Mechanical impact is an important factor that damages the stator bar insulation material. At present, systematic researches on the damage of stator bar insulation materials by mechanical impact are still lack. In this paper, the effect of mechanical impact on the stator bar insulation material was studied by combining the finite element simulation and experiment. The results show that when the insulating material is subject to mechanical impact, the average equivalent stress-strain and electric strength firstly increase or decrease, and then become stable within a certain impact strength range under the same punch structure. Under the same impact strength, both the average equivalent stress-strain and electric strength increase with the increase of the tip area of punch head. The correlation between the average equivalent stress-strain and the electric strength can be used to evaluate the insulation damage of stator bar caused by mechanical impact.

In order to study the ablation mechanism of buffer layer of corrugation aluminum (Al) sheath high voltage cross-linked polyethylene (XLPE), firstly, we analyzed a ablation failure of 110 kV XLPE insulated cable, and proposed that the concentrated radial current was the cause of ablation failure. Secondly, a simulation model of the faulty cable was established. The current density and its distribution of the contact part of buffer layer and corrugated Al sheath were simulated, and the simulation results were proved by model experiment and calculation. It was found that the size and distribution of radial current were affected by the embedded depth of Al sheath in the buffer layer and the volume resistivity of the buffer layer. Finally, simulation experiments were designed to prove that the radial current concentrated was one of the causes of buffer layer ablation, and the experimental conditions of the simulated ablation experiment were controlled in the thermostat. The surface morphology of the experimental sample and the ablated Al sheath were compared by optical microscope. The results show that the ablation process in the ablation experiment is the same as that in the actual faulty cable, and with the increase of the current density in buffer layer, the ablation start time decreases. This paper reveals the physical mechanism of radial current concentration in the ablation fault of corrugated Al sheath, which provides guideline for relevant fault diagnosis and protection.

In order to study the ablation mechanism of buffer layer in cable, we analyzed the change of contact state between buffer layer and aluminum sheath according to the defect phenomenon, and then a circuit model was established to analyze the defect. According to the model, the induced voltage of insulation shielding layer and the main factors affecting the induced voltage were analyzed. A 15 m defective cable sample was intercepted from the breakdown accident line, and a partial discharge detection experimental platform was built with the defective cable sample. The results show that the induced voltage of insulation shielding layer is directly proportional to the number of defects, the resistivity of composite layer, and the thickness of white powder at the defect, and is inversely proportional to the contact area between buffer layer and aluminum sheath, and the discharge signals inside the defect cable have obvious characteristics of poor contact discharge.

In order to verify the applicability of DGA fault diagnosis methods in oil-filled submarine cable, we chose domestic dodecylbenzene (DDB) insulating oil as research object. First, the decomposition temperature of DDB insulating oil was determined by thermogravimetric test under different heating rates. Subsequently, a test system was built to carry out thermal fault simulation tests of DDB pure oil, oil-paper, and 25^# mineral oil at 150, 250, and 350℃. After test, the percentage of five characteristic gases (H₂, CH₄, C₂H₆, C₂H₄, C₂H₂) dissolved in the fault oils was measured to study the gas production law of DDB insulating oil under thermal fault. Finally, existing DGA diagnostic methods (classic Duval triangle, quadrilateral graphic method) were selected to analyze the gas data. The results show that the proportion of C₂H₄ dissolved in DDB insulating oil under thermal fault increase significantly with the increase of fault temperature, and the proportion of C₂H₄ in mineral oil is at a low level in the whole temperature range. In the thermal fault diagnosis, the classic Duval triangle and quadrilateral graphical method can detect thermal faults by the dissolved gas in DDB insulating oil, but the temperature range of thermal fault cannot be determined accurately, and the fault boundary need to be further modified.

High voltage power cables demand stable and reliable connections with the power system through cable accessories, and silicone rubber (SIR) and ethylene-propylene-diene monomer (EPDM) are the main reinforced insulation materials for cable accessory due to their excellent dielectric properties and mechanical properties. However, with the continuous improvement of high voltage transmission level, the electrical properties of cable accessories also need further development. In this paper, the research status inside and out of China was summarized, then the factors affecting the electrical properties of SIR and EPDM for high voltage cable accessories were discussed. The research progress in improving method of electrical properties were analyzed, and the research progress in the interfacial electrical properties of double-layer dielectric was introduced. At last, the research difficulties of electrical properties modification of rubber reinforced insulation for high voltage cable accessories were summarized, and the research trends of the rubber insulating materials for high voltage cable accessories were prospected.

