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.

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.

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.

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 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.

Multilayer ternary composite polypropylene (PP) films with different content of nano-ZrO₂ particles were prepared with a ternary composite PP film constructed by maleic anhydride grafted PP and nano-ZrO₂ particles as the outer layer and neat PP film as the middle layer, and their physical and chemical properties as well as electrical properties were measured. The results show that the nano-ZrO₂ exhibit good dispersibility in ternary composite PP system and there is a distinct interface between ternary composite PP film and neat PP film. The crystallinity of multilayer ternary composite PP films is higher than that of the single layer neat PP film. With the increase of nano-ZrO₂ content, the dielectric constant of the multilayer ternary composite PP film increases, while the DC electric strength increases at first and then decreases. When the mass fraction of nano-ZrO₂ reaches 1.0%, both the DC electric strength and energy storage density achieve the highest value (424.3 kV/mm and 2.14 J/cm³), which are about 10.6% and 31.3% higher than those of the single layer neat PP film. Besides, the dielectric loss factor of multilayer ternary composite PP film remains at the same level of 10^-3 as that of neat PP film. The ternary composite PP and interlayer interface can jointly suppress the migration of heteropolar space charges, which contributes to improve the internal electric field distribution of dielectric, increase the electric strength, and reduce the dielectric loss caused by electron migration.

In this paper, a multi-source partial discharge diagnosis method based on joint detection of pulse current method and ultraviolet pulse method was presented. A multi-source partial discharge experimental platform of switchgear was constructed for four basic defect models. The characteristics of partial discharge information obtained by joint detection were extracted and a database was constructed, and then the discharge types were identified by k-nearest neighbor (KNN) algorithm and directed acyclic graph SVMs (DAG-SVMs) algorithm. The results show that the change of discharge number and discharge quantity in discharge pattern measured by pulse current method are related to the defect type in model. The existence of void and surface defects will increase the discharge quantity and pattern symmetry, and the existence of corona defect will increase the discharge number. The discharge pulse number measured by ultraviolet pulse method is related to the defect number in multisource discharge model and the ratio of ultraviolet to visible light. The higher the number of defects and the ratio of ultraviolet to visible light, the larger the discharge pulse number. The recognition accuracy of the KNN algorithm can reach up to 99.67%.

Electron irradiation in the Geosynchronous orbit (GEO) will cause charge accumulation in aerospace insulating materials, which may cause electrostatic discharge of dielectric, while the electrostatic discharge will also affect the charge accumulation. In this paper, the joint measurement experiment of potential distribution and electrostatic discharge current was carried out on polyimide film materials under electron irradiation, and the surface charging and discharging process of polyimide film materials under the electronic irradiation of harsh GEO environment were studied. The results show that the surface potential of polyimide film is negative polarity under the electronic environment of 15 keV, 0.33 nA/cm², the distribution patterns include unimodal type, multimodal type, crater type, and flat top type, and the unimodal type and multimodal type have the highest discharge number. Short-term multiple discharges will change the potential distribution pattern and make the transformed distribution pattern maintain for a long time. The potential distribution pattern will affect the wavefront time of discharge current signal, while the potential level will affect the half peak time of discharge current signal, and the half peak time of the current signal at low potential level is about 28% higher than that at high potential level.

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.