Authors: Weiwang Wang | Shengtao Li
Source: Chinese Science Bulletin (Chinese Version) (article, 2020-03-24)
Field: Materials Science — Materials Chemistry

Research status and development of insulation breakdown in engineering solid dielectrics <p indent=0mm>Insulation breakdown is the key basic scientific issue in the development of high-performance engineering dielectric materials. With the development requirements of the third-generation power grid, super/UHV AC-DC (alternating current-direct current) power equipment, smart power grid, power internet of things and power equipment under extreme conditions present higher requirements on the engineering dielectrics with excellent breakdown performance. This paper summarizes the research status of the breakdown in engineering dielectric materials and discusses the theoretical mechanism of dielectric breakdown, the performance evolution, performance improvement, new high-performance nanocomposite dielectric, and micro molecular design/regulation. Firstly, based on the time-space hierarchical relationship of dielectric breakdown, the breakdown mechanisms related to the high field and energy accumulation effects are discussed. Moreover, the electric, thermal, electric and mechanical breakdown theory is extended. Considering the breakdown process of the actual dielectric, especially the polymer dielectric, and the complex factors, the current breakdown mechanism of the dielectric still has many problems. The electric breakdown is the main form of breakdown, which can explain the inducing and early process of breakdown. However, it is difficult to explain the formation and destruction of the breakdown channel. In addition, the breakdown mechanism may change as the thickness increases, requiring consideration of thermal or mechanical effects. Space charge can explain many of the characteristics of AC and DC breakdown, as well as the deterioration of dielectric materials, but when the thickness is small, the space charge is of limited use. Secondly, the dielectric breakdown characteristics and statistical analysis are expounded, and the relationship between the intrinsic breakdown field strength of polymer dielectric and temperature, voltage form, space charge accumulation, and sample thickness is analyzed. The breakdown strength of the material and the time required for the material to break down under the fixed field strength all meet the Weibull statistical distribution. It reflects the probability that the material is broken down under a certain electric field or fails after a certain electric field. Then, the breakdown characteristics of high-performance dielectric materials and the methods of performance improvements are discussed. By adding inorganic nanoparticles to the polymer to prepare nanocomposite dielectric materials, the breakdown field strength and dielectric constant can be improved, and the energy storage density of the dielectric can be improved. In this paper, the research status of nanocomposite dielectric and the mechanism involved in interfacial interaction are described. Many research results show that a small number of nanoparticles can improve the breakdown field strength of composite materials. The interfacial zone effect introduced by nanoparticles results in the increase of the depth or density of the system's deep traps, or the introduction of new deep traps improves the breakdown characteristics. Shallow traps are distributed on the edges of the conduction band and valence band, and it is easy to detach for the trapped carriers, which participate in the charge transport process and promote the breakdown. The modification method of polymer micro molecular design and the modification of breakdown are analyzed. The experimental results show that it is easy to destroy the conjugated structure for the ether bond structure in polyimide, which leads to the increase of the bandgap width of polymer material and the enhancement of the intrinsic breakdown field. Finally, the key problems and development trends of dielectrics with high breakdown performance are summarized based on the development demand for future power equipment. The development of new high-performance insulation materials in the future mainly include the breakdown theory, new preparation method, application technology, newly insulating material with high breakdown performance (design and regulate the molecular structure of the material). It provides a basis and strategy for the development of engineering dielectric in the new energy power system. Dielectric ; Dielectric strength ; Materials science ; Space charge ; Electrical breakdown ; Partial discharge ; Engineering physics ; Liquid dielectric ; Breakdown voltage ; Electric field ; Electrical engineering ; Electronic engineering ; Optoelectronics ; Voltage ; Engineering ; Physics High voltage insulation and dielectric phenomena