Contact method and non-contact method are two commonly used methods to measure relative dielectric constant of polymer films, and the electrode edge effect is one of the unavoidable errors in the measurement process. However, the error caused by the electrode edge effect is difficult to quantify. In order to solve this problem, COMSOL simulation software was used to model and simulate the three-electrode structure, and the errors caused by the electrode edge effect in the contact method and the variable capacitance method of non-contact method were obtained and compared respectively. The results show that the electrode edge effect of the variable capacitance method is much greater than that of the contact method. Taking the edge effect less than 0.50% as the standard, when the film thickness is less than 40 μm, the electrode edge effect of the contact method can be ignored, while for the variable capacitance method, only the film thickness is less than 30 μm, the electrode edge effect can only be ignored.

Aimed at the problems of low resolution and high data redundancy in traditional defect location functions, we proposed a cable defect location method based on Z transformation of reflection coefficient spectrum. Firstly, a reflection coefficient spectrum model of cable was established by the transmission line theory, and the feasibility of locating cable defect by the reflection coefficient spectrum was analyzed. Then, the principle of Z transformation was introduced. On the basis of reflection coefficient spectrum characteristics, the parameter values in Z transformation algorithm were determined, and a new cable defect localization function was constructed. The simulation and test results of defect location experiment show that compared with the traditional methods, the proposed cable defect location function has higher resolution and lower data redundancy, which can locate cable defect more accurately and reduce the effect of interference peaks, providing a new idea for cable defect location.

In order to improve the reliability of interlayer gap discharge faults diagnosis in winding, taking a hydrogenerator stator winding as the experimental object, the influencing factors of diagnosing interlayer gap discharge through partial discharge were studied. Firstly, the characteristics of interlayer gap discharge in winding under the superposition of multiple discharge sources were obtained through offline test, online test, and simulation test. Then, by simulating the electrical conduction attenuation of bar and combined with the generator winding structure and detection distance, the effect of detection distance on the detection results was analyzed. The results show that the winding interlayer gap discharge has independent characteristics, the pulse distribution is suspended in PRPD pattern and has symmetrical positive and negative polarities. The pulse peak values are located around 45° and 225°. In one phase, the positive and negative polarity pulse peak values simultaneously deviate to the right of 45° and 225°, while in the other phase, the positive and negative polarity pulse peak values simultaneously deviate to the left of 45° and 225°. When the winding structure is different, the distribution of discharge gaps and the length of lead ring are also different, resulting in significant differences in detection distance, which has great effect on the amplitude detection results of partial discharge signals. If only electrical conduction is considered, for every one meter increase in detection distance, the average attenuation of partial discharge amplitude is approximately 10%. When only one closer phase can detect gap discharge, the interphase analysis method fails. Even there are multiple discharge sources and gap discharge simultaneously in winding, the interlayer gap discharge can be identified through the suspended characteristics of gap discharge PRPD pattern. The detection range has an impact on the identification of partial discharge patterns. When the global spectra with large range is complete, while the local patterns overlap with each other, the specific faults cannot be identified. When the global spectra with small range is incomplete, while the local patterns are clear, the specific faults can be identified.

In this paper, the basic research and application progress of high temperature resistant epoxy molding compound (EMC) at home and abroad in recent years were reviewed. The property requirements of advanced power electronics on the molding compound, the high temperature degradation mechanism of traditional EMC, the relationship between structure and thermal stability of EMC, and the modification pathways for improving the thermal stability of EMC were presented. Especially, the development status of multi-aromatic ring (MAR) and naphthalene-containing EMC were reviewed. At last, the future development trends of high temperature resistant EMC for power electronic packaging were prospected.

In this paper, the developing history of polyesterimide (PEsI) materials, key monomers for synthesis, synthesis techniques of PEsI resins and their applications in electrical insulation, microelectronic packaging, flexible printing circuit board, liquid crystal display, flexible display, and wireless telecommunication fields were introduced. The development status of colorless and transparent PEsI film and low dielectric PEsI film were mainly reviewed. At last, the future developing trends of PEsI materials were prospected.

