This study investigates bubble dynamics and the buckling behavior of free liquid surfaces. Comsol Multiphysics was used to analyze bubble formation and collapse in a rectangular tank. The number of apertures and distance between them were studied to determine their effect on bubble characteristics and interface deformation. In addition, the application comprised information regarding bubble creation, prevalence, and path. It discussed the phenomenon of bubbling based on various heated cavities. There are minutiae concerning coexistence of bubble collapse aftermaths of single, double, and triple inlet cavity sources. Data analysis indicates likelihood of bubble detachment hikes with increasing cavity count. However, bubble leaving frequency decreases with increased source spacing. We realized that growth and bubbles could extend the base by raising wall temperature, but it curtailed bubble removal diameter and time. Whenever an electric field is strong, more bubbles leave the superheated cavity, and bubble size decreases. Fallout shows changes in these geometric criteria considerably impact deformation of free liquid surfaces caused by bubble bursting and other bubble characteristics. The above characteristics of bubbles under combined stress provide an understanding of one source of stream development in the power transformer. Using results from these studies, it is possible to design a device for bubble generation, reliable and efficient.

Surface charge accumulation is considered to be a critical factor in flashover failure of three-post insulators. However, surface charge accumulation characteristics on three-post insulators with complex structures and uneven electric fields are still unclear. Furthermore, the temperature gradient field makes charge accumulation more complicated. In this presentation, surface charge profiles of DC three-post insulators under electro-thermal coupling stress are studied by establishing a multi-degree-of-freedom movement measurement system. The abdominal area of the three-post insulator accumulaftes charges of identical polarity as the DC voltage, while the leg area accumulates heteropolar charges. Charge density from the bottom of the leg to the center of the abdomen presents a trimodal distribution pattern, including two homopolar charge peaks and one heteropolar charge peak. Asymmetrical surface conductance distribution arising from the temperature gradient leads to a significant increase in amplitude and distribution range of the homopolar charge peak at the legs of insulator. Increase of the temperature gradient will further magnify the homopolar charge peak at the legs. When DC voltage is 100 kV and conductive pole temperature is 70℃, surface charge density of the three-post insulator can reach 100 $\mathsf{\mu }$C/m ${}^2$. Therefore, surface conductance regulation of the leg region is the key to charge regulation and insulation optimization design of DC three-post insulators.

Chemically active by-products formed by corona discharge in SF ${}_6$ gas are prone to damaging the exposed epoxy resin, or even leading to an entire insulation failure of the operational GIS/GIL power equipment. In this proposed research, reactive force field molecular dynamic simulation methodology is applied to investigate the chemical reaction kinetics of epoxy polymer under the impact of highly energetic particles (F, S, SOF, SF, OH and O) so as to explain the degradation mechanism. Among all cases, SF particle-impacted epoxy resin suffers the most serious surface erosion with the lowest remnant mass of 9% and deepest damage penetration of 32.6Å, to which the S particle-caused damage showed similar results. Due to high reactivity of the S atom, it can merge into the epoxy molecules to promote long chain breaking, causing a six-membered ring opening and further dissociation of short carbon chains, which makes the epoxy resin molecules undergo faster spontaneous dissociation with increased temperatures. The changes of small molecular gas products, such as CO ${}_2$, H ${}_2$O and CH ${}_2$O, as well as that of the characteristic products, such as HF, CS ${}_2$, SO and H ${}_2$S, are also evaluated under the impact of different particles. The presented research indicates that enhancing the resistance strength of epoxy polymer against S and SF particles' corrosion is the key approach to improving chemical stability in the SF ${}_6$ environment. Further studies were implemented to optimize the concentration and diameter of nano-Al ${}_2$O ${}_3$ doped in the composites. According to this paper, aluminum nanoparticle with a diameter of 1nm could significantly reduce the erosion caused by SF and S particles. The micro-scale mechanism lies primarily within two aspects: the nanoparticles improve the surface heat transfer efficiency as to reduce temperature rise, and also provide an effective protection area by balancing distribution and self-exposing, which finally slows down the pyrolysis process of epoxy resin, as well as the reaction intensity with the incident particles.

Accelerated insulation aging problems under high frequency repetitive impulses in power electronic transformers are drawing more and more attention in modern power systems. Partial discharge (PD) characteristics including discharge inception voltage, phase distribution and statistical characteristics on polyimide (PI) surface under different impulse waveforms and the insulation life of PI films are studied in this paper. We carry out experiments based on PD and insulation lifetime test systems, using five different types of repetitive impulses, including three bipolar waves and two unipolar waves. The experimental results show that there is little variation in discharge inception voltage under different waveforms, but great variation in phase distribution and statistical characteristics of PD. In addition, insulation life is approximately the same under different waveforms with the same polarity, and the aging rate under bipolar waveforms is larger than that under unipolar waveforms. We explain the differences between the bipolar and unipolar waveforms on insulation life, which can be concluded that the surface charge under unipolar waveform accumulates more significnatly compared with bipolar waveform and decreases the electric filed strength in discharging the air gap and inhibits surface discharge from occurring.

Condition monitoring and maintenance are essential for ensuring stable and reliable operation of facility transformer, reducing costs, and increasing expected life. Foam cannot be avoided within the power transformer which illustrates at least one of the principal roots of insulation deterioration. Due to the intricacy of the dynamics within the insulation system, involving bubble creation, migration, and accumulation, challenges arise in understanding these mechanisms. Consequently, the problems caused by bubble dynamics require further investigation. This paper provides a scientific review of issues related to bubble formation, migration, and dispersion and their electrical effects on power transformers. Various descriptions are given to highlight impact of the dynamics of the bubble within high voltage insulation fields, which covers bubble generation mechanism, and therefore, the quintessential influencing factors, state-of-the-art advances in multi-physics coupled modeling of bubble dynamics, etc. Moreover, pending issues on bubble control and mitigation are addressed, as well as recommendations for future investigations. Nonetheless, this paper contains a useful quotation guide for researchers within an equivalent field of research, which can motivate readers to explore scientific solutions to prevailing bottleneck problems.