DC cable mainly uses oil-paper and crosslinked polyethylene (XLPE) as insulation, and the conductivity characteristics of the two materials are different, which has a significant effect on the electric field distributions in cable. In this paper, a finite element model was established based on the 500 kV typical DC cable structure, and the thermal-electrical coupled simulation analyses were performed on the oil-paper and XLPE insulated cables. The electric field distribution characteristics in the two insulation under different temperatures and temperature drops were studied, and the influences of the conductivity temperature and electric field coefficient on the field strength distribution were analyzed. The conductivity variations of oil-paper and XLPE insulations among the same temperature and field ranges were compared. The results show that the electric field distribution in oil-paper insulation is affected by the insulation temperature difference in the electric field strength range of 10-25 kV/mm and temperature range of 20-90℃, and hardly changes with the insulation temperature under definite temperature difference, while the electric field distribution in XLPE insulation is affected by both insulation temperature and temperature difference. In addition, the overall conductivity of oil-paper insulation is higher than that of XLPE insulation, and its change amplitude with temperature and field strength is larger, which may be the reason why the electric field inversion in oil-paper cable insulation occurs at a lower temperature difference. For the insulating materials used in HVDC cables, the conductivity temperature coefficient should to be controlled small so as to reduce the temperature sensitivity.

In order to improve the adhesion of thermoplastic polyimide (TPI) between thermosetting polyimide (PI) film and copper foil in two-layer flexible copper clad plate (2L-FCCL), a series of TPI samples were prepared by one-step reaction using flexible aromatic dianhydride monomers and aromatic or alicyclic diisocyanate monomers. Then, the selected TPI solution was directly coated on the pretreated commercial thermosetting PI film to obtain the composite film, and the corresponding 2L-FCCL was obtained by hot pressing at high temperature. By observing the state of the TPI reaction solution and conducting DSC testing, TPI-8 is selected, which is soluble in organic solvent and has a T_g of 226.5℃. Then, TGA, TMA, and tensile tests show that the 2% thermal decomposition temperature (T_2%) of TPI-8 is 464℃, the thermal expansion coefficient (CTE) of 50-200℃ is 64.25×10^-6℃^-1, the tensile strength is 64.52 MPa, the elastic modulus is 1.75 GPa, and the elongation at break is 62%, and its chemical structure is confirmed by FTIR. Finally, the effect of alkaline pretreatment time of two kinds of thermosetting PI films on the bonding properties of resulting FCCLs was studied. It is found that the 90° peel strength (90°PS) of FCCLs are over 0.7 N/mm and the maximum value is 0.94 N/mm after SPI films treated with alkaline water at 60℃ for 1 min and 3 min. However, the 90°PS of FCCLs obtained by UPI films treated with the same hot alkaline water for 1-7 min are all less than 0.6 N/mm. Therefore, this method can be used to quickly and simply prepare TPI by one step, which is soluble and has good thermal, mechanical properties and dimensional stability. Meanwhile, it has good bonding properties for copper foil and SPI that the surface was pretreated with alkali water, and meets the requirements of relevant FCCL standards.

Polyvinylidene fluoride (PVDF)-based polymer has promising applications perspectives in the field of high energy storage density and high pulse energy storage. In this paper, barium titanate (BTO) nanoparticles were doped with polyvinylidene fluoride-chlorotrifluoroethylene (P(VDF-CTFE)) solution, and P(VDF-CTFE)/BTO composite films were prepared by solution casting method. The effects of different BTO doping contents on microstructure, dielectric properties, and energy storage characteristics of the composite films were investigated. Then the BTO was modified by dopamine (DA) to enhance the compatibility between BTO and polymer matrix and improve the dielectric constant and electric strength of composite films. At the same time, on the basis of the "breakdown blocking effect" between the films layers, the laminated composite films were prepared to enhance the energy storage properties. The results show that using the P(VDF-CTFE)/DA@BTO composite film with a DA modified BTO mass fraction of 10% as the interlayer, and the P(VDF-CTFE) as the outerlayer, the prepared PV-BT-PV laminated sandwich composite film has a dielectric constant of 10.44, a maximum electric strength of 362.25 kV/mm, and a charge discharge efficiency of 86.63% at an electric field strength of 500 kV/cm.

Room temperature vulcanized silicone rubber (PRTV) material is the most commonly used anti-pollution flashover coating in power system at present. In order to further improve the insulating performance of PRTV material, the boron nitride (BN) nanoparticles was modified by silane coupling agent KH570, and a BN/PRTV composite was prepared. The effects of BN doping content on the electrical properties and hydrophobicity of the composite material were studied. The results show that the surface of the BN nanoparticle is successfully grafted with coupling agent. With the increase of BN nanoparticle content, the section interface roughness of the composite increases and the mastoid structure appears. The introduction of BN nanoparticles reduces the dielectric constant of PRTV material, and introduces more deep traps inside PRTV, which inhibitis the charge detrapping ability and increases the flashover voltage of PRTV material. When the mass fraction of BN nanoparticles is 5%, the hydrophobicity of the composite is the best and the and flashover voltage is the highest.

