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The diagnosis of partial discharge(PD) in power transformer is of great significance to the evaluation of transformer operation state. The traditional method which is based on pattern recognition of Phase Resolved Partial Discharge(PRPD) Pattern is limited to the morphological characteristics of partial discharge spectra analysis. The lack of deeper research of the characteristic of partial discharge leads to low recognition rate and inaccuracy. This paper presents a method of partial discharge pattern recognition based on the chaos theory and the cumulative energy function. A chaotic analysis of the cumulative energy function of partial discharge signals is carried out to calculate the maximum Lyapunov exponent and obtain the maximum Lyapunov exponent distribution characteristics of different types of partial discharge defects. In this paper, different types of partial discharge defects, such as protrusion discharge, void discharge and surface discharge, were placed on the 35kV experimental transformer. The experimental results show that the overall recognition of partial discharge type of transformer is better than traditional method by using chaos characteristics.

Surface discharge in vacuum occurs under intense external field, also called flashover. The flashover threshold over which surface flashover occurs is of vital importance in vacuum-solid interface. It is widely assumed that flashover is initiated by single surface multipactor and develops as a plasma discharge along dielectric surface, namely secondary electron emission avalanche (SEEA). Yet SEEA model is not versatile for all practical vacuum-solid interfaces and there remain experiment results contradicting theory predictions without resolute answer. Here we further expand previous theories and consider conventional SEEA model under arbitrary field distributions. An example of conical insulator is then given to test the validity of SEEA model under arbitrary field. It is found that obtained flashover threshold is only consistent with experiment at low cone angle where field near cathode triple junction is strong, while remarkable discrepancies appear when anode field is significantly enhanced. The discrepancies can be understood if a different discharge model, i.e. anode-initiated flashover (AIF) is included. Both particle-in-cell simulation and optical diagnostics are employed to visualize this unique discharge, which are then formalized on theoretical ground to elucidate the early stage of AIF. Transition between two flashover phases are then clarified. Plasma-surface interaction and sheath dynamics during discharge are analyzed theoretically, showing distinct sheath evolutions in two flashover models. Additionally, a new factor reflecting field distortion is introduced to estimate discharge threshold under SEEA framework.

A one-dimensional fluid simulation model of He/N2 dielectric barrier discharge with parallel plate electrodes was established to study the effects of different parameters (such as gap width, secondary electron emission coefficient γ, and driven frequency) on the characteristics of multiple current pulse (MCP) discharge and the discharge mode conversion. The discharge can be divided into Townsend discharge, transition state, and glow discharge. The results show that with the increase in γ, the number of discharge current pulses increases, making it more difficult to form a glow discharge. When γ is larger, the first discharge approaches the glow discharge mode, but the positive column region is not completely formed, and the subsequent discharge sequence undergoes a transition state to Townsend discharge gradually. Under the condition of larger γ, MCP discharge with a short gap is Townsend discharge. With the increase in the gap width, the transition state will appear in the first discharge, and the subsequent discharge sequence may be converted into Townsend discharge. When the gap width increases further, the discharge can be completely transformed into glow discharge. The pulse number of discharge current decreases with the increase in frequency, and the higher frequency is conducive to the formation of glow discharge.

To observe the protective effect of irbesartan on myocardial fibrosis in diabetic rats, and analyze the role of extracellular signal-regulated kinase (ERK) pathway in this protection.Thirty two male SD rats were randomly divided into two groups:normal control group (CON,Compared with CON group, in diabetic rats, the levels of FBG, H/B and LVWI were increased while BW was decreased. The contents of col I and col Ⅲ were increased as well as the protein expression of p-ERK1/2 and the ratio of p-ERK1/2/ERK1/2(Diabetes can induce the happening of myocardial fibrosis, and irbesartan can induce the damage of myocardial fibrosis through inhibitting the activation of ERK.

In recent years, molecular simulation technology, as the third mothed besides experiment and analysis, has been widely used in various fields. In the field of high voltage, molecular simulation is widely used in oilpaper and polymer insulation characteristics analysis, pyrolysis analysis and so on. In this paper, in order to clarify the electric aging mechanism of cross-linked polyethylene(XLPE), a simple XLPE molecular model is established with the ORCA package and the basic sets 3–21G, 6–31G and 6–311G(d, p) are utilized to optimize and get the most stable structure. We have chosen the band length, band gap and charge transfer within the molecule to characterize the XLPE molecule's status under electric field. The results show that the structural parameters and energy of the molecule present linear changes with electric strength. Especially, the band gap presents a downward trend, which means the insulation property of the material has decreased with the electric strength increases. These phenomena reveal the aging mechanism of XLPE molecule under electric field conditions, which is of great significance to the status evaluation of XLPE cable.

Prior to the occurrence of vacuum flashover a stable stage combined with surface charging phenomenon can be achieved which is called the saturated secondary electron emission (SSEE) stage. The effects of the external electric field perpendicular to the insulator surface as well as a magnetic field parallel to the insulator and normal to the applied electric field on flashover phenomenon are studied based on our simulation using 2D Monte Carlo and particle-in-cell (PIC) method under DC condition. The results show that the field dragging electrons down can reduce the surface charge while the field in opposite direction can increase the surface charge. The latter can also delay the formation time of multipactor and increase the flashover voltage. Different distributions of external field are also investigated in simulation which proves that a cathode field is sufficient in mitigating vacuum flashover. It is notable that in certain cases the SSEE stage is still to be achieved with the influence of external electromagnetic field, and the modification of surface charge provides a complete compensation of external field which eventually leads to a stage similar to the situation where no extra field is applied. A theory of equivalent charge layer is therefore proposed to explain such influence on surface charge and a parallel with the situation of preset surface charge can also be drawn accordingly.

