Electrical equipment filled with sulfur hexafluoride (SF₆) may experience overheating or discharge when there are internal insulation defects, which will cause SF₆ to decompose and produce some gaseous by-products. By testing the type and concentration of these by-products, we can determine whether there were insulation defects in electrical equipment and the type and severity of these defects. As an important tool of gas detection, gas sensor had been paid more and more attention in the gas detection method of insulation defects. In this paper, the method of detecting SF₆ decomposition products by using gas sensor was reviewed, the dissociation process of SF₆ and the generation path of characteristic gas were introduced, and the gas-sensitive principle, advantages, and disadvantages of the sensor used for detecting SF₆ decomposition characteristic gas were described in detail. The algorithm for diagnosing insulation defect using characteristic gas information was mainly discussed, and the development direction of using sensors to detect gas decomposition components for insulation defect diagnosis was prospected.

Dry reactors are widely used due to their advantages of stable parameters and small losses. However, with the wide application of dry reactors, related accidents occur frequently, among which the turn-to-turn fault is the most common. In this paper, the causes and mechanisms of turn-to-turn faults of dry reactors were briefly summarized. Then, the research status of turn-to-turn insulation condition monitoring of dry reactors at home and abroad in recent years was reviewed from different perspectives. Finally, based on the deficiencies in the researches, the development trend of turn-to-turn insulation condition monitoring technology for dry reactor was prospected.

TiO₂ nanoparticles surface modified with acetic acid, hexanoic acid, and oleic acid were synthesized via liquid-phase method and used to prepared modified transformer oils. The morphology and surface modification state of the nanoparticles were measured by transmission electron microscope (TEM) and Fourier infrared spectroscopy (FTIR). The positive impulse breakdown voltage and streamer development pattern of the transformer oil before and after modification were tested, and the effect of nanoparticle surface modification on the breakdown performance of transformer oil was studied. The results show that the surface modified nanoparticles greatly improve the positive impulse breakdown voltage of transformer oil, and significantly prolong the breakdown time. Among them, the acetic acid modified nanoparticles have the best modification effect, which increases the impulse breakdown voltage from 84.73 kV of pure oil to 116.42 kV, an increase of 37.4%, and the breakdown time is extended to 1.86 times that of pure oil. The surface modification of nanoparticles greatly increases the shallow trap density in the oil, changes the streamer propagation pattern, significantly inhibits the development speed of streamer, and thus improves the impulse breakdown properties of the transformer oil.

In this study, 4,4ʹ-diaminobenzanilide (DABA), 2,2ʹ-dimethyl-[1,1ʹ-biphenyl]-4,4ʹ-diamine (m-TB), dianhydrides pyromellitic dianhydride (PMDA), and 4,4ʹ-oxybisphthalic anhydride (ODPA) were used as raw materials, and a polyimide (PI) film for oganic light emitting diodes (OLED) flexible substrates was successfully synthesized. The results show that when the molar ratio of diamine to dianhydride is 0.990, the feeding time is 120 min, the reaction temperature is 0-30℃, the stirring speed is 200-250 r/min, and the reaction time is 240 min, the gel amount during the synthesis of polyamide acid is small, and viscosity can meet the requirements of industrial synthesis. After thermal imimization at 400℃, the glass transition temperature of the polyimide film is 450℃, the 1% weight loss temperature is 554℃, the thermal expansion coefficient is 4.1×10^-6 K^-1, the tensile strength is 326.9 MPa, the tensile modulus is 9 572.8 MPa, the electric strength is 623 kV/mm, and the dielectric constant is 3.251, which meet the industrial application requirements of OLED flexible substrate.

