Showing papers on "Insulator (electricity) published in 2020"

Electret formation in transition metal oxides by electrochemical amorphization

Abstract: Transition metal oxides (TMOs) are an important class of materials that show a wide range of functionalities involving spin, charge, and lattice degrees of freedom. The strong correlation between electrons in d-orbitals and the multivalence nature give rise to a variety of exotic electronic states ranging from insulator to superconductor and cause intriguing phase competition phenomena. Despite a burst of research on the multifarious functionalities in TMOs, little attention has been paid to the formation and integration of an electret—a type of quasi-permanent electric field generator useful for nanoscale functional devices as an electric counterpart to permanent magnets. Here, we find that an electret can be created in LaMnO3 thin films by tip-induced electric fields, with a considerable surface height change, via solid-state electrochemical amorphization. The surface charge density of the formed electret area reaches ~400 nC cm−2 and persists without significant charge reduction for more than a year. The temporal evolution of the surface height, charge density, and electric potential are systematically examined by scanning probe microscopy. The underlying mechanism is theoretically analyzed based on a drift-diffusion-reaction model, suggesting that positively charged particles, which are likely protons produced by the dissociation of water, play crucial roles as trapped charges and a catalysis to trigger amorphization. Our finding opens a new horizon for multifunctional TMOs. A material that generates its own electric field has been developed by scientists in South Korea. An electret is the electrical equivalent of a magnet in that it is formed of two electric poles rather than two magnetic poles. Just as magnetic dipoles give rise to permanent magnets, electret materials create a quasi-permanent electric field. They are useful for microphones, photocopiers and many other electrical devices. Yong-Jin Kim and Chan-Ho Yang from the Korea Advanced Institute of Science and Technology, Daejeon, have created an electret using transition metal oxides. The researchers used a sharp tip of platinum-coated silicon to “write” a charged pattern with a density similar to that of commercially available electrets into a thin film of lanthanum manganite. These patterns persisted for more than a year. An electret can be created in a complex transition metal oxide LaMnO3 by tip-induced electric fields with a considerable surface height change via solid-state electrochemical amorphization. The surface charge density of the formed electret area reaches ~400 nC cm−2 and persists without significant charge reduction for more than a year. Our finding opens a new horizon for multifunctional transition metal oxides by providing an electric counterpart to permanent magnets.

Wireless Power Transfer Using Domino-Resonator for 110-kV Power Grid Online Monitoring Equipment

Abstract: Nowadays, smart grid online monitoring systems are widely used in high-voltage (HV) power transmission networks, leading to the requirement of reliable power supply units for the monitoring equipment. In this article, we present a novel solution to harvest energy from the magnetic field around a 110-kV transmission line and transmit the energy to the online monitoring equipment on the transmission tower over 1.1 m insulation distance. Printed circuit board resonators are covered by the composite insulation material forming the first HV insulator with wireless power transfer (WPT) capability. The prototype of the HV insulator has passed the rigorous HV tests at 550 kV. The WPT characteristic of the HV insulator including the effects of corona rings is analyzed and verified by practical measurement.

Dynamics of surface charge and electric field distributions on basin-type insulator in GIS/GIL due to voltage polarity reversal

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

Surface charge accumulation and pre-flashover characteristics induced by metal particles on the insulator surfaces of 1100 kV GILs under AC voltage

Abstract: With the increase in the voltage and capacitance of gas-insulated transmission lines (GILs), the insulation failure of GIL has attracted more and more attention. Further understanding of the partial discharge (PD) and flashover characteristics of metal particles on the insulator surface, as well as the flashover mechanism, is necessary to reduce the failure rate and improve the reliability of the equipment. In this study, an ultra-high voltage (UHV) AC insulator PD test and measurement system based on the cross-reference pulse current (PC) and ultra-high frequency (UHF) methods were established. The PD development and flashover characteristics of 5 mm-long metal particles at different positions on the surface of a UHV AC insulator, as well as the surface charge accumulation, were studied. The results show that the discharge of millimetre-scale metal particles on the insulator surface under PD test conditions is relatively low (generally lower than 2PC), and it is difficult to be detected by the conventional PC and UHF methods due to their insufficient sensitivity. Moreover, it is found that the weak PDs of the millimetre-scale metal particles will result in a charge accumulation on the insulator surface under AC voltage, which eventually will lead to the insulator flashover. The PDs of the UHV AC insulator before flashover are generally small, which will make it difficult for online monitoring systems to give an effective alarm before flashover.