The characteristics of the initiation and the propagation of streamer in the transformer oil are investigated through a two-dimensional axially symmetric needle-to-plane electrode model. The simulation model is based on the approximation of hydrodynamic drift-diffusion, in which transformer oil is treated as a kind of dense fluid and the fluid physical processes of the streamer are dominated via three drift-diffusion equations regarding to positive ions, negative ions and electrons coupled with Poisson equation. In numerical calculations, the finite element method based on advanced computing software is used in solving the model. Through the simulation, the distribution of electric potential, space charge density, electric field and particles of electrons, positive ions and negative ions can be obtained. By means of the above parameters, the streamer current, streamer propagation speed, and the threshold of inception voltage can be calculated. The streamers under different of applied voltage amplitude, polarity, and the shape of electrode are modeled and discussed. The amplitude influences the speed of the streamer, and the shape of electrode has a comprehensive impact. Also, the difference between positive and negative streamer is presented.

SF 6 /N 2 Mixture has good insulation properties and reduces the use of SF 6 , thus it has drawn more and more attention. In addition, Surface charge accumulation on insulating materials is a major factor that greatly distorts the electrical field and reduces the insulation level. Therefore, it is necessary to research the characteristics of surface charge accumulation in SF 6 /N 2 mixture. In this paper, the difference between the time-dependent variation of surface accumulated charge of spacer in 5atm pure SF 6 and that in 5atm 20% SF 6 /N 2 is researched. The downsized truncated cone-type spacer made of 70% Al 2 O 3 filled epoxy resin and coaxial cylinder electrodes are used to model a GIL. In the experiment, ±30kV and ±40kV DC voltage are applied to the central electrode for 30–1080 min, then the surface potential of spacer is measured by a Kelvin vibrating electrostatic probe, and the corresponding surface charge density is further calculated by a calibration method. The results reveal that in both gases, the surface accumulated charge exhibits a time-dependent variation characteristic that the local fluctuates and the whole tends to saturate. Under the DC voltage of same amplitude and same applied time, the total amount of surface charge in 20% SF6/N2 is far more than that in pure SF6. However, the maximum of surface charge density in 20% SF6/N2 is not much different from that in pure SF6 under the same condition of DC voltage. Moreover, in pure SF6, the total amount of surface charge under negative DC voltage is far more than that under positive DC voltage, which means there is polar effect in pure SF6. However, in 20% SF 6 /N 2 the polar effect does not exist.

A particle-in-cell and Monte-Carlo collision (PIC-MCC) model is constructed in order to emulate the development of surface flashover on insulator in vacuum, which involves secondary electron emission avalanche (SEEA), outgassing, and ionization. It is found that multipactor first expands from cathode to anode, subsequently, an ionization avalanche due to increased local pressure occurs near anode and leads to gas breakdown. The spatial distribution of electrons is presented in both saturated secondary electron emission (SSEE) stage and the initiation of gas breakdown stage. Time evolution of electron, ion, desorbed gas molecule and surface charge are investigated in detail. Also the influence of applied voltage and insulator length on flashover are studied carefully. Simulation results show that higher applied voltage enhances the electron collisions on insulator and the speed of pressure build-up. Meanwhile, longer insulator is more vulnerable under the same applied electric field on account that electrons are further accelerated in a greater distance, possessing higher energy and triggering consecutive ionizations more rampantly.

The charges accumulated on spacer surface is an important factor to cause surface flashover. To investigate surface charge distribution characteristics of GIL spacer, a downsized truncated cone-type spacer is designed and manufactured. An experimental and measurement system is established to scan surface potential of this spacer under DC voltages in SF 6 by electrostatic probe method. A calibration method with high resolution is built to compute the actual surface charge distribution. There are two classes of charge distribution observed on spacer surface, including centrosymmetric distribution (the first class), streak-like distribution and spot-like distribution (the second class). It is analyzed that surface conductivity, SF 6 gas conductivity and volume conductivity contribute to different classes of charge distribution respectively.

The electrical and optical characteristics of DBD are different from those of bare electrodes, while the Paschen curve reflects the relationship between breakdown voltage and gas pressure and gap distance. The specific characteristics in DBD need to be differentiated. The electrical characteristics of DBD are closely related to the discharge mode. The mode of DBD discharge can be divided into filamentous discharge and uniform discharge. The plasma contains a large number of excited particles, which radiate at low energy level. After being recorded by ICCD camera, the emission spectrum of plasma can be obtained. By analyzing the intensity and location of the spectrum, we can get a lot of information inside the plasma, such as electron excitation temperature, excited particle species, relative number density and the width of cathode falling zone, etc. The spectral diagnostic method used in this experiment is a non-contact plasma diagnosis method. First, based on the experimental platform of plasma, a DBD device for parallel plate electrode is set up. The medium frequency power supply is 22.0kHz, the working gas is argon, through the observation of the initial discharge voltage, discharge current, ICCD image, study the Paschen curves' characteristic of Ar-DBD, to investigate the mechanism of discharge, volt ampere characteristics and discharge mode evolution characteristics of argon gas, familiar with DBD. Then, through the ICCD camera emission spectra and nanosecond discharge dynamics image shooting, evolution of its time and space, including types, the discharge process of energetic particles in the reaction particle concentration, the cathode falls region width and electron excitation temperature relationship.

