SF₆ is often used in GIE as an insulating medium, it will decompose when overheating or appearing partial discharge inside GIE, the decomposition products, such as SO₂, SOF_2, SO₂F₂, H₂S, and CO will produce after further reaction. In this paper, the components H₂S and CO were quantitatively measured by photoacoustic spectroscopy detection technology, and the factors affecting photoacoustic signal were discussed theoretically. A photoacoustic spectrum experiment platform was built, and the gas was measured quantitatively based on the photoacoustic effect. Appropriate gas absorption lines were chosen as characteristic spectrum line to avoid the potential cross-interference of other gas components. According to the results of HITRAN simulation, the characteristic spectrum line of H₂S was chosen as 6 336.6 cm^-1, and the characteristic spectrum line of CO was chosen as 6 380.3 cm^-1. The results show that the linearity between the gas concentration of CO and H₂S and the amplitude of pure photoacoustic signal is extremely high, which suggests that the gas concentration can be accurately calculated through the measurement of photoacoustic signal value of gas. With the background gas of SF₆, the lower limit of detection for CO is 9.88×10^-6, and the lower limit of detection for H₂S is 1.75×10^-6.

In the actual manufacturing and field installation, defects such as air, metal impurities, and uneven distribution are easily introduced into the silicone rubber insulation layer of cable joint, which endangers the safe operation of power grid system. At present, the detection of power equipment defects are mostly destructive tests, and the experimental results can only reflect the overall situation of equipment. As a non-destructive testing technology, ultrasonic testing can accurately locate and image defects inside the material, and reflect the changes of local performance inside the device. In this study, a set of ultrasonic testing platform were independently designed and built, and ultrasonic testing was conducted on the artificial silicone rubber samples with different defects. The results show that for flexible materials such as silicone rubber, ultrasonic testing can better image the bubbles, air gaps, and steel needle defects in the sample. Compared with similar X-ray testing, ultrasonic testing has an obvious amplification on the tiny bubbles defects. In addition, the ultrasonic testing technology can reflect the change of stress and density inside the material, and can accurately locate the specific depth of the defect according to the ultrasonic echo. This technology has broad application prospects in the location identification and online detection of internal defects in the silicone rubber insulation layer of cable joints.

Combining with the relationships among the DC submarine selection, voltage level, and transmission capacity of HVDC submarine cable projects in China, taking the raw material input of DC submarine cable required per unit transmission capacity as a typical economic index, we find that with the increase of voltage level and current capacity of the single loop DC submarine cable, the economy of DC submarine cable increases. By comparing the materials consumable variation of different routes after improving the voltage level and transmission capacity, we find that it is more effective to improve the economy of DC submarine cable by increasing the electrical level of DC submarine cable insulation and the maximum operating temperature of conductor to improve the voltage level and transmission capacity, respectively. In addition, a ±525 kV DC submarine cable with the highest conductor operating temperature of 70℃ was selected as the typical specification, and its insulation field strength distribution variations were analyzed through finite element simulation when the applied voltage and conductor operating temperature increased to 972 kV and 90℃, respectively. The results show that the increase of voltage level and conductor operating temperature will both cause a further increase of field strength close to insulation shield after the insulation field strength reversal, and there is a synergism effect between them. On this basis, a semicircular protuberance with 0.125 mm of depth was set on the interface of insulation shield into insulation, and the finite element simulation results show that the field strength at the protuberance increased by 35.4% compared with the case without protuberance.

With the miniaturization and lightweight of electronic equipment, graphite film materials with high thermal conductivity were widely concerned recently. In this paper, the preparation of polyimide (PI) based graphite film was reviewed, and the influence factors of their performance, which included molecular structure, molecular orientation, and the inducement of other materials, were introduced in detail. The research and patent situation of graphite film composite materials were summarized, and the future research and development direction were suggested and prospected.

