Withstand Voltage Research Articles

Breakdown Strength and Energy Density Improvement of Polypropylene by Parylene Deposition for Film Capacitor

In this article, a surface modification method is proposed for improving the breakdown strength and the energy density of polypropylene (PP) films for power capacitors based on chemical vapor deposition (CVD). The results indicate that after 5% thickness deposition, the leakage conductivity of the composite films decreases by 77% at 30 °C and declines by 96.2% at 85 °C compared with the pristine PP samples. The dielectric constant is increased from 2.19 to 2.34 at 1 kHz. The dielectric loss decreases from 0.0425 to 0.0047. The dc breakdown strength is enhanced from 553.7 to 658.5 kV/mm, and the energy density is improved by 40%–50%. The parylene deposition successfully increases the withstand voltage and the energy density by inhibiting charge injection. The results provide a reference for optimizing the performance of capacitor by interface modification.

AC Voltage Withstand Test Method and Risk Suppression Measures of Energized GIS Based on Phase-frequency Control

It is essential to carry out an AC voltage withstand test after GIS extension and maintenance. At present, the common methods of GIS AC withstand test include double isolation gap, reduce the test voltage, and narrow test range. These methods generally have some defects, such as complex test processes, all bus de-energized, some devices failed to test, unreliable test results, and so on. This paper presents a distinctive GIS AC voltage withstand test method. The method controls the phase-frequency (PFC) parameters of the test voltage so that it maintains the same phase-frequency relationships as the in-service bus voltage during the process of testing. At this moment, the GIS can carry out an energized AC voltage withstand test. The article introduces the process of the PFC AC withstand voltage test method in detail and demonstrates the feasibility of the method. The phase difference margin of the PFC method is optimized through simulation and numerical calculation, and a variety of protection measures are proposed to ensure the safety of the test process. The proposed PFC AC voltage withstand test method will not affect the in-service bus and has great practical application value for the field GIS AC voltage withstand test.

10‐1: Layout of 1.50‐inch, 3207‐ppi OLED Display with OSLSI/SiLSI Structure Capable of Division Driving Fabricated through VLSI Process with Side‐by‐Side Patterning by Photolithography

We fabricated a 1.50‐inch, 3207‐ppi OLED display with drivers capable of 32‐division driving, which is achieved by monolithically stacking OSFETs over SiFETs. Taking advantages of minute OSFETs with a high withstand voltage, Si‐OS connection regions were provided in subpixels to connect Si drivers and OS pixel arrays at given positions.

Experimental study on discharging current to reduce voltage stress during underwater shock wave generation

In food processing using underwater shock waves, the intensity of shock waves is determined by a discharging current from an output capacitor. In past studies, to realize efficient food processing, the underwater shock wave has been generated by charging a high voltage to the output capacitor with high withstand voltage characteristics. For this reason, the conventional method suffers from high manufacturing costs. Furthermore, the conventional method is dangerous due to high voltage requirements such as 3.5 kV. In this work, a low-cost and safe non-heat treatment technology using underwater shock waves is presented for food processing. Unlike the conventional methods, the proposed method generates underwater shock waves by using multiple large output capacitors with low withstand voltage characteristics. Therefore, the proposed method can achieve safe and low-cost non-thermal food processing, because the output capacitors do not need to be charged at high voltage. In the proposed method, the output voltage is about one-fourth that of the conventional methods. The effectiveness and reliability of the proposed technique are confirmed by several experiments using a laboratory experimental system. The experiment revealed that the proposed technique can process a target food at 865 V output, where the rise time of the high voltage generator is 126 s and the output capacitor is 3300 μF.