The EVA material was modified by electron beam melting irradiation, and the effects of different irradiation does on gel content, mechanical properties, volume resistivity, dielectric properties, breakdown characteristics and molecular structure of EVA samples were studied. The results show that the gel content of EVA sample first increases and then decreases with the increase of irradiation dose. When the irradiation dose is 100 kGy, the gel content reaches 95.7%. Irradiation can reduce the elongation at break of EVA samples, while the tensile strength first increases and then decreases with the increase of irradiation dose. After irradiation, the insulating properties of EVA samples improve to varying degrees, with the increase of irradiation dose, the volume resistivity first increases and then decreases, the dielectric constant first decreases and then increases, and the electric strength first increases and then decreases.

In order to study the effects of compression molding and extrusion molding on the dielectric properties of nanocomposites, these two molding methods were used to prepared the crosslinked polyethylene/organic montmorillonite (XLPE/OMMT) nanocomposites, respectively. The effects of the interlayer spacing change of OMMT in different composites on the resistance-temperature characteristics, dielectric constant, dielectric loss, and electric strength of the composites were discussed. The results show that the force field effect during the molding process can affect the intercalation dispersion effect of OMMT. The tensile stress during extrusion molding makes the OMMT sheets in the sample orient along the tensile direction, and form a regular arrangement unit, which hinders the migration of carriers, thereby improving the resistance-temperature characteristics of the sample. The movement of polymer molecular segments is lim-ited between the oriented lamella, which makes the dipole in the sample decrease, and the dielectric constant and dielectric loss factor decrease. At the same time, the effective intercalation of OMMT and the hybrid structure formed by the polymer cause diffuse reflection of electrons, extending the electron motion path, and improving the electric strength of the extruded sample.

The morphology and particle size of inorganic fillers are key factors that affect the surface voltage resistance of epoxy resin (EP) composites. In this study, the ZnO nanofibers and particle-shaped ZnO with different particle sizes were used to dope and modify epoxy resin to prepared EP composites, and the DC surface flashover performance and charge dissipation rate of the composites were tested. The results show that the doping of ZnO filler can effectively improve the flashover voltage of EP composites, and the improvement effect of fibrous ZnO filler is significantly better than that of particle-shaped ZnO filler. The flashover voltage of particle ZnO/EP increases with the decrease of filler particle size. When the mass fraction of ZnO nanofiber is 15%, the flashover voltage of EP composite increases by 27.1% compared with that of the pure EP. A finite element simulation model was constructed, and the calculation results show that the fibrous ZnO increases the non-uniform coefficient of the internal electric field in EP, and increases the current density of the composites.

In order to solve the problem of algae adhesion on the insulator surface, a self-healing algae resistant coating suitable for external insulation of power equipment was prepared, and the thermodynamic properties, mechanical properties, algae resistance, self-healing properties, and electrical properties of the coating were tested. The results show that when the frequency is 50 Hz, the algae resistance, mechanical properties, dielectric and electrical properties of the self-healing algae resistant coating with a mass fraction of 0.5% of anti-algae agent are the best. At the same time, the coating can self-heal micro-cracks, reduce the adhesion of mineral salts and moss spores, and inhibit the growth of moss.

In order to investigate the effect of thermal treatment on the dielectric relaxation of EP, a EP sample was prepared and conducted thermal treatment at 210℃/48 h. The changes of chemical structures, glass transition temperatures, thermal decomposition parameters, volume resistivities, and dielectric relaxation of the EP before and after thermal treatment were studied. The results show that the thermal treatment does not change the chemical structures and thermal decomposition temperatures of the EP, but the glass transition temperature decreases from 134℃ to 108℃. Furthermore, the dielectric constant of the sample increases after thermal treatment, with a smaller increase at high frequency (10⁶ Hz) and a more significant increase at low frequency (10^-1 Hz).

