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.

The contamination of DC silicone rubber insulator has an important influence on its insulation performance and service life, and the adverse effects of swelling effect under the insulation cleaning agent is the key issue to be solved. The volatilization rate of two kinds of electrified cleaning agent, the swelling and hydrophobicity of silicone rubber before and after cleaning by different cleaning agents were studied, and the corresponding mechanism was discussed. The results show that the volatilization rates of No.1 (fast volatilization) and No.2 (slow volatilization) electrified cleaning agents at 25℃ are 1 095.78 g/(h·m²) and 108.01 g/(h·m²), respectively. The swelling index of silicone rubber increases with the increase of time, it reaches saturation after 10 h, and the swelling index of the saturated silicone rubber are 55% and 130%, respectively. The hydrophobicity of silicone rubber is weakened by No.1 cleaning agent, and the contact angle decreases by 14% after soaking for 10 min. The hydrophobicity of silicone rubber is enhanced by No.2 cleaning agent, and the contact angle increases by 6% after soaking for the same time. Therefore, the cleaning agent with excellent volatility can reduce the adverse effect of swelling on the silicone rubber insulators, and can provide basis and reference for the electrified cleaning of silicone rubber insulation equipment.

In this paper, the low-temperature plasma was generated by DBD test platform, and the polyimide (PI) nanocomposite film was modified by the low-temperature plasma. The surface morphology, chemical bond structure, surface conductivity, and corona resistance of the nanocomposite film before and after the low-temperature plasma modification were tested to study the change law of the film surface characteristics. The results show that after surface modification, the nanocomposite film surface becomes rough gradually, and there are micropores and discontinuous protrusions appeared. Polar oxygen-rich groups were introduced on the surface by plasma modification with appropriate modification time. With the increase of modification time, the contact angle decreases, the surface energy and surface conductivity increase, and the corona resistance life increases at first and then decreases. When the low-temperature plasma modification time is 10 s, the corona resistance life of the modified nanocomposites film is 15.7% higher than that of the unmodified nanocomposites film. After modified by the low-temperature plasma, the nanocomposite film has more uniform surface than the pure PI film, and the modified nanocomposite film has the characteristics of small surface energy and large surface conductivity. The large surface conductivity will accelerate the dissipation speed of surface charge of the nanocomposite film, avoid the surface discharge produced by the concentration of local field strength, thereby improving the corona resistance life of the film. To obtain the same modification effect, the nanocomposite film need longer low-temperature plasma modification time than pure PI film.

In order to study the ageing process of composite insulator silicone rubber in the hot and humid climate in the southern region, we conducted 300 h, 500 h, and 1 000 h salt spray ageing tests on silicone rubber in the laboratory. The concentration of small molecule groups on the surface of silicone rubber with different degrees was detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS), and the ageing mechanism was analyzed combing the hydrophobicity and scanning electron microscope test results. The results show that Si⁺, C₂H₅⁺, SiCH₃⁺, SiC₃H₉⁺, H^-, CH^-, O^-, and OH^- were detected on the surface of silicone rubber. The hydrophobicity of silicone rubber is positively correlated with the content of small alkyl molecules. The content of small alkyl molecules on the surface of silicone rubber is consumed by drip washing of salt spray, which lead to the decrease of hydrophobicity. In the salt spray atmosphere, oxidation and hydrolysis reactions are reacted on the surface of silicone rubber, which results in the broken of Si-O and Si-C bonds, and Si-OH bonds are formed. The hydroxylation lead to the collapse of silicone rubber three-dimensional network structure and the decrease of polymerization degree. The gases such as H₂ and CH₄, generated by the ageing reaction, would form voids on the surface of silicone rubber, which would cause powders and cracks on the surface of silicone rubber.

In order to realize the detection of surface discharge by the temperature sensor inside the composite insulator sheath, we used silicone rubber plate as research object, and established a thermal model to realize the indirect calculation of surface temperature on the silicone rubber plate based on internal temperature. Firstly, according to the heat transfer theory, a thermal model of silicone rubber plate was established. Considering the influence of nonlinear factors in the process of atmospheric convection, the air convection index n was introduced to modify the model, and the solution method of convection heat transfer coefficient h was proposed. Then, temperature rise tests were carried out to simulate the heating condition of silicone rubber plate surface, and the temperature data of the upper and lower surfaces of silicone rubber plate were measured. The measured value of upper surface was compared with the calculated value of model. The results show that the relative error of the steady-state temperature of silicone rubber plate surface calculated by the model based on internal temperature is less than 10%, which meets the accuracy requirement.

