The ultra-high frequency (UHF) method for detecting partial discharge (PD) is currently one of the important means to evaluate the state and insulation performance of gas insulated switchgear (GIS). In this paper, in order to solve the problem of a large number of missing and false alarms in UHF detection of GIS partial discharge, GIS insulator with metal foreign object attached on the surface was conducted long-term constant voltage experiments. The successful capture probability of discharge signal was analyzed by combining with the existing UHF detection strategies, and optimization schemes of the existing UHF signal detection strategies were proposed from detection time and detection threshold. The results show that the partial discharge of metal foreign object defect attached on the insulator surface has intermittent characteristics, and the existing UHF live detection and online monitoring strategies have low detection probability of discharge. The capture probability of effective discharge can reach 85% by extengding the detection time to 2 247 seconds in optimization of live detection strategy. The detection probability of PD Event can increase by extengding the measurement time of forming a partial discharge event (PD Event) and reducing detection threshold in optimization of online monitoring strategy. In engineering application, the combination of appropriate measurement time and detection threshold can be selected to detect the intermittent discharge.

To solve the problem that frequency domain reflectometry (FDR) can only distinguish defect polarity and cannot identify the defect length and type, a defect type discrimination method was proposed on the basis of signal attenuation intensity evaluation in this paper. The difference between the total refracted reflection intensity at each defect and the initial reflection intensity was calculated, and then the defect length and type can be discriminated by comparing the magnitude of difference. Combined with the polarity judgment method, the defect can be subdivided into four types. The results show that the method proposed in this paper can successfully identify the length and type of four common defects in cables, including grounding faults, excessive bending, cable body moisture, and long intermediate joints of cables, and the recognition results are consistent with the simulation modeling results. The defect type discrimination method in this paper can identify the common point defects and segment defects in cables.

In order to more finely evaluate the influence of factors such as the microstructure and material composition of the shed on the macroscopic performance of insulators, the mechanical properties, thermal weight loss, and Fourier infrared spectrum of AC composite insulators with different operating years were tested combined with the molecular dynamic simulation method in this paper. The results show that with the increase of operating years, the tear strength, tensile strength, and elongation at break of the insulator shed from low-voltage end to high-voltage end show a decreasing trend. The content of organic silicone and SiO₂ in the outer layer of shed significantly decrease, which can cause a decrease in macroscopic mechanical properties. In the electro-thermal environment, the bulk modulus, Young′s modulus, and Poisson′s ratio of the shed decrease with the increase of temperature and fluctuate with the increase of electric field strength. The high-voltage end of insulator has the most severe electric field distortion and the worst mechanical properties. The multi-scale model of the composite insulator shed ageing established in this paper can provide a reference for evaluating the ageing state of insulator.

In this paper, the space charge formation mechanism and space charge effect were systematically described. Three methods of constructing trap energy levels, including filling inorganic nanoparticles, doping small molecule semiconductors, and molecular structure design, were emphatically reviewed. The design strategy to improve the energy storage performance of the dielectric material were deeply discussed, and the preparation methods of high performance polymer dielectric materials were prospected.

In this paper, combined with the application of insulation varnishes on the market in traction motors, the research status and development trend of insulation varnishes for traction motors at home and abroad were reviewed. The insulation varnish systems developed from 180-class (H) diphenyl ether system to the 200-class (N) epoxy anhydride system, and then to the 220-class (R) silicone insulation system, indicating that the insulation varnish system for traction motors were developing towards high heat resistance direction, and the future development and application trend was still high heat resistant insulation varnish systems.

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.

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.

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.

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.