A hybrid current modulated DAB DC/DC converter for connecting PV modules to DC grid considering partial shading

The Maximum Power Point (MPP) voltage of a PV module can decrease significantly under partial shading conditions. Hence, high voltage gain converters are required to connect PV modules to DC grid. Generally, two-stage boost-based converters are preferred for their simplicity. However, they utilize a high number of semiconductors with high withstand voltages, and require an input filter inductance. In this paper, a hybrid current modulation that uses triangular (TRM) and trapezoidal (TZM) current modulations is proposed for Dual Active Bridge (DAB) converter to connect PV modules to DC grid. The proposed converter provides soft switching, low number of semiconductors, and reduces the breakdown voltages of input semiconductors compared with the two-stage Boost Full Bridge Isolated Converter (BFBIC). It also eliminates the input inductance and uses a 36% smaller core size than the total core size of BFBIC. The proposed converter is realized by an experimental prototype, and analyses are verified.

Partial discharge characteristics of free moving metal particles in gas insulated systems under DC and AC voltages

AbstractFree conductive particles in a gas‐insulated metal‐enclosed system produce partial discharges during movement, resulting in insulator flashover and insulation failures. This study focuses on the partial discharge property of free conductive particles under DC and AC voltages. The relationship between the micro‐discharge property and the intrinsic properties of the particles was obtained based on experimental tests. The results show that under DC conditions, the local discharge property varies linearly with particle size and density. The discharge probability of particles in SF6 is significantly reduced compared with that in air, while the discharge magnitude rapidly increases if the lift voltage exceeds a certain value. Under AC conditions, the partial discharge generated by the particle becomes less random, and the amplitude and phase angle of the discharge are not significantly related. As the size of the electrode decreases, the partial discharge current generated by the particles on the surface of the electrode with an uneven electric field increases significantly. This research provides a basis for the optimization of withstand voltage test method and its applications.

Significantly enhanced varistor properties of CaCu3Ti4O12 based ceramics by designing superior grain boundary: Deepening and broadening interface states

Significantly enhanced varistor properties via tailoring interface states were obtained in Ca 1–2 x /3 Y x Cu 3 Ti 4 O 12 -SrCu 3 Ti 4 O 12 composite ceramics. The breakdown field was improved to 35.8 kV cm −1 and the nonlinear coefficient in 0.1–1 mA cm −2 was enhanced to 14.6 for Ca 0.67 Y 0.5 Cu 3 Ti 4 O 12 -SrCu 3 Ti 4 O 12 . Noticeably, the withstand voltage of single grain boundary reached up to 24 V while the reported ones were constant to about 3 V. Greatly improved properties were attributed to the formation of superior grain boundary rather than the reduced grain size. Surprisingly, with distinct discrepancy of nonlinear performance in the composites, the resistance and activation energy of grain boundary exhibited little differences. Based on the double Schottky barrier at grain boundary and the field-assisted thermal emission model, it was found that the excellent electrical nonlinearity arose from the formation of deeper and broader interface states at grain boundary. In this case, interface states were not easily entirely filled and the barrier could maintain its height under applied voltage. This work provides a novel routine for enhancing the varistor properties of CaCu 3 Ti 4 O 12 based ceramics by manipulating interface states at grain boundary.

Influence of surface discharge on the deterioration characteristics of ethylene‐propylene rubber cable insulation under alternating current high voltage

To investigate partial discharge-induced deterioration characteristics of ethylene-propylene rubber (EPR) cable insulation under repeated alternating current (AC) voltage on high-speed trains, an experimental platform with a column-plate EPR insulation model is established. The surface condition and breakdown voltage of insulation samples after discharge treatment are observed and measured. In addition, a fitting formula to evaluate the deterioration extent of EPR samples is proposed. The results show that under repeated discharge pretreatments, the volume resistivity increases first and decreases afterwards when discharge magnitude is low. When partial discharge (PD) intensity increases to 100 pC, the volume and surface resistivity decrease monotonously, and the decreasing rate is positively correlated with PD intensity. During PD pre-treatment, a white circle appears near the electrode and turns to pale yellow with PD intensity. For PD pretreatments of 50 and 100 pC, withstand voltage of EPR insulation increase first and decrease afterwards, and the downward trend is slow. For PD pre-treatments of 200 and 400 pC, the withstand voltage decreases significantly with the degradation time. The fitting formula model shows that under the action of a strong electric field, the relationship between the reliability of EPR insulation samples, the probability and rate of molecular chain breakage, and the intensity of discharge activity is not linear.

