Abstract：

Nano sepiolite (hereinafter referred to as sepiolite) was used as a synergist to prepare flame-retardant ethylene-vinyl acetate copolymer (EVA) composite materials. Influence of sepiolite on the mechanical, thermal, and flame retardant properties of magnesium phosphorus flame retardant EVA was studied through hardness, tensile testing, thermogravimetric analysis (TGA), oxygen index (LOI), and cone calorimeter testing. Results showed that with the increase of sepiolite addition, hardness of samples showed an upward trend, breaking strength showed a downward trend, percentage of breaking elongation showed a trend of first increasing and then decreasing. In terms of insulation resistance, when the addition of sepiolite was less than 2 g, the volume resistivity of EVA composite materials increased. when the addition of sepiolite was more than 2 g, the volume resistivity of EVA composite materials decreased sharply. In terms of thermal properties, with the increase of sepiolite addition, the initial melting temperature, melting peak, crystallization temperature, and crystallinity of EVA composite materials increased first and then decreased. There were three stages of weight loss during heating process, the first decomposition peak temperature changed slightly when the addition of sepiolite was less than 2 g, and decreased significantly when the addition of sepiolite was more than 2 g. The second decomposition peak temperature decreased from 383.8 ℃ to 375.9 ℃ with the increase of sepiolite addition, and the third decomposition peak temperature remained basically unchanged. In the limiting oxygen index (LOI) test, LOI gradually increased with the increase of sepiolite addition, rising from 32.7% to 34.7%. In the cone calorimeter test, adding an appropriate amount of sepiolite could effectively reduce fire behavior parameters, such as heat release rate (HRR), total heat (THR), total smoke release (TSP), and mass loss rate (MLR). The ashes photos showed that a dense crust layer with flame retardants could form when the addition of sepiolite added was 2 g, which could hinder the spread of flames inward.

Abstract：The cable industry plays an instrumental role in supporting the national economy,contributing to the stable growth of economy and the safe operation of society.Technological advancements in China’ s cable industry was comprehensively summarized,with a focus on developments in power cables,equipment cables,winding wires,communication cables,conductor materials and overhead power lines,covering localisation of insulating materials,innovation of production equipment,and diversified development of cable products.In addition,the application prospects and industrialization challenges of high-performance carbon fiber,copper-graphene and aluminum-carbon nanotube synthetic materials in cable industry were discussed,to provide reference for scientific and technological workers in the field of cable.

Abstract：

Polypropylene insulation power cables have been widely concerned in related fields at home and abroad because of their excellent electrical properties, eco-friendly and recyclable features. With the popularization and application of polypropylene cables, several standards and specifications for polypropylene cables and their materials have been formed. In view of a number of group standards on thermoplastic polypropylene cables and polypropylene cable materials published by domestic industry, the test items, conditions and requirements of each normative documents were compared, the problems concerned were discussed in the engineering application of polypropylene cables, and the research directions for standardization process of polypropylene cables were proposed. These could provide reference and guidance for more scientific and standardized development of polypropylene cables system in the future.

Abstract：

In recent years, polypropylene (PP) insulation power cables have been vigorously developed and promoted due to its excellent high temperature electrical performances and environmentally friendly properties. However, at present, thermal shrinkage, low temperature shrinkage and aging mechanical characteristics of the polypropylene cables are not thoroughly studied, especially the mechanical characteristics of PP cable after cabling. In order to meet the needs of cable laying and maintenance in operation, thermal shrinkage, low temperature shrinkage, and body insulation aging tests of 110 kV grafted PP insulation power cables were carried out, horizontal and longitudinal comparative analysis was made. Results showed that thermal shrinkage of grafted PP insulation power cables was lower than that of cross-linked polyethylene (XLPE) cables at operating temperature. After low temperature test with −40 ℃ and 48 h, the shrinkage of insulation outer perimeter of grafted PP cables was only 0.46% to 0.68%, and shrinkage rate of longitudinal length of PP cables with non-conductor was closed to 0.60%, while that of PP cables with conductor was only about 0.20%. After 360 h of aging at 150 ℃, mechanical characteristics of grafted PP cables could still meet the requirements of no more than ±25% change rate of tensile strength and break elongation. In this paper, mechanical characteristics of grafted PP insulation power cables were preliminarily explored, which could provide the basis for engineering design and operation criteria of grafted PP power cables in the future.

Abstract：

In order to better design the structure of high voltage direct current (HVDC) crosslinked polyethylene (XLPE) insulated submarine cable and speed up insulation localization process of DC submarine cable, conductivity of XLPE material from HVDC submarine cable at different temperatures and different electric field intensities were determined by testing method of cable insulation conductivity. Simulation software COMSOL Multiphysics was used to analyze temperature field, electric field intensity and space charge distribution inside the insulation of DC submarine cable under the same laying condition and different load currents by step-by-step coupling analysis method. Simulation results showed that step-by-step coupling analysis method could significantly reduce model solution time and improve computational efficiency. Under the normal working condition, temperature gradients and electric field intensity gradients would be generated inside the insulation of DC submarine cables, which could lead to variations in conductivity and furtherly affect the distribution of electric field intensity in the insulation. When load current inside the cable core increased to a certain extent, field intensity inversion phenomenon appeared. Besides, space charge accumulation occured on both inner and outer surfaces of insulation. Corresponding simulation results could provide reference for the subsequent structural design of DC submarine cable, and provide theoretical basis for the development of domestic raw materials of DC submarine cable.

Abstract：

Due to complex operating environment of submarine cables, fault location often suffers from poor accuracy and low efficiency. Based on the principle of electromagnetic induction, combined with a construction case of submarine cable location for offshore wind farm fan collectors in China, magnetic field waveform characteristics of the faulty submarine cable were studied, and the difference of magnetic field waveform under different electrical wiring conditions was analyzed. At the same time, measurement data of global positioning system (GPS) was coupled to achieve accurate fault location. Results showed that electromagnetic technology could effectively realize the accurate fault location of submarine cables, which could provide a feasible case for similar fault location, and was of great significance for the implementation and promotion of related technologies in the future.

Abstract：To investigate thermoplastic polyurethane elastomers (TPU) for low-smoke halogen-free flame retardant cables, TPU was prepared by using aluminium hydroxide (ATH) and diphenyl phosphate (BDP) as flame retardants, zinc borate(ZB) and organically modified montmorillonite(OMMT) as synergists. Vertical burning test, limiting oxygen index (LOI) and NBS smoke density test were used to evaluate the performance of TPU sheath material for low-smoke halogen-free flame retardant cables. Results showed that surface treated ATH had higher mechanical properties than the untreated ATH. Phosphate ester improve flame retardant performance of the material, and also reduce performance damage to TPU in the modification process. ZB and OMMT could improve flame retardant performance of TPU, and reduce smoke density of the material, but improvement effect of OMMT on flame retardant performance and smoke density was better than that of ZB.