Withstand Voltage Research Articles

An Online Condition Monitoring Method for Series-Connected IGBTs to Avoid Cascading Failure

The series-connected insulated gate bipolar transistors (IGBTs) have numerous applications in industry and research fields. One of the risks of the resultant series high-voltage switch (RSHVS) is the IGBTs short circuit failure. The number of the IGBTs in a RSHVS is usually designed with an appropriate voltage de-rating factor to make it resilient against a limited number of the IGBTs short circuit failures. However, by the increased number of failures, the withstand voltage of the healthy IGBTs finally violates the IGBTs' tolerable voltage in the off-state. In such conditions, a cascading failure occurs and breaks all remaining healthy IGBTs. This paper proposes a condition monitoring (CM) method to avoid cascading failure in RSHVSs. The proposed method works based on the change of the rising edge of the load current in the RSHVS turning-on time. It will be shown when some of the IGBTs in the series structure fail short, the turning-on time of the RSHVS increases. Thus, the rising edge of the current also increases which leads to the decrement of high-order harmonics magnitude. The proposed CM analyzes such harmonics and provides a constant voltage as the CM output. The performance of the proposed CM is evaluated using simulations and experiments for a RSHVS consisting of eight IGBTs.

Dielectric Failure Analysis of Distribution Transformer

The distribution Transformer acts an important function in the electrical distribution network. Failure of the transformer ends in an outage of power supply to end users. Failure of the distribution transformer usually results in the spare time of some weeks transformer accompanied by commercial misfortunes and the necessity to fix the system at the earliest. The prime reason for the outage of distribution transformers is a short circuit, insulation breakdown, and prolonged overloading. This paper investigates failure analysis of distribution transformers during separate source voltage withstand tests, induced over-voltage withstand tests and short circuit withstand strength tests. In this paper failure cases of three distribution transformers are resolved and the results are analyzed.

Optimization design of electrode structure of GaAs photoconductive semiconductor switch

Previous studies revealed that changing the electrode structures of a gallium arsenide photoconductive semiconductor switch (GaAs PCSS) can significantly affect the local electric field and current density at the electrodes. Knowing the optimization of the electrode structures of GaAs PCSS can improve the withstand voltage performance and current carrying capability. In this work, we optimize the surface contact electrode structure of GaAs PCSS, and numerical simulations are performed to systematically study the electric field and current density distribution in the bulk of the device. The result shows that the maximum transverse current density and maximum longitudinal current density of the embedded 172° isosceles trapezoid electrode structure are smaller than other kinds of electrode structures, which is the most favorable for improving the withstand voltage and current carrying capability of GaAs PCSS.

Assessing the impact of long-term operation, pollution and housing damage on the medium voltage surge arresters using non-destructive diagnostic techniques

Surge arresters installed in substations and overhead lines play a fundamental role in limiting atmospheric and switching overvoltages. In principle, surge arresters help to protect devices against fatal damage by choosing the specified protection level below the equipment withstand voltage. The reliability of surge arresters is still an important topic in many studies. Pollution and damage affect the performance of surge arresters and significantly impact their lifespan. It is necessary to analyze pollution problems and the effect of internal or external damage of surge arresters to find out the possibility of failure. The paper focused on an extensive study of medium voltage surge arresters from different manufacturers in various operation time, surface contamination, and damage types. In this study, we investigated new, used, damaged, and polluted metal-oxide medium voltage surge arresters to determine how these problems affect the performance of the surge arrester and whether the selected parameters exceed the standardized values defined in the standards. Research deals with the volt–ampere characteristic, Fourier analysis, reference voltage, and active losses to analyze the surge arrester’s performance.

Performance and Properties of a Ti-Al Composite Anodic Oxide Film on AC-Etched Al Foil

AC-etched aluminum foils for an Al electrolytic capacitor were covered with a TiO2 film by a sol–gel coating and then anodized to 25 V in an ammonium adipate solution. The structure, properties, and performance of the anodic oxide films were examined by transmission electron microscopy (TEM), scanning electron microscopy (SEM), electrochemical impedance measurements (EIS), a general digital LCR meter, a TV characteristic tester, and multicycle pulse charging–discharging. It was found that the anodizing of aluminum coated with TiO2 films led to the formation of Al-Ti composite anodic oxide films, which consist of an outer Al-Ti composite oxide layer and an inner Al2O3 layer on the metal substrate. The capacitance (C25V) of the anodic oxide films formed on specimens with a TiO2 coating was about 10% larger than without a TiO2 coating. The specific resistance (Rox) of the Al-Ti composite film measured by EIS was lower than the blank one, accounting for a greater increase in the rise time (Tr) and a slight reduction in the withstand voltage (Vt). After hydration and a multicycle pulse charging–discharging destructive test, the Al-Ti composite anodic oxide film maintained the same good, comprehensive dielectric properties and performance as the blank one, thereby proving to be promising for acting as dielectric layers.

