to 300 μm for the field-plated SBDs. The on and off state power losses are also analyzed and compared with the non-field-plated devices and the switching losses are estimated analytically.

Analysis of AC breakdown strength of vegetable oils and effect of mineral oil

• AC breakdown strength of coconut oil is studied as against commercial soybean oil. • Analyzed the effect of aging (120 °C, 2 weeks) and mineral oil on AC breakdown strength. • AC breakdown data are statistically analyzed using Normal and Weibull distributions. • Aging or mineral oil reduces the withstand voltage, but the effect is less intense in coconut oil. • Coconut oil can be a potential replacement for traditional mineral oils. The effect of residual mineral oil on the AC breakdown strength of vegetable oil is widely studied to understand vegetable oil's reliability and dielectric integrity in retro-fitting a mineral oil-filled transformer. This paper describes the analysis of experimental results on two types of vegetable oil, namely –refined, bleached, and deodorized (RBD) coconut oil and commercial vegetable oil (MIDEL eN1215) derived from soybean oil seeds. The latter is also to act as a benchmark in analyzing the breakdown performance of RBD coconut oil, which is recently studied as a potential alternative to replace mineral oil from transformers located in tropical countries. The AC breakdown voltage tests were conducted using ASTM D1816 method at normal ambient conditions for both fresh and aged oils and considering 10 and 30% mineral oil in these vegetable oils. It is found that the distributions of breakdown voltages in RBD coconut oil, especially the lowest AC breakdown voltage, are similar to those of commercial vegetable oil for transformers. Therefore, from the viewpoint of AC withstand voltage, RBD coconut oil is equivalent to commercial vegetable oil under new conditions and even better under aged conditions or when mixed with mineral oil.

Application of N parallel-connected SiC MOSFETs to solid-state circuit breakers based on UIS tests

N parallel-connected SiC MOSFETs were investigated to apply to solid-state circuit breakers (SSCB), and it is an extension of a method that was proved valid by experiment of two parallel-connected SiC MOSFETs. The unclamped inductive switching (UIS) test was considered as the emergency interruption of SSCBs in this research. Because of the variations of breakdown voltage among SiC MOSFETs, the current flowing through devices is imbalanced during emergency interruption of SSCBs, which can drive some of the devices into thermal destruction prematurely. There are many compound cases for several SiC MOFETs with a certain maximum breakdown voltage variation. And the worst case, where the breakdown voltage of one device is assumed as the lowest, whereas the other devices have the same breakdown voltage, was extracted from the calculated results of four parallel-connected situation. In the worst case, it was found that the relation of breakdown voltage variations and current capacity is linear. Moreover, the distributions of breakdown voltage were taken as normal distributions. Using the worst case and distributions, a linear relation of breakdown voltage distributions and rated current of an SSCB could be concluded as a function of paralleled-connected numbers (N). Utilizing the function, the necessary breakdown voltage distributions and N of SiC MOSFETs can be evaluated for SSCBs meeting a certain yield ratio and current.

Prediction of Impulse Breakdown Voltage in Dry Air at High Pressure Using Volume-Time Theory

Dry air is promising as an alternative insulation medium for SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas in high-voltage equipment. Since its dielectric strength is about one-third of that of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas, one of the most effective ways to apply dry air to high-voltage gas-insulated switchgears (GISs) is to further increase gas pressure. In this article, impulse breakdown strength of dry air at high pressure under quasi-uniform electric field is measured. Furthermore, the probability distribution of breakdown voltage is predicted using the volume-time theory in consideration of initial electron generation probability in gas gap and field electron emission from an electrode. The predicted distribution of breakdown voltage by the volume-time theory is in line with the experimental results.

Elevated barrier height originated from electric dipole effect and improved breakdown characteristics in PtOx/β-Ga2O3 Schottky barrier diodes

