Partial discharge (PD) measurement is an effective way to diagnose the defects and ageing of insulation system in high-voltage electrical equipment. The variation of applied voltage waveform can contribute to deeper understanding of discharge physical process. In this work, symmetrical trapezoidal-wave voltage was employed to investigate the effect of waveform parameter on PD characteristics, based on the PD activity produced in a spherical-plane asymmetric electrode structure on the stator insulation of electrical machines. The results show that apparent PD charge mainly concentrates around 300-500 pC, and it has little relation with the waveform parameter in the trapezoidal-wave voltage. Maximum PD charge in the negative half cycle of applied voltage is larger than that in the positive half cycle. This is mainly due to the metal-dielectric asymmetrical structure of test cell and space charges deposited on the dielectric surface. With the increase of voltage change ratio dU/dt, average PD charge increases, while time delay caused by the phase shift decreases. With the increase of constant-voltage period, both average PD number and average PD charge exhibit almost exponential increasing trend.

The dielectric spectrum experimental data of epoxy resin material for ultra high voltage (UHV) power equipment was fitted by Havriliak Negami (HN) equation, and the HN mathematical model parameters of epoxy resin material were established. In the frequency range of 10^-1-10⁶ Hz and temperature range of -40-200℃, the frequency spectra and temperature spectra of epoxy resin were measured using broadband dielectric spectrometer. Then the experimental data was fitted by the improved HN equation, and the characteristic parameters of dielectric spectrum mathematical model were obtained. The results show that the uniqueness and accuracy of the fitting parameters can be guaranteed combining with genetic algorithm and least square method. The characteristic parameters of dielectric spectra, including direct current conductivity and relaxation polarization time, have significant temperature dependence, which basically accords with Arrhenius formula.

Using ethyl acrylate (EA) and butyl acrylate (BA) as soft monomers, methyl methacrylate (MMA), styrene (St), and acrylonitrile as hard monomers, methyl Hydroxyethyl acrylate (HEMA) and methacrylic acid (MAA) as crosslinking monomers, sodium dodecyl sulfate (SDS) as emulsifiers, and ammonium persulfate (APS) as initiators, an acrylate base emulsion was prepared through semi-continuous seed emulsion polymerization. And then a modified acrylate adhesive for FPC was prepared by adding suitable amount of curing agent and vulcanizing agent to emulsion. The optimal formulation of the acrylate base emulsion was obtained by simple variable method and orthogonal experiment, that is as follow: m(soft monomer) : m(hard monomer) : m(crosslinking agent) : m(emulsifiers): m(initiators)= 65:30:4:3:0.3, w(SDS)=2%, w(APS)=0.3%. With this formulation, the peel strength of the encapsulation sample is 0.92 N/mm, the peel strength of the single panel is 2.15 N/mm, and the soldering resistance pass rate is 100%, the moisture absorption rate of the film is 3.11%, which can all meet the performance requirements of adhesivein the FPC substrate.

A pure epoxy resin model and an h-BN/EP composite model were established. The thermal, mechanical, and dielectric property of epoxy resin before and after h-BN nano-doping were calculated by molecular dynamics method. And the effect of different h-BN doping content on the properties of epoxy resin was studied. The results show that when the mass fraction of h-BN is 4%-5%, both the thermal conductivity and thermal stability of epoxy resin increase, the rigidity and toughness increase by more than 10%, and the relative dielectric constant reaches the minimum value about 1.236, indicating that the material maintains good dielectric property.

In order to study the influence rules of repetitive square wave frequency on the corona-resistant lifetime of polyimide, a test platform with bipolar square wave was constructed to test the corona-resistant lifetime and partial discharge statistical characteristics of polyimide at different frequencies. The results show that with the increase of frequency, the corona-resistant lifetime of polyimide decreases， and the trend becomes less steep gradually. This is because with the increase of repetitive square wave frequency, the discharge amplitude and phase at the rising edge and the falling edge reduce gradually, which leads to the weakening of electrical ageing effect by discharge in a single cycle. Therefore, when the insulation was accelerated aged by increasing the square wave voltage frequency, the above characteristics need to be considered.