Partial discharge (PD) caused by interface defects is one of the main causes of interface breakdown, but the initiation and evolution of interface PD of cable accessories is not clear now. In this paper, the electric field distribution of actual cable accessory interface was simulated and analyzed. According to the calculation results of electric field, an interface test unit was designed and manufactured using the built-in electrode method, and then the test unit were conducted partial discharge initiation experiments. The results show that the electric field distribution of the interface test unit is similar to that of the actual cable accessory interface, and the PD development law obtained by the interface test unit is the same to that of the actual cable accessory interface. The interface test unit can effectively simulate the electric field of actual cable accessory interface, and at the same time, the introduction of metal electrodes were avoided into the test interface. It is concluded that the test unit can be used to study the initiation and evolution of PD at the cable accessory interface.

SF₆ is often used in GIE as an insulating medium, it will decompose when overheating or appearing partial discharge inside GIE, the decomposition products, such as SO₂, SOF_2, SO₂F₂, H₂S, and CO will produce after further reaction. In this paper, the components H₂S and CO were quantitatively measured by photoacoustic spectroscopy detection technology, and the factors affecting photoacoustic signal were discussed theoretically. A photoacoustic spectrum experiment platform was built, and the gas was measured quantitatively based on the photoacoustic effect. Appropriate gas absorption lines were chosen as characteristic spectrum line to avoid the potential cross-interference of other gas components. According to the results of HITRAN simulation, the characteristic spectrum line of H₂S was chosen as 6 336.6 cm^-1, and the characteristic spectrum line of CO was chosen as 6 380.3 cm^-1. The results show that the linearity between the gas concentration of CO and H₂S and the amplitude of pure photoacoustic signal is extremely high, which suggests that the gas concentration can be accurately calculated through the measurement of photoacoustic signal value of gas. With the background gas of SF₆, the lower limit of detection for CO is 9.88×10^-6, and the lower limit of detection for H₂S is 1.75×10^-6.

In the actual manufacturing and field installation, defects such as air, metal impurities, and uneven distribution are easily introduced into the silicone rubber insulation layer of cable joint, which endangers the safe operation of power grid system. At present, the detection of power equipment defects are mostly destructive tests, and the experimental results can only reflect the overall situation of equipment. As a non-destructive testing technology, ultrasonic testing can accurately locate and image defects inside the material, and reflect the changes of local performance inside the device. In this study, a set of ultrasonic testing platform were independently designed and built, and ultrasonic testing was conducted on the artificial silicone rubber samples with different defects. The results show that for flexible materials such as silicone rubber, ultrasonic testing can better image the bubbles, air gaps, and steel needle defects in the sample. Compared with similar X-ray testing, ultrasonic testing has an obvious amplification on the tiny bubbles defects. In addition, the ultrasonic testing technology can reflect the change of stress and density inside the material, and can accurately locate the specific depth of the defect according to the ultrasonic echo. This technology has broad application prospects in the location identification and online detection of internal defects in the silicone rubber insulation layer of cable joints.

Three typical stator defect models were fabricated using the generator stators in actual operation, and then conducted accelerated thermal ageing tests. The difference on partial discharge characteristics of the three typical defects before and after ageing was studied using pulse current method. The results show that after ageing, the partial discharge inception voltage (PDIV) of the model with internal defect increases, while the PDIV of the model with slot discharge and end discharge decrease, this is because there are large number of cracks on the epoxy mica tape insulation surface due to thermal ageing. The phase resolved partial discharge (PRPD) pattern of internal discharge model is symmetrical, and the width of discharge phase becomes narrow after thermal ageing; the PRPD pattern of slot discharge model changes from hill shape to semi ellipse shape after thermal ageing, and the discharge density increases significantly; the PRPD pattern of end discharge model shows the characteristics of corona discharge, and the discharge characteristics at the positive and negative half-cycle of alternating current is obvious asymmetry.

The effect of nano-Al₂O₃ on the microscopic properties of vegetable insulating oil was studied by molecular simulation, and its result was verified by tests. The mechanism of surface interaction between nano-Al₂O₃ and vegetable insulating oil molecules was analyzed, models of vegetable insulating oil before and after nano-Al₂O₃ modification were established. The hydrogen bond, radial distribution function (RDF) of oil molecule, and diffusion coefficient of water molecule were studied, and the thermal ageing experiment was conducted on vegetable insulating oils with different concentration of nano-Al₂O₃. The results show that compared with the vegetable insulating oil without modification, there are more hydrogen bonds in the modified vegetable insulating model, the peak value of RDF is greater, and the diffusion coefficient of water molecules is smaller. In the process of thermal ageing, the dielectric loss of the modified oil is smaller than that of the unmodified oil, which shows that the nano-Al₂O₃ modified vegetable insulating oil has excellent stability, and its thermal stability and insulation performance are enhanced.