Plasma discharge has great many advantages in water treatment and the relevant industrial applications require large volume discharge in water to increase the efficiency. In the paper, the optical images of large volume discharges in water with sphere-to-cylinder and rod-to-cylinder electrode were achieved under different impulse voltage parameters such as amplitude, polarity and pulse width. Additionally, by means of the evolution images of streamer propagation in water, a stepwise trend during the wave front time of streamer propagation is obtained, which is explained by the interactions with streamer resistance, charge distribution and discharge conditions change.

For large power transformers, the hot-spot temperature (HST) of windings has a significant effect on its thermal aging rate and operation reliability. However, the computation of HST is a sophisticated engineering problem all the time because of varied external environment, multi-heat source and the sensitivity of heat transfer coefficients. This paper proposes an improved model of HST for oil-immersed transformers based on the heat transfer theory, which could analyze the heat dissipation process of transformers. In order to enhance the applicability of this model, the ambient wind velocity, which affects the cooling efficiency and the form of thermal convection between the tank walls and ambience of transformer, is regarded as a vital factor leading into the calculation formula of thermal resistance. On the other hand, the sunshine radiation power absorbed by transformer is also introduced as one of the heat sources. Besides, the changes of load loss and oil viscosity with temperature is considered to guarantee the accuracy of this model, too. Lastly, the proposed model has been verified by utilizing experimental data, which was collected by a 220kV transformer operating under different load conditions. Compared with the measured values of HST and the calculated results by the IEC guide, it is found that this method can improve the calculation accuracy of HST by 2.64% and has more real-time performance and faster dynamic response capacity.

This paper introduces a new method to calculate the weight of influence factors on cable failure in 10kV network. A large number of statistical data of cable failure in recent years are investigated to analyze the main causes and influence factors in detail. Different from traditional methods of calculating the weight of factors, the methodology introduced in this paper eliminates subjective judgement by using statistical data. Based on these statistical data, information theory is employed as objectively calculating the weight of influence factors. In this theory, information entropy (IE) reflects the degree of uncertainty. Therefore, using statistical data above, IE of cable status can be obtained. Moreover, under the effect of various external factors, the uncertainty of cable status will get changed. Due to the fact that mutual information entropy (MIE) indicates the variation of IE influenced by outer factors, MIE is used to calculate the weight of influence factors. With the use of algorithm above and detailed information of cable failure, the weight of service years, laying methods and load rate on cable status is obtained. The research results have significant reference values for analyzing influence factors of cable failure and assessment of cable status.

The insulation diagnosis method based on frequency domain dielectric spectrum is widely used in field test because of its nondestructive testing, rich insulation information and so on. FDS measurement results are easy to be affected by many factors. However, interpretation on the dielectric properties of oil paper insulation with moisture content, impurity ion concentration influence mechanism of the current research is not very ideal, so it is necessary to determine more appropriate and effective dielectric response simulation and experimental analysis of characteristics. In addition, moisture content (m.c.) is an extremely important factor which can determine the insulation state of Oil-immersed paper. Therefore, the evaluation of moisture content of oil-immersed paper has obvious significance. In this paper, based on the experimental results, the extended Debye model parameters of the field transformer are obtained. Then, the influence of the insulation resistance value in the Debye model on the FDS curve is simulated by MATLAB modeling. The simulation and experimental verification show that the regularity of the change of the FDS conductance process is obviously different from the moisture content influenced by the impurity ions. The impurity ions mainly affect the low frequency section of the imaginary part of the complex capacitor. A non-linear phenomenon in dielectric response with different moisture contents under different is observed. We found that the non-linear phenomenon has relationship with the hindrance effect of cellulose (m.c.

Surface flashover across solid insulators in vacuum-dielectric system greatly weakens the overall performance of pulsed power equipment. It is reported that flashover is crucial in relation to surface charging behaviors on insulator surface. Therefore, it is of great significance to study mechanism of surface charge accumulation in vacuum. In this paper, surface charging behaviors on alumina ceramics insulators were experimentally investigated under negative impulse voltage. Surface potential distribution were measured by an electrostatic voltmeter with a vibrating Kelvin probe utilizing field nullifying technique. Surface charging behaviors for different amplitudes and number of negative impulse voltage were both studied, and the metal granule was introduced to research the development of surface charge accumulation. For impulse voltage, Schottky injection of homo-charges from electrode into sample surface layer has little influence on surface charging as the voltage duration is too short for charge injection and migration on surface layer. Surface charging is mainly caused by the secondary electron emission (SEE) process on sample surface due to its extremely fast establishment process. The insulator surface is merely positively charged. Surface charges gradually expand from cathode toward anode with the application of impulses, which needs ∼10 impulses to reach a saturated charged surface. A linear relationship is obtained between saturated surface potential and applied voltage.

Dissolved gas analysis (DGA) has been proven an effective method to diagnose the internal fault of transformers for decades. This paper proposes an approach of DGA based on Deep Belief Networks (DBN) which belongs to deep-learning theory. With composed of Restricted Boltzmann Machines (RBMs), DBN can built the mapping relationship between the characteristic gas and the fault types automatically to achieve the accurate diagnosis, namely Pattern Recognition (PR). In this paper, DGA data is divided into three categories, called training data, fine-tuning data and test data. Training data is used for unsupervised-learning to initialize parameters of RBMs in DBN, and fine-tuning data is for supervised-learning with fault modes to optimize parameters. Finally, the test data is used to calculate the recognition rate of transformer fault diagnosis. It comes to conclusion that DBN model proposed shows a promising results of transformer fault diagnosis with high accuracy of 84.87% Compared with Back Propagation Neural Network (BPNN) method, DBN model not only achieves a high recognition rata of transformer fault, but also have strong generalization ability under big data, which could provide a powerful tool for the internal fault diagnosis of transformers.