Predicting the DC pollution flashover voltage on the insulation surfaces with superhydrophobicity

Cleanliness and desiccative are necessary for outdoor insulation surfaces to maintain the voltage withstand capability especially in humid and polluted operation conditions. Once the voltage withstanding capability of insulation coatings is reduced by contaminant electrolyte, flashover accidents would be easier to happen, causing tremendous economy and energy losses. Superhydrophobic coatings, due to their self-cleaning property, are deemed to have great application potential in maintaining outdoor insulation performance, especially in humid and polluted environments. The water patterns on superhydrophobic coating in humid and polluted conditions are obviously different from those on traditional insulation coatings. Flashover voltage is one of the indices for quantifying insulation strength, while to date it is still unclear whether the commonly-used flashover voltage prediction models based on Obenaus’s theory are still suitable to be applied in the cases with superhydrophobic surface. Here we proposed a facile and low-cost preparation method of superhydrophobic coating. By analyzing the specific surface condition under humid and polluted conditions, and considering the development of arc path, a novel theoretical model for predicting flashover voltage of superhydrophobic coatings is established from the perspective of electric field. The flashover voltage of the synthesized coating as well as Room Temperature Vulcanized (RTV) silicone rubber coating are tested and compared, for investigating the insulation strength on the synthesized superhydrophobic coating, and verifying the accuracy of the proposed prediction model. It is found the synthesized superhydrophobic coating shows self-cleaning property during the wetting and voltage applying process, the flashover voltage of superhydrophobic coating is higher than that of RTV coating, and is affected less obviously by the change in pollution degree, compared with RTV coating. The established model shows better accuracy in predicting the flashover voltage of superhydrophobic coating than the traditional one, with errors of less than 6%. Based on the proposed model, the flashover voltage of polluted superhydrophobic coating surface is positively and negatively related to the volume and the contact angle of the polluted electrolyte droplet, respectively.

Statistical evaluation of the AC breakdown voltages of vegetable oil exposed to direct sunlight

This paper presents the results of the AC breakdown voltage test for the two types of vegetable oil – coconut and soybean oil, stored under dark conditions and direct sunlight for 6 months. Statistical techniques - Normal and Weibull distribution, were used to determine the AC breakdown voltage at 1, 10, and 50% failure probabilities from at least 60 breakdown measurements. It is shown that not only the average AC breakdown voltage in RBD coconut oil was, about 11% (or 15%), greater than the soybean oil (or virgin coconut oil) but its lowest AC breakdown voltage was considerably (or slightly) better than the virgin coconut oil (or soybean oil). Further, the oil storage for 6 months in dark at ambient conditions marginally influences their AC withstand voltages while the sunlight exposure considerably decreases the withstand voltage of only soybean oil with almost no change in AC withstand voltage of coconut oil.

Breakdown and Flashover Properties of Cryogenic Liquid Fuel for Superconducting Energy Pipeline

The cooling of cryogenic liquid fuel in a superconducting cable is an important technical means to realize efficient energy and power transmission. However, there are only few types of cryogenic liquid fuels that can maintain the superconducting strip below the critical temperature, and little is known about the insulating properties of fuels other than liquid hydrogen. Besides, cryogenic liquid fuels are flammable and explosive, and a safe operating procedure is essential to conduct the discharge tests. Based on the trinitrotoluene equivalent method, the safety distance of the discharge test is determined, and the safety precautions are summarized in this article. Taking the molar ratio of methane to propane as 3:1, the breakdown and flashover voltages of liquefied small molecular alkanes were studied, and the test of long-time withstand voltage was also carried out. At last, the discharge parameters and waveform, as well as the surface state of the polymer after flashover in the fuel, were analyzed. The breakdown field strength of cryogenic liquid fuel is 22.9 kV/mm, and the flashover field strength is 15.9 kV/mm. The reduction of breakdown strength is not found in the test of long-time withstand voltage. Therefore, it has some advantages for the liquid fuels to directly cool the superconducting strips from the cost and electrical performance. This study aims at the superconducting energy pipeline cooling by liquefied natural gas, and it can also provide technical references for the electrical property and safety research of other fuels.

