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The generation of abrasive particles is an unavoidable consequence of sliding electrical contact wear in conductive slip rings (SRs). The adhesion of abrasive particles to the insulators may lead to a decrease in flashover voltage, posing a risk to satellite power transmission. In this paper, the effect of abrasive particles on flashover is first studied. Surface abrasive particles can distort the surface electric field of the dielectric, absorb scattered electrons, and then re-emit them, thereby accelerating the development and formation of secondary electron avalanches. Flashover test results indicate that surface abrasive particles lead to a significant reduction in flashover voltage. To mitigate the impact of particle adhesion on flashover, a method of constructing particle traps on the surface of insulators is proposed. The location and structural parameters of the particle trap are further optimized and determined. The flashover test results using planar dielectric samples and SR insulator samples both demonstrate that the optimized particle trap can significantly improve the flashover voltage. The dielectric maintains high electrical strength even when particles are trapped in particle traps. The physical details of the impact of particles on flashover and the effect of particle traps are analyzed utilizing an electron movement simulation, corroborating the experiment from a microscopic aspect. [ABSTRACT FROM AUTHOR]

Cellulose insulating paper is widely used in the power industry for its good electrical insulating properties. Moisture sharply increases its conductivity, which directly leads to the weakening of insulation performance and greatly increases the risk of subsequent electric field distortion and insulation breakdown. This paper focuses on the microscopic mechanism of moisture changing the characteristics of charge transport in cellulose insulation and attempts to reveal the related conductivity mechanism. To achieve this purpose, microscopic and macroscopic perspectives are integrated and several simulation and experimental methods are utilized comprehensively. The molecular dynamics simulation results showed that most water molecules in damped cellulose were individually and uniformly adsorbed on the hydroxyl groups by hydrogen bond, and the quantum chemistry computation results showed that the lowest unoccupied molecular orbital more appeared on the water molecule and the corresponding density of state increased. Then, experimentally, it was confirmed that the trap energy level decreased by the thermally stimulated current method. On this basis, the promotion effect of moisture on charge transport is predicted and verified by polarization and depolarization current methods. As the moisture content increased, more charge carriers escaped from the trap by hopping and participated in long-range continuous charge motion. Therefore, after dampness, the current of cellulose insulating paper increased exponentially with the increase in electric field strength, which was consistent with the hopping conductivity mechanism. [ABSTRACT FROM AUTHOR]

• Extraction of distant and soft defect time–frequency distribution surrounded by interference. • Instantaneous filtering may help detect extremely weak impedance discontinuities. • The proposed method has better location accuracy compared with traditional Wigner-Ville distribution methods. Time-frequency domain reflectometry is a highly sensitive method to locate cable defect. However, locating a potential defect far from the cable head may be less accurate because of the signal amplitude attenuation and the interference parts. To solve the problem, this paper proposes an accuracy improvement method based on instantaneous filtering in time-frequency domain. The method extracts the frequency spectrum of the time-frequency signal, and then filters the spectrum and reconstructs the signal based on the difference between the signal and interference spectra, which can eliminate the interference and improve the location accuracy. In simulation, the location error of this method improves from 5.47 % to 0.57 %. In experiment, the proposed method reduces the location errors and magnifies the location peaks of the breakage defect, thermal aging defect, and ground faults. For the defects studied in this paper, the method improves the defect location accuracy and defect amplitude detectability of TFDR. [ABSTRACT FROM AUTHOR]

In recent years, frequency domain spectroscopy (FDS) is often used to evaluate oil paper insulation state in power transformer bushing. But it is still very difficult to evaluate the moisture content accurately and quickly. In order to solve this problem, this paper proposes an intelligent algorithm based on random forest regression (RFR) to construct an efficient evaluation method through segmented FDS curves. Furthermore, the characteristics of FDS curves were studied and the intelligent method was compared with support vector regression (SVR) and deep neural networks (DNN). The results show that the dielectric loss, the real part and imaginary part of complex capacitance all move upward with the moisture increasing, so they can be used as the input feature of the evaluation model; The moisture content evaluation accuracy of the RFR model in the whole frequency band is higher than that of SVR and DNN models; With the increase of lower cut off frequency (FDS test stop frequency), the FDS test time is greatly shortened, and the accuracy of the RFR model can still meet the evaluation requirements. Therefore, the data in a compromise frequency band can be used to evaluate the moisture content of oil paper insulation accurately and quickly. [ABSTRACT FROM AUTHOR]