Since the plasma “bullet” and ring shape were discovered by Teschke and coworkers in 2005, the hollow structure of the plasma “bullet” has been a hot topic as an important phenomenon. Clearing the mechanism back on the phenomenon is very important to research and application of atmospheric pressure plasma jet (APPJ). Although a lot of discussions on the generation and evolution of the hollow structure have been conducted in past years, there is a substantial divergence between the experimental researcher and the numerical simulation researcher. The former considers that the Penning effect has a main contribution, because the presence of impurities enables the Penning process to occur at the gas flow/air interface. On the contrary, numerical simulation claims that the Penning effect is not so decisive to the formation of hollow structure. Based on our previous work, this paper aims to clear the debatable topic by setting the special experiments. After comparing and analyzing the phenomena and mechanism, a better comprehension is reached on the contribution of the Penning effect to the hollow structure. We also give a promising conclusion for forming the hollow structure of plasma jet in the end of paper.

Oil-polypropylene (PP) composite insulation has been widely used in power capacitors, and also being extended to other equipment such as specific transformers, etc. As discharge can readily creep along PP surface, the interface between oil and PP is a weak point in the insulation structure. The oil-PP insulation degrades under the impact of thermal and electrical stress during normal operation. In this study, the influence of thermal degradation on surface discharge characteristics for oil-PP insulation is investigated. Degraded samples are obtained by thermally accelerated aging of virgin oil-PP samples. The microscopic morphology of PP samples are observed with SEM, and the physical and electrical properties of degraded oil are measured. In addition, the isothermal surface potential decay (ISPD) measurement is employed to investigate the charge keeping capability of PP samples. After that, surface discharge detection experiments under AC voltage are performed for the virgin and degraded samples. The ISPD results indicate that charge decay rate of degraded PP sample is faster than virgin sample, which imply that space charge memory effect of virgin PP samples is more remarkable. For this reason, the PD inception phase of virgin sample is smaller than those of degraded samples. It is found that thermal degradation of oil-PP insulation enhances the surface discharge activity. It is considered that rough surface profile and higher bubble conservation capability of degraded PP sample, and impurities in degraded oil are responsible for the enhancement effect of thermal degradation on surface discharge.

Disinfection and sterilization in hospitals and other public places have always been the focus of attention. In our studies, dielectric barrier corona discharge (DBCD) was used to generate low-temperature plasma (LTP) to treat Pseudomonas aeruginosa ( P. aeruginosa , one kind of bacteria responsible for nosocomial infections). The survival colonies of P. aeruginosa were counted with the standard plate-counting method after 30-, 60-, 90-, and 120-s exposures to DBCD. We discovered that LTP could lead to more than 5-log reduction of P. aeruginosa after 120-s treatment. Further experiments indicated that OH and excited N2 in LTP and lower pH value in bacterial suspension might synergistically inactivate P. aeruginosa by destroying its outer structure.

Nanosecond-resolved photographs of the nonequilibrium atmospheric-pressure plasma jet of helium, generated with the conventional dielectric barrier discharge device, were obtained at different sections of the experimental setup and at different development stages of the discharges, showing that various distinct mechanisms are simultaneous in operation. The streamer from the outer edge of active electrode sitting at downstream side forms a jet in air, which only turns out to be hollow when approaching the orifice of the gas conduct. The streamer from the inner edge temporally lags behind, and it propagates along a helical path and initiates the glow discharge when arriving at the ground electrode. The electron deposit beneath the active electrode expands inward from both sides, displaying a soliton-like behavior; while the very compact ion deposit beneath the ground electrode, a typical ionic streamer, extends outward from the inner edge of the electrode. The velocities of the jet in air and of the streamer between electrodes are much larger than those at other parts of the device. The resolution of these particular processes and features can improve the implementation of this valuable cold plasma source.

During the field service of composite insulators, high temperature vulcanized (HTV) silicone rubber (SIR) material used for insulator’s sheath and sheds is gradually aging, and thus how to effectively evaluate its aging state has become an inevitable issue. In this paper, artificially corona-aged and naturally site-aged SIR materials are employed as samples, and their properties such as hydrophobicity, leakage current, trap density/energy level, surface microstructure and chemical composition are investigated for comparative study. With the increasing of corona aging intensity, the contact angle of SIR samples drops gradually and recovers more slowly. The hydrophobicity of site-aged insulators also declines, from HC1 for 2-year service to HC5 for 15-year service. The leakage current of corona-aged and site-aged samples both increase with aging, which indicates that aging induces the increase of surface conductivity of SIR material. The peak trap density of corona-aged and site-aged samples increases with the aging duration or service duration remarkably. The changes of these properties are attributed to the changes of micro-structures and compositions in the surface layer of SIR. The scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) analysis results reflect that a hardened inorganic silica-like (SiO2) layer with many polar chemical groups and distributed micro-pores is formed on the surface of SIR material after corona aging. Because of this silica-like layer, the hydrophobicity decreases while surface conductivity and trap density of SIR material increases. Besides the traditional properties like hydrophobicity and surface conductivity, the trap density is expected to be a novel parameter for effective evaluation of aging state of HTV silicone rubber material.

In recent years, in order to improve the efficiency of urban power supply, automatic reclosing operation is gradually applied in the XLPE cable-OHL mixed line. Operation experience shows that the grounding fault occurred in the overhead line, in most cases, is instantaneous and the success rate of reclosing is high. The grounding fault occurred in the cable line is almost permanent and the success of reclosing is quite low. In this paper, a typical mixed line of urban power network was built in PSCAD software. The amplitude-frequency characteristics of overvoltage, caused by single-phase grounding fault of cable segment and overhead line segment, were studied. And the characteristic parameters of two kinds of overvoltage were extracted. According to these parameters, the fault location could be determined and the basis of reclosing strategy was provided.