Dielectric Properties of Mg2TiO4-Doped Ca0.65Sr0.35Zr0.65Ti0.35O3 with High Withstand Voltage and Low Loss

Mg2TiO4-doped Ca0.65Sr0.35Zr0.65Ti0.35O3 (CSZT) thin films with different Mg2TiO4 concentrations were deposited on the LaNiO3(LNO)/p-Si substrate using radio-frequency magnetron sputtering technology. The dielectric response of the prepared x% Mg2TiO4-CSZT thin films with frequency, voltage, and temperature was systematically studied. The tanδ and leakage current density of CSZT thin films were reduced effectively by introducing Mg2TiO4 content. The prepared 6% Mg2TiO4-CSZT thin film, due to its low loss (tanδ ~0.01 at 1 MHz), satisfied temperature stability (TCC ~−68 ppm/°C, from −55 °C to 205 °C), high withstand voltage (>160 V), and small leakage current density (about 3.34 × 10−6 A/cm2 at operating voltage of 160 V). This may be useful for capacitor materials in the next generation of portable electronic systems.

Shape effect of Co nanoparticles on the electric and magnetic properties of Co–SiO2 nanogranular films

Controlling the magnetic anisotropy of nanoparticles is a crucial but challenging step for developing new magnetic functions. Here, we demonstrate a simple approach to controlling the shape of Co nanoparticles in a Co-SiO2 nanogranular film from oblate to prolate spheroid by varying the substrate rotation speed during the tandem fabrication process without changing the film composition (Co:SiO2 = 3:7). Changing the nanoparticles from oblate to prolate, increasing perpendicular length of ellipsoidal nanoparticles, changes the magnetic anisotropy axis of Co–SiO2 nanogranular films from in-plane to out-of-plane, which indicates that the shape anisotropy profoundly affects the magnetic properties. Despite the small tunneling current of a few tens of nanoamperes, a maximum tunneling magnetoresistance effect of up to 2.8 % was realized under an applied magnetic field of 12 kOe in the film plane. Achieving both in-plane and perpendicular spin-dependent tunneling, the anisotropic nanogranular films imply direction controllable tunneling materials as future topological nanoarchitecture. Such high-resistivity nanogranular films with a controllable magnetic nanoparticle shape facilitate the design of new magneto-optical devices with high withstand voltages.

50~500㎊ 커패시턴스 가변형 진공커패시터의 전극 설계 및 평가

A variable vacuum capacitor (VVC) is used to match impedance between an RF generator and a plasma load for manufacturing semiconductor devices and display panels. However, VVC requires a very narrow gap between electrodes and a high degree of vacuum to implement high dielectric strength and capacitance variability at compact sizes. In addition, it is difficult to manufacture and maintain quality of the electrode unit, and is not easy to access to development due to the difficulty of the brazing process. For this reason, there are no VVC manufacturers in Korea yet, so it relies entirely on imports.<BR>In this study, we designed and manufactured VVC with AC withstand voltage of 12 ㎸ and capacitance of 50 to 500 ㎊, which are widely used in RF matchers, etc. As a result of the test, the required performance was confirmed, and the possibility of localization was verified.