When detecting the oil-paper insulation status of transformer based on frequency domain dielectric response (FDS), the nonlinear changes in FDS of oil-paper insulation will affect the accuracy of insulation assessment. Therefore, it is necessary to study the nonlinear changes in the FDS of oil-paper insulation with different ageing degree. The multiple sets of oil-paper insulation models with different ageing degree were prepared in laboratory, and the nonlinear FDS of oil-paper insulation were tested at different temperatures. The results show that the larger the test excitation amplitude, the more significant decrease in the low-frequency range of FDS curve. As the testing temperature and ageing degree increase, the characteristic frequency range of the dielectric loss factor curve showing non-linear changes moves towards the high-frequency direction. On the basis of the modified Davidson-Cole model, the shape parameters in the model were obtained by curve fitting calculation, and then the equivalent circuit model based on the transfer function was established. The nonlinear variation of the impedance modulus of oil-paper insulation was simulated and calculated. According to the simulation results, the circuit parameters of various impedance models are closely related to the nonlinear changes of the dielectric properties of oil-paper insulation, while the change of impedance makes the curve change in the corresponding frequency range.

The voltage endurance coefficient n of XLPE insulation can characterize the electrical life characteristics of the insulation, and the n value can be obtained by analyzing the failure data obtained from the accelerated life test. However, the accuracy of the n value is affected by the applied field strength in the accelerated life test and the analysis method of the failure data obtained in the test. In this paper, the evaluation method of voltage endurance coefficient n was studied. The constant stress test and the step stress test were conducted on XLPE insulation samples, respectively, and a test data analysis method based on damage eigenvalues was proposed. This method established the mapping relationship between accumulated damage threshold (D_c) and n in the test through the damage matrix, and used the change of matrix rank as the selection criteria of n value. The results show that according to the proposed method, the XLPE insulation voltage endurance coefficient n₂ obtained in constant stress test is 12.43 and n₃ obtained in step stress test is 12.04, which compare with the XLPE insulation voltage endurance coefficient n₁ of 12.83 obtained by linear fitting, the difference is only 3% and 6%. Moreover, the proposed method can save more than 75% of the test time, which verifies the effectiveness of the method.

Space/surface charge accumulation is a potential cause for the decrease of surface flashover voltage of DC GIL insulators. Applying nonlinear conductive coating is an effective method to improve the surface insulation performance. In this paper, a mathematical model was established for the regulation of space/surface charge and surface electric field of insulator by electric field dependent nonlinear con-ductive coating. The nonlinear relationships between the current density of insulating gas and the solid conductivity of insulator and the electric field intensity were comprehensively considered. The internal charge distribution law of insulator under temperature gradient distribution and the influence mechanism of nonlinear conductive coating on the surface charge accumulation of insulator were studied through this model. The results show that the nonlinear conductive coating promotes the dissipation of space charge obviously, and the homopolar charge near the high voltage electrode dominates the surface charge distribution. Due to the improvements of surface charge distribution and tangential electric field, the surface flashover performance improves. The positive charge may accumulate between the insulator and the coating interface, and decrease gradually from the high voltage electrode to the ground electrode.

In order to study the influence of ageing status of oil-paper insulation of EMU on-board traction transformer on its residual life, the dissolved gas content in oil was used as the characteristic parameter to reflect the ageing of oil-paper insulation in this paper. Since the ageing process of oil-paper insulation has dynamic characteristic, a hidden Markov model was established according to the corresponding hidden state and observation state between the ageing status of oil-paper insulation and the characteristic parameters. Firstly, the number of hidden states is determined using Bayesian information criteria, and then the observation sequence is clustered by using the k-Means algorithm. On this basis, the state of the observation sequence is identified by the Viterbi algorithm to determine the ageing state of oil-paper insulation. Finally, the reliability function is determined by combining the proportional risk model. The accuracy of the model is verified according to the online monitoring data of the dissolved gases in the oil of on-board traction transformer of CRH2 EMU, and it is obtained that the remaining life of the oil-paper insulation is basically consistent with the actual life, which can provide theoretical reference for the subsequent development of traction transformer maintenance strategy.