Nano ZnO/epoxy coating to promote surface charge dissipation on insulators in DC gas-insulated systems

Abstract: This paper describes the addition of ZnO nanoparticles to epoxy resin at concentrations of 20, 25, and 30wt%, and the application of this ZnO/epoxy coating to the surface of an epoxy insulator. This coating significantly suppresses the charge accumulation on the surface of the insulator, reduces the number of charge speckles, and increases the flashover voltage. These effects are enhanced as the doping concentration of ZnO nanoparticles increases. Through isothermal surface potential decay tests, we find that the ZnO/epoxy coating introduces numerous shallow traps, which help to dissipate the surface charge. Analysis shows that the ZnO/epoxy coating promotes surface charge dissipation through its nonlinear conductivity. The nonlinear characteristics of the 30wt%-doped samples are 55.3% greater than those of the 20wt%-doped samples. The coating adapts to the external electric field and can achieve the effect of a uniform electric field. This article analyzes the feasibility of using ZnO/epoxy coatings to suppress the accumulation of charge on insulator surfaces, and provides a feasible solution for practical engineering applications.

Epoxy insulator with surface graded-permittivity by magnetron sputtering for gas-insulated line

Abstract: To reduce the electric field concentration induced flashover in AC gas insulated line (GIL), a novel concept of surface functionally graded material (SFGM) is proposed in this paper, and the continuously graded high-A layer was fabricated by depositing BaTiO 3 on the insulator surface. The iterative method was introduced to optimize the thickness distribution of the BaTiO 3 layer. After four iterations, the layer thickness distribution almost reaches its optimal solution, and the maximum electric field strength is reduced by approximately 70% compared with that of the conventional insulator. To fabricate the optimized SFGM insulator, a rotatable baffle with the designed gap was placed above the insulator during the sputtering process. For comparison, a uniformly sputtered insulator with the 4μm BaTiO 3 layer and a discretely graded insulator with four gradients were prepared. Both electric field simulations and experiments were performed to evaluate the electrical performance of different insulators. The results show that, compared with the conventional insulator, the sputtered insulators, especially the optimized SFGM insulator, can significantly improve the uniformity of the electric field distribution along the insulator surface under a 50 Hz voltage. Accordingly, the discharge inception voltage and flashover voltage of the insulator both increased significantly. Under negative standard lightning impulse voltage (1.2/50 μs), the sputtered insulators show insulation performance comparable to that of the conventional insulator.

Electric field control of disorder-tunable superconductivity and the emergence of quantum metal at an oxide interface

Abstract: We report on an extraordinary field effect of the superconducting LaAlO3/KTaO3(111) interface with Tc ~2 K. By applying a gate voltage (VG) across KTaO3, the interface can be continuously tuned from superconducting into insulating states, yielding a dome-shaped Tc-VG dependence. The electric gating has only a minor effect on carrier density as evidenced in the Hall-effect measurement, while it changes spatial profile of the carriers in the interface, hence the carrier's disorder level significantly. As temperature is decreased, the resistance saturates at lowest temperature in both superconducting and insulating sides, despite an initial dramatic dropping or increasing, which suggests an emergence of quantum metallic state associated with failed superconductor and/or fragile insulator. A VG-modulation of the magnetic-field-driven superconductor to insulator quantum phase transition reveals a non-universal criticality.

A Cumulative Pollution Index for the Estimation of the Leakage Current on Insulator Strings

Abstract: The pollution performance of insulators installed in transmission and distribution lines plays a key role in maintaining the reliability, safety and cost-effectiveness of power systems. Among the different insulator monitoring techniques, leakage current stands out as one of the most meaningful pollution performance indicators as it gives a measure of how close the insulators string is to flashover. This paper presents a novel methodology for the prediction of the leakage current on insulator strings considering the environmental and weather information of the insulators location. It is based on the combination of a new developed Cumulative Pollution Index (CPI), which estimates the soluble pollution deposit on the insulator string, and a machine learning technique such as Random Forests algorithm. The method is valid for ceramic insulators, i.e., toughened glass, as well as RTV silicone-coated insulators with hydrophobic transfer properties. The research is supported by an extensive field monitoring program where three different insulator strings composed by non-coated, half-coated (bottom part) and full-silicone-coated glass insulators were monitored in a period covering twenty-two consecutive months. Finally, the performance of the proposed prediction model is evaluated using real data.

