scholarly journals Composite Micro-Nanoarchitectonics of MMT-SiO2: Space Charge Characteristics under Tensile State

Polymers ◽  
2021 ◽  
Vol 13 (24) ◽  
pp. 4354
Author(s):  
Hongtao Jiang ◽  
Junguo Gao ◽  
Xiaohong Zhang ◽  
Ning Guo

Low density polyethylene (LDPE) is a good insulating material which is widely used in cable materials due to its excellent insulation and processability. However, in the DC high voltage environment, pure polyethylene materials still face many problems, the most serious of which is space charge accumulation. The cable will inevitably be subjected to tensile stress during production, installation and operation. Therefore, it is of great significance to study the effect of stretching on the microstructure and space charge characteristics for polymers and their composites. In this paper, MMT/LDPE micro-composites, SiO2/LDPE nano-composites and MMT-SiO2/LDPE micro-nano-composites were prepared by melt blending. Mechanical stretching was carried out on pure LDPE materials and the above three kinds of composite materials. Each material was stretched according to four stretching ratios, which are 0%, 5%, 10% and 20%. The crystal morphology was observed by polarizing microscope (PLM), the crystallization perfection was tested by differential scanning calorimetry (DSC), and the space charge distribution inside each sample was measured by pulsed electro-acoustic (PEA) method. At the same time, the average charge density and apparent charge mobility for samples during depolarization were calculated and analyzed. The experimental results show that when the pure low density polyethylene sample is not stretched, its crystal structure is loose. Tensile stress can make the loose molecular chains align in LDPE and improve its crystalline structure, which is helpful to restrain the accumulation of space charge inside the sample. For MMT/LDPE, SiO2/LDPE and MMT-SiO2/LDPE composites, their internal crystal structure is compact. Stretching will destroy their original crystal structure at first, and then disorder molecular chains inside the three composite materials. With the increase of stretching ratio, the molecular chains begin to orient along the direction of force, the crystallization tends to be perfect gradually, and the space charge accumulation in samples also decreases. From the calculation results of apparent charge mobility for each sample, with the increase of stretching ratio, the trap depth and trap density inside samples firstly increased and then decreased.

2003 ◽  
Vol 10 (1) ◽  
pp. 148-154 ◽  
Author(s):  
Y. Tanaka ◽  
G. Chen ◽  
Y. Zhao ◽  
A.E. Davies ◽  
A.S. Vaughan ◽  
...  

Polymers ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 587 ◽  
Author(s):  
Guochang Li ◽  
Jiaxing Wang ◽  
Wang Han ◽  
Yanhui Wei ◽  
Shengtao Li

Temperature is one of the key factors affecting space charge accumulation in high voltage direct current (HVDC) cable insulation material. The influence of temperature on charge accumulation in low density polyethylene (LDPE) has been investigated with a combined thermally stimulated depolarization current (TSDC) method and pulsed electro-acoustic (PEA) method. The experimental results indicate that there exists a transition temperature region of charge accumulation around 50 °C. The total accumulated charges all firstly increase and then decrease with the increasing polarization temperature under three typical polarization electric fields, and they have more accumulated charges in LDPE around 50 °C. The phenomenon has a close link with the dynamic processes of charge trapping and de-trapping, which were verified by TSDC results. At room temperature, the trapped charges are difficult to release from the traps, and these homocharges near the cathode can depress the further injection of the charges. More charges can be injected from the electrodes with the increase of temperature, while the charge migration is relatively lower before 50 °C, leading to more accumulated charges. When the temperature exceeds around 50 °C, the molecular movement is accelerated which can enhance the hopping probability of charges between the adjacent traps, resulting in few accumulated charges.


Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4119
Author(s):  
Hongtao Jiang ◽  
Xiaohong Zhang ◽  
Junguo Gao ◽  
Ning Guo

Low-density polyethylene (LDPE) is one of the most comprehensive products used as insulation materials in power equipment. How to improve its dielectric properties by doping inorganic particles in LDPE has always been the focus of many researchers. In this paper, silica (SiO2) particles and montmorillonite (MMT) particles were added to LDPE, the order of adding particles was changed, and different micro-nano composites was made. The crystallization characteristics of composites were analyzed, the curves of the conductance current with the change of field intensity were analyzed, and the space charge distribution of each material were investigated. The results of crystallization show that the crystalline properties and crystallinity of the composites are higher than the matrix LDPE, the addition of SiO2 particles increases the composites’ crystallinity significantly, and the intercellular spacing of micro-nano composites is the smallest among all materials. The curve of conductance current versus electric field intensity shows that the tightness of the crystal structure can effectively hinder the movement of the molecular chain, inhibit carrier migration, while shortening the free travel of electrons, thereby reducing the electric conduction current of the material. The experimental results of the space charge accumulation curve further show that the compact crystal structure of the material is beneficial to the dissipation of space charge in the dielectric.


e-Polymers ◽  
2018 ◽  
Vol 18 (1) ◽  
pp. 49-56
Author(s):  
Zhiyu Yan ◽  
Hong Zhao ◽  
Baozhong Han ◽  
Jiaming Yang ◽  
Junqi Chen

AbstractSpace charge accumulation within insulating material poses a threat to the reliability in the operation of DC power cables. To investigate the influence of carbon black (CB) on the space charge accumulation of low density polyethylene (LDPE), both conductive carbon black (C-CB) and insulating carbon black (I-CB) were employed as filler particles. The space charge distributions of LDPE and CB/LDPE nanocomposites were obtained by the pulsed electro-acoustic (PEA) method. Additionally, dynamic mechanical analysis (DMA) and thermally stimulated current (TSC) spectroscopy were applied to explore the mechanism of improving space charge performance. Both the C-CB/LDPE and I-CB/LDPE nanocomposites can effectively suppress space charge accumulation. It was concluded that the improvement in space charge characteristics of CB/LDPE nanocomposites was attributable to the interaction between the CB particles and the LDPE, which reduces the number of defects formed from molecules participating in α relaxation and decreases the density of traps within the LDPE.


Sign in / Sign up

Export Citation Format

Share Document