The dissociation of impurities such as crosslinking by-products can easily lead to the accumulation of heteropolar space charges, resulting in local field strength distortion. At the same time, after the cross-linked polyethylene (XLPE) DC cables is degassing, the crosslinking by-product impurity in the insulating layer will form a concentration gradient distribution of "high inside and low outside", and the effect of impurity concentration gradient on the space charge is still unclear. Therefore, based on the bipolar charge transport model, the effect of cross-linked by-products impurity with uniform distribution and gradient distribution on the XLPE space charge and electric field distribution were simulated and calculated, and various factors affecting the gradient effect of impurity were analyzed. The results show that under the impurity gradient distribution, the space charge and electric field distribution of XLPE show obvious impurity gradient effect, that is, there are more opposite polarity charges accumulated on the low concentration side, which leads to the enhancement of the nearby electric field. While the impurity dissociation barrier and the impurity distribution concentration are the main reasons of affecting the impurity gradient effect. When the impurity concentration gradient is constant, the lower the activation energy, the higher the temperature, the lower the dissociation barrier, and the lower the carrier mobility, which results in the impurity gradient effect more obvious. The larger the insulation layer thickness, the higher the concentration of impurity distribution, and the more obvious the impurity gradient effect.

In order to obtain carbon-ceramic linear resistor with stable performance, the preparation of high resistance layer glaze slurry used in the manufacturing of carbon-ceramic resistor was studied systematically in this paper. Firstly, the glazing technology of glaze slurry prepared by different binders was compared, then the mixing time and water material ratio of slurry were systematically studied to obtain the influence of mixing time and water material ratio on the viscosity of glaze slurry, and finally the optimal mixing process parameters were determined. The results show that the glaze slurry has good suspension and coating properties when the Zuoyun clay is used as binder. When the mass fraction of Zuoyun clay is 15%, the glaze slurry has good processability and adhesion. The optimum mixing process parameters of high resistance glaze and binder is as below: Zuoyun clay is used as binder, the mass fraction of clay is 15%, the ratio of water and material is 0.6∶1, and the mixing time of ball glaze is 1 h. The breakdown strength of carbon-ceramic resistors coated with high resistance layer is 78% higher than that of the uncoated resistors, and the dispersion is smaller.

In this paper, the performance and characteristics of low smoke halogen-free flame retardant cable material was reviewed. The advantage and disadvantage of ethylene-vinyl acetate copolymer (EVA) as the base material was introduced.The types and flame retardant mechanism of halogen-free flame retardant were reviewed. Finally, the development direction of low smoke halogen-free flame retardant cable material was prospected.

An epoxy resin-based sheet molding plastic (E-SMC) was prepared by using multi-function epoxy resin as the resin matrix, dicyandiamide as main curing agent, and mica as fillers. Then the epoxy molding composite was prepared by molding process, and its mechanical properties, thermodynamic properties, and electrical properties were systematically tested and studied. The results show that the epoxy molding composites have high mechanical strength, and the tensile strength, bending strength, vertical compression strength and parallel compression strength of typical samples can reach 64, 178, 440, and 332 MPa, respectively. At the same time, the epoxy molding composites have low density (1.69-1.76 g/cm³), high glass transition temperature (T_g up to 201℃), and excellent electrical strength properties, and the breakdown voltage of typical samples is up to 100 kV, the electric strength can reach 17.1 kV/mm, the comparative tracking index (CTI) is 600 V.

In order to study the effect of organic and inorganic fillers on the performance of insulating paper, nano titanium dioxide (TiO₂) treated with dopamine hydrochloride was coated with nano-fibrillated cellulose to get a multiple mixed filler (PDA-TiO₂@NFC). Then the multiple mixed filler was filled into the cellulose insulating paper, and a sandwich structure insulating paper modified by different multiple mixed fillers was prepared. The optimal concentration of multiple mixed fillers was explored, and the tensile strength, DC volume resistivity, breakdown characteristics, and space charge of the modified insulating paper with different multiple mixed fillers were analyzed. The results show that when the multiple mixed fillers concentration is 0.5%, compared with the unmodified insulating paper, the tensile strength of the modified insulating paper increases by 17.90%, the AC and DC breakdown strentgh of oil-paper increase by more than 17%, and the injection of space charge can be effectively inhibited. The effect of multiple mixed fillers on the DC volume conductivity is not obvious. The mechanical properties and electric strength improvement of the sandwich structure insulating paper prepared using this method are significant, which provides reference for jointly improving the performance of insulating paper.

HVDC cross-linked polyethylene (XLPE) cables will be damaged by operation impulse voltage caused by switching and other operations in the power system under working condition, which will affect the insulation. However, at present, there is a lack of relevant research on the cable insulation deterioration generated by space charge accumulation caused by multiple impulse cumulative effect. Based on the PEA space charge measurement system under DC superimposed impulse voltage in the laboratory, the space charge characteristics of XLPE cable insulation under DC voltage, impulse voltage, and DC superimposed impulse voltage were measured in this paper. The results show that XLPE is dominated by heteropolar charges under positive DC voltage, and negative charges of the same polarity appear on the SC electrode under negative DC voltage. Continuous high-amplitude impulse voltage can cause large number of homopolar charges injection on the two electrodes, and the amount of injected charge is larger under negative impluse voltage. Under DC superimposed impulse voltage, the same polarity superimposition method can promote the injection of homopolar charge on the two electrodes more than the opposite polarity superimposition method. Moreover, the longer the impulse voltage is applied, the more charge accumulates in the XLPE sample.