A Digital Twin System of Capacitive DC Bank Using Rogowski Coil to Monitor Individual Capacitors

The reliability of dc link capacitors is closely related to the operational safety of the whole power electronic system. To meet the application requirements, it is usually necessary to use a series or parallel structure of multiple capacitors to increase the capacity and withstand voltage, which also makes it difficult to monitor the individual capacitors in the capacitor bank. This article proposed a digital twin system for dc-link capacitor banks with PCB integrated Rogowski coils as sensors. The system uses highly integrated Rogowski coils to obtain the operating currents of individual capacitors in order to realize parameter correction of the digital twin system and ensure that the digital twin system can accurately reflect the electrothermal behavior of the dc-link capacitor bank. In addition, the effect of operating temperature on capacitor parameters is also considered, and the capacitor parameters and the operating temperature monitored by the digital twin system simultaneously are used to standardize the parameters. The standardized parameters are used as indicators to realize the health status assessment of each capacitor in the capacitor bank, which further provide an important basis for operation and maintenance.

Study on Resonance Phenomenon Caused by Voltage Fluctuation of Power Supply in JT-60SA EF Coil

For the large research Tokamak JT-60SA, evaluating the withstand voltage between conductors is one of the most critical factors for the coil design. The power supply feeding the coil injects a wide spectrum of frequency components. The transient response and resonance phenomena induce a non-uniform voltage distribution in the coil. The transiently concentrated voltage can cause the insulation breakdown between conductors, and JT-60SA may not be able to operate safely. This study conducted an impulse test to evaluate the withstand voltage between adjacent conductors for an equilibrium field (EF) coil. The actual power supply voltage for the EF coil was measured to investigate the ramp rate (dv/dt) and frequency spectrum. In addition, based on the results of a resonance test of the EF dummy coil, a circuit simulation model for the EF coil was developed to evaluate the effect of the transient response and resonance phenomenon on the voltage in the coil. The results of this study provide fundamental data that can be used to ensure that the EF coil does not cause insulation breakdown.

Aging Impact on Relative Permittivity, Thermal Properties, and Lightning Impulse Voltage Performance of Natural Ester Oil Filled With Semiconducting Nanoparticles

This study is focused on exploring the change in the dielectric and cooling efficiency of vegetable oil following the integration of semiconducting SiC and TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles in two different weight percentages by comparing the corresponding behavior of nanofluids at the time of their synthesis and after one month of ageing. The thermal response has been evaluated by means of diffusivity and conductivity, while dielectric properties are measured with non-destructive tests (relative permittivity and dissipation factor) and destructive ones in terms of lightning impulse withstand voltage. The results of the latter property measurements are also compared to numerical model findings. The analysis of results proves that the properties under study are worsened with increase in nanoparticles’ concentration, probably attributing it to quicker agglomeration, as it is also confirmed by the simulation results.

Restrike characteristics of vacuum circuit breaker in its opening process under DC voltage

AbstractThe restrike of vacuum circuit breaker during the breaking process causes overvoltage and intensifies the insulation deterioration of high‐voltage equipment. To solve this problem, the vacuum breaker aging test method and the restrike characteristics are researched. A withstand voltage test platform of 40.5‐kV vacuum circuit breaker was established to obtain the effects of the contact spacing and loop and inrush currents of vacuum circuit breaker on the number of restrike, the wavefront steepness of the breakdown voltage, and the breakdown duration. The number of restrike during the breaking of vacuum circuit breaker decreased and the duration of the repeated‐breakdown arc increased with the increased contact spacing of vacuum circuit breaker. As the loop current of the test system increased, the number of restrike during the breaking of vacuum circuit breaker, the wavefront steepness of the breakdown voltage, and the duration of the restrike arc increased. As the inrush current amplitude increased during the closing of vacuum circuit breaker, the number of restrike and the duration of the repeated‐breakdown arc during the breaking of vacuum circuit breaker increased. The results provide a theoretical basis and data support for the preventive test of 40.5‐kV vacuum circuit breaker and the optimization of the withstand voltage test.

