Partial discharge (PD) is one of the major causes of insulation accidents in oil-immersed transformers, generating a large number of signals that represent the health status of the transformer. In particular, acoustic signals can be detected by sensors to locate the source of the partial discharge. However, the array, type, and quantity of sensors play a crucial role in the research on the localization of partial discharge sources within transformers. Hence, this paper proposes a novel sensor array for the specific localization of PD sources using COMSOL Multiphysics software 6.1 to establish a three-dimensional model of the oil-immersed transformer and the different defect types of two-dimensional models. “Electric-force-acoustic” multiphysics field simulations were conducted to model ultrasonic signals of different types of PD by setting up detection points to collect acoustic signals at different types and temperatures instead of physical sensors. Subsequently, simulated waveforms and acoustic spatial distribution maps were acquired in the software. These simulation results were then combined with the time difference of arrival (TDOA) algorithm to solve a system of equations, ultimately yielding the position of the discharge source. Calculated positions were compared with the actual positions using an error iterative algorithm method, with an average spatial error about 1.3 cm, which falls within an acceptable range for fault diagnosis in transformers, validating the accuracy of the proposed method. Therefore, the presented sensor array and computational localization method offer a reliable theoretical basis for fault diagnosis techniques in transformers.

Insulating oil plays a crucial role in internal insulation of oil-impregnated transformers. It has been demonstrated in a variety of experimental studies that mineral oil (MO) and vegetable oil (VO) can be blended in different ratios to improve insulation properties; however, the mechanisms underlying this phenomenon remain unclear. In this study, a molecular dynamics (MD) simulation approach was used to investigate diffusion of water molecules in VO/MO blends and dielectric constants of a mixture. The results show that the diffusion coefficient of water molecules is negatively correlated with the proportion of VO; thus, addition of VO helps to improve the insulation properties of a mixture. Due to introduction of strong polar functional groups, a decrease in the diffusion behavior of water molecules can be attributed to an increase in the interaction energy and formation of hydrogen bonds between water molecules and the mixed oil system. There is a direct correlation between the dielectric constant of a mixture and VO content; however, it is very sensitive to water content. The presence of strong polar water molecules or functional groups in a mixture leads to an increase in the dielectric constant, which results in a reduction in insulating properties. Accordingly, presence of polar groups plays an important role in determining the insulating properties of a mixture. To increase the insulation performance of a mixture, it is important to consider the diffusion-inhibiting and dielectric effects of the stronger polar groups in vegetable oil compared to those in mineral oil.

The operating safety of spacecraft in space environments is closely related to the surface discharging phenomenon of dielectrics such as polyimide (PI) film in solar arrays; moreover, carrier traps in the dielectric can affect its insulation performance. Therefore, to improve the vacuum surface flashover characteristics of PI film by nano modification and reveal the effect of trap distribution on the flashover of PI composite film, first, the original PI and nano-ZnO/PI composite films with different additive amounts (0.5, 1, 2, and 3 wt.%) were prepared by in situ polymerization and their performance was evaluated by the physicochemical properties characterized by methods such as thermogravimetric analysis; second, the surface traps of the original and nanocomposite films were measured and calculated by surface potential decay method, and the carrier mobility was also obtained; finally, the vacuum direct current (DC) surface flashover characteristics and bulk resistivity of all the film samples were measured and analyzed. The experiment results showed that with the increase in the amount of nano-ZnO, both the shallow and deep trap density increased significantly, while the trap energy varied slightly, and the surface flashover voltage also increased obviously. Based on the multi-core model, the increases in the shallow and deep trap density after the introduction of nano-ZnO into the PI matrix was analyzed from the microscopic perspective of the interface. Based on the comparative analysis of the trap distribution and surface flashover voltage characteristics, a bilayer model of vacuum DC surface flashover development was proposed. In the bilayer model, deep traps and shallow traps play a dominant role in the vacuum–solid interface and the inner surface of the dielectric, respectively, and increasing the trap density could effectively inhibit secondary electron multiplication on the surface and accelerate charge dissipation inside the film. Consequently, nano-ZnO can purposefully control the trap distribution, and then improve the flashover characteristics of nano-ZnO/PI composite films, which provides a new approach for improving the spacecraft material safety.

Due to the injection of energetic particles, such as electrons in space environment, the internal charging–discharging characteristics of spacecraft dielectrics need to be evaluated for the safety of spacecraft, and the evaluation results from experiments and simulations should be comparatively validated. An in-site pulsed electroacoustic (PEA) measurement system under high-energy electron radiation was established for evaluating the charging characteristics of thick plate samples about 3 mm, while a joint simulation method based on Geant4 and COMSOL was also proposed. The deposited charge distributions were compared through experiment and joint simulation method under 0.7, 1.0 and 1.3 MeV for 30 min and 1.0 MeV for 10, 60 and 120 min, respectively. Meanwhile, the electrostatic discharging characteristics were also comparative evaluated by both methods under 0.3 MeV for 20 min under 5, 10 and 15 µA beam current, and the total discharging times and initial discharging time were compared and analyzed. Overall, a good consistency existed between experimental and simulation results of charging–discharging characteristics under electron radiation while the difference was also analyzed in the perspective of dielectric properties, such as charge leakage by conduction. Through the comparative study, both evaluation methods are validated, which offers effective reference for the safety evaluation of spacecraft dielectrics in future.

Spacecraft operating within the geosynchronous orbital (GEO) environment often experience deep dielectric charging effects in their internal insulation materials, while researchers have attempted to optimize the internal electric field through material modification and internal grounding techniques. Therefore, this paper combined the advantages of material modification and structural optimization to establish a glass fabric modified polyimide structure. We employed a Geant4-COMSOL joint simulation method to obtain the electric field strength distribution under the Flux Model for Internal Charging (FLUMIC) electron radiation environment for both single layer glass fabric modifications at different positions and multilayer glass fabric modifications at varying layer counts. The results indicate that under a single-layer glass fabric modified structure, the modified glass fabric at Position 3 exhibits the lowest maximum electric field strength. Additionally, according to the glass fabric position, the charge transport behavior in the single layer glass fabric modified structure was analyzed through 3 typical cases by a charge transport model. Finally, the engineering value of the multilayer glass fabric modified structure was assessed from three dimensions: process design, maximum electric field strength, and electric field distortion rate. For multilayer glass fabric structures, as the number of layers increases, the maximum electric field strength is progressively suppressed, but the mass and manufacture complexity also increase, imposing an additional burden on the spacecraft. The comprehensive analysis suggests that for practical engineering applications, a three layers glass fabric modification at Positions 1, 3, and 5 should be adopted to suppress the occurrence of charging phenomena in 1.6mm polyimide under GEO environment.