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.

In order to study the influence of metal wire defect on the electric field distribution of basin insulators in GIS, using the actual 1 100 kV basin insulator in GIS as the research object, we simulated and calculated the electric field distribution of basin insulators with metal wire defect using ANSYS by finite element method. The influence of the distribution direction, radial distance, length, and width of the wire on the electric field distribution of basin insulators was studied. The results show that the wire defects in basin insulator can distort the electric field severely, the maximum electric field strength is 10.76 times larger than that of the basin insulator without wire defect, and the transverse distributed wire has greater effect on the electric field of the basin insulator. The distortion degree of electric field of basin insulator is related to the distribution direction, radial distance, and length of wire.

In order to study the reliability of traction motor insulation system, according to the operation condition of traction motor, we established a reliability verification method with electrothermal ageing, temperature variation, constant damp heat, mechanical vibration, and sand and dust as ageing factors. The comparative tests were conducted on the reference insulation structure of locomotive traction motor and one to be evaluated, and the non-destructive characteristic parameters including insulation resistance, dielectric loss factor, and PDIV were measured. The results show that the reliability verification method can quickly compare the reliability of insulation system. During the test, the insulation performance increases at first and then decreases. Dielectric loss factor and PDIV have more obvious characterization effect on the ageing of insulation system than insulation resistance.

In the electrical test and operation of generator, the hypotenuse electric field at the end of stator winding is very high, which is a weak part that corona discharge often occurs. In this study, an analytical model and a finite element model of the hypotenuse electric field at the end of stator winding were established. The influencing factors and laws of the hypotenuse electric field were studied, and the influence of the hypotenuse clearance, rotating angle, and dielectric constant of the filling medium on the maximum electric field was analyzed. An effective method to optimize the electric field at the end was presented. The results show that under the in-phase winding, the hypotenuse electric field can be optimized by decreasing the surface electric field of stator bar, the width of bar, and the rotating angle of bar or increasing the hypotenuse clearance; Under the out-of-phase winding, the hypotenuse electric field can be optimized by increasing the dielectric constant of filling medium and the hypotenuse clearance of winding. The finite element model of hypotenuse electric field can accurately analyze the maximum electric field and the distribution trend at the end of winding. The correctness of the model is verified by corona test of UV imaging equipment, which indicate that that the model has good engineering application value.

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 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.

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%.

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.

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.

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.