Dielectric Reliability Research Articles

A Review of Reliability Assessment and Lifetime Prediction Methods for Electrical Machine Insulation Under Thermal Aging

The thermal aging of insulation systems in electrical machines is a critical factor influencing their reliability and lifetime, particularly in modern high-performance electrical equipment. However, evaluating and predicting insulation lifetime under thermal aging poses significant challenges due to the complex aging mechanisms. Thermal aging not only leads to the degradation of macroscopic properties such as dielectric strength and breakdown voltage but also causes progressive changes in the microstructure, making the correlation between aging stress and aging indicators fundamental for lifetime evaluation and prediction. This review first summarizes the performance indicators reflecting insulation thermal aging. Subsequently, it systematically reviews current methods for reliability assessment and lifetime prediction in the thermal aging process of electrical machine insulation, with a focus on the application of different modeling approaches such as physics-of-failure (PoF) models, data-driven models, and stochastic process models in insulation lifetime modeling. The theoretical foundations, modeling processes, advantages, and limitations of each method are discussed. In particular, PoF-based models provide an in-depth understanding of degradation mechanisms to predict lifetime, but the major challenge remains in dealing with complex failure mechanisms that are not well understood. Data-driven methods, such as artificial intelligence or curve-fitting techniques, offer precise predictions of complex nonlinear relationships. However, their dependence on high-quality data and the lack of interpretability remain limiting factors. Stochastic process models, based on Wiener or Gamma processes, exhibit clear advantages in addressing the randomness and uncertainty in degradation processes, but their applicability in real-world complex operating conditions requires further research and validation. Furthermore, the potential applications of thermal lifetime models, such as electrical machine design optimization, fault prognosis, health management, and standard development are reviewed. Finally, future research directions are proposed, highlighting opportunities for breakthroughs in model coupling, multi-physical field analysis, and digital twin technology. These insights aim to provide a scientific basis for insulation reliability studies and lay the groundwork for developing efficient lifetime prediction tools.

Synthesis and Characterization of PVC/(Co3O4/CNT)@Au Semiconductor Nanocomposite for Enhanced Medium-Voltage Cable Insulation

Abstract This study presents the synthesis, characterization, and application of a novel PVC/(Co3O4/CNT)@Au nanocomposite for enhanced medium-voltage cable insulation. The nanocomposite was developed by incorporating Co3O4 octahedron nanoparticles, carbon nanotubes (CNTs), and gold nanoparticles (Au) into a polyvinyl chloride matrix. Compared to standard PVC insulation, the nanocomposite exhibited a 3% improvement in relative permittivity (increased from 2.34 to 2.41) and significantly enhanced field uniformity, as evidenced by simulation studies. Fourier-transform infrared spectroscopy, X-ray diffraction, and electron microscopy confirmed the successful integration of nanofillers and highlighted their contributions to the composite’s properties. Optical characterization revealed a direct bandgap of 4.60 eV and an Urbach energy of 0.3674 eV, indicating a wide-bandgap semiconductor with moderate structural disorder. AC conductivity measurements demonstrated frequency-dependent behavior, while dielectric constant and loss analyses suggested the material’s potential for energy storage and insulation applications. The choice of Co3O4 and CNTs was guided by their synergistic impact on charge trapping, field grading, and thermal management, while Au nanoparticles enhanced charge transfer and local electric field distribution. These findings demonstrate the nanocomposite’s promise in addressing the limitations of traditional PVC insulation, offering improved dielectric performance, reliability, and durability for power transmission and distribution systems.