In the process of injection molding of the epoxy insulator on EMU roof, there will be two closing joints on the surface of the umbrella skirt along the vertical direction, the convex edges will distort the electric field near it. In this paper, the influence of the closing joint on the flashover path of the epoxy insulator on EMU roof under wet conditions was studied. Through the spray flashover test, the flashover probability between the closing joint and other parts of the umbrella skirt was compared, the motion characteristics of water droplets on the surface of the epoxy resin umbrella skirt were observed, and the effects of the closing joint on the formation of water band, electric field intensity, and current density distribution were analyzed by simulation. The results show that the flashover channel is easily form at the closing joint, and under the action of electric field, the water band near the closing joint will stretch or even bridge the adjacent skirt. The current density of water band at the closing joint of high voltage end umbrella skirt is more than one time higher than that at other parts of the umbrella skirt. The water band bridging skirt will distort the local electric field, decrease the creepage distance and increase the voltage value borne by the unit creepage distance.

In order to improve the cracking resistance of the encapsulating insulating material for dry-type air-core reactor, it is necessary to improve the toughness of the epoxy resin composite while ensuring the good electrical properties. In this paper, an epoxy glass fiber composite with good mechanical and electrical properties was obtained by adding different content of epoxy-terminated liquid nitrile butadiene rubber (ETBN), different content and partical size of Al₂O₃ powders to the epoxy glass fiber (EP/GF) composite, and its structure and morphology, mechanical and electrical properties were tested. The results show that when the mass fraction of ETBN, 5 μm Al₂O₃, and 100 nm Al₂O₃ is 10%, 30%, and 3%, respectively, the bending strength of the EP/GF composite reaches the highest of 291.0 MPa, which increases by 33.5% than that of the unmodified composite, and the electric strength is 24.3 kV/mm, the comprehensive properties are the best.

COMSOL finite element simulation software was used to study the effect of bird droppings with different morphological characteristics on sulator flashover. By studying the influences of the length and viscosity of bird droppings on the flashover and the process of insulator flashover caused by the bird droppings falling, the calculation method of the combined air gap breakdown voltage composed of multiple sections bird droppings with different viscosities was obtained. The results show that the higher the viscosity of bird droppings, the better the continuity of bird droppings, the lower the breakdown voltage of the air gap, which is easy to cause the composite insulator flashover. Therefore, in order to improve the protection ability of anti-bird shield to high viscosity long bird droppings. the anti-bird shield must have the ability to reduce the length of bird droppings. In this study, a deflector groove was designed on the surface of anti-bird shield, and the high viscosity long bird droppings can be divided into several sections of short bird droppings through the deflector groove. By reducing the length of bird droppings, the air gap length increases, so as to increase the breakdown voltage and decrease the probability of bird droppings flashover.

In this paper, tetracyano-benzoquinone dimethane organic small molecules with narrow band gap were introduced, and polyethylene/tetracyano-benzoquinone dimethane composites were prepared by solution blending. The effects of doping content of tetracyano-benzoquinone dimethane on DC breakdown properties, high field conductance and trap distribution properties of the composite were investigated. The results show that the electric strength of the composite increases first and then decreases with the increase of the doping content of tetracyano-benzoquinone dimethane, the addition of tetracyano-benzoquinone dimethane increases the electric strength of polyethylene by a maximum of about 54%, and effectively decreases its conductivity. Trap distribution measurement and quantum chemical simulation confirm that tetracyano-benzoquinone dimethane introduces charge deep traps, enhances the trapping effect of charge carriers, and improves the DC electric strength of polyethylene.

The research on the pyrolysis gas generation law of cable can provide a basis for cable fire early warning. In this paper, a high temperature pyrolysis experiment platform was set up for common cables. The pyrolysis gas generation laws of PVC outer sheath of cables at 75, 100, 120, and 150℃, as well as the pyrolysis gas generation laws of cable internal materials at 185℃ and 225℃ were studied, respectively. The results show that PVC outer sheath of cables has been pyrolyzed at 75℃, and the pyrolysis gases are CO and CO₂. When the temperature is below 120℃, the pyrolysis gas components are only CO and CO₂, so CO and CO₂ are suitable as early characteristic gas components for commonly used cable fires. When the temperature is 150℃, gas components such as CH₄, C₂H₄, C₃H₆, and CH₃Cl appear in the pyrolysis gas, so the CH₄, C₂H₄, C₃H₆, and CH₃Cl can be used as the characteristic gas components of cable overheating faults.

In order to meet the stress grading requirements of the 18 kV hydro-generator in a large hydropower station with an altitude of 2 500 m, the air breakdown field strength and its influencing factors at the target altitude were analyzed theoretically, and the overhang electric field characteristics was evaluated by establishing a three-dimensional simulation model of stator winding overhang, the influences of the clearance distance and binding structure on the electric field at overhang hypotenuse were analyzed, the scheme of controlling the minimum clearance distance at the overhang hypotenuse of the stator winding to 15 mm was determined. Finally, the stress grading performance of 18 kV hydro-generator stator coil and winding was tested and verified in a large high-altitude environmental simulation laboratory. The results show that the stress grading performance of the 18 kV hydro-generator is good and can meet the stress grading requirements at an altitude of 2 500 m.