Electrical properties of palm oil and rice bran oil under AC stress for transformer application

This paper presents the investigation on the dielectric properties (dissipation factor, relative permittivity, and resistivity) and AC breakdown voltage behaviour of Palm Oil (PO) and Rice Bran Oil (RBO). The dielectric properties experiment was carried out according to the IEC 60247 standard using an automatic ADTR-2K Plus instrument. The AC breakdown test was carried using two different setups (automatic oil tester and BHT AC Generator) using similar VDE electrodes with 23 mm in diameter and comply with IEC 60156 standard. The data of AC breakdown voltage were statistically analysed to predict the withstand voltage (1%) of oil samples by using Weibull distribution. The results show that RBO has lower DDF than PO in which will give better insulating oil capability than PO. For relative permittivity, PO has the highest value among the oil samples which gives advantages in terms of stress distribution between solid and liquid inside the transformer. The relative permittivity of PO is 2.176 closer to that of solid insulation (4.0) which leads to an evener stress distribution between solid and liquid materials. On the other hand, for resistivity, RBO has the highest value among the oils, and it is correlated well with the results in AC breakdown. In the AC breakdown voltage study, two different equipment which having da differences in the volume of oil, electrodes arrangement and as well stirrer were investigated. In the AC breakdown study, RBO has the highest breakdown voltage for both test setups. PO is the second-best in AC breakdown voltage while MO shows the lowest breakdown voltage among oil samples. The percentage difference between using BAUR oil tester and BHT AC generator setup is between 4% and 10% at a 2.5 mm gap distance which is comparable for both types of equipment. For various gap distances studies, the breakdown voltage is increased with the increase of gap distance between the electrodes, for all oil samples. The Weibull distribution of MO, PO and RBO has well fitted with the fitting line of AC breakdown data. From the Weibull distribution, the empirical withstand voltages equations with gap distances of PO and RBO are derived.

Development of Broadband Resistive–Capacitive Parallel–Connection Voltage Divider for Transient Voltage Monitoring

The on-site measurement of transient voltages is of great significance in analyzing the fault cause of power systems and optimizing the insulation coordination of power equipment. Conventional voltage transformers normally have a narrow bandwidth and are unable to accurately measure various transient voltages in power systems. In this paper, a wideband parallel resistive–capacitive voltage divider is developed, which can be used for online monitoring of transient voltages in a 220 kV power grid. The structures of the high-voltage and low-voltage arms were designed. The internal electric field distribution of the high-voltage arm was analyzed. The influence factors and improvement techniques of the upper frequency limit were studied. The parameters of the elements of the divider were determined. The voltage withstand performances and scale factors under lightning impulses and AC and DC voltages, the temperature stabilities of scale factors and the step response and bandwidth of the developed voltage divider were tested. The results show that the deviations of the scale factors under various voltage waveforms and different temperatures ranging from −20 to 40 °C are within 3%. The withstand voltage meets the relevant requirements specified in IEC60071-1-2011. The step response 10~90% rise time is approximately 29 ns, and the 3 dB bandwidth covers the range of DC to 10 MHz.

Analysis of radiation effect of a novel SOI-Like LDMOS structure

This study proposes a new SL LDMOS structure similar to a silicon-on-insulator. The P+/N structure is used to replace the buried oxygen layer of traditional SOI LDMOS devices. The N-type layer is made of SiC material, and the highly doped P-type layer is used to partially deplete the SiC layer to achieve the SOI Like effect. At the same time, the highly doped buried layer is formed by ion implantation in the SiC layer to adjust the electric field in the drift region and improve the breakdown voltage. The Silvaco TCAD software is used to conduct a two-dimensional simulation of the proposed structure. The breakdown voltage of the device is 306 V. Compared with the SOI LDMOS under the same withstand voltage, the proposed SL LDMOS has about 32.9% lower the on-resistance and better electrical characteristics. In the study of radiation effects, the burnout threshold of the proposed structure is LET = 0.93 pC/μm and Vd = 222 V, which shows that the device has good anti-single event burnout performance. In the study of the total-ionizing-dose, when the total dose is higher than 119 Krad(Si), the breakdown voltage of the proposed device is significantly higher than that of the SOI LDMOS device. This can effectively address the shortcomings of SOI LDMOS devices regarding the total-ionizing-dose. Therefore, the proposed structure is suitable for application in harsh environments such as those with high radiation.