Fluorinated epoxy insulator with interfacial conductivity graded material for HVDC gaseous insulated pipeline

Abstract: In this paper, a novel procedure is put forward to fabricate epoxy insulators with surface functionally graded material (SFGM) with optimized surface conductivity as obtained from the field non-uniformity and the leakage current. For fabrication, a temperature control system is employed to form a spatial temperature gradient, thus regulating fluorination from top to bottom of the insulator surface. Flashover tests are reported under DC voltage, and with DC voltage with polarity reversal; the results show the effectiveness of the SFGM to improve the performance of the insulator. A trap distribution and carrier transport model are utilized to analyze the improved flashover characteristics.

MXene-doped epoxy resin to suppress surface charge accumulation on insulators in a DC gas-insulated system

Abstract: In an HVDC gas-insulated system, the surface of the insulator accumulates electric charges that distort the surface electric field and reduce the flashover voltage. Therefore, it is crucial to find a material that can effectively suppress the surface charge accumulation. In this work, MXene, a two-dimensional nanomaterial, is doped into an epoxy resin at different concentrations. By doping a small amount of MXene (30ppm), the resistivity of the composite is improved by about 4 times compared to pure epoxy resin. At the same time, the trap level of deep traps increases to 1.07 from 1.04 eV of pure epoxy. Measuring the surface potential of the insulator and using an inversion algorithm to calculate the surface charge establishes that a doping level of 30 ppm of MXene effectively suppresses the accumulation of the surface charge of the insulator, which is only about 1/3 of that of the pure epoxy resin. The surface flashover voltage is also increased by 10%. However, when the doping amount of MXene is increased to 100 or 150 ppm, the insulation performance is lowered. We used a potential barrier model to explain the effect of MXene doping in the epoxy resin. This work presents a possible way to suppress the charge accumulation on the surface of insulators in HVDC gas-insulated systems and provides a link between the microstructure and the macroscopic properties in the material.

Metal particle encouraged surface charge accumulation on epoxy insulator with multi-arc surface profile under DC voltage

Abstract: Surface charge accumulation on epoxy insulator installed in gas insulated switchgear (GIS) or gas insulated transmission line (GIL) has been recognized as an important factor for electric field distortion that results in reduction of surface flashover voltage. This paper reports on surface charge accumulation behavior on a actual epoxy insulator for 100 kV GIL prototype with multi-arc surface profile. A coaxial electrode system is used to investigate the charging behavior under DC voltages with metal particles positioned at various positions of the surface so as to estimate its influence on the charge accumulation behavior using a Kelvin type probe. The results show that positive charges are accumulated mainly on the nonplanar region around the high voltage electrode in the shape of speckles, and the average charge distribution along the radial direction presented a double-peak feature. Moreover, the charge accumulation is enhanced by metal particles contacting to the grounded electrode. Using a numerical simulation method, it is suggested that the charge accumulation is mainly determined by gaseous ionization which is enhanced by the metal particle induced electric field distortion.

New high-voltage and high-speed β-Ga2O3 MESFET with amended electric field distribution by an insulator layer

Abstract: The high wide-band-gap β-gallium oxide (β-Ga2O3) has attracted attention for high-voltage and high-speed applications over other wide-band-gap materials. In this work, we propose and demonstrate a β-Ga2O3 metal semiconductor field effect transistor (GO-MESFET) with an insulator layer (Si3N4) at the bottom of drift region (IL-GO-MESFET) to amend the potential and electric field distributions. In the proposed structure, we improve the electrical properties of the device such as unilateral power gain (U), maximum available gain (MAG), parasitic capacitance, noise figure, and breakdown voltage. The results show the IL-GO-MESFET structure has improved electrical properties and it has the great potential for using in high-voltage and high-speed applications.

