[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Introduction to heat transfer

Epoxy is a crucial engineered thermosetting polymer with wide industrial applications in adhesive, electronics, aerospace and marine systems In this review, basic knowledge of epoxy resins and the challenge for the preparation of epoxy nanocomposites are summarized The state-of-art multifunctional epoxy nanocomposites with magnetic, electrically conductive, thermally conductive, and flame retardant properties of the past few years are critically reviewed with detailed examples The applications of epoxy nanocomposites in aerospace, automotives, anti-corrosive coatings, and high voltage fields are briefly summarized This knowledge will have great impact on the field and will facilitate researchers in seeking new functions and applications of epoxy resins in the future

An overview of multifunctional epoxy nanocomposites

Review of Polymer‐Based Nanodielectric Exploration and Film Scale‐Up for Advanced Capacitors

Electron-avalanche breakdown in solids is explained by a theory that is predictive and agrees with experimental results for the magnitude of the breakdown field and its temperature dependence, pulse-duration dependence, material-to-material variation, and wavelength dependence for λ > 1 μm. The good agreement between experiment and theory with no parameters adjusted is obtained by using improved magnitudes and energy dependences of the electron-phonon relaxation frequencies. The contributions of both optical and acoustical phonons to electron loss and diffusion must be included. The breakdown field E B is calculated by solving an eigenvalue equation obtained from the diffusion transport equation. Simple models and interpretations of the diffusion equation afford physical insight into breakdown and render the breakdown conditions predictable. Preliminary results indicate that the diffusion approximation fails for wavelengths considerably shorter than 1 μm, but that E B decreases with decreasing X as a result of multiphoton absorption before the diffusion approximation fails.

Theory of electron-avalanche breakdown in solids

Traditional insulation material is thermally insulating and has a low thermal conductivity. The miniaturisation and higher power of electrical devices would generate lots of heat, which have created new challenges to safe and stable operation of the grid. The development of insulating materials with high thermal conductivity provides a new method to solve these problems. The improvement of thermal conductivity would increase the ability to conduct heat and greatly reduce the operating temperature of the electrical equipment, which could reduce the equipment size and extend service life. On the other hand, inorganic thermally conductive particles and the improved thermal conductivity may have great effect on thermal breakdown. In this study, the factors affecting the thermal conductivity of dielectric polymer composites were explored. Intrinsic thermal conductive polymer and particle-filled thermal conductive composites were discussed. Effect of thermal conductivity, shape, size, surface treatment of the particle and prepare process on thermal properties of the composites were illustrated. This study focused on the electrical and thermal properties of thermally conductive epoxy, polyimide and polyethylene composites. Tracking failure caused by thermal accumulation is a typical thermal breakdown phenomenon. The performance of the resistance to tracking failure was studied for these composites. The results showed that thermal conductive particles improved the resistance to tracking failure. Finally, application of thermally conductive epoxy in electrical equipment was discussed.

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Review of high thermal conductivity polymer dielectrics for electrical insulation

As the critical barriers to advanced high-temperature superconducting (HTS) device technologies are overcome, practical HTS devices and systems have been enabled and become available for commercial application. In identifying the applicability of various HTS devices, their operation principles, characteristics, performance, and efficiency are fundamental. Consequently, the corresponding verification of a wide range of HTS devices, especially the HTS power devices and their system technologies, has been comprehensively carried out, and the analytical results are presented in detail towards their practical applications.

HTS Power Devices and Systems: Principles, Characteristics, Performance, and Efficiency

High-voltage DC (HVDC) power transmission plays a key role in the global power grid today and will continue to play a key role in the future, particularly for high-voltage, largecapacity, long-distance power transmission and regional power grid interconnection [1]. HVDC was first developed in the 1930s as a reliable technology that can effectively convert AC electricity produced at the point of generation to DC electricity for transmission. In 1954 the world’s first commercial HVDC project connected the Swedish mainland and the Island of Gotland with a ±100 kV mass-impregnated cable with a power rating of 20 MW [2], [3]. Since the 1960s the number of HVDC systems has grown rapidly with the maturation of thyristor and transistor technologies. Two main technologies were developed in the past half century:

Polymeric insulation for high-voltage dc extruded cables: challenges and development directions

The electric field distributions along gas-solid interfaces determine the reliability, lifetimes and sizes of gaseous insulated switchgears/pipelines (GIS/GIL), which also affect the reliability of power systems. In this study, the characteristics of steady and transient electric field distributions were first introduced, followed by the concept of functionally graded materials (FGMs). The development histories of FGM applied in electrical engineering and the related optimisation methods were described in detail. The field regulation effect and fabrication technology of different FGM insulators were also compared. To overcome the limitations of traditional FGM insulators, the design of surface FGM (SFGM) was proposed, together with their preparation methods and electrical performance. Furthermore, the future development prospects of FGM and SFGM insulators for compact GIS/GIL were summarised.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/hve.2019.0327

Promising functional graded materials for compact gaseous insulated switchgears/pipelines

Polypropylene (PP) has been paid much attention due to its high melting point, excellent electrical insulting performance and thermoplastic property, which is potential to replace the XLPE as HVDC cable insulating material. Blending PP with polyolefin elastomer (POE) is an effective way to modify its stiffness and brittleness at room temperature. However, space charge behavior of PP/POE blend, as a great concern under dc stress, is not clear and needs further investigation. To research the space charge behaviors, pure PP, PP/POE blend and its nanocomposites with different contents were prepared. Then, mechanical properties, permittivity constant, breakdown strength, volume resistivity, space charge behaviors and trap level distribution were investigated. The results indicate the addition of POE enhances the mechanical flexibility of PP greatly, and nano-sized ZnO doping has little effect on the mechanical flexibility of PP/POE blend. The nanocomposites show lower permittivity constant, higher breakdown strength and higher volume resistivity than the PP/POE blend. Compared to pure PP, the space charge accumulation and electric field distortion get severe in PP/POE blend. However, by nanoparticles doping, space charges are remarkably suppressed, which is related to the increased trap level density in nanocomposites. It indicates the PP/POE/ZnO nanocomposites have much potential for HVDC cable application, which show high mechanical flexibility as well as excellent electrical performance.

Boxue Du

Papers

Review of high thermal conductivity polymer dielectrics for electrical insulation

HTS Power Devices and Systems: Principles, Characteristics, Performance, and Efficiency

Polymeric insulation for high-voltage dc extruded cables: challenges and development directions

Promising functional graded materials for compact gaseous insulated switchgears/pipelines

Space charge behaviors of PP/POE/ZnO nanocomposites for HVDC cables