Impact of MV Standards on Shipboard DC Cable System Size

There is rising interest in medium-voltage direct current (MVDC) power systems for several reasons, including compatibility with DC loads and avoidance of alternating current (AC) frequency synchronization issues when combining multiple source outputs [1]. However, few MVDC systems are currently in operation, and there is relatively little experience compared to the knowledge available for medium-voltage alternating current (MVAC) systems. Presently, IEEE Std. 1709 is the only standard that provides guidance for MVDC systems [2]. This work&#x2019;s objective is to harmonize the information within MVAC standards to produce prospective design and test values for shipboard MVDC cables and evaluate their impact on cable system sizes. Standards for MVAC cable design and test parameters including Basic Lightning Impulse Insulation Level, Withstand Voltage, and cable insulation thickness are compiled to understand the range of parameter values deemed acceptable for MVAC cables. Based on existing shipboard MVAC standards and IEEE Std. 1709, this study produces prospective design and test values for a shipboard MVDC system with a 12 kV Nominal System Voltage. Additionally, a tradeoff was identified with the thickness of cable insulation where a small reduction in cable system size can be achieved but at the expense of substantially greater electric stresses within the insulation.

Naprezanja izolacije elektroenergetske opreme pri nestandardnim talasnim oblicima prenapona

During its operation, electrical equipment is constantly exposed to overvoltages of various waveforms, such as lightning discharges, switching operations, faults, etc. Therefore, adequate selection of overvoltage protection and equipment insulation withstand voltages are key factors in increasing system reliability. In general, insulation coordination is carried out by analyzing the insulation behavior for standard impulse and switching overvoltage waveforms. However, overvoltages that occur in operating conditions can significantly deviate from the standard waveforms of insulation withstand voltages, in terms of the front time, the duration of the wave, the existence of highfrequency components as result of reflections in the facility and other factors. This paper presents possible methods of assessing the behavior of equipment insulation for real voltage waves to which the insulation is exposed during exploitation and which deviate from standard waveforms, by analysis in the frequency domain. As there are different components in the overvoltage signal at different frequencies, which a different energy, the main goal of this paper is to analyze the insulation characteristics of a specific transformer from the point of view of the energy spectral density of the voltage wave that occurs at its terminals when an atmospheric discharge occurs. The analysis is based on the determination of the safety margin on the entire frequency spectrum of the overvoltage wave, that is, on the calculation of the so-called FDSF (Frequency Domain Severity Factor). The calculation results show that although the overvoltage amplitude is lower than the withstand voltage of the transformer insulation with an appropriate safety margin (the condition of the classic approach to insulation coordination is satisfied), the spectrum analysis of the voltage wave in the frequency domain shows that the insulation may still be compromised.

The Effect of Deep JFET and P-Well Implant of 1.2kV 4H-SiC MOSFETs

1.2kV 4H-SiC MOSFETs with different junction depths of JFET and P-well regions were fabricated. For each JFET/P-well depth combination, channel lengths and JFET widths were also varied to compare specific on-resistance, breakdown voltage, and short-circuit withstand time. It was discovered that deep JFET structure provides low specific on-resistance (12% lower) with high breakdown voltage. On the other hand, MOSFETs with deep P-well result in high breakdown voltage with low leakage current even in shorter channel length (0.4 lm). Moreover, trade-off relationship between Ron,sp and short-circuit withstand time is discussed for MOSFETs with different JFET widths and channel lengths; the deep JFET implant provides better trade-off relationship due to the feasibility of narrow JFET width. For the further improvement of trade-off relationship, MOSFETs with deep JFET and P-well implant are proposed. Lastly, the importance of high channel mobility for not only static characteristics but also short-circuit characteristics was investigated. The in-depth understanding of measured electrical characteristics was supported by 2D-device simulations.