Partial discharge often occurs due to condensation on the surface of insulator inside the switchgear of box-type substation at the bottom of the wind turbine tower, which seriously threatens the operational safety of equipment. In order to further understand the electric field distribution and discharge process on the surface of epoxy resin with condensation, we used artificial spray condensation was to simulate the natural condensation process in this study. The influence of condensation on the electric field distribution of the insulation surface was simulated and analyzed when the electric field non-uniform coefficient was changing. The spectrogram of partial discharge on the epoxy resin surface under different condensation amount was measured, and the change law of the insulation surface discharge was further discussed. The results show that the artificial spray condensation can quantitatively simulate the condensation amount on the insulation surface under natural condensation. Condensation at different locations can cause the distortion of partial electric field, leading to the accumulation and increase of surface charges on the discharge path, which increases the possibility of partial discharge. When the non-uniformity coefficient of surface electric field is larger, the partial discharge initial voltage is lower, and partial discharge is easier to occur. The increase in the adhesion amount of condensation on the insulation surface promotes the partial discharge. With the increase of condensation amount, the degree of surface electric field distortion and the probability of water droplet fusion increase, while the initial discharge voltage decreases, the number and amplitude of surface discharge increase.

In recent years, buffer layer ablation failure occurs frequently in high voltage cables with corrugated aluminum sheathed structure, but there is a lack of effective method to determine the severity of ablation defects in cable buffer layer. In order to explore the evolution law of gas product concentration during buffer layer ablation, and use it to diagnose the severity of ablation defects, a simulated experimental platform for buffer layer ablation was established in this paper. The law of ablative characteristic gas concentration of buffer layer with different water contents changing with ablation time was investigated,and the variation law was quantitatively analyzed by using a negative exponential function n=-Aexp(-t/τ)+n₀. The results show that the concentration of C₂H4, C₂H₆, and H₂ increases in a negative exponential relationship with the increase of ablation time. With the increase of water content, the concentration of C₂H₄ and C₂H₆ decreases slightly, while that of H₂ increases. The generation rate coefficient(A/τ) of C₂H₄ and C₂H₆ can reflect that whether the buffer layer is damp, and the A/τ of H₂ increases gradually with the increase of water content in buffer layer, which is expected to be one of the bases for judging the degree of damp of buffer layer.

Polyurethane foam adhesive has good expansion filling characteristics, electrical insulation performance, and waterproofness. To achieve its application in filling the inner layer of the cable joint protective shell, at first, we tested the thermal, electrical, and mechanical properties of polyurethane foam adhesive with different foaming ratios. Then, a two-dimensional axisymmetric model of the cable joint was established, and the steady-state temperature field distribution of the cable joint under different filling adhesive conditions was simulated and analyzed. Finally, a physical model of the 110 kV intermediate joint was established, and thermal cycling tests were conducted on cable joints using different filling adhesives. The results show that all the performance test results of polyurethane foam adhesive are good. With the increase of foaming ratio, the thermal conductivity, insulation performance, and mechanical property of the foam adhesive decrease, with a foaming ratio of 3 times, the foam adhesive shows optimal comprehensive performance. The absolute error between the simulated and measured temperature values of various structure inside the joint using different filling adhesives are basically no more than 10%, which verifies the effectiveness of the simulation model. The steady-state temperature distribution of the joint filled with foam adhesive is similar to that of the joint filled with traditional waterproof adhesive.

Due to its advantages of high flash point, high ignition point, and biodegradability, natural ester insulating oil is gradually being promoted and applied in high voltage level power transformers. In order to provide basic data support for the insulation structure design of high voltage and large capacity natural ester transformer, we took mineral oil as a reference, and selected natural ester insulating oil as the test object to analyze its breakdown characteristics and gas generation law under lightning impulse voltage. The results show that the lightning impulse breakdown voltage of natural ester turn-to-turn insulation is above 200 kV, with the increase of turn-to-turn insulation thickness and insulation gap distance, it shows an upward trend and is slightly lower than the breakdown voltage of mineral oil under the same conditions. H₂ and C₂H₂ dissolved in oil are the main characteristic gases under lightning impulse voltage, and their relative percentage content increases with the increase of insulation gap. The Duval pentagon method is used for fault diagnosis of dissolved gases in oil, and the discharge at the fault points are basically diagnosed as high-energy discharge, which are consistent with the energy released by lightning impulse.

Cable joint is a key accessory of high-voltage DC cable, its insulation performance determines the stability of high-voltage DC transmission system. To verify the effectiveness of the charge transport model in calculating the electric field distribution of cable joints, we calculated the mobility of injected charge carriers and the conductivity of ionized charges through blocking experiments, and proposed a charge transport model that simultaneously considered the effects of injected and ionized charges, the undetermined parameters in the transport model were simplified. Then the electric field distribution of the XLPE-EPDM double-layer structure was simulated and calculated by using a simulation model, and the results were compared with the experimental results. The results show that with the increase of electric field intensity, the polarity of charge on the interfacial of the XLPE-EPDM double-layer structure is reversed. The simulation results calculated by the simulation model are in good consistency with the experimental results, which proves the effectiveness of the simulation model.

