External force is the significant factor affecting the buffer layer ablation faults development of high voltage cables. The actual cable laying conditions and cable core gravity will lead to inhomogeneous force on the buffer layers. However, the influence of inhomogeneous force on the development process of buffer layer ablation faults is still unclear. In this paper, a simulating ablation experiment platform of buffer layers under inhomogeneous force was built. The influence of local inhomogeneous force on the buffer layer ablation development process was studied under dry and wet conditions. Then combining with the variation of buffer layer local volume conductivity, micromorphology and the components of ablation products, the affecting mechanisms of inhomogeneous force on the fault development were analyzed. The results show that in the dry condition, the current density of buffer layer decreases gradually with the ablation time, and the decreasing rate is higher in the force concentration region. While in the wet condition, the current density of buffer layer surges dramatically in the initial ablation stage, and then drops rapidly, exhibiting the characteristic of a current density peak. In the local force concentration region, the peak value of current density is larger, and the current density variation rate inner the peak is faster. It is analyzed that the local force concentration could increase the effective contact area between the buffer layer semi-conductive fibers, leading to the rising of current density and aggravating of ablation process.

In order to study the surface potential and electric field variation law of porcelain insulators under suspended sand and dust weather, a simulation model of xp-70 ceramic suspension insulator was established on the basis of electrostatic field model of finite element method, and the potential and electric field distribution law of porcelain insulators in various suspended sand and dust environments was summarized on the basis of finite element software calculation. The results show that the electrically neutral sand particles in the air can cause small distortion of the surface potential and electric field of porcelain insulator. When the sand and dust around the insulator are all positively charged, the surface potential will increase, and the surface electric field will decrease near the high voltage end and will increase near the low voltage end. When the sand and dust around the insulator are all negatively charged, the surface potential will decrease as a whole, the surface electric field will increase near the high voltage side of insulator string and will decrease near the low voltage side, and its distortion amplitude is proportional to the absolute value of dust particle size, concentration, and charge-mass ratio. When the insulator is in a mixed sand and dust environment of half charged and half electro-neutral, its surface potential and electric field will be distorted, and its distortion amplitude is less than that when the entire sand and dust are charged, and greater than that of the insulator alone in the sand and dust environment. When the insulator is in a "positive and negative" sand and dust environment, the distortion amplitude of surface potential and electric field is similar to the distortion amplitude in the electro-neutral sand and dust environment.

Composite cross arm has wide application prospect because of its good insulation performance, light weight, and saving transmission corridor. However, the research on the production design, test acceptance, construction operation and maintenance, standards and specifications of composite cross arms, especially for 500 kV and above of composite cross arms is still blank at home and abroad. The electric field distribution characteristics of high-voltage composite cross arm during operation is a problem that must be solved in the process of design and acceptance of composite cross arm. In view of the above situation, an electric field distribution and potential calculation model of 500 kV composite cross arm was established in this paper. The 500 kV composite cross arm and its connected tower were simulated and analyzed by the finite element analysis software. In addition, for the convenience and operability of subsequent ageing and insulation experiments, a 500 kV composite insulation cross arm scaling model was established and its test voltage was determined. The results show that the maximum field strength on the surface of composite insulated cross arm occurs at the high voltage of cross arm, and the electric field strength is 3.82×10⁵ V/m. The maximum electric field strength on the surface of the cable-stayed insulator is 86.38% of maximum electric field strength of the strut cross arm, and the maximum electric field strength is 3.3×10⁵ V/m. The test voltage, which make the maximum surface electric field strength reach expected electric field strength, is determied as 60 kV when the scale model is reduced according to 1∶5, which provides theoretical basis for the initial test of composite cross arm.

Infrared temperature rise detection is an effective means to screen faulty composite insulators. However, the causes of abnormal heating of composite insulators are diverse, and not all causes will evolve into malignant faults. Therefore, it is particularly important to distinguish the abnormal heating caused by different causes for the safe, stable, and economic operation of power grid. In this paper, the physical and chemical properties of two 220 kV retreated composite insulators with different heating characteristics were studied by SEM and FTIR, and their dielectric properties were also studied. The results show that the causes of different abnormal temperature rise are different. For the composite insulator whose heating part is concentrated at the end of high-voltage end and temperature rise is lower than 5℃, the epoxy resin of the core rod at the heating part has no obvious degradation, and the dielectric constant and dielectric loss factor have no obvious increase, while the sheath has holes and shallow microcracks, and the dielectric constant and dielectric loss factor increase with the increase of humidity. For the composite insulator whose heating part extends to multiple umbrella skirts and temperature rise is up to 40 ℃, the epoxy resin of the core rod has obvious degradation, and the dielectric constant and dielectric loss factor are 3.67 times and 79.4 times bigger than those of the normal part, respectively.

