In order to investigate the influence of copper and insulating paper on the properties of alkylbenzene insulating oil inside oil-filled high-voltage cables, alkylbenzene insulating oil was placed in four different environments and subjected to a thermal ageing experiment at 120℃ for 50 days. Ageing characteristic parameters of oil sample such as acid value, dielectric loss factor, interfacial tension, and water content were measured during the ageing process, and the correlation between the four indicators was studied using regression analysis. The results show that as the ageing time increases, the ageing degree of oil sample intensifies, copper accelerats the ageing of alkylbenzene insulating oil, while insulating paper has no significant effect on the ageing of the oil. The dielectric loss factor of insulating oil is positively correlated with its acid value and water content, and negatively correlated with interfacial tension, both of which are exponential functions. The regression fitting equation is y=A₁·exp(±x/t₁)+y₀, and the goodness of fit is greater than 0.94. In the results of multiple linear regression, there is a common constraint relationship between the dielectric loss factor, acid value, interfacial tension, and water content.

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 order to explore the ageing resistance of nitrile rubber products, such as high-temperature resistance, transformer oil resistance, and heat-compression resistance, we conducted accelerated ageing tests on nitrile rubber (NBR) under high temperature conditions of 90, 120, and 135℃ in hot air, hot oil, hot air compression, and hot oil compression, respectively. The effects of ageing temperature, ageing time, and ageing environment on the mechanical properties of NBR were researched, and compression set was used as an evaluation index to predict the actual service life of NBR. The results show that the ageing rate of NBR increases with the increase of temperature. During the ageing process, with the increase of ageing time, the Shore hardness and compression set of NBR increase, while the elongation at break decreases. 25^# transformer oil can slow down the decrease in Shore hardness and compression set performance of NBR, while it slows down the decrease at first and then accelerates the decrease in fracture elongation. Based on the Arrhenius law, the predicted service life of NBR in hot oil compression environment at temperatures of 40, 50, 60, 70, and 80℃ is 3.726, 1.877, 0.985, 0.542, and 0.303 years, respectively.

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.

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.

To address the issues of inadequate high-temperature insulation performance and thermal stability of wires, a high-temperature resistant ceramic coating was prepared using the nano alumina and a small quantity of nano silica as the primary raw materials by nanoparticle surface modification technology, then the ceramic coating was coated on quartz fiber braided layer to prepare a high-temperature composite insulating material. The structure, composition, and thermal stability of the coating were analyzed by X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FTIR), and thermogravimetric-differential scanning calorimetry (TG-DSC). The morphology, volume resistivity, and electric strength of the high-temperature resistant ceramic coating-quartz fiber composite insulation layer before and after calcination were analyzed by scanning electron microscopy (SEM), high insulation resistance tester, and automatic voltage tester. The results show that the ceramic coating forms a ceramic protective layer on the quartz fiber braided layer after high temperature calcination, which can enhance the temperature resistance rating of the quartz fiber and improve its insulation performance. When the temperature exceeds 800℃, the insulation resistivity of the high-temperature resistant composite insulation layer still exceeds 2×10⁶ Ω·m, and the average electric strength at room temperature is as high as 400 kV/m, which has certain application prospects in the wires on specialized equipments such as aerospace engines, excitation coils, transformers.

Using bisphenol A and bisphenol F epoxy resin as main resin, aluminum hydroxide and spherical silicon micro powder as fillers, combined with anhydride curing agent and epoxy toughening agent, a film capacitor epoxy potting material for new energy vehicle was prepared, and the effects of each component on the properties of potting materials were analyzed. The results show that the film capacitor epoxy potting material for new energy vehicles prepared by optimized formula has high glass transition temperature, good mechanical properties, good adhesion performance, small linear expansion coefficient, and the performances of capacitors are excellent. The prepared potting material has comparable performance levels to similar potting materials abroad and is suitable for thin film capacitors used in new energy vehicles.

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%.

Partial discharge inception voltage (PDIV) detection is an essential test method for evaluating the insulation performance of random wound inverter-fed motor stators. As an important parameter of pulse-width modulation voltage, the effects of pulse width on the PDIV of interturn insulation and interphase insulation in random wound inverter-fed motors are noteworthy. In this paper, the PDIV distribution laws of interturn insulation and interphase insulation in motor under different pulse widths were studied in the frequency of 50 Hz, rise time of 75 ns, and pulse widths within of 0.5-20 μs. The results show that when unipolar pulse square waves are input into random wound inverter-fed motors for PDIV testing, the overall trend of PDIV decreases as the input pulse width increases. Due to the combined effect of overvoltage from the rising and falling edges of short pulses, a turning point occurs in PDIV at a pulse width of 4 μs. It is necessary to consider the effects of pulse width and overvoltage and select appropriate pulse widths to obtain conservative values of stator insulation PDIV when conducting the PDIV test of interturn insulation and interphase insulation in random wound inverter-fed motor under unipolar pulse.

The main insulation of large motor will produce many kinds of insulation defects during its operation process, and only used the phase resolved partial discharge (PRPD) pattern cannot reflect the characteristics of the defects fully. In this paper, four typical insulation defects such as internal air gap, coil wear in slot, overlapping part fault of end semiconductor coating and anti corona layer, and surface contamination were simulated in laboratory, their partial discharge (PD) information were collected in the electromagnetic shielding chamber, and the PRPD patterns and PSA patterns were drawn respectively. Combined with the characteristics of PRPD and PSA patterns under different voltage levels, the discharge characteristics of the typical insulation defects were analyzed. The results show that considering the symmetry, discharge amplitude, spectrum envelope shape of PRPD pattern and the discharge cluster number, discharge cluster distribution position, discharge cluster shape of PSA pattern, the four typical insulation defects can be identified accurately.