In view of three common defects of 10 kV cables, three-dimensional cable defect models were established and conducted electromagnetic-thermal coupled temperature field analysis to study the transient temperature models of three defective cables. The effects of different operating currents and laying conditions on the temperature of three defective cables were analyzed. The results show that the harm of defects on the cable ranked from high to low is metal tip defect, air gap defect, and scratch defect. Under the same current carrying capacity, the temperature at the metal tip defect is higher than that at the other two defects. It is determined that the heat dissipation effect of tunnel laying is the best when the cable has defects. The internal temperature of the cable without defects decreases gradually from the core to outer sheath in the radial direction, and the internal temperature field of the cable is distorted under the action of defects. The fitting coefficients between core temperature and outer sheath temperature of the defective cable, and the fitting coefficients between temperature at the defect and the core temperature of cable are both close to 1. The simulation fitting results provide theoretical support for the judgment and identification of cable defects.

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 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.

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 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.

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.

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.

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.

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.

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.