The fault type recognition and condition assessment play the crucial roles in fault diagnosis and maintenance. Different defects will produce partial discharge signals with difference, and the partial discharge signal also changes with the defect severity and the evolution of partial discharge. This situation can be regarded as pattern recognition of different severity levels and evolution stages, and the pattern recognition is a typical classification problem. In this paper, classification problems such as pattern recognition and state assessment were reviewed. Compared to classification results based on mathematical statistics, artificial intelligence has achieved nearly 100% of recognition accuracy. However, there are still some shortcomings in current research, this paper gives some solution strategies and prospects future research direction.

In order to obtain a silicone rubber composite with both good resistivity nonlinear characteristics and high electric breakdown characteristics, a copper calcium titanate (CCTO) ceramic powder was prepared, and the CCTO was mixed with two-component liquid silicone rubber to prepare CCTO/silicone rubber composite (the volume fraction of CCTO ceramic powder was 3%, 5%, and 10%, respectively). Their microstructure, dielectric spectrum characteristics, DC breakdown performance, and DC nonlinear resistivity were tested, and their application performance was compared by establishing a high-voltage DC cable terminal simulation model. The results show that the CCTO ceramic powder has obvious characteristic diffraction peaks, and the powder particle size is about 500 nm; with the increase of CCTO ceramic powder content, the dielectric constant of the CCTO/silicone rubber composite increases, the DC breakdown strength decreases, and the non-linear characteristics of resistivity are significantly enhanced. With the enhancement of the nonlinear characteristics of resistivity, the electric field strength in the reinforced insulation of cable terminal stress cone decreases significantly. When the volume fraction of CCTO ceramic powder in the composite is 5% or 10%, the composite can be used as a reinforced insulating material of stress cone for high voltage DC cable accessory.

A MWCNTs/T-ZnOw/PVB composite was prepared via solution blending method by using multi-walled carbon nanotubes (MWCNTs) and zinc oxide whisker (T-ZnOw) as fillers and polyvinyl butyral (PVB) as matrix. The thermal diffusivity of the composite was measured by transient electro-thermal technique (TET). The effects of different mass fraction ratio of fillers, heat treatment time and temperature, and ultraviolet accelerated ageing on the thermal conductivity of the composite were investigated. The results show that under the same mass fraction of fillers, the thermal conductivity of the composite increases at first and then decreases with the increase of MWCNTs content. When the heat treatment time is 1 h, with the increase of the heat treatment temperature from 80℃ to 140℃, the thermal conductivity of the composite decreases at first and then increases. When the heat treatment temperature is 140℃, the thermal conductivity increases after heating for 1 h, but it decreases with the extension of heating time. When the composite is accelerated aged by ultraviolet irradiation, the thermal conductivity of the composite decreases with the increase of irradiation time.

In order to research the influence of processing temperature of master-batch on the properties of HVDC cable insulation, three kinds of master-batch were prepared at different processing temperatures, and then the insulating properties of HVDC cable insulation manufactured by the master-batch were studied. Impurity detection was carried out at first, and then the chemical structure of crystal points detected by impurity detection was analyzed by attenuated total reflectance infrared spectroscopy (ATR-IR). At last, the electrical and mechanical properties of three HVDC cable insulation were compared. The results show that there are more crystal points detected in the HVDC cable insulation prepared by the master-batch under an excessive processing temperature, and part crystal points are light yellow. Compared with semitransparent crystal points, there is no strong absorption peaks in the infrared spectra of light yellow crystal points, but the excessive processing temperature has a greater negative effect on the electrical properties of HVDC cable insulation, while has a smaller effect on its mechanical properties.

A high temperature resistant insulating varnish for traction motors was prepared by modifying polyester-imide insulating varnish with meta-aramid resin. The effects of meta-aramid resin on the adhesion, electrical properties, flame retardancy, and heat resistance of the insulating coating were studied. The results show that when the content of meta-aramid resin is 15%, the electrical strength, the adhesion, the oxygen index of the insulating coating reaches 65 kV/mm, 12.9 MPa, 28.7%, respectively. After high temperature test at 220℃ for 500 h, the paint film shows slight discoloration without cracking and peeling off, which can meet the requirements of the traction motors.