Boxue Du

By Boxue Du, Yu Gao and Yong Liu

Part of the book: Nuclear Power

By Boxue Du

Converter transformer is the extraordinarily vital apparatus in the high-voltage direct current (HVDC). Transformer oil and oil-impregnated paper are considered as the essential parts of converter transformer, which has suffered various complex electric fields such as AC/DC composite electric field and polarity reversal. The occurrence of discharge or insulation failure in oil-paper insulation system will threaten the safety of the entire grid. Hence, efforts should be focused on investigating the charge behavior and improving the property of dielectric.

Part of the book: Polymer Dielectrics

By Boxue Du, Zhaohao Hou and Jin Li

Due to its excellent electrical and thermal performance, as well as satisfying the needs for developing the environmentally friendly and recyclable cable insulation material, polypropylene has caused widespread concern. Nanodoping can effectively improve the electrical, thermal and mechanical properties of polypropylene nanocomposites, which provides a new method to solve the problems in its application in HVDC cable insulation. This chapter introduces research achievements on polypropylene and polypropylene/inorganic nanocomposites, which states the effects of nanodoping on the electrical properties, such as space charge behaviors, electrical tree aging, breakdown strength, etc. thermal conductivity and mechanical properties of the polypropylene and its multi-blends. The aging mechanism under different conditions is also discussed. The analysis shows that the surface treatment of nanoparticles can reduce the aggregation of nanoparticles and strengthen the interface effect, thus improving the comprehensive properties of polypropylene nanocomposites. This chapter also summarized the feasibility and future development of the polypropylene and its nanocomposites application in the insulation of HVDC cables.

Part of the book: New Trends in High Voltage Engineering

By Boxue Du, Jin Li and Zhuoran Yang

HVDC cable accessories made of ethylene-vinyl acetate copolymer (EVA) by incorporation of specific fillers have to face the problem of space charge accumulation. The effects of doping contents on the space charge behaviors of EVA/ZnO composite are not completely clear. EVA composites are prepared with the fraction of 0, 1, 5 and 10 wt%, respectively, with which 5 wt% nano-sized plus 5 wt% micro-sized ZnO-doped samples are chosen for comparison. Obtained results show that the particles in EVA composite are in homodisperse. The permittivity is increased by ZnO doping and the dissipation factor of EVA composites with 1 and 5 wt% nanoparticles is lower at the lower frequencies. The homocharge injection occurs in cathode instead of anode when ZnO nanoparticles are introduced and 5 wt% nanoparticle doping performs well in suppressing space charge injection. The electric field in the 5 wt% nanoparticle-doped EVA distributes more uniformly under the high electric stress than that of others. During the depolarization procedure, the total remnant charges of 10 wt% doped samples are the least in the final. The above results are well explained by the DC conduction, apparent mobility and trap distribution characteristics.

Part of the book: Nanocomposites

By Boxue Du, Hucheng Liang and Jin Li

A majority of the high voltage (HV) electrical equipment which has solid-gas insulation has suffered greatly from the accumulation of the surface charges generated from the corona discharge. The local electric field may be distorted by the surface charge’s existence and in turn causes the surface flashover faults in excessive circumstances. Consequently, it’s significant to work out the mechanism of the procedure of the surface charge accumulation. A simulation model which combines both the charge trapping-detrapping procedure and the plasma hydrodynamics was created. The outcome of the simulation has agreed with the experimental results. The corona discharge intensity rises in the initial stage and then reduces as time goes by. There are various shapes of the surface potential distribution curves at various times. The central value increases quickly with time first and at last becomes saturated. Surface charges are observed in the epoxy insulator’s skin layer, some of them are mobile but some are captured by traps.

Part of the book: Atmospheric Pressure Plasma

By Boxue Du, Ranran Xu, Jiwen Xing and Jin Li

Polyimide (PI) is widely employed as winding insulation in high voltage devices, such as extra-high voltage electric reactor and inverter-fed motor. The injection and accumulation of charges on the surface of PI films will lead to electrical field distortion and reduced lifespan of winding insulation, especially for the operation environment of high temperature and high voltage. This chapter focuses on effects of surface molecular modification and nanoparticles on dynamic characteristics of surface charge and space charge of pure PI films, including three sections. The effect of molecular structure on the surface charge dynamics of PI films was studied firstly. The chapter investigated that how molecular structure affects surface charge of polyimide nanocomposite films. Furthermore, the effect of surface molecular modification on space charge characteristics of multilayer PI films was researched. The results illustrate that surface molecular modification and nanoparticles can comprehensively suppress space charge accumulation and improve dielectric property.

Part of the book: Polyimide for Electronic and Electrical Engineering Applications