Frequency Domain Spectroscopy (FDS) is a powerful tool to study the dielectric properties of oil-paper insulation, which is widely used under high electric field strength. The motion of charge carriers under high electric field strength will cause new dielectric characteristics in FDS curves, from which more information could be extracted for insulation state assessment. In this paper, FD spectra are measured under high electric field strength. The electric field dependence of the loss peak in middle frequency and the characteristics of dielectric loss in low frequency are studied. With the influence of trapping on the motion of charge carriers under electric field being considered, charge carriers hopping polarization model and charge carriers motion dependent conductance model are proposed. The trap energy level of oil-paper insulation decreases when the moisture content increases, thus, the motion characteristics of charge carriers change, leading to decreasing loss peak in middle frequency and inverse dielectric loss characteristics in low frequency. These two models introduce the influence of traps on carrier motion into the dielectric response and enable one to gain a better understanding of the dielectric properties of oil-paper insulation under high electric field strength. [ABSTRACT FROM AUTHOR]

Moisture ingress is one of the major causes of aging in oil–paper insulated transformers; the measurement of the moisture content of the insulating material is thus necessary during transformer disassembly for maintenance. One critical engineering consideration is the need for rapid and nondestructive moisture content measurement of the oil–paper insulation to minimize the power-outage time. Herein, a rapid characterization method for the moisture content of oil–paper insulation based on the dielectric response obtained using a microstrip petal-like ring resonator (MPRR) is proposed. The geometric parameters of the resonator and dielectric response model were established based on simulations and theoretical analysis. The geometry of the resonant ring was optimized by modifying the originally circular ring structure of the microstrip ring resonator (MRR) into a petal-like ring structure; this increases the number of resonant peaks from five to seven in the frequency range of 0.5–6.0 GHz for the same electrode area. The effects of the coupling mode, coupling gap, and microstrip ring size on the resonance characteristics of the MPRR were simulated and analyzed. Compared with the MRR, the MPRR has the advantages of a reduced fundamental resonant frequency and a smaller resonant-ring area that improves radiation efficiency. The impact of moisture content on the dielectric response of the pressboard obtained using the MPRR was studied. A moisture-calculation equation based on the measured dielectric response for a selected type of pressboard was established by the Lasso regression. The results of verification experiments show that the error of the proposed method is sufficient for practical applications. [ABSTRACT FROM AUTHOR]

Epoxy‐impregnated paper transformer bushings are prone to water absorption due to the presence of water‐attracting moieties in the cellulose chemical structure and epoxy resin, leading to moisture‐induced insulation defects. To understand the mechanism of moisture's impact on epoxy‐impregnated paper, this study developed a testing platform that integrated moisture diffusion, adsorption, and dielectric properties of insulating materials. Insulation specimens made of epoxy resin and epoxy‐impregnated paper were prepared and their water diffusion characteristics were investigated using the Fick diffusion model and the Langmuir model, respectively. The Guggenheim–Anderson–de Boer equation was used to examine the vacuum vapour adsorption characteristics of the materials, providing a theoretical foundation for examining the form of water present within them. The dielectric response of materials with varying moisture levels was then tested to study the effect of water on the dielectric spectrum curve. Using the Extended Derivative Method, the characteristic frequency reflecting the water content of the epoxy‐impregnated paper was extracted. The results demonstrate that 0.01‐Hz characteristic frequency provides superior accuracy for moisture assessment in epoxy resins compared to 50 Hz, and extracting and fitting the relaxation peak characteristic frequency in epoxy‐impregnated paper moisture evaluation yields higher accuracy than using tan δ at the power frequency. [ABSTRACT FROM AUTHOR]

Frequency Domain Spectroscopy (FDS) is widely used to estimate oil–paper insulation. The high moisture and long aging change the FDS characteristics of the insulating oil–paper, so normalization processing is required. Still, the choice of single activation energy needs further research. This paper studies the FDS characteristic of oil–paper insulation samples with different moisture and aging degrees and improves the traditional temperature correction method. The enhanced Arrhenius model uses the segmented activation energy to make the normalized FDS curve coincide better with the target curve, and the error is reduced. In addition, to verify the method's effectiveness, this paper proposes an iterative correction process. It corrects the tan δ-f curve of the bushing with an aging time of 800 h based on segmented activation energy, and the overall normalization effect is improved. [ABSTRACT FROM AUTHOR]