Research on Trap Characteristic Mechanisms of Thermochromic Phase Change Epoxy Composite With Confined Structure

Thermochromic phase change insulating composite can realize a series of advanced functions under electrothermal stimuli, which has been widely applied in numbers of intelligent electrical and electronic devices. However, due to the confined structure of thermochromic phase change insulating composite, the trap characteristics cannot be analyzed by current interface models of nanodielectrics, inhibiting the scientific improvement of dielectric reliability under the electrothermal stress. In this paper, the trap characteristic and mechanism of thermochromic phase change epoxy composites are studied by the isothermal surface potential decay (ISPD) and the Kelvin probe force microscopy (KPFM). Results show that the variation trends of trap characteristics after introducing confined structures are opposite at 30℃ and 70℃, which could derive from the confined phase change or the confined interface. Theoretical analysis shows that the influence of confined phase change on temperature dependent trap characteristics is inconsistent with experimental results, which could not be the essential reason influencing the trap characteristics. KPFM in-situ characterization directly verifies the existence of potential barriers in the confined interface, which originates from the contact electrification mechanism. The temperature dependent charge quantity variation due to contact electrification at the confined interface could impact the barrier height, which substantially affecting the temperature dependent trap characteristics.

Outstanding energy storage properties and dielectric temperature reliability in Na0.35Bi0.35Sr0.3TiO3-based relaxor ferroelectrics through entropy engineering

It is challenging to realize excellent overall properties of relaxor ferroelectrics to overcome the demands of capacitors. In this research, an effective strategy of entropy engineering addresses the above problem. The (1-x)Na0.35Bi0.35Sr0.3TiO3-xCa0.85Sm0.1(Mg1/3Nb2/3)O3 (NBST-xCSMN) ceramics were prepared via a solid-phase reaction method. The linear dielectric CSMN was adopted as additive to adjust the configuration entropy (∆Sconfig) of samples. The outcomes indicate that the enhancement of ∆Sconfig is beneficial to reduce grain size and interfacial polarization, improve activation energy and optimize dielectric features. The superior energy storage capability (Wrec = 5.2 J/cm3, η = 88 %) as well as dielectric temperature reliability (∆C/C25°C ≤ ± 15 %, −57–323 °C) in accordance with X9R was gained in NBST-0.15CSMN with ∆Sconfig = 1.91R. This study indicates that entropy engineering is a shortcut to design next-generation capacitors with high comprehensive performance.

Defect engineering design and electrical breakdown model improve dielectric properties and reliability of rare-earth doped BaTiO3-based ceramics

The incorporation of rare-earth elements into BaTiO3-based multilayer ceramic capacitors (MLCCs) plays a pivotal role in enhancing the dielectric constant and reliability. In this study, The BaTiO3-based ceramics doped with La and Dy were prepared separately and their dielectric properties and reliability were thoroughly compared. The La-doped sample exhibited a significantly enhanced dielectric constant, which can be attributed to the short-range migration of liberated oxygen vacancies (VO••) facilitated by the incorporation of defects [LaBa•‐MgTi″-LaBa•]. However, the presence of free VO•• in the La-doped sample led to a significant reduction in insulation resistivity during the initial application of the electric field. Microstructural analysis of the failure points resulted in the proposal of an electrical breakdown model, which elucidates the superior breakdown strength observed in the La-doped sample. This study provides novel insights for the development of MLCCs with high dielectric constants and high reliability.

Response and Reliability of Composite Post Insulators Under Random Earthquake

Abstract This article examines the stochastic response and seismic reliability of composite post-insulators under random seismic excitation. A random seismic motion model, tailored for power facility seismic research in China and compliant with the “Seismic Design Specification for Power Facilities” (GB50260-2013), is developed. This model accounts for both amplitude and frequency non-stationary. A nonlinear dynamic model for composite post insulators is then established, incorporating the nonlinearity at the multi-section insulator and flange connections. Numerical methods are employed for random seismic response analysis to address the non-stationary nature of seismic motion. The proposed model’s validity is confirmed by comparing it with the vibration table test results. Finally, the seismic reliability of composite post insulators, with root stress as the control criterion, is assessed using the probability density evolution method.