The partial discharge (PD) in high voltage switch cabinet might develop into non-penetrating or penetrating arc under extreme conditions, which can lead to insulation failure in severe case. From the optical radiation characteristics of discharge, an optical detection method for PD and abnormal arc was proposed. Multi-spectral characteristics of creeping discharge and arc discharge were obtained by the synchronous monitoring of ultraviolet, visible, and infrared optical signals, and the average intensity of light pulse, the light intensity ratio of three bands, and discharge repetition rate were analyzed and compared. The results show that there is a good corresponding relation between the amplitude of discharge light signal and the applied voltage. The statistical characteristics of three bands show large difference in low and high energy discharge, and according to the characteristic, the threshold value of low energy discharge and high energy arc discharge can be determined, thus the confidence of status warning and active protection of switch cabinet can be improved.

In order to explore the effect of compound anhydride curing agent on the cured product of epoxy resin, we built crosslinking models of methyl tetrahydrophthalic anhydride (MTHPA)/phthalic anhydride (PA) (their compounding ratio was 10:0, 9:1, 7:3, 5:5, 0:10, respectively) and bisphenol A-type glycidyl ether (DGEBA) by molecular dynamics method. The effect of different compounding ratios on the structure, thermal properties, and mechanical properties of the crosslinking epoxy resin with the same crosslinking degree was studied. The results show that when the compounding ratio of MTHPA and PA is 10:0, the free volume proportion of system reaches maximum, and the motion ability of molecular chains is the strongest. When the compounding ratio is 7:3, the comprehensive mechanical properties of system reach the maximum. When the compounding ratio is 9:1 and 7:3, the glass transition temperature of system reaches the highest and the lowest, respectively.

The influence of the geometric size and complex capacitance measurement error on the dielectric spectrum measurement errors of contact and non-contact methods was theoretically analyzed, and the two errors were compared. The influence of electrode gap distance and dielectric constant of sample on the dielectric spectrum measurement errors was simulated and analyzed. On the basis of dielectric spectra of high temperature vulcanized silicone rubber obtained by dielectric spectrometer, the influence of measurement errors of the geometric size (sample thickness) on the accuracy of measurement results for contact and non-contact methods was analyzed. The results show that the non-contact method is much more affected by the measurement accuracy of the geometric size and complex capacitance than the contact method, and it has high requirement on the instrument accuracy and is easier to produce significant errors than the contact method. With the increase of relative dielectric constant of the sample, the measurement error of relative dielectric constant by non-contact method dramatically increases and then gradually becomes stable. When the relative dielectric constant of the sample is no more than 5, with the increase of electrode gap distance, the measurement error of the relative dielectric constant dramatically increases. The non-contact method is suitable for the occasion with high measurement accuracy of the geometric size and dielectric constant.

The surface corrosion rate of superhydrophobic coating during chemical corrosion was evaluated by using mass change representation method, and a modified superhydrophobic coating by adding fluorine-containing compound to the final coating was proposed. Under room temperature, acid, alkali, and salt corrosion resistance experiments were conducted on glass substrates coated with fluorine-containing superhydrophobic coatings, fluorine-free superhydrophobic coatings, and RTV coatings, respectively, and different corrosion time and corrosive medium concentration were set. The results show that the acid and salt resistance of superhydrophobic coating is stronger than the alkali resistance. The addition of fluorine-containing compounds can significantly improve the chemical resistance of superhydrophobic coating. The acid and alkali resistance of the fluorine-containing superhydrophobic coatings is similar to that of the RTV coatings, but its salt corrosion resistance is significantly better than that of the RTV coatings.

In order to study the influence of phase change on the space charge characteristic and electric strength of polylactic acid (PLA), we prepared PLA samples and studied their physical and chemical properties, conduction current, space charge, and electric strength. The results show that the phase change (glass transition) temperature of PLA is 59℃, and before and after the phase change, the PLA nucleates and the unite cell grows, respectively. As a result, the conductivity of PLA first increases then decreases and increases again with the increase of temperature. More shallow interface traps are introduced in the phase transition process, resulting in the average trap depth of PLA decreases with the increase of temperature. Before and after phase change, PLA is in glass state and rubber state, respectively. When the temperature increases by 20℃, the electric strength of PLA in glass state decreases by 12%, while the electric strength of PLA in rubber state decreases by 40%.