Exploration of the Relationship Between Tyndall Effect and Moisture Content in Transformer Oil

Moisture content in oil detection technology such as offline method and online monitoring method has several shortcomings. In this paper, the Tyndall effect of moisture content in transformer oil was excited by a laser with a wavelength of 633 nm, and the relationship between Tyndall effect and moisture content in transformer oil was investigated. The relationship between the grayscale of laser beam column and particles in oil and the relationship between the grayscale of laser beam column and temperature are also investigated. It was found that withstand voltage of the oil was negatively correlated with the gray pixel statistics of the light column, while the micro water content was positively correlated with the pixel statistics of the light column. The attenuation of the light column is only related to particle size. When the micro water content is below 10 ppm, the light column will have a significant brightening process with the increase of temperature, but it will gradually slow down above 10 ppm. The statistical value of gray pixels and the proportion of gray intervals can be used to moisture content determination. This method provides a new direction for the insulation performance detection technology of transformer oil.

Failure Characterization of Silicone Rubber in Corrosive Environments Based on Leakage Current Characteristics

Due to the growing usage of composite insulators in transmission and distribution networks, the development of composite insulators has reached the stage of systematic reliability study. This paper discusses the failure properties of HTV silicone rubber in different energized corrosive environments and explores the characteristics that can characterize insulation failure. The findings demonstrate that the leakage current characteristics (the maximum values, the number of characteristic pulses, and cumulative charge) can effectively characterize the surface state of silicone rubber in corrosive environments. The flashover tests during the withstand voltage experiment accelerated the electrical performance degradation of silicone rubber and increased the leakage current. The three leakage current characteristics increase with experimental time, applied voltage, and fog conductivity. The occurrence of flashover is related to the fluctuation range of leakage current. The three leakage current characteristics in the alkali fog with the same conductivity and applied voltage are significantly higher than those in salt and acid fog. A failure characterization method of silicone rubber based on the proportion of pulse number and cumulative discharge is proposed in this paper. The findings are helpful in forecasting pollution flashovers and insulation failure in heavy fog, coastal, and industrial pollution areas.

Effect of Source–Drain Opposite Side Gate on the AlGaN/GaN High Electron Mobility Transistor Devices

To explore the influence of different gate positions on the performance of AlGaN/GaN high electron mobility transistor devices, two model structures are proposed in this paper: an inverted T‐type gate and source–drain opposite side structure (ITGS–DOSS), and an embedded ITGS–DOSS. It is shown in the simulation results that compared with the traditional T‐type gate structure, these two structures have better transfer characteristics and significantly reduce the on‐state resistance, which can effectively improve the virtual gate effect and suppress the current collapse effect. Furthermore, these two structures can also improve the frequency characteristics of the device, with a maximum cutoff frequency of about 625 and 635 GHz, respectively. The threshold voltage of the ITGS–DOSS is about −30 V, which is significantly shifted to the left compared to the traditional T‐type structure. With a gate–drain spacing of 4.4 μm, the breakdown voltage is still as high as 1661 V. As the device size and gate–drain spacing decrease, this structure has better voltage withstand characteristics, thus achieving low threshold and high breakdown device performance.

Structure and Electric Properties of Anodized Aluminum with PEDOT:PSS Conductive Polymer Cathode

Aluminum solid electrolytic capacitors using a conductive polymer as a cathode material has the advantages of low equivalent series resistance (ESR) and high thermal stability compared to aluminum electrolytic capacitors using liquid electrolytes. A disadvantage of aluminum solid electrolytic capacitors with a conductive polymer is the low breakdown voltages, limiting the operating voltage of the capacitors to ∼100 V or less. In this study, for a possible future increment of the withstand voltages of solid electrolytic capacitors, PEDOT:PSS-coated aluminum with an amorphous or crystalline alumina layer formed at 500 V has been characterized using SEM, STEM/EDS, and conductive AFM to understand the distribution of PEDOT:PSS conductive polymer and its influence on the electric properties. The crystalline alumina layer, developed beneath a porous hydrated alumina layer, contains many voids, which increase the leakage current compared to the void-less amorphous alumina layer. However, the crystalline alumina layer with PEDOT:PSS exhibits a higher breakdown voltage than the amorphous one. The limited incorporation of PEDOT:PSS into the inner part of the porous hydrated alumina layer may introduce a resistive surface layer, possibly contributing to the increased dielectric breakdown.