Partial discharge (PD) in power transformer degrades the dielectric insulation and results in insulation failure and breakdown after a long period. In fact, a partial discharge detector can gather signals from two or more PD sources which increase the difficulty on pattern recognition and insulation state assessment. How to separate multiple PD signals is meaningful to subsequent data processing. In this paper, a PD separation algorithm based on cumulative energy (CE) function is introduced. The CE functions in time domain (TCE) and frequency domain (FCE) are calculated from PD waveforms and their FFT spectra, respectively. By using an oblique line to cross the CE curves, width features are extracted from the intersection points between them. Through the mathematical morphology gradient (MMG) operation, sharpness features are extracted to characterize the rise steepness of CE. A clustering algorithm is adopted to discover different clusters in feature space and separate PD signals. After that, a transformer experiment platform is introduced and some different defects are placed at different places in this transformer to produce PD signals. The pulse current method is applied to gather their PD waveforms and to record phase resolved partial discharge (PRPD) which can be used to analyse discharge characteristics of different defects. The separation algorithm is examined with mixed PD current pulses acquired from experiments. The results prove the feasibility of separation algorithm with different PD defects.

The potential applications of low temperature plasma (LTP) in wound healing have aroused the concern of many researchers. In this study, an argon atmospheric pressure plasma jet was applied to generate LTP for treatment of murine fibroblast cell (L929) cultured in vitro to investigate the effect of NF-κB pathway on fibroblast proliferation. The results showed that, compared with the control, L929 cells treated with plasma for less than 20 s had significant increases of proliferation; the productions of intracellular ROS, O2− and NO increased with prolongation of LTP treatment time; NF-κB pathway was activated by LTP in a proper dose range, and the expression of cyclinD1 in LTP-treated cells increased with the same trend as cell proliferation. After RNA interference to block p65 expression, with the same treatment time, RNAi-treated cells proliferated more slowly and expressed less cyclinD1 than normal cells. Furthermore, pretreatment with N-acetyl-L-cysteine (NAC) markedly prevented the plasma-induced changes in cells. In conclusion, the proliferation of L929 cells induced by LTP was closely related to NF-κB signaling pathway, which might be activated by appropriate level of intracellular ROS. These novel findings can provide some theoretical reference of LTP inducing cell proliferation and promoting wound healing.

This paper describes an experimental study of streamer inception and propagation characteristics from a protrusion in transformer oil under AC voltage. The information acquired by partial discharge detection, such as current pulse sequences, phase-resolved PD (PRPD) pattern and statistical parameters are obtained; moreover, optical properties of streamer in transformer oil are captured by fast-imaging technique. The experimental results show that the pulse sequences represent different mechanisms. The stopping length of streamer are highly dependent on the amplitude of applied voltage. Both PRPD patterns and the shapes of streamer indicate that the positive and negative streamers show a strong polarity effect under AC voltage. The space charges formed periodically at the alternative half cycle of high voltage are responsible for the phenomena in the experiments.

The surface flashover phenomena of insulating materials in vacuum greatly weakens the overall performance of vacuum-dielectric system, which seriously limits its development. The improvement of surface flashover characteristics of insulators in vacuum becomes a significant challenge for the development of high voltage electrical equipment. In this paper, we report a simple and convenient way to achieve the high surface flashover performance of low density polyethylene (LDPE) and alumina ceramics (Al 2 O 3 ) in vacuum based on direct fluorination technique. The direct fluorination of test samples was performed in a fluorination apparatus for different time of 30, 60, and 90min by using F 2 /N 2 mixture of 12.5% F 2 with the pressure and temperature keeping constant as 0.1MPa and 55°C. Then the surface flashover characteristics of LDPE and Al 2 O 3 at different fluorination time was investigated. The results show that for LDPE samples fluorinated with 30 and 60min, the hold-off voltage increased by 21.9% and 34.1% than the virgin sample. However, the hold-on capability decreased apparently for the case of 90min fluorination. However for Al 2 O 3 samples, direct fluorination had little influence on the surface flashover characteristics. This research could make a contribution to understand the influence of direct fluorination on dielectric flashover characteristics in vacuum.

The surface flashover phenomena of insulating materials in vacuum greatly weakens the overall performance of vacuum-dielectric system. The improvement of surface flashover characteristics of insulators in vacuum becomes a significant challenge for the development of high voltage electrical equipment. In this paper, we propose a convenient avenue to achieve the high surface flashover performance of polymethyl methacrylate (PMMA) in vacuum based on adopting two kinds of electrode dielectric contacts, one is to insert electrodes into samples, and the other is to sputter gold coating on the samples surface. Furthermore, the surface electric field distribution of PMMA samples under different embedded electrode structures were simulated in the COMSOL software. The results show that all the two kinds of electrode dielectric contacts treatment can apparently improve the flashover voltage of PMMA in vacuum. For the embedded electrode structure, when the electrode height is higher or lower than the embedding depth, flashover voltage is lower than the structure that electrode height is as high as the embedding depth. And the bigger difference between the electrode height and the embedding depth is, the lower its flashover voltage is and the smaller its dispersion is. Besides, sputtering gold coating on dielectric surface can effectively improve the contact between electrodes and dielectrics. But comparing with the situation of sputtering both bottom side and flank side, the flashover voltage of only sputtering bottom side is much higher and its dispersion is much smaller. This research provides two methods for improving the dielectric surface flashover characteristics in vacuum.

