In the partial discharge test and detection of power transformers, multi-source pulse overlap seriously affects the identification of partial discharge signals. In this paper, a clustering separation method of partial discharge signals based on multi-terminal pulse amplitude ratio was proposed. Firstly, the partial discharge test of 220 kV transformer was carried out, and the pulse overlapping phenomena in PRPD and T-F spectra under different test voltages were analyzed. Then, based on the propagation attenuation law of different types of pulses in transformer, a three-dimensional amplitude ratio pulse clustering separation method based on multi-terminal detection of transformer was proposed, and the method was realized by DBSCAN algorithm. Finaly, multi-terminal detection was carried out during the partial discharge test of 220 kV transformer, and the clustering separation and pulse source analysis of the pulse were carried out. The results show that utilizing the multi-terminal amplitude ratio clustering separation method can accurately divide the multi-source overlap pulses during partial discharge process in to interference pulse and two kinds of discharge pulse, and the initial location of the pulse source can be realized according to the amplitude ratio . The multi-terminal pulse amplitude ratio clustering separation method realizes the extraction of transformer partial discharge pulse, and its development and application will be conductive to improve the anti-interference capability and detection accuracy in transformer partial discharge testing.

Algae is a special kind of biofouling, its attachment on the insulator surface of electrical equipment will significantly reduce the fouling flash resistance of insulator , which poses a threat to the safe and stable operation of power grids. In this paper, a semantic segmentation algorithm of insulating algae integrated multi-scale convolution attention mechanism was proposed. Firstly, a model for insulating algae class semantic segmentation was constructed on the basic U-Net network model, and VGG16 was used as the backbone feature extraction network. The model adopts a U-shaped structure, and the left side is the feature extraction part of the VGG16 backbone, which can effectively extract the informations of five feature layers. The right side was the enhanced feature extraction part. CBAM module was selected for attention module, and the multi-scale convolution was introduced based on CBAM module. Then the CABM convolutional attention module was added to the encoder and the decoder of U-Net network before up-sampling and down-sampling. Finally, the model was compared with Deeplabv3+ and Transfuse network on the self-constructed algae-covered insulator image dataset. The results show that compared with the basic U-Net model, the mIoU value of this model improves by 0.28, mPA value improves by 0.27, Dice coefficient improves by 0.06, Hausdorff distance reduces by 11.77, and the RVE value reduces by 0.06. The visualization results of the segmentation process demonstrates that the model in this paper can pay more attention to the algal coverage region, and locate the boundary of the algal coverage region more accurately, which reduces the segmentation error effectively.

This paper introduced the research and application progress on green solvents in the preparation of polyimide from the views of the classification, manufacturing procedures, solvent composition of polyimide films, and the application status of green solvents. Emphatically, the current research status of biobased solvents, including γ-valerolactone (GVL), dimethyl isosorbide (DMI), and dihydrolevoglucosenone (Cyrene^TM) and their applications on the preparation of PI films were presented. The future developing trends of the applications of green solvents in the manufacturing of PI films were prospected.

Firstly, a Y-shape diamine monomer 4-(4′-tertbutyl)phenyl-2,6-di(4′-aminophenyl)pyridine (TPAPP) containing pyridine ring structure and tertbutyl group was synthesized. Then, it was polymerized with 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP) and 4,4′-(4,4′-isopropyldiphenyloxy)bis(phthalic anhydride) (BPADA), and a series of copolyimide (PI) films were prepared by thermal imidization. The structure and optical, mechanical, and thermal properties as well as solubility of the PI films were investigated by infrared spectroscopy, X-ray diffraction, UV visible spectra, tensile tests, dynamic thermo-mechanical analysis, thermogravimetric analysis, and solubility tests. The results show that as the molar ratio of TPAPP increases, the optical transparency and glass transition temperature of the copolyimide films exhibit an increasing trend. When the molar ratio of diamine and dianhydride is 5:5, the copolyimide film shows the best mechanical properties, with the tensile strength of 144.9 MPa, the Young's modulus of 3.4 GPa, and the elongation at break of 9.3%. In addition, these copolyimides demonstrate good solubility in aprotic polar solvents.