With the development of high-density and highly integrated electronic devices, the insulation characteristics between the interconnects of printed circuit boards (PCBs) are the key issues to be considered in their design and production. Most of the existing studies on insulation characteristics are based on parallel interconnect structures; however, the possibility of flashover or breakdown on PCB at parallel interconnects is relatively low compared to other irregular structures. The flashover characteristics of PCB interconnects need to be more comprehensively presented. In this paper, the commonly used interconnects were divided into three typical structures. Under the same DC excitation, the "interconnect with pad" structure had the most severe electric field concentration, and the insulation characteristic of this structure was the worse of the three. Furthermore, the effects of the distance between the interconnect and pad size on the flashover voltages of the "interconnect with pad" structure were investigated and explained by the maximum electric field strength, which could be approximately calculated by the existing equation. [ABSTRACT FROM AUTHOR]

• Novel rapid moisture test for oil-paper insulation. • Microstrip ring resonator analyzes dielectrics properties. • Precise moisture level distinction found. • New model assesses the moisture content accurately. Moisture ingress significantly accelerates the aging of oil-paper insulated equipment, making accurate assessment of moisture content critical for the operation and maintenance of oil-immersed insulated power equipment. In this paper, a novel method for rapid moisture content evaluation is proposed based on a microstrip ring resonator (MRR) designed with a fundamental frequency of 1.16 GHz. A calculation model for the dielectric response analysis using MRR is established to characterize dielectric properties of the material layered on the substrate. ANSYS HFSS electromagnetic simulation software was used to study the impact of dielectric material thickness and the substrate on the MRR test results. Experimental measurement demonstrated that the maximum deviation in resonance frequency was merely 0.542 %. The dielectric properties of uniformly and non-uniformly damp insulating pressboard were analyzed across the frequency band from 1 to 6 GHz. The MRR test results were compared with those of the standard resonant cavity method and frequency domain dielectric spectroscopy (FDS) test. Using the regression algorithm and curve analysis, moisture assessment models for both uniformly and non-uniformly damp oil-paper insulation were established. The experimental results show that the MRR test can clearly distinguish between the pressboard samples with varying moisture levels under uniform conditions, with a maximum moisture evaluation error of 8.19 %. The results demonstrate that the MRR test method, requiring only 56 s, can quickly and effectively evaluate the moisture content of insulating pressboard. [ABSTRACT FROM AUTHOR]

• A data fusion approach with high spatiotemporal resolution for wall temperature measurement is reported. • This approach is tested at different number of thermocouples and the IR camera sampling rate. • This approach is validated against different experimental conditions. A high spatial and temporal resolution of wall temperature measurement is beneficial for liquid film cooling design for thermal protection of rocket engine combustor chamber. The conventional thermocouple method has a high sampling frequency up to 50 kHz, but it is based on point measurement. The infrared (IR) thermal technique can achieve a two-dimensional surface temperature measurement, but the current sampling frequency is limited to a few hundreds of Hz. Here we report the application of the data fusion approach, which is integrated with proper orthogonal decomposition (POD) and compressed sensing (CS) to reconstruct the temperature field of a wall with high spatiotemporal resolution. In this approach, the low-frequency IR thermal camera data was analyzed by POD to acquire the POD modes. The high-frequency thermocouple data with the POD modes were utilized to get the high-frequency mode coefficients by CS. Subsequently, the temperature information reconstruction was completed with POD modes and the mode coefficients. The data fusion method was applied to reconstruct the 250 × 400 pixels temperature field with a frequency of 100 Hz. Using 10 thermocouples and the IR camera with sampling frequency f = 2 Hz, the root mean square error (RMSE) of the reconstructed temperature field is 1.11%, which shows the reliability of the present approach. The less thermocouple and the lower IR camera sampling frequency leads to poorer reconstruction quality, though the effect of IR camera sampling frequency is less significant than the number of thermocouples. The optimized sensor number and sampling frequency were determined by the RMSE in this paper. The RMSE of the data fusion method with the initial temperature T 0 from 40 °C to 120 °C and the flow rate Q from 45 mL/min to 120 mL/min are less than 1.4%, which shows wide applicability of the present approach. A data fusion method which integrates the high spatial resolution IR camera data with the high temporal resolution thermocouple data for wall temperature measurement is reported. The typical steps are shown in above figure. The coherent structure is extracted from the IR camera data based on proper orthogonal decomposition (POD). The coefficients of POD modes are then optimized by the compressed sensing from thermocouple data. The average root mean square error (RMSE) of the reconstructed result with 105 points and 100 Hz is around 1.11%. This method is also validated against different wall temperature and jet flow rate conditions and largest RMSE is found to be less than 1.4%. [Display omitted] [ABSTRACT FROM AUTHOR]