The motor is the key drive component of new energy vehicles, and the insulation system is an important guarantee for motor reliability. Once the motor insulation fails, it will pose a threat to the safe operation of the vehicle. The severe electric heating stress is the main factor causing insulation failure, so it is of great significance to test the motor insulation level under complex pulse parameters and environmental conditions. This paper had reviewed the latest research results at home and abroad from several aspects of performance evaluation methods and influencing factors, voltage distribution calculation, and weak spot location of new energy vehicle drive motor insulation system. Combined with the development trend of voltage level improvement, power density improvement, breaking frequency improvement, and switching speed increase, the problems and challenges faced by insulation evaluation of variable frequency motor were pointed out, which provided reference for the future research in this field.

In recent years, with the rapid development of new energy vehicles and flexible direct current transmission projects, and other fields, there was an increasing demand for the metallized film capacitors with high volume ratio and high temperature resistance. Especially under extreme conditions such as high temperature and high electric field, higher requirements were put forward for the electrical performance of dielectric films in capacitors. In this paper, the current research status and development trend of dielectric film materials for metallized film capacitors in recent years were summarized. Firstly, the key factors affecting the energy storage performance of dielectric films were introduced and the failure reasons of metallized film capacitors under operating conditions were analyzed. Secondly, the modification methods of energy storage performance for dielectric films designed on the basis of four aspects, such as molecular chain structure, aggregation state structure, doping of functional fillers, and surface modification were summarized. Finally, the strategies to improve the energy storage performance of dielectric films of metallized film capacitors were summarized and prospected.

An ANF/mica composite insulating paper was prepared by vacuum assisted filtration and hot pressing technology taking aramide nanofiber (ANF) as matrix and natural mica (mica) as filler. The microscopic morphology, tensile strength, electrical insulation properties, and temperature resistance of the composite insulating paper were studied systematically. The results show that the mica and ANF are superimposed in order during vacuum filtration process, and the mica fragments fill the gaps in paper effectively, creating a dense "brick-and-mortar structure", which significantly enhances the electric strength and insulating properties of the composite insulating paper. Furthermore, the glass transition temperatures of pure ANF insulating paper and ANF/mica-10 composite insulating paper are higher than 300℃, exhibiting excellent thermal stability. Although the addition of mica slightly reduces the tensile properties of pure ANF insulating paper, its insulation strength and tensile performance remain superior to traditional mica paper.

Excessive free electrons in thin film capacitors will increase the leakage current density, reduce the electric strength, and promote the breakdown of capacitors, thus preventing them from obtaining excellent energy storage performance. To mitigate the impact of free electrons and secondary impact ionization electrons (SIE) on energy storage performance, this study introduced perylene diimide (PDI), 1,4,5,8-naphthalenetetracarboxylic dianhydride (NDI), and 4-cyano-4′-pentylbiphenyl (5CB) into polyvinylidene-hexafluoropropylene (PVH) to construct an all-organic composite films, respectively, and the structure, thermal properties, and energy storage performance of three kinds of films were studied. The results show that PDI/PVH composite film with PDI mass fraction of 0.5% has the better thermal properties, smaller grain size, and tighter lattice structure, which is helpful to achieve higher electric strength and discharge energy density. Through comparison, it is found that PDI possesses a more suitable band structure and conductivity, which makes PDI/PVH composite film have better energy storage performance. The discharge energy density of 0.5%PDI/PVH composite film achieves 16.6 J/cm³ at 499.7 MV/m, and maintains a high charge-discharge efficiency of 80.5%.

The one-dimensional ANF and two-dimensional edge-hydroxylated BNNS (BNNS-OH) were mixed to prepare ANF/BNNS-OH composite insulating papers with “brick -mud” structure by vacuum filtration technology. The mechanical properties, thermal conductivity, dielectric properties, and breakdown properties of the composite insulating paper were studied. The results show that the BNNS-OH arranges in ANF orderly, and the structure is dense. The ANF/BNNS-OH composite insulating paper has excellent mechanical properties, thermal conductivity, and breakdown properties. When the mass fraction of BNNS-OH is 10%, the tensile strength and electric strength of the composite insulating paper are 242.4 MPa and 312.9 kV/mm, respectively. When the mass fraction of BNNS-OH is 40%, the thermal conductivity of the composite insulating paper reaches 6.76 W/(m·K), which is 158.02% higher than that of pure ANF insulating paper. At same time, the composite insulating paper has excellent high temperature wideband dielectric stability.