In this paper, a test platform for partial discharge characteristics and flashover characteristics of insulation molding parts for power transformer was built, and the distribution laws of partial discharge initial field strength, partial discharge initial discharge quantity, partial discharge extinguishing field strength, and surface flashover field strength of different insulation molding parts were obtained. The results show that the partial discharge initial field strength of insulation molding parts decreases with the increase of electrode spacing. When the electrode spacing increases from 10 mm to 25 mm under parallel components, the partial discharge initial field strength decreases by about 40.6%. The partial discharge initial discharge quantity under different components is 8.51-13.70 pC. Under the parallel component, the partial discharge initial field strength of insulating strip and insulating spacer is 2.55-2.85 kV/mm and 1.43-1.78 kV/mm, respectively. Under the vertical component, the partial discharge initial field strength of insulating strip and insulating spacer is 2.65-3.35 kV/mm and 4.31-5.49 kV/mm, respectively. The surface morphology of different insulation molding parts has a significant impact on their surface flashover characteristics. The denser and larger the surface embossed grooves, the better the effect of hindering the development of surface discharge. On the basis of test sample database, a comprehensive performance evaluation method for insulation molding parts based on entropy weight method is proposed. The weight of different performance indicators, which is determined by using four indicators of discharge characteristics of insulation molding parts, as well as the dispersion degree of apparent density and size deviation, is used to evaluate the comprehensive performance of different insulation parts, and the rationality of this evaluation method is verified.

In view of the voltage dip/swell in the power system, a programmable power supply was used to modulate the applied voltage, and the effect of voltage fluctuation on the internal partial discharge characteristics of epoxy resin was analyzed. The results show that the voltage fluctuation will lead to the change of partial discharge pattern of air gap, which exhibits asymmetry in positive and negative half cycles. The greater the applied voltage fluctuation, the more significant the asymmetry of partial discharge. The reason for the change of partial discharge pattern is due to the combined effect of external electric fields and surface charges accumulated inside the air gap. On the one hand, the electric field generated by surface charges can overlap the applied electric field to adjust the total electric field in air gap. On the other hand, as the discharge continues, the dissipation and neutralization of surface charges can also affect the total electric field in air gap, resulting in the partial discharge exhibit asymmetry in positive and negative half-cycle of the applied voltage.

In order to select an appropriate cable joint insulating materials to improve the electric field distribution in joint, the effects of the conductance temperature and field strength dependence characteristics of silicone rubber of common joint insulating material on the electric field distribution in prefabricated joint of XLPE DC cable were studied. Firstly, a simulation model was constructed according to the prefabricated joint structure of 10 kV XLPE insulated DC cable. Secondly, through changing the conductance nonlinear characteristic parameters of silicone rubber, the electric field distribution in the joint insulation with full load condition was obtained. The results show that with the increase of the conductance activation energy or the decrease of the conductance field strength dependency coefficient of silicone rubber material, the field strength at the joint insulation interface increases, and the field strength at stress cone root increases obviously. From an economic point of view, the recommended values of the ratio of conductance activation energy of silicone rubber and XLPE insulating materials and the ratio of their conductance field strength dependency coefficient are not higher than 0.95 and not lower than 0.50, respectively, which can provide reference for the selection and determination of suitable joint insulating materials in engineering.

Three brands of commercial cross-linked polyethylene insulating materials for high-voltage cables were selected as the research objects. At first, the scorching resistance of three insulating materials was compared and analyzed by the change rule of melt torque of insulating materials with temperature under the action of high temperature shearing, and the scorching degree of the scorched sample was characterized by the gel content. Then, the method of using the torque change rate of insulating material melt under high temperature as the characteristic quantity to characterize the scorching resistance of insulating material was proposed, and the effectiveness of this method was verified by characterizing the scorching degree of different brands of commercial insulating materials. In addition, the crosslinking agent content and antioxidant content in the three insulating materials were compared and analyzed by infrared spectrum, and the correlations between the additive content of insulating material, the molecular weight of base material, and its scorch resistance were established on the basis of molecular weight of insulating material base material measured by gel permeation chromatography. The results show that the scorching resistance of different commercial insulating materials can be effectively distinguished by the torque analysis on insulating materials under the action of high temperature shearing. It is found that the high content of crosslinking agent is the main reason for the poor scorching resistance of insulating materials, and the scorching resistance of insulating materials can be improved by appropriately reducing the crosslinking agent content, increasing the antioxidant content, and reducing the weight average molecular weight.

In this study, a method of using ultrasonic technology to detect the internal defects of composite insulator silicone rubber for high-voltage transmission lines was proposed. Taking composite insulator silicone rubber samples with different internal defects as the research object, a phased array ultrasonic probe with 1/4 wavelength of sound transmission layer thickness was selected, and the samples were conducted multi-angle scanning and non-destructive testing by direct contact method. A two-dimensional cross-section finite element model of samples was constructed by ANSYS software to analyze the defects. Then, the detection accuracy of internal defects of composite insulator silicone rubber was improved by reducing the influence of blind spots and sidelobes and improving the resolution ratio. The results show that the ultrasonic waveforms of defective silicone rubber samples differ greatly from that of normal silicone rubber sample. The internal damage or structural penetration defects of composite insulator silicone rubber can be effectively detected by the ultrasonic technology, and the location of defects can be accurately located. The metal fittings on composite insulators will affect the accuracy of ultrasonic detection.