Elevating the magnetic exchange coupling in the compressed antiferromagnetic axion insulator candidate Eu In 2 As 2

Abstract: The magnetic topological materials have attracted much attention recently for their potential realization of various novel quantum states. However, the onset of magnetization in these materials usually occurs at low temperatures, impeding further applications. Here, by means of high pressure, we have significantly increased the magnetic transition temperature in an antiferromagnetic axion insulator candidate $\mathrm{Eu}{\mathrm{In}}_{2}{\mathrm{As}}_{2}$. Both crystal and magnetic structures remain the same with pressure up to 17 GPa. The N\'eel temperature can be monotonously increased from 16 K (ambient pressure) to 65 K (14.7 GPa). This is mainly attributed to the enhancement of intralayer ferromagnetic exchange coupling by pressure. With increasing pressure up to 17 GPa, a crystalline-to-amorphous phase transition occurs, which impedes further enhancement of the N\'eel temperature. Our results show that high pressure is an effective pathway to greatly enhance the magnetic transition temperature in topological materials. It is helpful for the realization of novel quantum states at elevated temperatures.

Adversarial Reconstruction Based on Tighter Oriented Localization for Catenary Insulator Defect Detection in High-Speed Railways

Abstract: The catenary insulator maintains electrical insulation between catenary and ground. Its defects may happen due to the long-term impact from vehicle and environment. At present, the research of defect detection for catenary insulator faces several challenges. 1) Localization accuracy is low, which causes the localized object to be incomplete or/and merge with unnecessary background. 2) Horizontal localization brings inevitable unnecessary information because horizontal box cannot fit well with the shape of insulator. 3) Supervised learning models for defects recognition are unreliable as the available defect samples are insufficient to train models well. To address these issues, this article proposes a novel two-stage defect detection method. In the localization stage, a novel localization network called TOL-Framework is constructed to reduce the background and realize tighter oriented localization. Compared with general basic framework Faster R-CNN, the TOL-Framework cascades a regression module inside basic framework and adds an external postprocess network, which is adversarially trained by standard insulators to refine the localization. These two novel steps greatly improve the oriented localization accuracy. In the defect detection stage, an adversarial reconstruction model that is trained only using normal samples is proposed to evaluate the defect states. A comparison with other methods is conducted using a dataset collected from a 60km section of the Changsha-Zhuzhou railway line in China. The results show the proposed method has the highest localization accuracy, and is effective for insulator defect detection.

A 16 kV PCB-Based DC-Bus Distributed Capacitor Array with Integrated Power-AC-Terminal for 10 kV SiC MOSFET Modules in Medium-Voltage Inverter Applications

Abstract: This paper presents the insulation design and assessment of a medium-voltage (MV), printed circuit board (PCB) based dc-bus distributed capacitor array. A generalized insulation design process is introduced with considerations for insulator material stress as well as surface discharge on external interconnections. Finite-element analysis (FEA) simulation studies of the multilayer PCB bus are used to analyze several approaches to control electric field distribution in the design layout. A specific implementation of a dc-bus for a 16 kV rated MV three phase inverter is described to demonstrate the proposed design procedure to achieve partial discharge (PD) free operation up to 18 kV (for 10 % design margin). The designed dc-bus also features a low inductance, modular architecture to improve the power density and specific power of the MV system. Experimental results of partial discharge behavior are presented for insulation design validation.

Metal nanoparticle-doped epoxy resin to suppress surface charge accumulation on insulators under DC voltage

Abstract: In high-voltage direct current (HVDC) transmission systems, electric charge accumulates on insulator surfaces, causing surface electric field distortion and flashover voltage reduction. Therefore, studying a material that can improve the insulator surface insulation strength is of great engineering value. In this work, several types of metal nanoparticles with different particle sizes and concentrations are doped into epoxy resin. The experimental phenomena enables some interesting conclusions: when no agglomeration of doped nanoparticles occurs, a higher doping concentration provides a better insulation performance. The larger the doping particle size is, the lower the insulation performance. Additionally, under the same conditions, different types of metal nanoparticles lead to slightly different results after doping. Especially after doping with low concentration (approximately 120 parts per million (ppm)) and small particle size (approximately 10 nm) nanocopper particles, the insulator surface charge accumulation was effectively suppressed, and the flashover voltage was significantly improved. Our analysis suggests that it may be related to the single-electron tunneling phenomenon. Relevant results provide a new way to improve the surface insulation strength of insulators in the future.

