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.

A kind of porous adsorbent was developed by low temperature hydrothermal method, and it was compared with 801 adsorbent, silica gel, activated aluminum oxide, and 13X molecular sieve through the regeneration tests of degraded mineral transformer oil. The composition change of oil after regenerated by the adsorbent were analyzed by infrared spectrum. The results show that the adsorbent has the characteristic diffraction peak of β zeolite, the aperture of the adsorbent is 0.8-1 nm, the particle size is mainly 0.7-0.9 μm, the specific surface area reaches up to 680 m²/g, the molar ratio of Si and Al is 3:1-5:1, and it has strong polarity and selective adsorption. The adsorptive capacity of the porous adsorbent is stronger than 801 adsorbent, silica gel, activated aluminum oxide, and 13X molecular sieve. It can efficiently adsorb the unsaturated hydrocarbons from degradation transformer oil without damaging the basic components of the oil.

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.

Vegetable insulating oil is easy to oxidate during operation and it will affect the service life of transformer. In this study, 2,6-di-tert-butyl-p-cresol (BHT) was chosen as antioxidant, and the characteristic parameters of the vegetable insulating oil were compared by the ageing tests. The effect of BHT antioxidant was analyzed by measuring the acid value, peroxide value, and moisture content. The effect of BTH antioxidant on the insulating properties was studied by detecting the dielectric loss factor, breakdown voltage, and FDS curves. The results show that BHT antioxidant can effectively improve the dielectric constant of vegetable insulating oil. Through the molecular formula analysis on the reaction mechanism between BHT reagent and unsaturated oil in natural ester insulating oil, the oxidation resistance process of BHT in natural ester insulating oil can be reflected more intuitively. When the addition amount of BHT is 0.20%, it has a better effect on improving the insulation performance of vegetable insulating oil.

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.

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 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 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 find out the effect of adding nano-SiO₂ on the relative permittivity and conduction characteristic of ethylene propylene diene monomer (EPDM) insulation, we prepared EPDM composite dielectrics with different mass fractions of nano-SiO₂ by melt-blending method. The dispersion of nanoparticles in the EPDM matrix and the bonding properties between nanoparticles and EPDM matrix were analyzed. The relative permittivity and the steady-state current of the EPDM nanocomposite dielectrics at different temperatures and electric fields were measured, and the conductance characteristic were analyzed. The results show that when the mass fraction of nano-SiO₂ is 0.5%, the dispersion of nano-SiO₂ is the best in EPDM. The steric hindrance, which formed by doping of low content, reduces the mobility of the EPDM molecular segments and its side groups, and the interface effect is obvious in the nanocomposite dielectrics, making the relative permittivity and conductance decrease, the threshold electric field strength of space charge injection enhance, the insulating performance improve significantly. With the increase of the mass fraction, the interface effect between nanoparticles and EPDM matrix is weakened. When the mass fraction of nano-SiO₂ is 2.5% or 5.0%, the agglomeration caused by doping makes the relative permittivity and the conductance increase, and the threshold electric field strength of space charge injection decreases. The interface effect caused by the addition of nano-SiO₂ is a key factor affecting the properties of EPDM nanocomposite dielectrics.

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.