With the constant updating of flexible display devices, the researches on colorless transparent polyimide (CPI) films as substrate materials have attracted considerable attention. In order to solve the inherent contradictions among optical performance, high-temperature resistance, dimensional stability, and mechanical properties of CPI, we synthesized a series of semi-aromatic CIP films with side chains containing benzimidazole by copolymerization using cyclobutanetetracarboxylic dianhydride (CBDA) as the dianhydride monomer, 2,2′-bis(trifluoromethyl)-4-diaminobiphenyl (TFMB) and 2-(3,5-diaminophenyl)-benzimidazole (BBIA) as diamine monomers. The influence of hydrogen bonding, free volume, and main chain structure on the properties of films was systematically investigated by the Materials Studio software simulation and experimental results. The results show that the prepared CPI films have excellent optical transparency, thermal resistance, and mechanical properties. The average transmittance of CPI films in wave length of 380-780 nm is higher than 85%, the glass transition temperature (T_g) is above 400℃, the linear coefficient of thermal expansion (CTE) is 15×10^-6-17×10^-6 K^-1, the maximum tensile strength is 165 MPa, and the modulus is in the range of 3.7-5.2 GPa.

In order to improve the solution processability of traditional thermoplastic polyimide (TPI) and enhance its adhesion and heat resistance, several soluble thermoplastic polyimide (TPI) resins were prepared from different commercial dianhydride monomers and self-made diamine monomers with pyridine and diphenyl ether structures and active phenol side groups or benzene side group in the main chain through the two-step method. And then the corresponding TPI films and flexible copper clad laminates (FCCLs) were prepared. The properties of TPI resins were analyzed by solubility test and gel permeation chromatography (GPC). The structure, water absorption, mechanical properties, and dielectric properties of TPI films were tested, and the related properties of the FCCLs were also tested. The results show that all the TPI resins can dissolve in strong polar organic solvents such as NMP, and the glass transition temperature (T_g) and 5% thermal weight loss temperature (T_5%) of the corresponding films are in the range of 236.8-325.6℃ and 508.7-553.7℃, respectively, and the residue rate at 800℃ (R₈₀₀) is higher than 64%. The coefficient of thermal expansion (CTE), tensile strength, elongation at break, and water absorption is in the range of 56.36×10^-6-78.30×10^-6℃^-1, 64.93-109.18 MPa, 9.09%-24.60%, and 0.74%-3.75%, respectively. The dielectric constant and dielectric loss of TPI-4 with better comprehensive properties are also lower than that of other samples, and the peeling strength of the corresponding FCCL reaches 0.95 N/mm, but it can only pass the floating welding test at 288℃ for 10 seconds. In addition, the polar phenol side group in TPI-4 not only ensures its organic solubility, but also significantly enhances its heat resistance and mechanical strength, and also reduce its CTE. The existence of reactive phenol side groups provides great convenience for the subsequent chemical modification of TPI. By adding a small amount of cyanate ester resin (CE01) to modify the TPI, the peel strength and the floating welding resistance of the responding FCCLs can be obviously improved.

Polyimide films with high porosity were prepared using 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-diamino-2,2′-dimethyl-biphenyl (mTB) as monomers. During the preparation process, pore-forming agent was added into the system, and the high-temperature thermal imidization of polyamide acid was controlled by the principle of thermo-induced phase separation. The micropore morphology, mechanical properties, and dielectric properties of the films were analyzed. The results show that the porosity of porous films reach 50%-60%. Under the frequency of 10 GHz, the dielectric constant and the dielectric loss factor of the sample PI-1-250-4 h is 2.14 and 0.002 8, respectively, while maintaining good mechanical properties and heat resistance. Due to the introduction of rigid biphenyl building blocks, the porous film still maintains a low coefficient of thermal expansion. The adhesive-free double-sided copper clad laminate, which prepared by combining the porous film with thermoplastic polyimide (TPI) and then pressing copper foil at high temperature, has good interface adhesion and solder resistance, and can apply to high-frequency and high-speed flexible copper clad laminates.