A Metal-Insulator-Semiconductor Non-Volatile Programmable Capacitor Based on a HfAlO ₓ Ferroelectric Film

Abstract: In this letter, we proposed and experimentally demonstrated a metal-insulator-semiconductor (MIS) ferroelectric capacitor with non-volatile programmable capacitance. By switching the polarization of the Al-doped HfO2 ferroelectric insulator with the external electric field, the depletion width of the semiconductor can be modulated, leading to the continuously adjustable capacitance of the device. Due to the non-volatility of ferroelectricity, the programmed capacitance is stable without the constant DC bias. We also proposed some potential applications of the capacitor in the data storage and circuit design.

Fiber-based flexible composite with dual-gradient structure for sound insulation

Abstract: Sound insulation materials in the traditional sense are rigid, which are usually dense and bulky, while common porous materials have almost no sound insulation ability. Herein, a fiber-based flexible porous composite is presented as sound insulator fabricated via single-sided coating finishing on the one side of a nonwoven framework and has been demonstrated for high performance noise reduction. The enhanced acoustic insulation is identified to be structure dependent of the area density and microstructure of the sound insulator and the type of filler. The flexible sound insulator exhibits ≈100% enhancement in broadband acoustic insulation over the whole frequency range compared to the bare nonwovens. And the most sound transmission loss (STL) of at the peak is up to 37 dB, which is about 30 times that of bare nonwovens. Furthermore, the novel sound insulator has an admirable dual-gradient structure in which the concentration gradient of coating finishing agent is opposite to the pore gradient. Therefore, sound insulation capacity of the sound insulator exhibits obviously anisotropy according to the incident direction of sound waves. This flexible porous material for broad-band sound insulation has an easy and inexpensive scalable production, demonstrating its great potential for lightweight requirements for specific applications.

Performance of outdoor insulators in tropical conditions of Sri Lanka

Abstract: Ceramic insulators, specifically porcelain and glass insulators, have widely been used all over the world since the 19th century [1,2]. However, when such insulators are energized and exposed to different pollution environments under different climatic and weather conditions, leakage current (LC) develops along their surfaces [3–7] and eventually cause flashovers. Various remedial measures have been adopted by power utilities to mitigate this problem. Among the common methods are: (a) increasing insulator creepage (leakage) distance, (b) reducing supply voltage, (c) insulator washing (cleaning), (d) oiling or greasing (silicone) the insulator surface, and (e) insulator replacement. Composite insulators, also referred to as non-ceramic or polymeric insulators, have also been used during the last six decades as an alternative to the ceramic insulators [8–10]. The housing materials most often used have been silicone rubber (SIR) [11] and ethylene-propylene-diene-monomer based rubber (EPDM) [12]. Water repellent (hydrophobic) properties of composite insulators, light weight, resistance to vandalism are among the main reasons for their usage. This has been proven by positive outcomes of numerous studies performed in laboratory and field conditions [8,9,13–16]. However, due to exposure to harsh service stresses such as corona discharges, UV radiation and chemical attacks etc., the housing materials may lose hydrophobic properties and develop surface degradation (tracking, erosion). In addition to the ever-increasing use of composite insulators, polymeric coatings (mainly RTV silicone rubber) [17] and semi-conducting glazes [18] have also been adopted for improving performance of ceramic and glass insulators [19].

Review on characteristics, heating sources and evolutionary processes of the operating composite insulators with abnormal temperature rise

Abstract: This paper reviewed the research progress on abnormal temperature rise (ATR) of composite insulator. The ATR of composite insulator can be divided into two types, pointform temperature rise (PFTR) and bar-form temperature rise (BFTR). The composite insulators with PFTR only show significant temperature rise at high relative humidity (RH>70%), and the temperature rise locates in the area that 20 cm above the metal end-fitting. In low humidity environment (RH 70%) and low (<30%) RH. The temperature rise might reach more than 10 °C and the temperature rise area was wider, extending from the high-voltage end to several sheds units at the low-voltage side. And the GRP core in the composite insulator was found corroded. The heating energy was supplied by both conductance loss and polarization loss of the corroded GRP core. The decay-like degradation of GRP core was caused by the combination of damp condition, high electric field, discharge, mechanical load, et al and may evolve into decay-like fracture of composite insulator. The preventive methods concerning quality control, structure optimization, material modification and operation strategy were put forward. It was suggested that when PFTR was detected on the composite insulator, the inspection period of the insulator should be shortened properly. The composite insulator should be replaced as soon as the BFTR was detected.

