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.

The conventional properties, viscosity characteristics, gel characteristics, storage stability of YD319G3 epoxy modified unsaturated polyester impregnating varnish and its application in the partial model product of direct drive permanent magnet synchronous wind turbine generator were studied. The results show that the YD319G3 impregnating varnish has low toxicity and low volatility characteristics, which can meet the requirements of VPI insulation treatment process for large wind turbines, and the impregnated model and product have good insulating properties. It is a suitable impregnating resin for the VPI treatment of wind turbines.

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.

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.

The space charge accumulation and dissipation characteristics of the oil-paper insulation systems composed of different types of transformer oils were studied under the conditions of applying and removing different intensity of DC electric field. The results show that compared with paraffin-based transformer oil, the naphthenic transformer oils have higher naphthenic hydrocarbon content, more suitable aromatic hydrocarbon content, and higher charge transfer rate, and the oil-paper insulation systems composed by them has less charge accumulation and the charges dissipates more easily after applying and removing the high voltage DC electric field, which is beneficial to the dissipation of charge in oil-paper insulation for converter transformer.

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.

Partial discharges (PDs) in electrical equipment are normally detected with 50 Hz AC sinusoidal voltage stimulus in an online situation, but can also be measured at other non-sinusoidal and non-power frequency stimuli in off-line situations. In this work, three types of non-sinusoidal voltage waveforms, which are symmetric triangular-wave, symmetric trapezoidal-wave, and approximately square-wave voltages, were applied to investigate the effect of ambient temperature on the PD activity produced in an air gap between mica-epoxy surfaces, in combination with the frequency-domain dielectric spectroscopy (FDS) measurement of mica-epoxy dielectric. The results show that the PD inception voltage (PDIV) decreases greatly with the increase of temperature at three types of applied voltages. The PD behavior at symmetric triangular-wave and sinusoidal-wave voltages shows no obvious changing with the increase of temperature. With the increase of ambient temperature, the average PD charge exhibits regular increasing trend and the increment has almost proportional relation with the increasing rate of applied voltage; the maximum PD charge has the largest value at approximately square-wave voltage and also shows the increasing trend. The most obvious effect of temperature on PD activity lies in the constant voltage period of applied voltage. In this period, the average PD number and average PD charge both exhibit almost exponential increasing trend with the increase of temperature.

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.

The ageing characteristics of composite insulators are often obtained by the accelerated ageing test at laboratory, but this method is difficult to simulate the actual complex environment, and the equivalence between accelerated ageing and natural ageing need further verification. In view of this, we selected 153 composite insulators in operation with different operating years and operation environments in Ningxia area to conduct multiple tests, and studied their natural ageing characteristics from three aspects, including the physical and chemical properties of silicone rubber material, the electrical properties and mechanical properties of insulator. The results show that the operating years, pollution degree, and pollution composition are the main factors affecting the ageing of silicone rubber material, and the chemical pollution can accelerate the ageing of materials. Under the same operating years, the ageing degrees of electrical and mechanical properties of insulator are lower than that of the electrical and mechanical properties of silicone rubber material. The mandrel of insulators operating for more than 15 years in heavy pollution areas can still maintain good performance. The junctions of mandrel and sheath, mandrel and hardware are the weak points of the electrical and mechanical properties of insulator, respectively. The manufacturer formulation and process are the important factors affecting the natural ageing, and there will be agglomeration performance degradation in low-quality batches. In the operation and maintenance sampling inspection of composite insulators, it is necessary to pay attention to the insulators with long service life in the heavy pollution area or chemical pollution area, and the composite insulators in operation with performance aggregation degradation from the same manufacturer batch need to conduct supplementary sampling inspection.

This paper introduces the research and application of polymer insulating materials in power module packaging, including silicone gel, epoxy potting adhesive, epoxy molding compound, plastic frame and other materials, and their performance indicators and research status at home and abroad were elaborated. Finally, the application direction of polymer insulating materials in power module packaging was prospected, including optimizing the use process, improving the stability and insulation performance, developing materials with temperature shock resistance, low linear thermal expansion coefficient, and high dielectric strength and studying new applications technology.