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.

Epoxy molding compounds (EMC) play important roles in packaging of chips for electrically controlling systems of electric vehicles (EV). The increasing working temperature of EV controlling system puts forward higher and higher requirements for the thermal stability of traditional EMC materials. In this paper, the progress on the high temperature resistant molding compounds at home and abroad in recent years was reviewed, and the development status of high temperature resistant resins and the progress of high temperature resistant resins modified traditional epoxy resin based EMC materials were described. Especially, the development status of high temperature resistant EMC materials modified by bismaleimide (BMI), cyanate ester (CE), and polybenzoxazine (PBZ) and phthalonitrile (PN) based molding compounds were reviewed. Finally, the future development trend of high temperature resistant molding compounds for packaging of electronic control chip in EV was prospected.

In this paper, the research status and future developing trends of polyimide (PI) film carrier materials for flexible solar cells was reviewed. The basic structure of flexible solar cells, the property requirements of substrate materials and the research and application status of PI flexible substrate were introduced. Emphatically, the research and application progress of high temperature resistant PI films for the substrate-types flexible solar cells and the colorless and transparent PI films for the superstrate-types flexible solar cells were reviewed. At last, the future developing trends of PI film substrate materials for advanced flexible solar cells were prospected.