The higher Schottky barrier height of PtOx/β-Ga2O3 Schottky barrier diode (SBD) was derived from the electric dipole effect of PtOx Schottky electrode. And the higher Schottky barrier height effectively improved the reverse breakdown characteristics of β-Ga2O3 SBD. In this work, PtOx/β-Ga2O3 and Pt/β-Ga2O3 SBDs were fabricated, and the Schottky barrier height of PtOx SBD increased with the increment of oxygen element component in PtOx electrode, which were all higher than the Schottky barrier height of Pt SBD. Kelvin probe force microscope measurement indicated that Fermi level pinning effect and the variation in work functions of Schottky electrodes were irrelevant to the higher barrier height. Moreover, with the increment of inserting PtOx layer thickness in Pt/PtOx/β-Ga2O3 SBDs, the Schottky barrier height increased from 1.32 eV to 1.82 eV. Bright-field scanning transmission electron microscopy image demonstrated that PtOx was mainly polycrystal with layer structure near the Schottky interface. The layer structure composed of Pt ions and O ions induced electric dipole effect, and the electric dipole effect led to the increase of Schottky barrier height for PtOx SBD. Lower leakage current density, higher breakdown voltages and more concentrated breakdown voltage distribution were obtained for PtOx SBDs. Furthermore, the barrier heights of PtOx SBDs gradually increased as the temperature raised, resulting in their reverse leakage current increased much more slowly with temperature than that of Pt SBD. The above results demonstrated that PtOx/β-Ga2O3 SBD had great potential in enhancing reverse blocking characteristics and high-temperature environment applications.

DC breakdown characteristics and charges accumulation behaviour of thermally upgraded paper aged in natural ester

Considering that the working temperature is much higher in high-voltage direct-current (HVDC) convert transformers than in conventional AC transformers, the combination of thermally upgraded paper and natural ester might be a better choice to withstand high temperature in long-term operation. This study compares the chemical structure, DC breakdown voltage, space charge and trap distribution of thermally upgraded paper aged in natural esters and mineral oil. The relationship between DC breakdown and accumulated charges was analyzed. Results show that the thermally upgraded paper aged in natural ester (NEI-TUP) has a higher volume resistivity and DC breakdown voltage than that aged in mineral oil (MOI-TUP). The NEI-TUP group has a larger deep trap density than the MOI-TUP group due to the chemical structure of natural ester. The larger deep trap density could contribute to the lower charge accumulation quantity and higher DC breakdown voltage. The thermally upgraded paper immersed in natural ester presents better insulation capability under thermal and DC electrical stress than that immersed in conventional mineral oil. This research indicated that the combination of thermally upgraded paper and natural ester might be a potential alternative for the mineral oil immersed paper in the future.

Bifurcation of distribution function of electric breakdown voltages of polymer enamel-lacquer coatings

On the basis of general physics representations, the statistical model of multilayer enamel-lacquer polymer coatings is proposed. Such coatings contain randomly distributed air inclusions. The solution of statistical problem connected with the distribution of electric breakdown voltages of such coatings permits to explain the observed the violation unimodality of histograms of their dielectric strength.

Relative breakdown voltage and energy deposition in the liquid and gas phase of multiphase hydrocarbon plasmas

Pulsed electrical discharges in a gas–liquid mixture deposit energy into both phases. Here, we propose a model to simulate breakdown in multiphase based on experimental data. Furthermore, we estimated breakdown voltage in each phase and then estimated energy deposition in each phase. Discharge in pure liquid showed a highly stochastic nature, having a wide breakdown voltage distribution, while the mean value closely follows a one term power law as a function of gap spacing. When there is external gas injection to the gap, breakdown voltage increased significantly due to charge dissipation on bubble surface. This effect was simulated to predict breakdown voltage in liquid with gas injection at different rates. A multiphase system model was developed to simulate breakdown in the gas–liquid phase. The model is a superposition of power law and Meek criteria physical models for the liquid and gas phases, respectively, with empirically derived coefficients. Energy deposition into each phase was estimated by this model. The gap spacing is the primary factor determining breakdown voltage and energy distribution. In studied conditions, we were able to predict the breakdown voltage and estimate energy deposition into different phases. When the gap and flow rate vary between 2 and 10 mm and flow rate 0–1 LPM, 50%–93% of electrical energy is deposited into the liquid. This model allows for predicting breakdown voltage in a multiphase. Furthermore, it allows for control of the energy distribution among the phases in a multiphase pulsed discharge system.

Electrical properties of polymer blend composites based on Silicone rubber/EPDM/clay for high voltage insulators

Silicone rubber (SR) and ethylene-propylene-diene monomer (EPDM) are widely-used polymers as housing for high voltage insulators. In this work, SR/EPDM/clay nanocomposites were obtained by two-roll mill mixing for outdoor polymeric insulators. Morphology, dielectric properties, dielectric breakdown strength (DBS), and surface and volume resistivity of different weight contents of nanoclay (Cloisite 15A) incorporated in SR, EPDM, and SR/EPDM hybrid nanocomposites were characterized. In addition, the distribution of breakdown voltages was fit to the distribution of Weibull and estimated the scale and shape parameters. The polar groups of the clay particles enhanced the polarization capability of the nanocomposites. Moreover, DBS results showed an enhancement of the dielectric strength proportional to clay content. Finally, the surface and volume resistance of all nanocomposites decreases but maintains very high electrical resistance. The experimental data presented in this study will be useful for designing and manufacturing the outdoor insulators.