GaN-on-sapphire JTE-anode lateral field-effect rectifier for improved breakdown voltage (>2.5 kV) and dynamic RON

In high-power switching applications such as electric grids, transportation, and industrial electronics, power devices are supposed to have kilo-voltage (kV) level blocking capability. In this work, 1200-V gallium nitride (GaN) lateral field-effect rectifiers (LFERs) are demonstrated. The GaN-on-sapphire epitaxial structure is adopted to prevent vertical breakdown. To address electric field crowding, a p-GaN/AlGaN/GaN junction termination extension (JTE) is embedded in the anode region of the LFER. Comparing to the conventional LFER (Conv-LFER) fabricated on the same wafer, the JTE-anode LFER (JTE-LFER) achieves an improved breakdown voltage (>2.5 kV) and a lower dynamic ON-resistance (RON). The proposed p-GaN/AlGaN/GaN JTE offers a semiconductor-based solution (contrasted to the dielectric-based solution, i.e., field plate) to mitigate the high electric field, which is highly desirable for wide bandgap semiconductor power devices as it enhances the dielectric reliability.

Demonstration of 800°C SiC MOSFETs for Extreme Temperature Applications

Silicon Carbide (SiC) enhancement mode MOS electronics offer several benefits for realizing analog, digital and mixed signal electronics, but limitations on gate dielectric reliability has limited the adoption of MOS in high temperature application. In this work, we report GE’s lateral SiC MOSFETs exceeding previously reported temperature capabilities for SiC MOSFETs with experimental results that have shown that >500°C operation of SiC MOSFETS is possible with >400 hours demonstrated at 620°C, and short-term functionality demonstrated to 800°C. The result shows that MOS-based SiC electronics can continue to be a viable choice for circuit implementations at extreme temperatures >600°C.

Ge-friendly gate stacks: Initial property and long-term reliability

This work presents specific exploration on the novel gate stack strategies for the intriguing Ge p-MOSFET, where high pressure oxidation (HPO) process is utilized for sufficient oxidation and thus fewer oxygen vacancies, while yttrium doping is developed to strengthen the dielectric bonding for higher ruggedness. Superior gate controllability and stability have been achieved correspondingly, where then detailed comparison on the gate dielectric reliability is conducted. The HPO based GeO2 gate stack exhibits larger susceptibility to the gate bias stress, and could even breakdown under negative bias, which has been attributed to the local bond breakage that facilitates the irreversible network change. The yttrium-doped GeO2, on the other hand, presents impressive ruggedness against gate bias stress. Based on detailed bond breakage analysis, cation-doping in GeO2 is suggested to be effective in enhancing the bond rigidness, promising for a wider safe operation range for the gate bias in Ge MOSFET.

Design and characteristics of a fiber laser powered repetitive micro-plasma jet triggered gas switch.

To satisfy the need for low jitter in gas switches at repetition rate and enhance insulation reliability during high voltage operation of the trigger, we propose a micro-jet triggering system. This system requires less energy and can use a laser power supply as an energy source. It effectively improves the insulation stability of the trigger when working at high potentials and achieves a good triggering effect with low jitter at low working coefficients. The breakdown characteristics were tested by double-pulse experiments. Ensuring the same operating conditions for both pulses, the pulse interval was varied to obtain the breakdown voltage dispersion at different repetition rates. The results indicate that the dispersion of the breakdown voltages can reach 0.16% at a frequency of 50Hz with a pulse front of 30 μs, representing an order of magnitude reduction compared to the 1.45% at switching self-breakdown, and decreases further as the air pressure rises. In addition, the size of the microcapillary has an impact on the dispersion of breakdown voltage. It was found that for a range of lengths from 2 to 6mm and aperture sizes from 80 to 400μm, the trigger jitter was lower when the length was larger and the aperture was smaller. Furthermore, a trigger life test was performed on the ceramic capillary, and after one million triggers, the system remained stable with no degradation in trigger performance.

Insulation coating via hydrothermal oxidation for high-frequency FeSiAl soft magnetic composites

Soft magnetic composites (SMCs) play a crucial role in electronic devices owing to their high saturation magnetization. However, conventional insulation methods employed in SMCs exhibit inadequate insulation reliability, thereby restricting their further application in high frequencies. In this study, hydrothermal oxidation is introduced for insulation coating in the preparation of FeSiAl SMCs. When treated at 150 ℃ for 2 h, an insulation layer comprising of Al2O3, SiO2, Fe3O4 and Fe2O3 is formed on the surface of FeSiAl. The most optimal sample is achieved with saturation magnetization of 134.3 emu/g, presenting no significant reduction in saturation magnetization compared to the untreated sample. Cut-off frequency exceeding 300 MHz, and power loss of 503.7 kW/m3 (@7 MHz, 5 mT) are also obtained. This study suggests that hydrothermal oxidation could be a dependable method for fabricating high-frequency SMCs.

