Study on the dynamic mechanical properties of winding-block axial structure considering short circuit strain rate effect

Transformers may suffer multiple short-circuit impacts during long-term operation,and axial instability is one of the typical types of serious accidents caused by short-circuit faults.The axial instability form of the winding-block structure is analysed,and the dynamic solution of the winding short-circuit electromagnetic force is obtained by estab-lishing the three-dimensional magnetic-circuit-force multi-physical field coupling simulation model.The influence of strain rate on the cushion block constitutive equation is corrected,and the modified model is verified by short-circuit impact test and quasi-static test.The research results show that for 110 kV 31.5 MVA transformers,the maximum electromagnetic axial resultant force of winding is 363.16 kN,and the ultimate tilt force is 1214.2 kN.The pre-tightening force configuration is accordingly recom-mended to range from 363.16 to 608.28 kN,which is narrowed by 18.49%compared with the static calculation method;Meanwhile,adding a logarithmic strain rate correction term to the classical constitutive equation of the cushion block can achieve a good correction of the stress-strain relationship with the coefficient of determination above 0.99,and the cushion block has a larger elastic modulus under high strain rate load.The research results provide an important theoretical reference for the axial stability structure of transformers.

The synergistic effect of micro structure/nanofiller/superhydrophobicity on the surface flashover

The surface flashover is affected by many factors,such as surface roughness,nanofillers and chemical functional groups.In this research study,polyamide mesh was utilised as a scaffold to systematically study the synergistic effect of micro structure/nanofiller/superhydrophobicity on the surface flashover.Based on the dissolution and resolidification method,nanofillers were partially embedded into the mesh fabrics.Here,Al_(2)O_(3)nanoparticles were used as a typical non-conductive nanofiller,and carbon nanotubes were used as a typical conductive nanofiller.Moreover,the micro structure was determined by altering the mesh size,and chemical fluorination was utilised to change the surface chemical group.It was found that the polyamide mesh with 300#demonstrated best anti-flashover properties.Chemical fluorination could effectively improve the flashover voltage.By further adjusting the ratio of Al_(2)O_(3)to carbon nanotubes,the flashover voltage can be increased by up to 30%.

Effect of organophilic group of coupling agent on the electrical performance of Boron Nitride/meta-aramid composite paper

Organophilic groups of coupling agents can be the key factor for the electrical performance of Boron Nitride(BN)/meta-aramid composite paper.In this article,four types of triethoxy-silane coupling agents with different organophilic groups,including mercaptopropyl(MP),glycidylether-propyl(GP),amino-propyl(AP)and trideca-fluoro-octyl(TFO)were studied.The structural and electrical properties of modified papers were compared,and the molecular simulation was conducted to reveal the interface interaction of modified BN and aramid.The results show that AP,GP and MP follow the same mechanism,improving the electrical performance by modifying the interface stability and paper structure,and the ranks of improving effects are AP,MP and GP.While,TFO mainly relies on the fluorine components to implement the electrical reinforcement,which compensates for the shortcoming in the paper structure.By choosing TFO and filler content of 15 wt%,the optimal breakdown strength of the paper can be increased to 28.17 kV/mm,1.8 times that of the paper doped with the hydroxylated BN.

Study on operation voltage monitoring and electrothermal coupling simulation of electric multiple unit(EMU)roof arrester

The roof arrester of electric multiple units(EMU)can efficiently limit the overvoltage,and ensure the safe operation of the EMU electrical equipment.In the process of high‐speed operation,the traction power supply system is often affected by overvoltage.In addition,roof arrester explosion accidents occasionally occur.In this paper,the on‐line voltage measurement system of the EMU arrester is developed.By analysing a large number of voltage waveforms,the abnormal voltage is divided into three categories:over‐phase voltage,high harmonic voltage and steep impulse overvoltage.The charac-teristics of abnormal voltage waveforms are then summarised.The electrothermal coupling simulation model of the arrester is developed,and the current response and temperature distribution of the arrester under abnormal voltage are calculated.The impact of the impulse voltage energy on the arrester temperature is studied by applying a triangular wave voltage to the model.Finally,some suggestions are proposed for the operation and maintenance of the roof arrester.