Breakdown point transfer theory for Si/SiC heterojunction LDMOS with deep drain region

Abstract Heterojunction terminal technology, especially Si/SiC heterojunction, has been widely used in the power semiconductor device. Si/SiC heterojunction LDMOS combines the advantages of Si and SiC while the breakdown point is transferred due to employing the deep drain region structure to improve the BV of the device. Based on the existing research, a new theory about breakdown point transfer terminal technology is proposed for silicon on silicon carbide lateral double-diffused metal oxide semiconductor field effect transistor with deep drain region based on the electric field modulation in this paper for the first time. A concise and efficient analytical theory is presented to predict the breakdown voltage and electric field (E-field) distributions of Si/SiC LDMOS. The mechanism of surface electric field modulated and optimized by breakdown point transfer terminal technology is explained. Introducing the drain region impact factor into the analytical model to decouple the lateral and vertical depletion below the drift region. The analytical model proves that the deep drain region structure can modulate both the lateral and vertical electric field. Meanwhile, the location of the breakdown point can be determined by the E-field distribution at y = TDr and the E-field distribution at y = TSi, which is demonstrated by both theoretical interpreting and simulation. The derivations were verified using the ISE TCAD with a good agreement in the analytical model by changing the key structural parameters of the device. This analytical theory can be applied to other heterojunction power devices.

Method of calculating the electric strength of oil channels of the main insulation of power transformers

The most damage-sensitive unit of power transformers is the main insulation of the oil barrier type. The breakdown of such insulation occurs as a result of the breakdown of the oil channel near the high voltage winding. In accordance with traditional methods of calculating the dielectric strength of insulation, the value of the breakdown strength is determined by empirical formulas depending on the selected width of the oil channel. The existing methods do not consider the influence of the oil channel volume, of the electric strength the statistical characteristics of the oil, the design features of the insulation of power transformers, and do not contain recommendations for creating design models. Thus, to improve the calculation accuracy, it is relevant to develop the evaluation method of dielectric strength of the main insulation of power transformers taking into account the volume and parameters of the breakdown voltage distribution of transformer oil, design features. The research results of the breakdown tension in oil channels with different volumes of transformer oil were used. To improve the accuracy of the calculation and taking into account the design features, the model of the main insulation of power transformers was made in the ANSYS program. Boundary data and assumption of linear stress distribution of transformer coils were considered. A method for calculating the dielectric strength of oil channels of the main insulation of power transformers, considering the volume and parameters of the breakdown voltage distribution of transformer oil was proposed. Unlike the existing methods, when calculating the minimum breakdown strength in the model of the main insulation, the design features of power transformers are taken into account and assumptions are justified to improve the accuracy of the calculation. In accordance with the methodology, the parameters of the dielectric strength of the transformer oil in the oil channel of the high voltage winding of the transformer were calculated. It was concluded that with increase of relative value of breakdown tension, dielectric strength of oil channel is decreasing, and it corresponds to physical sense of breakdown. The method for calculating the dielectric strength of transformer oil can be used when choosing the main insulation of power transformers in design.

Fast rise breakdown in dielectric filled air gap for surge protection

Electric discharge across an air gap can be self-healing, providing a unique capability for repetitive, fast, high-voltage/current switching applications through arc conduction. Furthermore, incorporating dielectric granules in the air gap stimulates gas ionization, which lowers the breakdown voltage and narrows breakdown voltage distribution, thereby enabling engineered surge protection from multiple lightning strikes on aerospace vehicles and sensitive solid-state electronics in critical systems. This study investigates the effect of the permittivity of dielectric granules, gap filling, surface roughness, and metal work function on fast-rising, high-voltage breakdowns. In addition to the air gap width, these factors play important roles in gas ionization, field concentration, and initiation of electrical discharge and arcing. Therefore, they could potentially be used to control and narrow operational breakdown voltages for practical applications. Additionally, a modified Langevin–Debye model is developed to correlate the breakdown voltage and the permittivity of the dielectric filler. These investigations identify and highlight key underpinning mechanisms governing the gas discharge behavior across a dielectric filled air gap during voltage surge events.

