The research status and development tendency of semi-alicyclic colorless and transparent polyimide(CPI) film was reviewed from several aspects, including its developing history, important monomers, resins synthesis technology, film production technology, and the practical applications of CPI films in advanced optoelectronic fields. Emphatically, the current hot-topics in the development of semi-alicyclic CPI films were presented, and the future developing trends of semi-alicyclic CPI films were prospected.

As the weakest insulation link of gas insulated substation (GIS), the surface defects of basin-type insulator are the key problems in the research of improving the insulation strength of GIS. This paper firstly introduced the generation and development mechanism of common surface defects of basin-type insulator, such as bubble defects, impurity defects, dirty surface, and crack defects. Secondly, the mechanism of flashover induced by surface defects of basin-type insulator was analyzed and summarized, it is explicit that the surface electric field distribution and surface charge accumulation of basin-type insulator are the important factors affecting the flashover of insulator; In addition, the advantages and disadvantages of the existing diagnosis methods of basin-type insulator surface defects were summarized. Finally, In view of the shortcomings of partial discharge detection methods for basin-type insulator surface defects under power frequency voltage excitation, starting with the voltage mode of partial discharge excitation, the current situation of partial discharge detection methods for basin-type insulator surface defects under different voltage excitation was studied and summarized.

In order to compare the properties of domestic and imported meta-aramid paper for traction motor, we tested and analyzed the structure, mechanical properties, and dielectric properties of domestic paper A and B and imported paper. The electrical properties of stator models using the three kinds of paper were tested. The results show that the structure of paper A is relatively loose, and its tensile strength is slightly lower than that of paper B and imported paper; The elongation at break of the three meta-aramid papers is stably maintained at 17%‒19%. The edge tear strength of paper A and B is generally higher than that of imported paper. The breakdown voltage of paper A is slightly lower than that of paper B and imported paper, but the breakdown voltage of paper A is higher than that of paper B and imported paper after impregnation. This is due to the loose structure of paper A, which is conducive to the entry of insulating paint into the paper to fill the gap. The dielectric loss factor, resistance, capacitance, and withstand voltage performance of the stator models are normal, which shows that the two kinds of domestic meta-aramid paper can replace the imported one as slot insulation and filler strip.

The electret effect can improve the adsorption capacity of the filter membrane for polar impurities. In this paper, BaTiO₃ doped composite nanofiber filter membrane for transformer insulating oil was prepared by combining electret technology with electrospinning process. The electrospinning conditions for preparing PVDF nanofiber membranes with small diameters and pores without beading were obtained by system study on the relationship between electrospinning parameters and the morphology of fiber membrane. And then the regeneration experiment for transformer insulating oil was carried out. The results show that the filter membrane can remove polar substances, and has high specific surface area and high porosity. After doping BaTiO₃ and corona discharge treatment, the filter membrane can be stably charged. The dielectric loss factor and breakdown voltage of the aged insulating oil are significantly optimized after filtering by the BaTiO₃ doped composite nanofiber filter membrane. Compared with other filter membrane electret-doped composite nanofiber membranes, it has better regeneration effect on transformer insulation oil.

In order to master the viscosity, thermal conductivity, electrical conductivity, and dielectric properties of transformer oil with different moisture content from normal temperature to extreme cold, we prepared four samples of 45^# transformer oil with different moisture content, and tested their viscosity, thermal conductivity, electrical conductivity and dielectric properties from +30℃ to -50℃. The results show that with the decrease of temperature, the viscosity of transformer oil increases exponentially, the higher the moisture content, the higher the viscosity of transformer oil. The thermal conductivity is less affected by temperature and moisture content. The electrical conductivity and dielectric loss factor increase at first and then decrease with the decrease of temperature, the higher the moisture content, the higher the peak value of conductivity and dielectric loss factor, and the larger the corresponding peak temperature. While the relative dielectric constant increases approximately linearly with the decrease of temperature, the variation trend of relative dielectric constant of transformer oil with different moisture content is the same and the difference is small.

Dopamine (DA) and 3-glycidoxypropyltrimethoxysilane (KH560) were used to double-layer surface modification of boron nitride nanosheet (BNNS), the effect of the modified BNNS on thermal stability of epoxy-based (EP) insulating materials was discussed combining FTIR, TGA, and SEM experimental test with reactive molecular dynamics simulation. The results show that both methods of grafting KH560 at the end of polydopamine (PDA) and grafting DA at the end of KH560 can modify the BNNS surface successfully, and the double-layer surface modified BNNSs have better dispersion in composites. Besides, the breakdown strength of double-layer surface modified BNNS/EP composites is higher than 31.2 kV/mm. The thermal stability of composites can be obviously improved by double-layer surface modification, the improving effect of grafting DA at the end of KH560 is optimal. The modification of double-layer covalent bond grafting long chains that grafting DA at the end of KH560 can improve the interfacial compatibility, which can enhance the interaction force between BNNN and EP matrix. Moreover, the long chain branch is beneficial to fill the void inside the materials, and so that the thermal stability of composites increases.

