In order to better use the repetitive surge oscillograph (RSO) method to quantitatively evaluate the turn-to-turn insulation defects of generator rotor winding, we conducted turn-to-turn short circuit simulation tests under different positions, different short circuit coils, and different short-circuit resistance on a real rotor when the generator was being repaired. The response waveform and characteristic waveform of the two poles were obtained by the RSO device. Three characteristic parameters that is voltage deviation rate, time deviation rate, and fault severity factor were proposed to study the characteristic waveform. The results show that RSO can be used to quantitatively evaluate the severity of turn-to-turn insulation defects of rotor, the fault type of rotor winding can be quickly determined according to the amplitude and deviation rate of voltage of characteristic waveform, and the fault location can be basically realized according to the time deviation rate. The voltage amplitude of the RSO characteristic waveform has a linear positive correlation with the number of short-circuit coils, and has an exponential relationship with the short-circuit resistance and the center time, respectively. The fault severity factor has a linear positive correlation with the number of short-circuit coils. According to the analysis results, two methods to quantitatively evaluate the severity of rotor turn to turn insulation defects are proposed, which can be used to accurately evaluate the turn-to-turn insulation status of rotors.

The composite insulation cross arm has the characteristics of light weight and high strength, which can play an important role in reducing the area of the line corridor and strengthening the insulation capacity of the power grid. The electrical insulation performance of the internal insulation interface is related to the safe and stable operation of the power system. In this study, based on IEC 62217:2012, a 144-hour water diffusion test was carried out on the interface specimens of the inner-filled composite crossarm, and the leakage current and breakdown at different stages were measured. Combined with the test results, the insulation crossarm samples were analyzed. Interface ageing characteristics under water diffusion test conditions. The results show that when the water diffusion time is 144 h, the leakage current of the sample is as high as 20 mA, which is 1000 times that of the sample without the water diffusion test, and the interface breakdown time is faster than that of the sample without the water diffusion test. 65%, water molecules have a destructive effect on the interface under the action of high temperature diffusion, and the longer the water diffusion time, the greater the damage to the polyurethane/glass fiber reinforced plastic interface.

When we design and optimize the insulation structure of a DC cable, its electric field distribution characteristics is an important reference basis. A simplified model of 320 kV DC cable was established by COMSOL simulation software, and its steady-state and transient electrical characteristics were studied. Then the reliability of the simulation model was verified by experiments. The result shows that the maximum temperature of conductor and the maximum temperature difference between inner and outer surfaces of insulating layer were used as the constraint conditions, when the ambient temperature is lower than 12℃, the decisive factor of DC cable ampacity is the tem-perature difference between inner and outer surface of the insulating layer (20℃). When the ambient temperature is higher than 12℃, the decisive factor of DC cable ampacity is the maximum operating temperature of conductor (70℃). In the process of simulated switching impulse test, lightning impulse test, and load cycle test under 30℃ of insulation temperature difference, the maximum transi-ent and steady-state breakdown field strength are 58 kV/mm and 25 kV/mm, respectively. According to the performance parameters of DC insulating material, the DC cable structure can meet the design requirements. The test results indicate that the COMSOL multi-physical field simulation has important guiding significance for the structure design of DC cable.

With the development of advanced electronics and high frequency communication technology, polyimide (PI) film faces more and more high thermal conductivity requirements as an important polymer insulating material. The intrinsic thermal conductivity of traditional PI film is smaller, which cannot meet the rapid cooling requirement of electronic components. In recent years, researchers had carried out a lot of researches on thermally conductive PI films and a series of polyimide-based composite films were prepared by adding inorganic thermally conductive fillers. In this paper, we summarized the latest research progress in thermally conductive PI-based insulating films and discussed the relevant thermal conduction behavior. The key factors influencing the thermal conductivity of films, which include fillers types, particle sizes, addition amount, and the interface interaction between fillers and polyimide matrix, were described systematically. In addition, the technical challenges of high performance polyimide-based thermally conductive insulating film materials were summarized and proposed.

The interface of thermal conductive polymer composite matrix and filler can affect the overall thermal conductivity of the composite. However, limited by traditional testing technologies, it is difficult to study the interface thermal conduction mechanism from microscopic view. In this paper, the interface thermal conduction mechanism of boron nitride (BN)/low density polyethylene (LDPE) composites was studied by scanning thermal microscope (SThM), and the interface thermal properties of the BN/LDPE composites were analyzed quantitatively. The test process of SThM was simulated by finite element analysis, and the interface thermal conduction process at the inorganic-organic interface was revealed. The results show that with the increase of BN content, the thermal conductivity of the composite increases. When the mass fraction of the BN reaches 20%, the thermal conductivity of the composite increases by 22%. The sample morphology in micro-nano scale and the voltage distribution image reflecting the thermal properties were obtained by SThM, it is found that the thermal conductivity interface width of the BN/LDPE composite is 150–200 nm. At the area that two BN particles are in contact with each other, the high thermal conductivity area increases, and the thermal conductivity interface width changes little. The fitting curve between thermal conductivity and the square of output voltage is obtained by testing the standard samples, and the interface thermal conductivity of the BN/LDPE composites is calculated to be 0.33–39.81 W/(m·K). The simulation results show that the probe tip can distinguish the filler, interface, and matrix, and the thermal conductivity of the composite increases with the increase of the interface width and thermal conductivity.