Three fluoro-containing polyimide (PI) resins (PI-II_a, PI-II_b, and PI-II_c) were prepared by two-step chemical imidization procedure using a fluoro-containing dianhydride 9,9-bis(trifluoromethyl)xanthene-2,3,6,7-tetracarboxylic dianhydride (6FCDA, II) and three kinds of aromatic diamines, including 2,2ʹ-bis(trifluoromethyl)-4,4ʹ-diaminodiphenylether (6FODA, a), 1,4-bis[(4-amino-2-trifluoromethyl)phenoxy]benzene (6FAPB, b) and 2,2-bis[(4-aminophenoxy) benzene]propane (BAPP, c), respectively. For comparison, the referenced PI resins (PI-I_a, PI-I_b, and PI-I_c) were prepared with the same procedure except that 6FCDA was replaced by 4,4ʹ-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). And then six kinds of PI films were prepared by high temperature curing process, and their properties were studied. The results show that the solubility of PI-II_a, PI-II_b, and PI-II_c resins in organic solvents is lower than that of PI-I_a, PI-I_b, and PI-I_c resins. Compared with PI-I_a, PI-I_b, and PI-I_c films, PI-II_a, PI-II_b, and PI-II_c films show higher glass transition temperature (T_g), lower linear coefficient of thermal expansion (CTE), little lower optical transparency, and relatively higher dielectric constant (D_k). The PI-II_a film has the optimal comprehensive properties, its T_g and CTE is 362.5℃ and 39.6×10^-6 K^-1, respectively, its optical transmittances at the wavelength of 450 nm (T₄₅₀) is 83.9%, and the D_k at the frequency of 10 GHz is 3.00.

Four kinds of copolymerized polyimide (PI) membranes were prepared through thermal imidization method after solution polymerization between two kinds of self-made diamine monomers 9,9′-bis[4-(4-amino-3-hydroxyphenoxy) phenyl] fluorene (BAHPPF) and 4-(4′-tertbutyl)phenyl-2,6-di(4′-aminophenyl)pyridine (TPAPP) and 4,4′-(hexafluoroisopropene)phthalic anhydride (6FDA), and the molar ratio of BAHPPF and TPAPP is 9∶1, 8∶2, 7∶3, and 6∶4, respectively. Then the corresponding copolymerized thermal rearrangement (TR) membranes were obtained after heat treatment at 450℃. The thermal, mechanical, and gas separation properties of the membrane materials were measured. The results show that the glass transition temperature of the copolymerized PI membranes is around 350℃. As the molar ratio of TPAPP increases, the tensile strength of the copolymerized PI membranes decreases. After thermal rearrangement, the mechanical properties of the copolymerized TR membranes decrease significantly, while the d values increase. When the molar ratio of BAHPPF and TPAPP is 8∶2, the copolymerized TR membrane exhibits the best gas permeability, and the permeation coefficients for H₂, CO₂, O₂, and N₂, is 346.4, 304.5, 72.43, and 13.34 Barrer respectively. Meanwhile, the O₂/N₂ separation performance of the four TR membranes is close to the Robeson upper limit in 2008.

In order to improve the weak dispersion of two-dimensional nanosheets in polymer matrix and improve the electrical performance of composite materials, a two-dimensional micron expanded layer molybdenum disulfide (E-MoS₂) was prepared by hydrothermal method, and then polyimide (PI) based super-large lattice molybdenum disulfide nanosheets (PI/E-MoS₂) composite films were prepared by in-situ polymerization method. The surface/cross section structure of the composite films was observed by scanning electron microscopy (SEM), the molecular valence bond composition of the composite film was analyzed by Fourier infrared spectroscopy (FTIR), and the phase structure of the composite film was analyzed by X-ray diffraction (XRD). Furthermore, the dielectric constant, DC electrical conductivity, and dielectric loss factor of the composite films were tested, and the effect mechanism of extended lattice on the breakdown and polarization behavior of composite films was studied. The results show that when a small amount of E-MoS₂ nanosheets is added into PI film, there is little agglomeration phenomenon on the surface of PI/E-MoS₂ films, and there is little obvious holes and a small number of structural defects on the cross section, which indicates a good compatibility between fillers and matrix. The incorporation of E-MoS₂ nanosheets can enhance the interfacial polarization of the composite films, improve both the dielectric constant and electric field strength, and decrease the dielectric loss.