Comparative Study on Selected Insulating Materials for Industrial Piping.

This paper describes the results of an experimental assessment of the thermal conductivity of pipe insulation. The need for reducing energy loss in industrial piping systems makes the availability of relevant and reliable insulation materials of special importance. Several specimens of pipe laggings, made of different materials, including mineral wool, polyethylene foam (PEF), expanded polystyrene (EPS), flexible elastomeric foam (FEF) and polyurethane foam (PUR), were tested in accordance with the European standard ISO 8497. The thermal conductivity of the materials was measured for a wide range of temperatures. The results were compared with the values reported in the technical specifications as well as with the literature data. The assessment of measurement uncertainty was also described. The results showed that, in a few cases, thermal conductivity turned out to be greater than that declared by the manufacturer by as much as over 10%.

High energy capability in poly(vinylidene fluoride-co-chlorotrifluoroethylene) nanocomposite incorporated with Ag@polyaniline@covalent organic framework core–shell nanowire

The development of polymer film with large electrical displacement is essential for the applications of lightweight and compact energy storage. The dielectric diversity at interface of polymer composite should be addressed to realize the film capacitor with high energy density and dielectric reliability. In this work, poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)) nanocomposite was incorporated by core–shell nanowire with covalent organic framework (COF) outer coating to alleviate the dielectric mismatch at interface. After the preparation of Ag nanowire through polyol reduction, polyaniline (PANI) and COF layers were sequentially deposited to construct core–shell Ag@polyaniline@covalent organic framework (Ag@PANI@COF) nanowire. According to the unique core–shell architecture, the COF framework is utilized to suppress the remanent polarization while high electrical displacement is preserved by the center Ag nanowire. The maximum energy density of 25.0 J/cm3 at 425 MV/m is obtained in 0.1 wt% stretched Ag@PANI@COF/P(VDF-CTFE) nanocomposite. The presence of core–shell nanowire depresses the distribution distortion of electric field and the diffusion of charge carriers under high field. This work demonstrates an effective method to develop the polymer film with large electrical displacement, and sheds a light on insightful exploration of interfacial polarized mechanism in polymer dielectric composite.

Enhanced dielectric reliability in the X9R‐type Bi1/2Na1/2TiO3‐CaZrO3 relaxor ferroelectric ceramics

AbstractHigh‐performance dielectric ceramic capacitors for automotive applications require high operation temperature, thermal stability, and reliability for dielectric ceramics. A broad composition search has been carried out to replace the existing BaTiO3‐based dielectrics having limited upper operating temperature due to the relatively low Curie temperature at around 120°C. However, most of the developed compositions are too complicated and compositionally sensitive, making them difficult to commercialize. This study introduces a dielectrically reliable ceramic system based on Bi1/2Na1/2TiO3 (BNT) with a wide operation temperature range simply by adding paraelectric CaZrO3 (CZ). At 15 mol% addition of CZ to BNT, the permittivity variation within ±15% from −55 to 280°C was achieved, which surpasses the EIA‐X9R standard. Moreover, the dielectric reliability was shown with low dielectric loss (tanδ < 0.02) for the aforementioned temperature range and remarkable dielectric breakdown strength (∼260 kV/cm) at room temperature. Along with the proposal of a promising high‐performance dielectric material, structural analysis and dielectric behavior investigation as a function of CZ contents were presented.