As cable insulation failure usually started with PD activity, a PD detection system based on pulse current was built to study the PD characteristics of typical defects in XLPE cable. To facilitate the test, the oil cup test terminal was used. Considering the installation procedure, three different kinds of insulation defects in cable accessory samples were made, which were knife incision defect, metal floating potential defect and misplaced stress cone defect. Under long time power frequency voltage of U», 1.7U0, 2.5U0 and 3.5U0 (U0=8.7kV), this paper proposed a variety of methods to characterize partial discharge of these samples by PRPD spectrum, δ t spectrum and PSA spectrum. Results showed the δ t spectrum presented a clear distribution of the peak and the sub-peak. The distribution regularity of partition probability in PSA pattern before the breakdown was found that the probability in the area 1.1 as from 50% to 60%, and the probability in the area 3.1 was from 30% to 40%.

In this paper, the epoxy composite insulating material is selected as the experimental sample. After the samples being charged under different voltages with different duration in SF 6 of atmospheric pressure, the surface potential distribution is measured with a Kelvin electrostatic probe. The 2dimensional Fourier transform with Wiener filter technique is applied to calculate the surface charges density distribution. The results reveal that the surface charges density shows a good correspondence with the surface potential, and the whole measuring system presents a definitely high spatial resolution.

The microdischarges generated in spatially confined geometries, such as microcavities and micropores of various materials, represent a promising method to create stable nonequilibrium plasmas at atmospheric pressure. Hybrid plasmacatalytic system utilizing porous ceramics loaded with catalysts shows the synergistic effect on volatile organic compounds (VOCs) decomposition, carbon dioxide reduction and methane reforming. In this paper, we investigated on the physical characteristics of dielectric barrier discharge (DBD) in porous ceramics at atmospheric pressure methane generated by sinusoidal waveform (20 kHz, 0–20 kV) power supply. Discharge images corresponding to the variety of parameters were visualized by intensified charge-couples device (ICCD) camera system. Voltage - current curves and emission spectra captured by a mechelle spectrometer (Mechelle 5000, Andor) referring to electrical and optical characteristics of the discharges were measured. Experimental results show that two types of discharges, surface discharge and pore microdischarges inside the ceramics, can be observed and develop simultaneously when applied voltage and pore size are above a critical value. The onset voltage of pore microdischarges increases with the increasing thickness of ceramics,and it decreases significantly due to the increase of porosity.Abundant active carbon-based components, such as CH $(\lambda =314.05$, 389.02, 431.31nm) and $\mathrm {C}_{2} (\lambda =471.6$, 516.2, 563.3nm) in the excited level, are produced in discharge. Temperature of the active particles is calculated by LIFBASE software to better understand the mechanism of the discharge process in porous ceramics. The work should be beneficial to determine optimum parameters to enhance the plasma catalytic process.

Polymeric materials such as Epoxy resin (EP) are widely used as insulating materials in the field of electrical and electronic engineering. For enhancing the surface electric withstanding strength of EP, the samples are treated by atmospheric pressure plasma jet (APPJ) with different time interval. Helium and tetrafluoromethane mixtures are used as working gas to produce active species. The flashover characteristics of modified EP samples in vacuum, air and SF 6 are investigated. The flashover voltages have different degrees of improvement in the three atmospheres under appropriate treatment conditions. The emission spectrum of He/CF 4 APPJ indicates that fluorine species are produced during plasma process, but the specific kinds of species can not be diagnosed from the emission spectrum. The XPS spectrum shows that fluorine groups are grafted into the surface of modified EP samples. Fluorine groups in modified EP surface like -CF 2 /-CF 3 with electronegativity are regarded as one of the reasons for flashover voltages improvement. In addition, surface roughness of EP samples is increased after plasma treatment. It is also an important reason for enhanced flashover characteristics. In conclusion, APPJ treatment is considered as a promising method to enhance the flashover strength of insulating materials like EP. It has an important significance to improve the reliability and reduce the size of an insulation system.

Power transformer is one of the most expensive equipment and plays a vital role in power transmission and distribution (T&D) systems. This paper presents a comprehensive risk assessment method of transformers, which integrates the operating condition of transformer and the consequences of transformer failure. Health index provides a practical tool for evaluating the state of transformers. Meanwhile, the probability of transformer outage is calculated by the historical operation and maintenance statistic data, which in some extent represents the possibility of transformer failure under certain health index level. Subsequently, based on the power flow analysis, the increment of network loss and emergence of load reduction induced by transformer outage are proposed. This method not only has a vital significance for the operation and maintenance of transformers, but also has a reference for improving the economic efficiency and the reliability of power network operating.

Atmospheric pressure cold plasma that contains numerous act ive components including electrons, ions, free radicals, reacti ve molecules and photons has been extensively researched as a promising anticancer treatment technology in recent years1. Melanoma is the most aggressive form of skin cancer with a high prevalence, a median overall survival of less than 2 year s, and resistance to current modalities of cancer therapy2. Plas ma can inactivate melanoma caner cells effectively, but the m echanism of the interaction between plasma and cells is not y et fully understood and needs to be investigated further. In this work, an improved atmospheric pressure plasma jet (A PPJ) with three electrodes in helium was utilized for treatmen t of murine melanoma caner cells cultured in vitro. After bein g exposed to APPJ with different time durations, the cell viab ility, transmission electron microscopy (TEM) images, intrac ellular superoxide dismutase (SOD), malondialdehyde (MD A), reactive oxygen species (ROS) and cell cycle distribution of melanoma cells were measured, respectively. It was show ed that, compared with the control cells, the cell viability and SOD activity decreased, the degree of cell damage, MDA an d ROS content increased in a time-dependent manner with 10, 30, and 60 s of plasma treatment. Furthermore, the APPJ ma y reduced cell viability of melanoma cells via inducing G1/S and G2/M cell cycle arrest. It was concluded that oxidative st ress in melanoma cells was mainly induced by the reactive ox ygen and nitrogen species (ROS and RNS) in the plasma jet, which were detected by optical emission spectroscopy.

