To suppress space charge accumulation and improve direct current (DC) electrical properties of insulation materials, crosslinked polyethylene modified with 2-(4-benzoyl-3-hydroxyphenoxy) ethyl acrylate (XLPE/BHEA) containing polar functional groups was prepared by melt blending. The gel content, thermal elongation, tensile strength, elongation at break, elasticity modulus, differential scanning calorimetry (DSC) and X-ray photoelectron spectra (XPS) measurement results demonstrated that the BHEA could slightly enhance the crosslinking of polyethylene (PE) and affect the mechanical properties and crystallization of XLPE, and the BHEA molecule was not easy to precipitate from XLPE after the crosslinking process. XLPE modified with 3.0 phr (parts per hundreds by weight) BHEA could effectively suppress space charge accumulation, reduce DC conduction and improve DC breakdown strength of XLPE at a higher temperature. Deeper traps were introduced in XLPE/BHEA composites due to the polar functional groups in BHEA, which could raise the potential charge injection barrier and reduce the charge carrier number and mobility to suppress space charge accumulation and reduce the conduction current density.

Space charge accumulation and electric field distortion in crosslinked polyethylene (XLPE) especially at a higher temperature are still urgent problems to be solved in the development of high voltage level XLPE insulated direct current (dc) cables. To improve the working temperature and transmission capacity of XLPE insulated dc cables, antioxidant N-(4-anilinophenyl) maleimide (MC) is grafted onto XLPE macromolecular chains in this article, and the space charge characteristics and dc breakdown strengths of the grafted XLPE at various temperatures are investigated. The experimental results show that the grafting modification of antioxidant MC can effectively suppress space charge accumulation and electric field distortion, and increase dc breakdown strength, especially at elevated temperatures. The immobile and dense deep traps introduced by the polar groups of antioxidant MC anchored on XLPE macromolecular chains can capture and scatter charge carriers to reduce the charge density and restrict the charge migration. At the same time, the grafted antioxidant MC is not easy to leach out of XLPE and maintains lasting antioxidative activity. Antioxidant MC grafted XLPE exhibits improved high-temperature electrical properties with the additional excellent thermal oxidation aging resistant performance and is suitable for application in the higher voltage level dc cable insulation.

Solvothermal reactions of copper salts with NaN₃ and carboxylate led to the formation of a new magnetic compound, [Cu(3-fba)(N₃)(C₂H₅OH)]_n (3-fba = 3-fluorobenzoic acid) (1). Single crystal X-ray analysis indicates that only one crystallographically independent Cu(II) ion in the asymmetric unit of 1 displays stretched octahedral geometry in which two azido N atoms and two carboxylic O atoms locate in the equatorial square, while two ethanol O atoms occupy the apical positions, yielding a 1D Cu(II) chain with an alternating triple-bridge of EO-azido, syn,syn-carboxylate, and μ2-ethanol. Magnetic measurements reveal that the resulting compound is composed of well-isolated 1D Cu(II) chains with strong intrachain ferromagnetic interactions. The dominant ferromagnetic couplings between neighbouring Cu(II) ions occurring in the compound (J = 59.74 cm⁻¹) are due to the counter-complementarity of the multiple superexchange pathways, contributing to inspiring plots of ferromagnetic order (T_c = 11.0 K) and slow magnetic relaxation that are rarely observed in most reported azido-Cu(II) architectures. Heat-capacity experiments further emphasize the characteristic long-range ferromagnetic ordering in 1. Moreover, density functional theory (DFT) calculations (using different methods and basis sets) have been performed on the compound to obtain the theoretical interpretation of the magnetic behaviors.

In this article, polyaniline (PANI) nanofibers were prepared and added to low-density polyethylene (LDPE) to produce PANI nanofibers/LDPE composites. LDPE and the composites were tested for direct current (DC) conductivity, breakdown strength, and space charge characteristics. The results suggested that DC breakdown strength of PANI nanofibers/LDPE composites significantly declined once PANI was added, and the decline was more evident with the increase of PANI nanofibers. Meanwhile, the addition of PANI nanofibers contributed to a decrease in the conductivity of LDPE. As the content of PANI nanofibers increased, the conductivity of the composites declined first and then raised. DC conductivity properties of LDPE could be improved by adding an appropriate amount of PANI nanofibers. Compared with LDPE, the space charge distribution was changed in LDPE due to the addition of PANI nanofibers. With the increase of content of PANI nanofibers, the amount of space charges close to the electrodes decreased gradually.

With the bulge of electrical load for big cities, acceleration of island exploitation strategy and rapid development of renewable energy power generation, the development and application of flexible direct current (DC) power transmission have become an inexorable trend. As a major carrier of flexible DC power transmission, cross-linked polyethylene (XLPE) insulated high voltage direct current (HVDC) cables become more and more important in recent years due to their light weight, good electrical and thermal performance, simple manufacturing process, convenient installation and maintenance in combination with non environmental pollution. The aging of XLPE insulation usually occurs under the effects of such factors as electricity, heat, oxygen, humidity, mechanical stresses, light, chemicals and microorganism encountered in service. It can lead to irreversible damage of XLPE insulation materials, even power accidents, which may bring hidden danger to the operation of power network. In this paper, a comprehensive review is presented on the worldwide research and development related to the aging of XLPE insulation in HVDC cables. The principal factors and mechanisms causing the aging of DC XLPE insulation are also introduced together with the inhibition methods of space charge, which is one of the major components of the aging process in XLPE insulation.