On the basis of the statistics of bird damage accidents and drainage line faults in Ningxia, the causes of drainage line faults caused by bird dropping were analyzed. The metal conductor was used to simulate bird dropping. Under the condition of power frequency, the flashover characteristics of insulated drainage lines with different structural parameters were studied. Combined with simulation analysis, the influence of insulation thickness, conductor diameter, end shape and other parameters on the flashover characteristics of insulated drainage lines was obtained. The results show that compared with the diameter of conductor, the thickness of insulation layer has big effect on the flashover characteristics of the insulation drainage line, and within a certain range, the greater the thickness of insulation layer, the greater the flashover voltage. The flashover voltage along the insulation drainage line is not always positively correlated with the increase of surface distance. Within a certain range, the flashover voltage increases with the increase of surface distance d and then tends to stable and close to a peak value. The installation of terminal head can increase the creepage distance along the surface of insulation drainage line, effectively improve the flashover voltage of the insulation drainage line, and effectively hinder the development of surface arc, which has a significant improvement on the surface flashover of insulation drainage line.

Enamelled rectangular magnet wires used in driving motor for electric vehicle need to test their partial discharge initial voltage (PDIV). However, the current IEC and national standards have no normative parameter on the PDIV test condition, and domestic motor manufacturers have different requirements on the PDIV performance. In order to obtain accurate PDIV data, the testing principle of instrument for measuring partial discharge was studied. The influence of test methods on the PDIV results of polyamide-imide and polyimide enamelled rectangular magnet wires under different voltage increase rate, determination threshold, and fitting length of wires was analyzed. The results indicate that if 10 V/s and 10 pC are taken as test condition and the fitting length of wires is more than 90 mm, the PDIV results are the closest to the theoretical value. If higher rising rate and higher threshold are used, the measured PDIV results will be higher, and the stability of test results will decrease.

In this paper, the modification methods of polypropylene, the development and operation of polypropylene cables, and the existing regulations and specifications of polypropylene cables were reviewed. According to the research and development status of polypropylene cables, the problems that may be encountered in the future operation of polypropylene cables were summarized and research suggestions were put forward, which can provide reference for the subsequent research and commercial application of polypropylene cable.

The thermal conductivity mechanism and common thermal conductive fillers of thermal conductive silicone composites for electronic packaging were presented, the preparation strategies and research progress of filled-type high thermal conductive silicone composites were reviewed, and the future research direction of thermal conductive silicone composites for electronic packaging was prospected.

In order to study the surface properties of different materials of insulators, epoxy resin and polytetrafluoroethylene (PTFE) were used as research objects. Firstly, the adhesion characteristics of insulators made of different materials were obtained through surface energy test. Then, the influence of different particle sizes of metal patticles on the surface flashover characteristics of insulators under natural adhesion conditions was studied through test. The results show that the surface energy of PTFE insulators is 30.44 mJ/m², which is lower than that of epoxy resin insulators, and the viscosity of PTFE is smaller. As the particle size of metal particles attached on the insulator surface decreases, the surface flashover voltage of epoxy resin and PTFE insulators increases gradually, and the surface flashover performance of the two materials of insulators is similar. The insulation failures caused by metal particles can be reduced by replacing the original epoxy resin interface with PTFE.

On the basis of the crystal structure of piezoelectric effect of polyvinylidene fluoride (PVDF) polymer, the effects of different annealing temperatures (60-160℃) on the surface crystal morphology, crystal size, crystallinity, and key dielectric parameters including polarization response curve and piezoelectric coefficient of PVDF film samples were studied. The results show that the sample crystal size and crystallinity increase with the increase of annealing temperature in the range of 60-140℃. The polarization curves show higher residual polarization intensity and hysteresis, and the piezoelectric coefficient increases from 11 pC/N to 27 pC/N with the increase of annealing temperature. When the annealing temperature reaches 160℃, cracks appear on the surface of sample, and consequently the breakdown is easy to occur in the polarization process, and the dispersity of piezoelectric coefficient is large.