Effect of oxygen vacancies on dielectric property and reliability of anti-ferroelectric PLZT applicable to EV-MLCC

Effect of oxygen vacancies on dielectric property and reliability of anti-ferroelectric PLZT applicable to EV-MLCC

Mechanisms of charge-induced surface discharge under positive impulse voltages

Abstract Charge-induced surface flashover is a critical factor leading to insulation failures in high-voltage direct current gas-insulated equipment, and the underlying mechanisms are still unclear. In the present study, the typical surface charge distributions are first summarized. Then, the impact of charge polarity and position on surface discharge characteristics in ambient air is studied, and the surface charge dynamics during multiple discharge processes are also focused. Comparative studies of the charge-induced surface discharge are conducted in SF6, and the effect of the gas atmosphere is discussed. The results indicate that the repulsive effect of deposited positive charges significantly inhibits the positive streamer development by reducing the electric field. The acceleration of negative charges on positive streamer propagation is the result of two competitive mechanisms: the enhancement of the electric field and the neutralization with positive charges in the streamer channel. In the multiple discharge process, positive streamers develop along the gap of positive streamer channels from the previous discharge. When the last discharge is intense enough, back discharges may occur along the pattern of the deposited positive channels from the previous discharge. The effects of the deposited charges on the surface discharge process are consistent in air and SF6. These findings will be advantages in improving the insulation reliability of gas-insulated equipment.

The Effect of Diluted N2O Annealing Time on Gate Dielectric Reliability of SiC Metal-Oxide Semiconductor Capacitors and Characterization of Performance on SiC Metal-Oxide Semiconductor Field Effect Transistor

We performed dry oxidation on n-type silicon carbide (SiC), followed by annealing in diluted N2O, and subsequently fabricated n-type MOS structures. The study aimed to investigate the impact of different annealing times on the trap charges near the SiC/SiO2 interface and the reliability of the gate dielectric. Capacitance-voltage (C-V) and current-voltage (I-V) measurements of the n-type MOS revealed that increasing the annealing time with N2O effectively reduces the density of electron traps near the SiC/SiO2 interface, mitigates the drift in flat-band voltage and enhances the oxide breakdown field strength. However, excessive annealing time leads to an increase in the flat-band voltage drift of the MOS, resulting in premature oxide breakdown. Using the optimized annealing conditions, we fabricated n-type LDMOSFETs and obtained the threshold voltage (Vth), field-effect mobility (μFE) and specific on-resistance (Ron-sp) from the transfer curve (Id-Vg) and output curve (Id-Vd) measurements. The research findings provide valuable insights for the gate oxidation process of SiC.

High-strength FeSiCr soft magnetic composite fabricated via liquid-phase sintering for high-frequency applications

Soft magnetic composites (SMCs) are essential materials for electronic devices due to their high saturation magnetization. However, traditional SMCs fabricated by cold-pressing method possess low strength and insufficiently reliable insulation, which restricts their further application. In this study, liquid-phase sintering technique is introduced and optimized to fabricate FeSiCr/MoO3 SMCs. During sintering, ammonium molybdate (AMT) decomposes to form liquid-phase MoO3, which helps to achieve insulation and promote the formation of a transition layer on the surface of FeSiCr. The most optimum sample (the 400 MPa/800 °C /6 wt% sample) is obtained with crushing strength of 329.8 MPa, real part permeability of 29.7 (1 MHz), cut-off frequency of 116 MHz, high saturation magnetization of 177.3 emu/g and power loss of 1224.4 kW/m3 (10 MHz, 5 mT). This study indicates that liquid-phase sintering may be a reliable means for developing novel SMCs.

Publisher’s Note: “Using highly accelerated life test to study insulation reliability of multi-layer ceramic capacitors sintered at different temperatures” [J. Appl. Phys. 134, 194101 (2023)

Publisher’s Note: “Using highly accelerated life test to study insulation reliability of multi-layer ceramic capacitors sintered at different temperatures” [J. Appl. Phys. 134, 194101 (2023)

Erratum: “Using highly accelerated life test to study insulation reliability of multi-layer ceramic capacitors sintered at different temperatures” [J. Appl. Phys. 134, 194101 (2023)

Erratum: “Using highly accelerated life test to study insulation reliability of multi-layer ceramic capacitors sintered at different temperatures” [J. Appl. Phys. 134, 194101 (2023)