In this paper, the rotating disc electrode atomic emission spectrometry (RDE-AES) was used to determine the content of 21 mental and pollution elements such as silver, aluminum, and barium and other pollutants in transformer insulating oil. The influences of the immersion depth of disk electrode and the homogenization method of oil sample on the test results were investigated, and the test method was verified with the standard oil and insulating oil samples. The results show that when the immersion depth of disk electrode is 1/3 of its diameter, the relative error of the detection results is small after 3 min of ultrasound and vigorous shaking. The detection limits of each elements is 0-1.07 μg/g, the relative standard deviations (RSD, n=6) are 0.7%-2.9%, and except for element V, the recoveries of the other 20 elements are 96.64%-110.01%. The element P content in insulating oil was used to evaluate the class A and class B uncertainties, and the uncertainty of each component was synthesized and expanded to obtain an uncertainty of (8.34±1.06)μg/g, (k=2). The uncertainty mainly comes from the standard oil, measurement repeatability, and daily standardization processes.

The circuit breaker nozzle is an important operating insulation component, which has a decisive impact on the opening and closing of circuit breakers. In order to strengthen the quality control of nozzle, the testing conditions of the nozzle material performance were studied. Comparing the tensile property test results of the nozzle material samples with different sizes and different tensile rates, it is found that the dispersion of tensile strength measured with smaller samples and faster tensile rates is smaller. Comparing the electric strength test results of the nozzle material samples under different voltage boosting modes, it is found that the dispersion of electric strength measured by 20 s stepwise voltage boosting mode is smaller. According to the test results, a more reasonable test condition for mechanical strength and electric strength of nozzle materials is selected.

Composite insulators are widely used in the field of power grid because of their superior performance. At present, due to the increase of the number of birds, the situation of bird pecking composite insulators is becoming increasingly serious, and the insulator structure is damaged after bird pecking, which will cause power grid line faults. Therefore, this paper studies the effect of bird pecking damage on the performance of composite insulators, and provides reference for power grid operation and maintenance management. Firstly, the mechanical and electrical properties of composite insulator after bird pecking were analyzed by experiments. Then, the effects of different damage proportions and different damage number on the surface electric field strength and pollution flashover voltage of composite insulators were studied by artificial simulation of bird pecking umbrella skirt damage. Finally, the electric erosion test, acid immersion test, and thermal ageing test of composite insulator sheath were carried out to evaluate the effect of sheath damage on the properties of composite insulator. The results show that the structure of the composite insulator is damaged after bird pecking, and its electrical properties, mechanical properties, and anti-fouling properties will be affected. At the same time, after the sheath is damaged, under the joint action of many factors such as local field strength, moisture, acid, discharge heat production, and mechanical stress, the core rod material deteriorates and degrades, the mechanical properties of the core rod decrease, and there is a risk of abnormal fracture of the composite insulator.

In this paper, a simulation and analysis model was established by finite element software to study the physical characteristics of interturn insulation faults in dry-type air-core shunt reactor windings, and explore the sensitive state variables for easy fault monitoring. Firstly, the "field-circuit" coupling model based on actual reactor was established in the finite element simulation software, and its correctness was verified. Then, interturn insulation faults were set at different layers and heights of its windings, and the variation laws of the total loop current, equivalent impedance, active power loss, and other electrical characteristic quantities with fault positions were studied, the changes of spatial magnetic induction intensity and winding force were analyzed. The results show that the change rate of the studied electrical characteristic quantity varies with the short circuit position between single turns of the winding, which increases from the inner layer to the outer layer in the radial direction, and decreases in the outermost layer, and gradually decreases from the middle to the end of the winding in the axial direction. The spatial magnetic induction intensity and the stress on the faulty winding under the condition of single interturn short circuit of the winding increase obviously, and the change rate of equivalent resistance, power factor, and active power loss are all above 500%, which change obviously and are convenient to obtain, they can be used as online monitoring quantities of interturn insulation fault in dry-type air-core shunt reactor.