Partial discharge (PD) phenomenon in power transformer is not only the main cause of insulation deterioration, but also the characteristic parameter to characterize the insulation condition. It is of great significance to accurately recognize the type of PD for the diagnosis of transformer insulation condition. A new method for identifying the type of multi-source PD spectrum based on Faster-RCNN algorithm was proposed in this paper, which can detect different types of PD clusters from multi-source spectrum. The results show that the average recognition accuracy of multi-source PD reaches 72.1% when the proposed algorithm was applied to the PD spectrum obtained from 35 kV transformer. Because the air gap defect has dense PD points and obvious characteristics, its missed and false detection rates are lower than other defects, leading to there be good discrimination for the air gap defect. Because the tip defect has the characteristics of intermittent discharge and high initial discharge voltage, its missed detection rate is high.

Partial discharge type is closely related to the early insulation deterioration degree of power capacitor film. The accurate identification of partial discharge type will effectively improve the operation state of capacitor and guarantee the safety of power grid. In this paper, the models of inter-film tip defects, air gap defects, and surface defects generated easily in metallic film capacitor were designed. The time series and phase distribution spectra characteristics of partial discharge in capacitor film and the development of average discharge quantity Q and discharge repetition rate F were analyzed. The curves of Q and F were fitted with points, and the correlation between them and partial discharge signal was analyzed. The correlation coefficient was taken as the characteristic parameter of time domain. The skew, steepness, and asymmetry of partial discharge phase distribution spectra were extracted as phase characteristic parameters. A partial discharge pattern recognition method of power capacitor film based on time-phase synthetic radar spectrum was proposed. The barycentric coordinates of the enclosed rectangle of characteristic parameters closed graph in the synthesis spectrogram were conducted cluster analysis, and the distribution quadrants of barycentric coordinates were used to recognize the partial discharge pattern of film. The results show that the method has more pattern recognition accuracy than the traditional single spectrum, which provides a theoretical basis for online monitoring and fault diagnosis of capacitor equipment.

High voltage cable fusion joint with defects operating for a long time is easy to cause operation failure. In order to timely troubleshoot the joint defects, we taked high-voltage cable fusion joints as research object. The main insulation and conductor recovery process of high-voltage cable fusion joint was detected by digital radiography (DR) technology, and the bending limit of conductors was analyzed by finite element method. The results show that the DR detection technology can effectively detect bubbles, conductor bending, eccentricity and other defects in the XLPE main insulation of fusion joint. The accuracy of detection results is demonstrated by field dissection, which provides an effective means for the defect detection of high voltage cable fusion joint. The bubble defect of XLPE main insulation is caused by the decrease of temperature and nitrogen pressure in the crosslinked pipeline. Considering the safety margin of the joint, it is recommended that the bending gap should not exceed 11 mm and the insulation thickness at the bending position should not be less than 30 mm.

In order to effectively adsorb the corrosive sulfur in transformer oil, XDK was used as adsorption material, and dibenzyl disulfide (DBDS) was used as the experimental object. The test oil was prepared by adding DBDS to new transformer oil. The removal effect of XDK on DBDS in test oil was studied under different adsorption conditions and regeneration conditions. The structure of XDK was characterized by scanning electron microscopy (SEM), thermogravimetry (TG), and specific surface area analyzers (BET). The results show that the optimal regeneration temperature of XDK is 600℃, and the regeneration XDK still has good adsorption effect after four times. When the XDK mass fraction is 10%, the adsorption times are two times, the adsorption temperature is 10℃, and the adsorption times is 2 h, the DBDS removal rate reaches 96.9%, the dielectric constant, breakdown voltage, and volume resistivity of the insulating oil after treated increases by 0.31%, 5.3 kV, and 0.23 Ω·m, respectively, and the dielectric loss factor decreases by 0.21%.

In order to study the effect of organic and inorganic fillers on the performance of insulating paper, nano titanium dioxide (TiO₂) treated with dopamine hydrochloride was coated with nano-fibrillated cellulose to get a multiple mixed filler (PDA-TiO₂@NFC). Then the multiple mixed filler was filled into the cellulose insulating paper, and a sandwich structure insulating paper modified by different multiple mixed fillers was prepared. The optimal concentration of multiple mixed fillers was explored, and the tensile strength, DC volume resistivity, breakdown characteristics, and space charge of the modified insulating paper with different multiple mixed fillers were analyzed. The results show that when the multiple mixed fillers concentration is 0.5%, compared with the unmodified insulating paper, the tensile strength of the modified insulating paper increases by 17.90%, the AC and DC breakdown strentgh of oil-paper increase by more than 17%, and the injection of space charge can be effectively inhibited. The effect of multiple mixed fillers on the DC volume conductivity is not obvious. The mechanical properties and electric strength improvement of the sandwich structure insulating paper prepared using this method are significant, which provides reference for jointly improving the performance of insulating paper.