Traditional cable insulation status diagnosis method is comprised of withstand voltage experiment. However, withstand voltage experiment injures the insulation part. Insulation resistance and tanδ provide the limited information because of single frequency test. However polarization and depolarization(PDC) can be used for determining the ageing extent of the cables. Existing equipments have poor anti-jamming capability, Aiming at the problems, we have developed cable insulation diagnosis equipment based on (PDC) process in dielectric insulation. This equipment can collect the low current which can be used to analyze cable insulation status by applying high voltage excitation. Due to possible device noise and environment electromagnetic interference, low current measurement encounters is usually the most difficult issue in device development. To solve this, first of all, the equipment using the modular components avoid self-interference. Then, to achieve good polarization/depolarization current measurement, software Butterworth filter is employed to deal with the noise in measured current waveforms. In addition, the equipment is designed with floating potential in order to have the ability to measure the current without disconnecting grounding wires of the device under test. Calibration of the equipment is also conducted with the usage of a precise RC network. In this paper, the equipment with high accuracy is verified, and tests in the field, which get good results. It can be used more widely due to small volume and reliable operation.

Cross-linked polyethylene (XLPE) insulation cable is the main type of cable in use now. Its main insulation is aging with the increasing of service years. Two methods are used to diagnose the condition of the cable insulation-polarization/depolarization current (PDC) and frequency domain spectroscopy (FDS). The PDC is a time domain method, while the FDS is frequency domain. In this paper, we put forward a method to get the dissipation factor curve of FDS under low frequency by carrying out the PDC experiment. This method is based on three R-C series branches extended Debye model. In this model each branch stands for a type of polarization process. Firstly, The measurement of cable samples aged for different days is carried out to get the PDC and dissipation factor curves. Then, the PDC curves are fitted with a third-order exponential decay function, and the parameters of the extended Debye model are calculated. Comparing the calculated dissipation factor curves with the measured, we find that they agree very well with each other under low frequency range. By this way, we can reduce the measuring time.

Surface charge accumulation on insulating materials is a major factor that greatly distorts the electrical field and thus reduces the insulation level. In this paper, the relationship between the surface charge density distribution and the output voltage of electrostatic probe is discussed, and an improved algorithm is built to calculate the charge density distribution, which employs two-dimensional Discrete Fourier Transformation (2D-DFT) to reduce the amount of calculation and the Wiener filter to reduce the influence of noise. Furthermore, because of the similar relationship between the electric field strength distribution and the surface charge density distribution, the field strength distribution can also be calculated by adopting this algorithm. In addition, the electrostatic probe is taken into consideration in this algorithm, and the spatial resolution of this measurement system including the inverse calculation process is investigated. It is estimated that the spatial resolution of this measurement system with 1mm gap between the electrostatic probe and the surface of the insulation is 0.3341mm. The charge density distribution as well as the field strength distribution is calculated by this improved algorithm when a lightning impulse voltage is applied to a PMMA plate of 1mm thickness, respectively. The results reveal that this algorithm has great accuracy and stability and can exactly calculate the surface charge density distribution and the electric field strength distribution.

In this paper, a novel +45° insulator is proposed. The insulator has a conductivity graded structure in which the high conductivity part performs as a shield to reduce the electric field concentration at anode triple point and along surface. Hence, the surface electrical withstanding strength would be enhanced. Computer aided simulation is performed to investigate the electric field distribution with different shape parameters of high-conductivity area and an electric field optimized insulator design is thus obtained. A Fused Deposition Modeling 3D printing technique is adopted to fabricate the conductivity graded insulator. The wide application of 3D printing in insulator fabrication is expected for its ability to fabricate special functional structure and high fabricating efficiency. Flashover tests are to be conducted to investigate the electrical withstanding performance of such insulators.

The accuracy of conventional DGA interpretation methods can be different when each of these methods are used in different places or different circumstances. Rogers Ratio Method (RRM), IEC Ratio Method (IRM) (Basic Gas Ratios Method), GB/T 7252 (National Standard of the People's Republic of China) are popular conventional methods for interpreting the possible faults indicator of transformer in Indonesia and China. This research proposes artificial intelligence to interpret DGA by combining conventional method and artificial intelligence method using weighting factor. The artificial intelligence method which are used in this research is fuzzy logic. DGA practical data which used as refer data for data mining in this research were taken from China and Indonesia. This research also uses Thompson tau method to filter the data from outlier and fuzzy c means clustering to cluster the data to make sure the data are used is valid and good enough to be used to build artificial intelligence through data mining. The output of this research is to create an artificial intelligence and the combination between artificial intelligence which have been built with conventional method to interpret DGA whether there is any fault in transformer or not.

Streamer and breakdown behavior of transformer oil under impulse voltage are investigated with experimental observations and simulation. The optical observation by using Intensified Charge-coupled Device (ICCD) fast snapshot technique indicates that streamer channel branching is of a stochastic nature. The 2-D axially symmetric modeling based on hydrodynamic drift-diffusion model is employed to depict the streamer dynamics of transformer oil. The experimental and simulation results reveal that bushy negative streamer requires higher excitation than filamentary positive streamer. Positive streamer travels faster than negative streamer from experimental estimation.