Ultra-Low Noise Defect Probing Instrument for Defect Spectroscopy of MOS Transistors

Abstract: It is commonly accepted that the performance and time-to-failure of modern semiconductor transistors are seriously affected by single defects located in the insulator or at the insulator/semiconductor interface. The impact of such single defects on the device current ranges from several pico-ampere up to hundreds of nano-ampere and their characterization poses a major challenge for measurement instruments. However, for an accurate description of the device behavior under operation, the understanding of the physical mechanism behind single-charge trapping is inevitable. For this a large variety of defects and devices with different geometries have to be studied. However, the impact of single defects on the device current rapidly decreases with increasing effective gate area. Thus, suitable measurement instruments have to provide a high current measurement resolution at a large signal-to-noise ratio (SNR) for monitoring single charge transitions. To enable defect spectroscopy at a very detailed level an ultra-low noise defect probing instrument (DPI) is invented. The compact implementation and optional usage of a lead battery supply unit for the DPI guarantees highest SNR and also long-term stability over more than two years, which is typically hard to achieve when instruments of different manufacturers are connected. Utilizing the DPI a measurement resolution of a few micro-volts in terms of threshold voltage shift can be achieved, which fairly outweighs the results obtained with general-purpose instruments.

Charge accumulation characteristic on polymer insulator surface under AC voltage in air and C 4 F 7 N/CO 2 mixtures

Abstract: Charge accumulation has always been a problem for the safe operation of gas insulated switchgear (GIS)/gas insulated transmission line (GIL) both under AC and DC. It is of great significance to investigate the behaviour of surface charge under high voltage. In this study, the charge distribution characteristics and accumulation mechanism on insulator surface in air and heptafluorobutyronitrile/carbon dioxide (C 4 F 7 N/CO 2 ) mixtures under AC voltage are studied via the means of surface potential measurement and inversion algorithm, combined with the improved method of controlling the truncated phase of AC voltage. The results show that under the needle–plate electrode structure, charge distribution on the insulator surface presents a three-tier concentric circle structure both in air and C 4 F 7 N/CO 2 gas mixtures, and the charge composition of the innermost circle is closely related to the truncated phase of AC voltage. Under the same amplitude of voltage, the range of charge distribution on insulator surface in C 4 F 7 N/CO 2 mixtures is smaller than that in air, with the negative charges domination. It is suggested that the characteristic of charge distribution in C 4 F 7 N/CO 2 mixtures is related to the larger electron attachment cross-section of C 4 F 7 N gas in a wide range of electron energy distribution.

Investigation on the Insulation Resistance Characteristics of Low Voltage Cable

Abstract: This study evaluated the insulation resistance characteristics of TFR-8 (Tray Frame Retardant power cable for fire service) and VCTF (Light PVC Sheathed Circular Cord) cables under external flame, over-current, and accelerated degradation tests. In the accelerated degradation test of the cable, aging times of 10, 20, 30, and 40 years were tested according to a temperature derived using the Arrhenius equation. The insulation resistance of the TFR-8 cables was reduced from a maximum of 7.5 T ohm to 0.008 T ohm during the flame contact and recovered to its original state after cooling. However, dielectric breakdown occurred in the VCTF cable during flame contact and the cable did not return to its original state, even after cooling. In the forced convection oven test, the insulation resistance of the cable was reduced at 160 °C, whereas the insulation resistance of the cable was reduced at 125 °C in the over-current test. This result implied that the over-current had a greater impact than did heat applied externally on the degradation of the cable insulator. In the accelerated degradation tests from 10–30 years, the TFR-8 cable did not show any reduction in insulation resistance at room temperature. However, after an induced aging time of 40 years, the cable showed a rapid reduction in insulation resistance at room temperature.

2D hole gas mobility at diamond/insulator interface

Abstract: The hole mobility of two-dimensional (2D) gas at (001) and (111) diamond/insulator interfaces is investigated theoretically and compared with experimental data from the literature. It is shown that the surface impurity scattering is the limiting mechanism at room temperature in most of the H-terminated diamond field effect transistors, where the negative charges created by transfer doping are in the vicinity of the 2D gas. By repelling the negative charges at the metal/insulator interface, as recently reported for the (111) h-BN/diamond interface, we demonstrate that it is possible to achieve high mobility values of the order of 3000 cm2/V s when a pure phonon scattering occurs. This work confirms the potential of two-dimensional hole gas diamond field effect transistors for high power and high frequency applications.