In order to improve the heat resistance of the water-soluble silicon steel sheet paint, we prepared water-soluble silicon steel sheets with excellent heat resistance, by adding composite inorganic fillers made of different proportions of precipitated BaSO₄ and inorganic adhesives into water-soluble polyester resin matrix. The mechanical properties, electric strength, and heat resistance of the paint were analyzed. The results show that when the composite inorganic filler disperse in the matrix resin evenly, the pencil hardness reaches to 9H, and the adhesion achieves level 1. With the increase of the proportion of BaSO₄ in the composite inorganic filler, the electrical strength, volume resistivity, and heat resistance increase at first and then decrease. When the mass fraction of BaSO₄ and inorganic adhesive is 5:2, the electrical strength of the paint film reaches a maximum of about 280 kV/mm, and the volume resistivity is as high as 1.5×10¹⁶ Ω·m. The maximum initial thermal decomposition temperature is about 273℃, and the final residual rate is 77%. The performance of the paint is basically unchanged after irradiation, it has stable dimensions and surface resistance after Flinklin burning, it is indicated that the insulating performance is still maintained at high temperature.

During the normal operation of converter transformer, moisture will cause the decline of the electrical performance of oil-paper insulation and accelerate its ageing, resulting in a decrease of life and insulation breakdown. In order to study the influence of moisture on the space charge characteristics and breakdown characteristics of oil-paper insulation under AC and DC composite voltage, we prepared oil-paper insulation samples with different water content, then we used space charge measurement under AC and DC composite voltage to get the influence of moisture content on the space charge characteristics of oil-paper insulation under the voltage forms of AC, DC, and AC and DC composite voltage, and studied the breakdown characteristics of samples with different moisture contents under different voltage types. The results show that the electric field distortion rate of oil-paper insulation under AC and DC composite voltage is greater than that under DC and under AC electric field; as the DC component increases, the increase amplitude of breakdown voltage of the samples with higher water content is significantly lower than that of samples with lower water content, and the electric strength of samples with low water content is more affected by the DC voltage component than that of samples with high water content.

In this paper, a photoelectric joint detection system composed of a photomultiplier tube and an electric field sensor was used to carry out the discharge tests of ball-plate electrode gap with burr of different gap distances under positive switching impulse voltage. Compared with the discharge tests of the rod-plate and that of ball plate, the 50% discharge voltage(U_50%) and the physical characteristic parameters under the initial streamer were obtained and compared. The results show that in the ball-plate electrode gap with burr defects, the initial delay, the field strength jump value, and the light power jump value of the initial streamer are positively correlated; in the initial stage of streamer, the burr can shorten the initial delay of discharge, especially for short gap. After the initial streamer developing, the development law of initial streamer of ball-plate electrode with burr is similar to that of rod-plate electrode gap, and the burr aggravates the development of discharge. For the whole discharge process, the burr defect will greatly reduce the discharge voltage of the ball-plate electrode, so that it is close to the discharge voltage of the rod-plate electrode gap under the same clearance.

The interface pressure between the cable accessories and the body is the key to the stable operation of the cable. In order to study the influence of long-term cooling and heating cycles on the interface pressure of cable accessories, we designed a test system to simulate the operation state of cable using the temperature control mode of cooling and heating cycles. The dynamic thermo-mechanical analysis of silicone rubber materials before and after the experiment was carried out. The results show that the elastic modulus of silicone rubber material under long-term cooling and heating cycles increases significantly at the test temperature. In addition, with the increase of ageing time and ageing temperature, cable accessories deform irreversibly, resulting in the decrease of interface pressure and the sealing performance. The experimental results are verified by finite element simulation of interface pressure based on cable accessory parameters.

Using bipolar repetitive square wave voltage, with the help of ultra-high frequency testing method, the influence of the voltage amplitude, frequency, duty ratio and rise time of repetitive square wave on the frequency domain energy distribution of inverter-fed motor inter-turn insulation discharge was experimentally studied. The results show that that the frequency domain energy of discharge above 0.50 GHz increases significantly with the increase of duty ratio; the energy of each frequency band increases with the increase of the pulse voltage amplitude, and the high-frequency energy above 1.50 GHz continues to attenuate with the increase of frequency; the rising rate of pulse voltage has a significant impact on the energy of the discharge frequency domain. The high-frequency energy of the discharge pulse at 1.00-2.00 GHz increases with the increase of the voltage rising rate. When designing the UHF sensor for PDIV test of inverter-fed motor insulation under high-frequency and steep pulse voltage, the influence of the above-mentioned pulse parameters on the energy distribution in frequency domain should be fully considered to improve the sensitivity and signal-to-noise ratio of the PDIV test.

