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 view of the problem and difficulty of isothermal relaxation current method in evaluating the insulation state of distribution cables, a new sample of domestic unaged 10 kV distribution cable was used as the test object in this paper, and the isothermal relaxation current of the cable section and the high-field conductance current of the insulation slice during the 288 hours of accelerated thermal ageing process at 140℃ were detected. The variation trend and range of current relaxation component, ageing factor A, and threshold electric field E_t during thermal ageing were analyzed. The results show that there are three obvious polarization relaxation peaks in the isothermal relaxation current, and the time constants τ₁, τ₂, and τ₃ are in the range of 7-12 s, 31-39 s, and 210-536 s, respectively. During the thermal ageing process, the material traps corresponding to isothermal relaxation current Peak2 and Peak3 change greatly, and the change of Peak3 is the most obvious. The ageing factor A based on the isothermal relaxation current is in the range of 1.72-3.17. The A decreases at first and then increases with the increase of ageing time, and the corresponding conductance threshold electric field E_t shows the opposite trend of rising at first and then decreasing, which indicates that there is a clear correlation between the threshold electric field E_t and the ageing factor A, they are both the macroscopic appearances of internal molecular structure of the insulating material. The ageing factor A of the domestic cable before ageing is 1.91, which is close to the "aged" state of the German standard DIN VDE 0276, and the A drops to 1.72 after ageing for 48 h, which reaches the "better" state of the German standard. The high A of the domestic cable may be related to the residues of cross-linking by-products of cables, so the degassing process should be improved in the production of domestic cables.

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.

EVA resin insulating blankets are widely used in distribution network non-stop operations, and they often suffer from thermal melting and mechanical damage under high temperature and high load conditions, which will lead to insulation failure. In order to analyze the effect of high temperature on the mechanical properties of EVA insulating blankets, EVA insulating blankets were conducted tensile test, X-ray diffraction analysis (XRD), and dynamic mechanical thermal analysis (DMA) analysis at different temperatures, and their mechanical properties and aggregated structure changes at high temperatures were characterized by parameters such as elongation at break, tensile strength, and storage modulus. The results show that with the increase of temperature, the crystal type in the structure of EVA insulating blanket remains unchanged, and the crystallinity tends to increase, the grain size in the main crystallization area decreases at first and then increases, and the corresponding grain spacing gradually increases, which results in the elongation at break of EVA insulating blanket showing the trend of increasing at first and then decreasing. However, the tensile strength of EVA insulating blanket tends to decrease. Under high temperature, the storage modulus of EVA insulating blanket shows a decreasing trend, which indicates that the EVA insulating blanket is less resilient and less rigid under high temperature, and 40℃ is an appropriate operating temperature for the EVA insulating blanket.

Insulating materials are more prone to early failure under pulsed voltage, which seriously threatens the stability of power electronic devices and equipment. In order to explore the microscopic mechanism of insulation failure under pulsed voltage, the effect of space charge density in polyimide on the charge-excited molecular vibration at the pulse edge was explored in this paper, and the molecular vibration mechanism at the pulse voltage edge was expounded from the perspective of frequency domain. The results show that there is a large amount of heteropolar space charges accumulated inside the polyimide sample under DC voltage, which leads to the reversal of polarity of the molecular vibration waveform. In the frequency spectrum of pulse voltage rising edge, the voltage component in the frequency band of 5×10⁶-1×10⁷ Hz plays a major role in the molecular vibration. The charge-excited molecular vibration will expand the insulation defects and eventually lead to insulation failure.

The general properties, viscosity-temperature relationship, storage stability, and heat resistance of ELAN 3322-300 HV1 epoxy impregnating resin were systematically studied. Winding bar and coil samples were made to simulate the insulation structure of high voltage motor, and their electrical performance was tested. The class H insulation structure was conducted thermal ageing tests. The results show that the ELAN 3322-300 HV1 epoxy impregnating resin has low curing volatile and good storage stability, its temperature index is 211, and its temperature classification is class H. The winding bar and coil samples after impregnating have excellent electrical insulation performance and thermal ageing resistance, and the temperature index of class H insulation structure is 182. The ELAN 3322-300 HV1 epoxy impregnating resin is suitable for VPI insulation treatment of class F and H high voltage motor.

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.

The meltable polytetrafluoroethylene (PFA) was used as the matrix resin. Firstly, the PFA resin was modified by blending and filling with polymer and inorganic fillers to prepare suspension. Then, the suspension was coated and sintered in turn to prepare fluororesin-based film. Finally, the fluororesin-based film and copper foil were pressed together to prepare flexible copper clad laminate (FCCL). The results show that the prepared FCCL has 0.001 5 (10 GHz) of dielectric loss, 38 MPa of tensile strength, 0.05% of water absorption rate, greater than 1.0 kgf/cm of peel strength, and there is no delamination, oxidation, foaming in the soldering resistance test (300℃, 10 s, 3 times), which indicates that the FCCL has better overall performance.

Thermoplastic polypropylene materials have excellent electrical properties and thermal properties, and their production process does not require cross-linking and degassing, with low energy consumption and recyclability. Compared with cross-linked polyethylene, it is environmentally friendly and one of the best materials for the production of power cable. Taking polypropylene materials as the discussion object, the basic structure and physical properties of polypropylene and their relationship with electrical properties were introduced in this paper. The effects of copolymerization modification, blending modification, chemical modification, and nano particle modification on the structure, mechanical, thermal and electrical properties of polypropylene were reviewed. The research progress and application of polypropylene cables at home and abroad were introduced. Finally, the furure development of polypropylene materials were summaried and prospected from the production and preparation technology of polypropylene, relationship between structure and properties, and modification techniques.

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.