Preparation of PI porous fiber membrane for recovering oil-paper insulation structure

PI fiber insulation paper has excellent insulation and heat resistance, which can replace traditional insulation paper to provide a new high-performance material. In this paper, we adopt a two-step method to synthesize PI, that is, firstly synthesize polyamic acid, and then perform electrospinning and thermal imidization to prepare PI porous fiber membrane. The test results show that the breakdown field strength of the PI porous film is 50 kV/mm. Further research shows that the insulation structure has the characteristics of continuous multiple breakdown. When the fiber film is repeatedly broken down to 25 times at the same point, the field strength of each breakdown of the fiber film changes between 40 and 55 kV/mm, and the average breakdown field strength is 53 kV/mm. Nano-Al2O3 was introduced into the fiber membrane by in situ polymerization. The breakdown field strength of the composite fiber film can reach 74.89 kV/mm after doping 2 wt% nano-Al2O3, which is higher than that of the pure film. At the same time, this kind of fiber paper also has repeatable breakdown characteristics, and the breakdown voltage distribution width of multiple breakdown is reduced. This characteristic provides the maintenance free characteristic of DC over-voltage for the insulation structure composed of this fiber paper, and can improve the service life of transformer under DC over-voltage such as lightning stroke.

Study of high DC voltage breakdown between stainless steel electrodes separated by long vacuum gaps

High voltage (HV) insulation across a single gap in vacuum and low-pressure gas is a critical issue in relation to the development and realization of the electrostatic accelerator for the ITER neutral beam injector (NBI) (Toigo et al 2017 New J. Phys. 19 085004). The present paper describes and analyzes the recent experimental results obtained at the High Voltage Padova Test Facility (HVPTF), the laboratory aimed at supporting the development of the prototype for the ITER NBI (De Lorenzi et al 2011 Fusion Eng. Des. 86 742–5). A voltage up to 800kVDC was achieved in the HVPTF during the experimental campaigns with a sphere-plane configurations having variable gap length (from 30 to 150 mm) and pressure ranging from high vacuum (10–7 mbar) to 10–3 mbar in argon. Such an experimental campaign represents one of the few examples where voltages higher than 500–550 kV DC are sustained by a single vacuum gap between electrodes (Rohrbach 1971 CERN Report 71-5) and therefore constitutes additional experience to improve the knowledge of voltage holding across large vacuum gaps. The results in high vacuum indicate that at the beginning of voltage conditioning the breakdown events occur at the same cathodic electric field irrespective of the electrode geometry. However, after sufficient conditioning time, the breakdown voltage distribution seems to depend also on the electric field at the anode and on the total voltage between electrodes. A benchmark between a numerical tool previously developed to predict the voltage holding in high vacuum (voltage holding prediction model, VHPM (Pilan et al 2011 Fusion Eng. Des. 86 742–5)) and the experimental results is also reported and discussed.

Evaluation of statistical methods used in the estimation of breakdown voltage distribution

Multiple-level and up-and-down test methods are commonly employed in laboratories to obtain the breakdown voltage distribution of self-restoring insulation, which is applied for equipment evaluation and for risk calculation in insulation coordination studies. This study investigates the reliability of the methods and proposes a methodology for evaluating their performance. The accuracy and precision of the estimated distribution parameters were analysed considering the variation of the test parameters. Algorithms that simulate the random nature of the tests were developed and applied in simulations. Then, a case study of risk calculation was carried out. The results indicated that both methods estimate the critical flashover voltage with acceptable accuracy and precision, even for the minimum parameters defined by standards. However, estimating the standard deviation is the critical step of the tests. The proposed methodology allows parameter definition for a given reliability requirement in the case of the constant voltage method. In the case of the up-and-down method, however, high dispersion was observed for all analysed cases, which indicates that this method presents low reliability for calculating flashover risk and, therefore, its use for insulation coordination studies is not recommended.

노후 IV 전선의 절연파괴시험에 따른 통계적 수명 추정

In this study, the dielectric breakdown test was performed on the aged PVC insulated wires and the statistical life was estimated using the log-normal distribution probability. The sample is a 450 / 750V single-core PVC insulated wire collected from the inspection field. The AC dielectric breakdown test is conducted for three life groups of 0, 19, and 34 years to verify the change in the electrical insulation performance. The failure criterion assumes 50 % of the minimum design dielectric strength of IEC 60216-1, and the lifetime distribution is based on the lognormal distribution. The lifetime-dielectric breakdown voltage relation equation was derived from the linear fitting function of the percentile B50 of each life group. As a result, the breakdown voltage distribution by life group showed that the insulation strength of the IV wire decreased as the service life increased. As a result, three aging groups have shown that the insulation resistance performance of PVC insulators on IV wires decreases with longer service periods. And the life expectancy of PVC insulators of the IV wires according to the failure judgment criteria (50 ∼ 90 %) and failure rate (1 % and 50 %) is calculated from the relationship equation. As a result, the failure criteria and high failure rates confirm that the failure life is short.