In this paper, the theoretical basis for ageing diagnosis of XLPE cables based on the electromagnetic wave velocity in cables was elaborated, and the calculating method of average wave velocity according to input impedance spectrum was introduced. Then the effect of uniform ageing and segmented ageing of cables on average wave velocity was studied by simulation, and a method to diagnose cable ageing on the basis of average wave velocity was proposed. Finally, cable models including uniform thermal ageing and segmented thermal ageing were built in the laboratory, and the effectiveness of the above diagnosing method was verified. The results show that the average wave velocity of the accelerated uniform ageing cable and the segmented ageing cable decreases from 166 m/μs to 139 m/μs and 152 m/μs, respectively. The more serious the ageing of cables, the lower the wave velocity in cables. The proposed method can provide more information for ageing diagnosis of XLPE cables.

In order to study the failure mechanism of water-blocking buffer layer in high voltage power cable, especially the electrochemical corrosion characteristics, we analyzed the composition of the white powders from failed cables, and confirmed the production mechanism of different composition in the white powders combining with theoretical analysis and simulation experiments. The moisture absorption characteristics of the buffer layer was tested, and the influence of the water content and current density of the buffer layer on its electrochemical corrosion characteristics was studied. Finally, based on electrochemical impedance spectroscopy, the influence of electrochemical corrosion on the electrical characteristics of the buffer layer was identified, and the evolution rule of the buffer layer from electrochemical corrosion to final ablation was determined. The results show that moisture ingress due to dampness or mechanical damage of the cable sheath causes electrochemical corrosion of the buffer layer and leads to the generation of white powder (consisting of NaHCO₃ and Al(OH)₃) and results in the final failure of the cable. The corrosion rate is closely related to the current density, while the final corrosion degree mainly depends on the moisture content of the buffer layer.

In order to solve the problem that the cable capacity much lower than the design standard due to the high thermal resistant environment in the running process of duct cable laying, this paper developed the cable pipe materials that graphene microchip and graphite flake modified HDPE (PG-GNPs-HDPE) with high thermal conductivity, then established a simulation model and verified the improving effect of using the high thermal conductive pipeline of PG-GNPs-HDPE under the common duct laying condition of the current urban distribution network. The results show that compared with the ordinary HDPE pipe, the carrying capacity of 110kV 500mm² cable group with 2×4 laying is increased by 9.32% after using PG-GNPs-HDPE high thermal conductivity pipe; for 10 kV 3×400 mm² cable group with 3×4 laying, the carrying capacity increases by 7.42%.

In order to explore the influence of high voltage cable oil filled terminal grounding system defects such as lack of copper net and lead seal defects of on the voltage and current of oil filled terminal, we built an RLC equivalent model of oil filled terminal. On the basis of capacitance parameters and test parameters computed by COMSOL, the change of terminal voltage and current characteristic under the defects was analyzed, and then it was verified by actual fault cases. The results show that the loss of copper net leads to the grounding failure of the outer semi-conductive layer, and the voltage of the outer semi-conductive layer increases significantly, results in the discharge. The lead seal fracture leads to the unreliability of the connection between the aluminum sheath and the tail pipe, results in the voltage suspension of terminal aluminum sheath, and causes the discharge between the aluminum sheath and the buffer layer under long-term operation. Defects between the lead seals reduce the contact area between the aluminum sheath and the lead seal, the minimum allowable contact area at the lead seal is about 10%.

Natural ester insulating oil is a kind of environmentally-friendly liquid dielectrics with good insulation properties, and it has been generally applied in oil-filled electrical equipment. Investigating the types and contents of fatty acids in different natural ester insulating oils will be beneficial to grasp the physical and chemical properties of different insulating oils. In this paper, a method of determining the fatty acid composition in natural ester by ¹H-NMR was presented, and the results were compared with that of GC-MS. The results show that this simple and rapid determination of fatty acid content in natural ester insulating oil by ¹H-NMR is feasible and reliable. The maximum error absolute value of fatty acids content measured by ¹H-NMR spectroscopy and GC-MS is 2.95%, which is in the tolerance interval.

During the operation of high-voltage DC cables, space charge generates in the insulation layer, it leads to electric field distortion and even insulation breakdown. In order to study the effect of space charge in the actual operation of cable, we obtained the temperature field of high-voltage direct current submarine-land composite cable under the conditions of rated current, maximum steady-state current, and short-term overload current, respectively. According to the simulation results, the temperature difference in the space charge test was set as 10℃, 20℃, and 40℃, respectively, and then the temperature field of 400 kV high-voltage DC cable under different condition was simulated. The results show that the temperature difference between the two sides of XLPE insulation layer is 8.1℃ and 18.7℃under rated current and the maximum steady-state current, respectively; while the temperature difference is 61.1℃ under the short-term overload for 1 hour; and that is 41.1℃ under short-term overload for 36 hours. The experimental results show that the temperature gradient enhances the accumulation of heteropolar charge at the low temperature side of positive pole of XLPE, which leads to the distortion of electric field. Through the correction computation of the electric field distortion rate, it is found that the maximum electric field distortion rate has a linear relationship with the average electric field strength. With the increase of temperature gradient, the electric field distortion rate also increases. The maximum electric field distortion rate is 1.68 under the temperature gradient of 40℃ with the applied electric field of 50 kV/mm.