In order to develop a high thermal conductive epoxy potting adhesive for dry-type transformer, we prepared a potting adhesive by adding self-made modified silica to epoxy anhydride system. The thermal conductivity and electrical insulation performance were tested, and the suitable pouring temperature and best curing process of the potting adhesive were studied. The results show that when the filling content is 75%, the potting adhesive has high thermal conductivity and excellent electrical insulation performance, the thermal conductivity is 1.494 W/(m·K), the dielectric loss factor is only 0.41%. When the pouring temperature is 70℃, the potting adhesive has good pouring process, the viscosity is low than 2 800 MPa·s within 2 h. The best pouring process for potting adhesive is 80℃ vacuum/0.5 h + 80℃/4 h + 90℃/3 h + 110℃/2 h + 140℃/5 h. Under the condition, the deposition of powder in potting adhesive is small, and the cured product has the best comprehensive performance.

In this paper, the effect of DC-temperature composite field on the electrical tree growth characteristics was introduced. The effect mechanism of charge transport on the electrical tree deterioration under temperature and electric field coupling conditions and the research progress in electrical properties of epoxy nanocomposite dielectrics were reviewed.

Spherical alumina was introduced in drawing and filtering process of graphene nanosheets to build a binary porous structure of “pea-pod-like” alumina-graphene, and an alumina-graphene binary structure reinforced epoxy resin composite was prepared. Its thermal conductivity was tested, and the mechanism of “pea-pod-like” alumina-graphene binary structure enhancing the thermal conductivity of epoxy resin was analyzed. The results show that the horizontal arranged graphene generates partial orientation transformation under the action of spherical alumina, showing a “pea-pod-like” structure, in which graphene provides an efficient heat transfer channel for epoxy composites in plane and out of plane directions and greatly enhances the thermal conductivity of epoxy composites. The thermal conductivity of “pea-pod-like” binary alumina-graphene reinforced epoxy composite is up to 13.3 W/(m·K) and 33.4 W/(m·K) in plane and out of plane directions, respectively with 12.1% of graphene and 42.4% of alumina loading. The “pea-pod-like” alumina-graphene binary structure has a significant effect in improving the thermal conductivity of epoxy resin, which has potential application prospects in the field of electrical packaging.

PI nano composite films were conducted long-term multiple ageing at 270℃, 70℃ and 90%RH, and 320℃, and their thickness, dielectric spectra, conductivity, partial discharge initiation voltage, and insulation life at different ageing stages were tested. The results show that the insulating properties of the PI film has no obvious change after ageing at 270℃. The high humidity environment has a significant impact on the dielectric spectra, conductivity, and partial discharge initiation voltage of the PI film, but it does not shorten its insulation life. The internal structure of PI film would change under the high temperature of 320℃, which will shorten its insulation life by about 30%.

Polymer materials such as epoxy resin have hidden dangers of thermal failure and insulation failure during long-term service since its low thermal conductivity. In this study, a high thermal conductive composite insulating material was prepared by filling micron boron nitride and nano alumina with high thermal conductivity and high insulation properties to epoxy resin, and the effect of filling amount and ratio of fillers on the thermal conductivity and insulation properties of composite materials were studied. The results show that when the total filling content is 30% and the mass ratio of micron boron nitride to nano alumina is 3∶1, the thermal conductivity, breakdown time, and imaginary part of complex permittivity (ε″) of the composite materials is 1.182 0 W/(m·K), 31.9 s, and 0.034, respectively, which is improved by 697%, 21.7%, and 406% compared with epoxy resin, respectively. The composite material has good resistance performance under high frequency and high electric field.

PTC resistance device, which made by positive temperature coefficient (PTC) material, can be used as a passive component to prevent overcurrent fault. In this paper, four kinds of polymer-based PTC materials were prepared by melting blending method, and the effects of conductive filler concentration, coupling agent, and supplementary conductive filler on their properties were studied. According to the temperature-resistance characteristics and heat transfer equation of polymer PTC composite, its current limiting process was simulated. The experimental results show that increasing the concentration of conductive filler will lead to the decrease of the resistivity of composite at room temperature. The PTC properties of the composites can be improved by using silane coupling agent to modify CB and adjusted by the interaction of various fillers. The simulation results show that under certain assumptions, the PTC resis-tor, as a passive component to prevent overcurrent fault, can limit the short-circuit current of power system in a short time.