A two dimensional axis-symmetric fluid model is developed to present the streamer discharge process in transformer oil under positive and negative sub-microsecond impulse voltage, which is based on the hydrodynamic drift-diffusion approximation to simulate the dynamics of discharge inception and propagation. The streamers' spatial evolution with time are obtained, i.e., the distribution of electric field and space charge density under different conditions such as the amplitude of applied voltage and rise time. Simulation results verify the breakdown voltage has a distinct polar effect: negative streamer requires more than 2 times voltage threshold than that of positive one. It is revealed that the negative streamer, which usually has a bushy profile, is much more diffusive than the positive one. The magnitude and rise time of the applied voltage have evident influences on the shape and speed of the streamer in oil. The formation of positive or negative streamers are both characterized by a self-generated field enhancement at the head, and space charges enhance the front field of ionization region to assist the growing discharge channel to propagate longer. In terms of the generation of charged particles, it is considered that field-dependent molecular ionization predominates the charge generation mechanism of streamer discharge processes in transformer oil.

The thesis takes a three-lane tunnel construction in Zhejiang as an example. Simulating the course of dynamic construction of large-span tunnel on geology condition of four-grade rock mass and shallow buried by FLAC 3D software ,it carries out comparative and stress situation in the runnel surrounding rocks .Getting the displacement and stress changes rule of the construction by using benching with a small pilot tunnel tunneling method can guide the construction scientifically.

There are some special requests for the insulating materials for high voltage electro-vacuum devices. Traditionally alumina ceramics and polymers are widely used, but both of them show some disadvantages such as difficulty of being manufactured to some complex shape due to the restriction of die arrangement, or lower mechanical and heat-resistant properties. The paper reports a newly invented low-melting temperature machinable glass ceramic (MC) for remedy these problems. The influence of crystallization preparation parameters (temperature and time) on its basic mechanical and electrical properties is investigated, such as bending strength, dielectric parameters, and desorbed gases, revealing its advantages suitable for vacuum utilization. Moreover, different metal oxides (Cu2O and Cr2O3) with low secondary electron emission (SEE) yield are doped into MC, and a better surface electrical withstanding capability is achieved.

SF $_{6}$ insulated current transformers (CTs) are widely used in high-voltage power systems due to their favorable insulating properties. Field experience shows that the high moisture content in an SF $_{6}$ -insulated CT is an important factor responsible for its insulation faults. Furthermore, the moisture content in an SF $_{6}$ -insulated system is generally dependent on the ambient temperature. Thus, in this paper, the temperature distribution and moisture content of an SF $_{6}$ -insulated CT are studied by considering current flowing through it and a sharp change in the ambient temperature. It is found that the temperature distribution of an SF $_{6}$ -insulated CT in operation is extremely uneven, and the measured moisture content becomes higher than the initial moisture content. The relative humidity in the lower part of the CT might reach a dangerous level when the ambient temperature changes rapidly. The mechanism of moisture condensation is proposed to explain the experimental results. Besides, the possible preventive measures for insulation failure are also discussed.

This paper is aimed to investigate the inhibition effect and mechanism of low-temperature plasma (LTP) on melanoma cells. An argon atmospheric pressure plasma jet is used to generate LTP for the treatment of B16 murine melanoma cells cultured in vitro . LTP treatment time intervals are set as 5, 10, 15, and 20 s, respectively. After being treated with LTP, cell viability, cell apoptosis, cell cycle distribution, and cycle-related proteins expression of melanoma cells are, respectively, measured. It is found that, compared with the control cells, treatment of melanoma cells with 10, 15, and 20 s of plasma, result in a significant reduction in cell viability. Furthermore, investigation demonstrates that LTP may reduce cell viability of melanoma cells via inducing G1/S and G2/M cell cycle arrest and cell apoptosis, and alteration of cell cycle is due to down-modulation of the expression of CyclinB1 and CyclinD1 protein induced by LTP.

Low temperature plasma (LTP) has emerged as a new research hotspot of promising therapy to fight against cancer. Autophagy is a multifunctional process that digests and recycles cellular contents within lysosomes to maintain homeostasis, which is the underlying mechanism of cancer cell death and anti-cancer treatment. This study aimed at investigating whether autophagy of HepG2 cells could be induced by LTP and revealing the related molecular mechanism. For this purpose, the atmospheric pressure plasma jet (APPJ) in helium was utilized to generate plasma-actived medium (PAM) to treat HepG2 cells in vitro. Catalase (CAT), superoxide dismutase (SOD) and 3-methyladenine (3-MA) were respectively added into the PAM as the intervention group. The cell viability, formation of autophagosomes, intracellular reactive oxygen species (ROS) level, expression levels of autophagy-associated proteins and key proteins involved in PI3K/AKT/mTOR pathways were detected. The results showed that LTP inhibited cell viability in a dose- and time-dependent manner. Autophagy was induced through the formation of autophagosomes, conversion of LC3-II/LC3-I, increased expression of beclin 1 and degradation of p62. The mechanism was deduced that LTP enhanced the intracellular ROS level and decreased the phosphorylation level of key proteins in PI3K/AKT/mTOR/p70S6K pathway. However, these effects were blocked by the autophagy inhibitor 3-MA and ROS scavengers (CAT and SOD). The therapeutic efficacy of LTP against HepG2 cells may involve autophagy via suppressing PI3K/AKT/mTOR signaling pathway by LTP-mediated ROS.