The problem of nanoparticle agglomeration in wire enamel can be solved by modification and gradual dispersion of nanoparticles. Five modifiers, emulsifier OP-10, silane coupling agent AP1231, silane coupling agent A112, γ-propyl trimethoxysilane (KH560), and N-[3-(trimethoxysilyl) propyl] ethylenediamine (KH-792), were used to modify the surface of nano silica particles. The effects of modifier type, modifier dosage, modification temperature and time on the modification effect of nano-SiO₂ particles were explored. The effects of nano-SiO₂ particles before and after modification on the performance of corona resistant wire enamel were compared by corona resistance test, and the dispersion of nano-SiO₂ particles before and after modification was observed by transmission electron microscopy (TEM). The results indicate that the nanoparticles modified by KH-560 have the best dispersion in wire enamel, and the best process conditions are as follows: the dosage of KH-560 is 1.5wt%, the modification temperature is 90℃, and the modification time is 4 h. The wire enamel with high stability and higher than 50 h of corona resistance time can be obtained by gradually dispersing modified nanoparticles into the wire enamel, and the appropriate addition amount of nanoparticles is 13.5wt%.

Effect of swelling effect of silicone rubber (SiR) caused by silicone grease coated on the interface between high voltage cable accessories and cable body on the electrical tree characteristics of SiR under monopolar impulse voltage (250/2 500 μs) was studied. The isothermal surface potential decay (ISPD) and equilibrium solvent swelling were carried out to characterize the influence of swelling effect on the trap characteristics and crosslinking structures of SiR. The results show that with the increase of swelling time, both the initiation probability and fractal dimension of electrical tree in SiR increase. After 340 h of swelling, the tree initiation voltage of 50% probability under positive and negative impulse voltage decrease from about 37 kV and about -41 kV to 32 kV and about -39 kV, respectively. In addition, the polarity effect can be observed in the electrical tree process of SiR under impulse voltage. The initiation and growth of electrical tree is easier under positive impulse voltage than negative impulse voltage. With the increase of swelling time, the shallow trap density increases, and the deep trap and physical crosslinking density decrease. The destruction of physical crosslinking structure leads to the expansion of free volume, which intensifies the collision ionization processes. Meanwhile, the decrease of deep trap density enhances the charge transport processes. Multiple physical processes intensify the fracture of molecular chains, which furtherly weakens the resistance to electrical tree of SiR. The polarity effect of electrical tree in SiR under impulse voltage is mainly caused by the different distribution of hole-type and electron-type traps.

In order to investigate the effects of glassfiber architecture on the mechanical and fire-resistant performance of insulating slot wedge, unidirectional glassfiber, laminated glassfiber fabric, and rolled glassfiber fabric reinforced slot wedge were prepared using fire-resistant resin, glass fiber, glassfiber fabric as raw material, and the 3 types of slot wedge samples were conducted longitudinal impact strength test, width-directional bending strength test, and combustion tests. The results show that with the same sectional dimension and the same content of glassfiber for slot wedges, the order of longitudinal impact strength from strong to weak is glassfiber fabric reinforced slot wedge, glassfiber fabric laminated slot wedge, unidirectional glassfiber reinforced slot wedge; the order of elastic deformation during width-directional bending from big to small is glassfiber fabric reinforced slot wedge, glassfiber fabric laminated slot wedge, unidirectional glassfiber reinforced slot wedge; the order of fire resistance from strong to weak is glassfiber fabric reinforced slot wedge, glassfiber fabric laminated slot wedge, unidirectional glassfiber reinforced slot wedge. When the glassfiber content increases from 50% to 70%, the total afterflame time of the unidirectional glassfiber reinforced slot wedge, glassfiber fabric laminated slot wedge, and rolled glassfiber fabric reinforced slot wedge increases by 51.7%, 31.8%, and 46.3%, respectively.

The equivalent extended Debye model of oil-paper insulation in the damp state no longer has linear characteristics, which makes the evaluation method of oil-paper insulation based on time-frequency conversion have errors. In this paper, the advantages of time domain and frequency domain dielectric spectroscopy were integrated, and the grey correlation algorithm was used to construct the evaluation model of oil-paper insulation damp condition on the basis of the time and frequency domain dielectric response parameters. Firstly, oil-paper insulation samples with different moisture content were prepared, and the influence of moisture and temperature on the polarization and depolarization current (PDC) and frequency domain spectroscopy (FDS) curves was analyzed. Furthermore, the characteristic parameters of PDC and FDS curves under different damp conditions were extracted. On this basis, the grey correlation algorithm was used to integrate the time and frequency domain dielectric characteristic parameters of oil-paper insulation to obtain its standardized reference vector. Finally, the accuracy of evaluation model was verified by laboratory sample data and field transformer data, which provides a new method for warning and diagnosis of transformer early fault.