Modeling and Simulation of Fe-Doped GaN PCSS in High-Power Microwave

In this article, the characteristics of linear GaN photoconductive semiconductor switch (PCSS) in high-power microwaves are investigated by Silvaco TCAD (Technology Computer-Aided Design). By comparison of optical absorption efficiency among three types of PCSS structures, the optimized Fe-doped GaN PCSS is designed in a side-illuminated, vertical structure with a spot size of 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 8 mm. The photocurrent of side-illuminated GaN vertical PCSS (vPCSS) begins to saturate at 1.65 mJ with the increase of applied optical energy. The average saturated switch resistance and electron concentration of vPCSS under a bias voltage of 5–20 kV are almost 8.2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pmb\Omega $</tex-math> </inline-formula> and 3.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\text{14}}$</tex-math> </inline-formula> cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-\text{3}}$</tex-math> </inline-formula> , respectively. As the device is in a saturated photocurrent state, the peak photocurrent is a linear function of bias voltage. As the device is in an unsaturated photocurrent state, improving the light energy is more effective than the withstand voltage of the device to increase photocurrent. Due to the short carrier lifetime, the GaN vPCSS has the response capacity to a 50-ps pulsewidth laser. Based on side-illuminated GaN vPCSS at the bias field 200 kV/cm, a narrowband microwave with adjustable frequency (3.3–5 GHz) could be generated. The maximum output power reaches up to 1.3 kW. Effects of anti-reflective (AR) and reflective coatings on optical absorption are investigated. The photocurrent of vPCSS with both AR and reflective coatings increases by 77.2% as compared with normal vPCSS.

Flashover voltage and external insulation design for EMUs’ insulators at high altitude with non‐uniform distributed pollution

AbstractPollution usually accumulates on the surface of the insulator rapidly on high‐speed electric multiple units (EMUs) under operation condition, and the flashover can occur frequently, especially when the EMUs is running on a high‐altitude line. To solve the problem, this paper proposes the calculation method of insulator withstand voltage under the condition of non‐uniform fouling distribution of high‐speed airflow based on the characteristics of high altitude of Lanzhou‐Xin Line in China, and gives the design and test verification of insulator support insulator for 3500‐km altitude. The design and test verification of the supporting insulator of the rolling stock applicable to 3500 km altitude are presented. The result shows that the insulator should be reliable operation on 4430‐km high altitude area if the insulator structure height is 430 mm, the creep distance is 1250 mm. The anti‐pollution performance is fine in high‐speed wind if the radiuses of the large and small shed of the insulator are 196 and 145 mm, respectively, and the shed spacing is 45 mm. The 50‐Hz withstand voltage of the developed insulator is 131 kV and the light impulse voltage is 228 kV which is suitable for lines running on 3500 m. This research provides a theoretical basis and data to support the safety of high‐speed rolling stock in high‐altitude areas.

Investigation of Delay Jitter of Avalanche GaAs PCSS for Triggering High-Voltage Gas Switch

The delay jitter characteristics of gallium arsenide (GaAs) photoconductive semiconductor switches (PCSSs) triggered in avalanche mode were experimentally investigated under dc bias. In the dark-state measurement, the PCSS was tested under a 40-kV bias voltage to verify its withstanding voltage and reliability. In the ON-state measurement, the delay jitter time of PCSS at different triggering positions was measured. The experimental results showed that the shortest delay jitter time was obtained when the laser was applied to the middle position of the cathode electrode. To evaluate the long-time stability, the delay-jitter time was recorded after continuous shots. It shows an ascending trend in delay jitter time with the increase in operating shots. The degeneration of the delay jitter time of the PCSS was mainly attributed to the device damage, including electrode ablation and filament current ablation, which was verified by the analysis of scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). Furthermore, a bipolar high-voltage gas switch integrated with PCSSs was successfully triggered by a low-energy fiber laser.