The problem of nanoparticle agglomeration in wire enamel can be solved by modification and gradual dispersion of nanoparticles. Five modifiers, emulsifier OP-10, silane coupling agent AP1231, silane coupling agent A112, γ-propyl trimethoxysilane (KH560), and N-[3-(trimethoxysilyl) propyl] ethylenediamine (KH-792), were used to modify the surface of nano silica particles. The effects of modifier type, modifier dosage, modification temperature and time on the modification effect of nano-SiO₂ particles were explored. The effects of nano-SiO₂ particles before and after modification on the performance of corona resistant wire enamel were compared by corona resistance test, and the dispersion of nano-SiO₂ particles before and after modification was observed by transmission electron microscopy (TEM). The results indicate that the nanoparticles modified by KH-560 have the best dispersion in wire enamel, and the best process conditions are as follows: the dosage of KH-560 is 1.5wt%, the modification temperature is 90℃, and the modification time is 4 h. The wire enamel with high stability and higher than 50 h of corona resistance time can be obtained by gradually dispersing modified nanoparticles into the wire enamel, and the appropriate addition amount of nanoparticles is 13.5wt%.

In order to investigate the effects of glassfiber architecture on the mechanical and fire-resistant performance of insulating slot wedge, unidirectional glassfiber, laminated glassfiber fabric, and rolled glassfiber fabric reinforced slot wedge were prepared using fire-resistant resin, glass fiber, glassfiber fabric as raw material, and the 3 types of slot wedge samples were conducted longitudinal impact strength test, width-directional bending strength test, and combustion tests. The results show that with the same sectional dimension and the same content of glassfiber for slot wedges, the order of longitudinal impact strength from strong to weak is glassfiber fabric reinforced slot wedge, glassfiber fabric laminated slot wedge, unidirectional glassfiber reinforced slot wedge; the order of elastic deformation during width-directional bending from big to small is glassfiber fabric reinforced slot wedge, glassfiber fabric laminated slot wedge, unidirectional glassfiber reinforced slot wedge; the order of fire resistance from strong to weak is glassfiber fabric reinforced slot wedge, glassfiber fabric laminated slot wedge, unidirectional glassfiber reinforced slot wedge. When the glassfiber content increases from 50% to 70%, the total afterflame time of the unidirectional glassfiber reinforced slot wedge, glassfiber fabric laminated slot wedge, and rolled glassfiber fabric reinforced slot wedge increases by 51.7%, 31.8%, and 46.3%, respectively.

A new type of insulating paper with aramid nanofiber as the basic structural unit was prepared, and its ageing characteristics in natural ester insulating oil and mineral insulating oil were systematically investigated and compared with the commercial Nomex T410 insulating paper. The results show that the aramid nanofiber-based insulating paper has better thermal stability and ageing resistance, and the mechanical and electrical properties of the aramid nanofiber-based insulating paper are better than those of Nomex T410 insulating paper after accelerated thermal ageing test under the same condition. In addition, the new oil-paper insulation system composed by natural ester insulating oil and aramid nanofiber-based insulating paper can effectively extend the life of the transformer, which provides a reference for the insulation design and development of green low-carbon electrical energy equipment.

HVDC cross-linked polyethylene (XLPE) cables will be damaged by operation impulse voltage caused by switching and other operations in the power system under working condition, which will affect the insulation. However, at present, there is a lack of relevant research on the cable insulation deterioration generated by space charge accumulation caused by multiple impulse cumulative effect. Based on the PEA space charge measurement system under DC superimposed impulse voltage in the laboratory, the space charge characteristics of XLPE cable insulation under DC voltage, impulse voltage, and DC superimposed impulse voltage were measured in this paper. The results show that XLPE is dominated by heteropolar charges under positive DC voltage, and negative charges of the same polarity appear on the SC electrode under negative DC voltage. Continuous high-amplitude impulse voltage can cause large number of homopolar charges injection on the two electrodes, and the amount of injected charge is larger under negative impluse voltage. Under DC superimposed impulse voltage, the same polarity superimposition method can promote the injection of homopolar charge on the two electrodes more than the opposite polarity superimposition method. Moreover, the longer the impulse voltage is applied, the more charge accumulates in the XLPE sample.

The accumulation of space charge is easy to cause the internal electric field distortion of cross-linked polyethylene insulation, resulting in insulation ageing and even failure. Nano-doping or modification can inhibit the accumulation of space charge, so it has received widespread attention. In this paper, the space charge properties and electrical conductivity properties of cross-linked polyethylene composite doped by silica and magnesium oxide nano filler were measured, and the action mechanism of nanofillers was analyzed combined with the theoretical band gap model. The results show that the MgO-doped cross-linked polyethylene composites have higher dielectric constant, lower space charge accumulation, and smaller electrical conductivity compared to silica-doped cross-linked polyethylene composites.