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.

Polymer film capacitors are widely used in many fields, such as high-pulse power technology, aerospace technology, and new energy vehicles due to their ultra-high charge and discharge efficiency. Polymer dielectrics used in energy storage applications often require high energy density and energy storage efficiency, and biaxial tensile polypropylene (BOPP) films, which are widely used in commercial thin-film capacitors, cannot meet the increasing demand for energy storage. Among many polymer dielectric materials, polymethyl methacrylate (PMMA) has attracted extensive attention due to its high breakdown strength, low dielectric loss, and easy processing. In this paper, the research progress of PMMA basic characteristic and composite dielectric materials in the field of energy storage was reviewed. The methods to improve the energy density and energy storage efficiency of polymer dielectric materials through chemical modification and physical modification were summarized, and the future development direction of dielectric materials was prospected.

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.

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.

The distribution transformers serving in the distribution network of urban villages have been in heavy overload operation for a long time, and the number of transformers approaching or even exceeding their design life is increasing. Prolonging their service life by replacing natural ester insulating oil is a feasible method of life extension. In this paper, the thermal ageing characteristic of aged mineral insulating oil-impregnated paper in natural ester was tested to analyze the pyrolysis characteristics of cellulose. Then the residual life of oil-impregnated paper after replacing natural ester was predicted by the pyrolysis kinetic model of oil-impregnated paper cellulose. The results show that the influence of the residual mineral insulating oil in the oil-impregnated paper on the pyrolysis process of cellulose after replacing the natural ester can be ignored. The moisture content of insulating paper is an important factor affecting its pyrolysis reaction, and the replacement of natural ester can significantly decrease the moisture content of insulating paper and delay the pyrolysis rate of insulating paper cellulose.

Epoxy composite is easy to accumulate space charge under high temperature and high electirc field condition, which would lead to local electirc field distort, and in severe case, partial discharge would produce and insulation would break down. Nano-MgO/EP composites with different doping rate were prepared by mixing nano-MgO particles into epoxy resin. Their glass transition temperature was measured by differential scanning calorimetry (DSC). Their trap characteristics were calculated by thermal stimulation depolarization current method (TSDC). Their space charge characteristics were measured by pulse electroacoustic (PEA) method. The results show that the addition of nano-MgO particles can increase the glass transition temperature of epoxy resin and inhibit the space charge accumulation in epoxy resin. With the increase of nano-MgO doping rate, the glass transition temperature of epoxy composite increases at first and then decreases, the deep trap energy level and density of nano-MgO/EP composite increase at first and then decrease, the space charge density of nano-MgO/EP composite decreases at first and then increases, and the electric field distortion trend is similar with that of space charge. When the doping rate of nano-MgO is 3%, the glass transition temperature of the nano-MgO/epoxy composite reaches the maximum value, and the ability to inhibit the space charge accumulation and electric field distortion is the best.

The thermal effect in the long-term operation of pumped storage generator sets will cause adverse effect on the main insulation performance of stator bars. Taking the VPI stator bar of an 18 kV pumped storage generator as the research object, we prepared samples and designed thermal ageing scheme. By means of dielectric property test, conductivity test, and breakdown characteristic test, the electrical properties of stator insulation under different ageing temperatures and different ageing cycles were explored. The test results show that there is obvious and complete loss peak in the bending section of stator bar. During the thermal ageing process, the dielectric constant frequency spectrum of insulating material shows an increasing trend with the increase of ageing period, and the dielectric constant of the bending section shows a stepwise decreasing trend with the increase of frequency. As thermal ageing progresses, the conductivity of samples increases gradually, and the absorption ratio and polarization index both show a decreasing trend. The breakdown strength of the straight section sample and the bending section sample continues to decrease, and the breakdown strength of the bending section sample decreases more significantly.

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.

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.

Partial discharge optical measurement method has strong anti-interference ability and high sensitivity, becoming one of the most important and effective methods to evaluate the insulation condition of electrical equipment, whose signal detection capability is closely related to the layout way of fluorescent fiber sensor. An experimental platform for fluorescent fiber PD detection was built in this paper. The influence of the relative distance between sensor and insulation defect on the PD detection effect was studied in linear layout and Archimedean layout, and then compared with the commonly used UHF method. The results show that the sensitivity of the Archimedes layout is better than the linear layout. When the distance between fluorescent fiber and PD defect is less than 45 cm, the two layout methods of fluorescent fiber sensors have higher detection sensitivity than that of the UHF sensors. For the linear layout, increasing horizontal distance has a more detrimental effect on PD detection than increasing vertical distance. For the Archimedean layout, the lateral offset of fluorescent fiber has a greater effect on the detection PD than the horizontal distance. Finally, according to the characteristics of the two layouts and the location of switchgear where PD is likely to occur, recommendations for placing fluorescent fibers in the switchgear were given.

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.

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.