Cellulose material is a dielectric with intricate microscopic relaxation processes due to its complex structure. However, conventional models and curve fitting methods used for tracing and analyzing these processes often fail to capture crucial dielectric information. This paper aimed to extract the Distribution of Relaxation Time (DRT), the most fundamental and effective dielectric information providing the time scale and relative contribution of all microscopic relaxation processes. First, a distributed extended Debye model with infinite branches was constructed based on the microscopic nature of dielectric relaxation. Then, an implicit equation of the DRT function was established, inspired by the mathematical principles of infinite subdivision and summation. To obtain the numeral solution of the DRT function, a regularization method was proposed and validated. Finally, the approach was applied to cellulose insulating paper with varying degradation degrees. The relaxation process with a long time constant played a significant role, and variations during the degradation process were attributed to reduced activation energy. With clear physical interpretation and robust mathematical foundation, our method sheds light on the intricate dielectric relaxation processes in cellulose. This not only enhances the theoretical understanding and practical application of cellulose materials but also provides valuable insights for the analysis and application of other materials. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, a displacement damage simulation model for proton-irradiated GaInP/GaAs/Ge triple junction (TJ) solar cells is constructed in Geant4, and the problem of the displacement damage dose curve deviation for low-energy protons is analyzed. The modeling results show that energy loss effects and local displacement damage are important factors for the deviation of the displacement damage dose curve. The non-ionizing energy loss (NIEL) values of GaAs sub-cells calculated by Geant4 can effectively improve the deviation of the curve caused by energy loss effects. The NIEL should be constrained by the structure and size of the device rather than just the proton energy and material type. In addition, the isotropic radiation field numerical method proposed in this paper allows the displacement damage simulation model constructed in Geant4 to be expediently applied to the radiation environment in space. [ABSTRACT FROM AUTHOR]

Ammonia received increased attention as a carbon-free fuel and hydrogen carrier. Poor combustion stability and high NOx emission are the main issues for ammonia combustion. Effects of rotating gliding arc (RGA) discharge plasma on the flame stability and NOx emission of NH 3 /air premixed swirling flames were investigated. The discharge characteristics of the RGA were studied. The flame stabilization mechanisms by plasma were revealed and analyzed according to the flame structure transition and the distribution of key intermediate OH radicals. The NOx emissions were measured by the Gasmet DX4000 Fourier Transform Infrared (FTIR) gas analyzer. Results showed that the RGA discharge plasma can enhance the stability and extend the lean blow-off (LBO) limits from 0.6 to approximately 0.43–0.57. A hysteresis phenomenon about the transition between the lift-off flame and the attached flame was observed without plasma and disappeared with plasma activation. The plasma reduces NO and NO 2 emissions mainly due to the kinetic and cracking effects of plasma. Extremely low NO emission below 300 ppm can be observed for very lean ammonia flames with an equivalence ratio (φ) lower than 0.6, which are stabilized by plasma, while a large amount of unburned NH 3 emission is accompanied. • A rotating gliding arc discharge plasma-assisted ammonia combustion in a swirl combustor is proposed. • A hysteresis phenomenon about the transition between the lift-off and attached flame disappears with plasma. • Applying plasma extends the lean blow-off limits and enhances flame stability due to the continuous ignition effect. • A rotating gliding arc discharge plasma can enhance flame stability and reduce NO and NO 2 emissions simultaneously. • NO emission below 300 ppm can be observed for extremely lean ammonia flames stabilized by plasma. [ABSTRACT FROM AUTHOR]