Mechanically tuned conductivity at individual grain boundaries in polycrystalline ZnO varistor ceramics

Mechanically induced changes in electrical properties have gained increasing interest over the last decade. The research field piezotronics, which describes the change in potential barrier height (e.g., at Schottky contacts) by piezoelectric charges, could lead to promising applications such as sensors or strain trigged transistors. In this contribution, the changes of potential barriers by mechanical stress at several grain boundaries of polycrystalline ZnO have been quantified. Rationalization is provided by concurrent measurement of crystal orientations of both neighboring grains. The highest changes in barrier height could be observed at ZnO–ZnO grain boundaries exhibiting varistor properties. In this case, the barrier height can be almost completely reduced by positive piezoelectric charges. Furthermore, an increase in barrier height is observed with negative piezoelectric charges. The developed physical model suggests an equivalent impact of externally applied voltage and induced positive piezoelectric charge on the barrier properties. In turn, not only the barrier height is modified by piezoelectric charges but also the breakdown voltage. This has, nevertheless, been only indirectly verified in experiments. These allow rationalizing the proposed model. Furthermore, a statistical study reveals a change in the distribution of breakdown voltages with changing stress conditions in the varistor ceramic.

Performance of n-on-p planar pixel sensors with active edges at high-luminosity environment

Future high-energy physics experiments require highly segmented silicon sensors of increased geometrical efficiency with the ability to withstand extremely high radiation damage. The performance of planar n-on-p sensors with active edges is simulated at high radiation fluences up to 1 × 1016 neq/cm2, using a three-level trap model for p-type silicon material. Taking advantage of the secondary ion mass spectrometry (SIMS) technique, an accurate representation of the structure was obtained in terms of doping profile. The breakdown voltage, leakage current, hole density and electric field distributions as well as the charge collection efficiency (CCE) are studied as a function of radiation fluence.

Statistical failure reliability analysis on edible and non edible natural esters based liquid insulation for the applications in high voltage transformers

In the recent decades, the natural esters have gained more attention as an alternate liquid insulation instead of the petroleum based mineral oil due to the development on power system networks and their environmental friendly nature. The failure free functioning of high voltage transformer mainly depends on the reliability of insulation used inside it. In this work, edible and non edible natural esters are studied and analyzed by using statistical distribution of the AC breakdown voltage in order to ensure their reliability. In this investigation work, sunflower oil (SFO), palm oil (PO) and sesame oil (SO) are studied under the category of edible natural esters, while honge oil (HO), neem oil (NEO) and punna oil (PAO) are analyzed under the non edible natural esters category. The applicability of investigated esters as liquid insulation is analyzed with distribution models like normal, Weibull and generalized extreme value (GEV) distributions. The statistical failure reliability analysis is carried out with the distribution functions such as survival rate, hazard rate and failure rate from the 100 distributed values of AC breakdown voltages of the investigating natural esters. The statistical analysis reveals the better characteristics for natural esters (edible and non edible) such as superior survival rate at higher value of electric stress, possibility of failure occurrence only at the wear out range and elevated statistical withstand voltage at various failure rates. Comparing both the category of natural esters, non edible natural esters have shown the superior characteristics than the edible natural esters. Consequently, it is evident that the natural esters are reliable and potential surrogate to the conventional liquid insulation for the application in high voltage transformers.

Investigation of statistical behaviour of electrical breakdown voltage distribution for nitrogen‐filled diode at 13.3 mbar pressure

The results of statistical analysis of the electrical breakdown voltage distribution in nitrogen are presented in this paper. For obtaining the experimental results, a nitrogen‐filled diode at 13.3 mbar pressure was used. The dynamic method was used for estimating the static breakdown voltage. One‐hundred voltage measurements were carried out for each value of the increase in the voltage rate from 1 up to 10 V/s. Wilcoxon test was used for checking the measurements' randomness for each rate. The experimental distribution functions are fitted with the three‐parameter Weibull distribution function. The coefficients of the Weibull distribution are also estimated.