The insulating properties of the doubly-fed motor stator coil after different cycles of cold and heat circulation was compared and its service life was assessed under different high frequency voltage to study the cold and hot shock resistance and high-frequency pulse electrical ageing performance of the doubly-fed generator stator coil. The results show that the cold and heat circulation has little effect on the insulating properties of doubly-fed generator stator coil. With the increase of high frequency ageing time, both the dielectric loss factor and its increment increase, and the insulation resistance increases at first and then decreases. The partial discharge inception voltage of the coil after high frequency pulse is smaller than that of the unaged coil, and the high-frequency pulse electrical ageing life of the stator coil is calculated to be more than 30 years.

When installing the cable accessories, we usually coat silicone grease on the interface between silicone rubber (SR) insulation of cable accessories and XLPE insulation of cable body, but the silicone rubber will affect the interface pressure after absorbing silicone grease. The interface pressure between SR and XLPE was studied by combining experiment and simulation methods. The elastic modulus variation of the silicone rubber after absorbing silicone grease was measured by experiment, and then the elastic modulus was distributed to three-dimensional model to conduct simulation. The results show that under the silicone grease environment, the greater the expansion degree of silicone rubber, the greater the mass change rate, and the smaller the elastic modulus. The interface pressure between SR and XLPE decreases with the increase of silicone grease absorption time. The larger the expansion degree of cable joint, the greater the interface pressure, and the faster the interface pressure decline speed. The interface pressure decreases slightly with the increase of friction coefficient.

A micro/nano co-doping epoxy/boron nitride (BN) composite was prepared using micro-BN and nano-BN as fillers, and the variations of thermal conductivity and breakdown characteristics of the epoxy composites with the nano-BN doping content were studied when the total doping content of BN was fixed. The results show that when the total mass fraction of BN is 20%, with the increase of nano-BN doping content, the thermal conductivity of the composite decreases slightly, the power frequency electric strength increases at first and then decreases, and the endurance time of the sample with thickness of 0.2 mm is shortened under the bipolar square wave voltage of 8 kV and 25 kHz. The thermal conductivity of the epoxy composite doped with pure micro-BN is the largest (0.83 W/(m·K)), and its endurance time is the longest (193 s) under high frequency bipolar square wave voltage, which are 277% and 408% higher than that of pure epoxy resin, respectively. When the mass fraction of nano-BN is 1%, the power frequency electric strength of the epoxy composite is the highest (131 kV/mm), which is 27% higher than that of pure epoxy resin. Therefore, for the micro/nano co-doping epoxy composite system, the addition of nanoparticles can improve the power frequency electric strength of composite, but it will reduce the thermal conductivity of the composites and shorten the withstand time under high frequency bipolar square wave voltage.

An oil-paper sample was conducted accelerate thermal ageing treatment, and its ageing process was divided into five ageing stages according to the variation of polymerization degree. Partial discharge tests were conducted on the air gap discharge model, and the PRPD patterns of the oil-paper sample were collected at different ageing stages. The feature quantities were extracted by using statistical operator, the dimension of the original feature data was reduced by factor analysis method, and the clustering characteristics of the feature data before and after dimension reduction were compared. A probabilistic neural network model (PNN) was established to identify the ageing stages of oil-paper insulation, and a back propagation (BP) neural network model and a support vector machine (SVM) model were built as comparison. The three models were trained by the same data, and their recognition results were compared. The results show that ageing will cause pores in the pressboard, which promotes the occurrence of partial discharge. Compared with other models, the FAM-PNN model has obvious advantages in recognition accuracy and operation efficiency. The ageing state of transformer oil-paper insulation can be evaluated accurately and efficiently using the FAM-PNN model.

A ±400 kV HVDC model cable was conducted DC withstand voltage test and impulse withstand voltage test, and the DC breakdown voltage and impulse breakdown voltage of the model cable under the highest operating temperature were obtained. The electric field distribution under DC breakdown voltage and impulse breakdown voltage were calculated. On the basis of average field intensity method and maximum field intensity method, the insulation thickness of ±400 kV HVDC cable was designed, and the electric field distribution of insulation layer was calculated under DC voltage and impulse voltage. At last, the insulation thickness of ±400 kV DC cable was obtained by comparing the electric field distribution of ±400 kV HVDC cable and model cable. The results show that when the insulation thickness of HVDC cables is designed by the average field strength method, the insulation thickness depends on the impulse voltage. When the insulation thickness is designed by the maximum field strength method, the insulation thickness depends on the DC voltage. By comparing the electric field distribution of ±400 kV DC cable and the electric field strength of the model cable when breakdown, it is obtained that the insulation thickness of 400 kV DC cable is 26 mm.