A Dual-Inductor-Connected Isolated DC–DC Converter With Direct Current Control and Low Current Harmonics

Renewable energy sources such as fuel cells and photovoltaics (PV) modules are widely installed in recent years. Due to these sources&#x2019; characteristics such as low port voltage, current-harmonic-sensitive and weak short-circuit withstanding capability, their interface converters usually require high voltage gains, low high-frequency (HF) current harmonics and short-circuit protection. At present, the existing step-up isolated dc-dc converters are usually combined with two capacitor-connected terminals or one capacitor-connected terminal plus one inductor-connected terminal, failing to obtain the low HF current harmonics and convenient direct current control (DCC) on both ports. Hence, a dual-inductor-connected (DIC) isolated dc-dc converter is proposed in this paper with the inductor connection on both ports. Then, low HF current harmonics and convenient DCC capability can be realized simultaneously through the connected inductors. Meanwhile, the proposed converter can also achieve voltage spike suppression and soft-switching operation without snubber circuits, and its inherent voltage boost function makes it suitable for high voltage-gain applications. Subsequently, the modulation scheme, topology characters and control scheme are elaborated in this paper. The experimental results based on a scale-down laboratory prototype are presented to verify the steady-state and transient-state performance of the proposed converter.

Feasibility study on substitution of SF6 insulated current transformer with environment-friendly natural gas

Many SF6 gas-insulated current transformers (CT) are used in the power grid. The global warming potential (GWP) of SF6 is 23,900 times that of CO2, and the leakage of SF6 will aggravate the global warming trend. It is a hot issue to carry out the study of environment-friendly gas substitution in the power grid. This paper systematically studied the voltage withstand, partial discharge, and temperature rise characteristics of dry air, N2, and CO2 gas-insulated CTs. Through the study, the permissible critical pressures in environment-friendly gas-insulated CTs were determined to be 0.9 MPa for dry air, 0.7 MPa for N2, and 0.8 MPa for CO2, respectively. The partial discharge intensity was less than 5 pC for environment-friendly gas-insulated CTs at 0.3 MPa∼0.8 MPa pressure. The experimental results of temperature rise characteristics showed that under the condition of a 600A rated operating current, the maximum temperature rise of the CTs was about 80 °C, and the maximum temperature rise happened at the conductive rod. The experimental results verified that environment-friendly gases could meet the requirements of insulation and temperature rise. Due to the increase of pressure in CTs, the action pressure of the explosion-proof membrane should be changed to meet the mechanical strength requirements. It is recommended that when using 0.9 MPa dry air, the action pressure should be designed as 1.8 MPa; when using 0.7 MPa N2, the pressure should be designed as 1.4 MPa; when using 0.8 MPa CO2, the pressure should be designed as 1.6 MPa. The results of this paper can provide a reference for development of environment-friendly gas-insulated CTs.

Satisfaction-Based Multiobjective Optimization of the Design of a 65 GHz Millimeter-Wave Connector

It is difficult to simultaneously ensure the radio frequency (RF) performance and mechanical strength of 65 GHz millimeter-wave connectors. To address this, satisfaction-based multiobjective method for connector design optimization is proposed. An optimization model is developed for the structural dimensions of 65 GHz millimeter-wave connectors to minimize the voltage standing wave ratio, insertion loss, and deflection and maximum stress of the center conductor. The proposed optimization model concurrently satisfies the design requirements in terms of characteristic impedance, transmission frequency, and dielectric withstanding voltage. The model is optimized by innovatively using the multiobjective chaotic optimization algorithm in microwave finite-element simulations. The resulting optimal structure satisfies all performance requirements, thereby proving the rationality and feasibility of the proposed method. Moreover, this study establishes a novel design for other microwave devices to solve the problem of multiple performance index restrictions.

A wide input range, external capacitor-less LDO with fast transient response

A high voltage, external capacitor-less low-dropout regulator (HVLDO) with transient enhancement loop is presented in this work. The proposed HVLDO is designed with high withstand voltage laterally-diffused MOS (LDMOS) transistors and a transient enhancement loop is proposed to properly inject/sink current to/from the gate and output nodes of the power transistors to achieve fast transient response and high stability. Fabricated in 0.5µm SOI BCD process, the HVLDO occupies an active area of 0.29mm2. Operating with an input voltage ranging from 5.2 to 20V, it supplies an output voltage of 5V and a maximum load of 100mA. For all load conditions, this design has the power supply rejection of -49dB@100kHz, the phase margin over 68.4deg and achieves a temperature coefficient of 13.15ppm/°C. Measurement results show that this design has a line regulation of 0.88mV/V and a load regulation of 0.22mV/mA. The proposed HVLDO features fast line transient response of 60/20mV@9.8V/µs, fast load transient response of 30/70mV@100mA/µs, and recovery time of 2µs without external capacitors. Compared with the prior art, this work achieves the best transient FOM of 12.19fs.