| State grid,as an effective power transmission method,has been widely used in China to deal with the large-scale and long-distance power transmission due to the unbalanced distributions of resource and productivity.However,China is an earthquake-prone country and the bushing has been proved to be vulnerable to damage during earthquakes.The failure of the bushing may interrupt the power supply and may also cause huge economic and property losses to the country and people.As the main insulation device outside the transformer,the composite bushing has the function of fixing the wire and ensuring the insulation of the wire to the ground.The composite bushing is connected with other equipment through the wire,and there exists a strong electromagnetic field at the top of the composite bushing.The additional seismic measures to high-rise structures are difficult to apply in composite bushing.The tuned mass damper at the top of the composite bushing will affect the function of the composite bushing due to the relative motion of the mass.The base-isolated device at the bottom of the composite bushing will increase the top displacement of the composite bushing,which may cause implicated damage of the adjacent equipment.Therefore,it is very necessary to propose an energy absorbing device that does not affect the function and electromagnetic properties of the composite bushing to improve its seismic performance.In this paper,both theoretical and numerical methods are adopted to systematically research the seismic mitigation measures of the composite bushing.The dome at the top of the composite bushing will be utilized as an energy dissipation device by adjusting the design of the dome.The tuned liquid dampers based on the energy dissipation of liquid linear sloshing,are proposed for seismic mitigation of the composite bushing.Furthermore,the vibration reduction measures based on the energy dissipation of liquid nonlinear sloshing are also proposed for the composite bushing under strong earthquake excitation.The main research contents and conclusions are presented as follows:(1)The dynamic characteristics of the liquid sloshing in annular cylindrical tank are derived based on the linear potential theory.The simplified formulas of the liquid sloshing frequency in annular cylindrical tank are presented,which have been proved by comparing with the existing experiments.The equivalent“spring-mass-damper”mechanical model is proposed based on the liquid linear sloshing in the annular cylindrical tank.And then,the parametric analyses of the liquid sloshing frequency and the equivalent mechanical model are performed.The results reveal that the radius ratio and the liquid depth ratio have a great influence on the liquid sloshing frequency.However,when the liquid depth is relatively large,the influence of the liquid depth ratio on the liquid sloshing frequency is negligible.The analytical results indicate that the first two sloshing mass and the impact mass should be considered in the equivalent mechanical model when the radius ratio of the shallow annular cylindrical tank is near 0.5,while,for other cases,it is sufficiently accurate to consider the first sloshing mass and the impact mass in the equivalent mechanical model.(2)Based on the simplified formulas of the liquid sloshing frequencies in the annular cylindrical tank,the design processes of the annular tuned liquid damper(ATLD),the multiple annular tuned liquid damper(MATLD)and the hybrid tuned liquid damper(HTLD)are presented with different composite bushings.Firstly,the optimal design of ATLD is directly carried out for the composite bushing with lower fundamental frequency.Then,the design process of MATLD is proposed based on the frequency response function curves of SDOF-MATLD system,and the optimal design of MATLD for the composite bushing is performed.Finally,the design scheme of HTLD is proposed for the composite bushing with higher fundamental frequency.The results of the harmonic analyses and the dynamic time-history analyses show that the proposed tuned liquid dampers are effective for seismic mitigation at the resonance reason and they can also reduce the dynamic responses of the composite bushing effectively under the small earthquake excitation.Moreover,the proposed MATLD provides a wider bandwidth for reduction and it is more effective for seismic mitigation than the ATLD.(3)The coupled SPH-FEM method is adopted to numerically simulate the dynamic responses of the composite bushing under strong earthquake excitation.Based on the optimal liquid depth ratio,a structural design of additional plate in the dome is proposed.At first,the effects of different liquid depth ratios on the seismic responses of the composite bushing are discussed under different peak accelerations.And then,the influence of the radius and position of the additional plate on effectiveness of the liquid nonlinear sloshing for energy dissipation is studied.The variance analysis method is also used to analyze the influence of the size and the position of the additional plate on the dynamic responses of the composite bushing.The numerical results show that the seismic reduction ratio of the composite bushing has little change when the bushing is suffered with strong earthquake excitations,and the best reduction ratio of the composite bushing is obtained when the oil filled depth ratio in the dome is 0.6.What’s more,the plate with smaller radius will increase the damping of liquid nonlinear sloshing in the dome and the radius of the plate has more significant influence on the liquid nonlinear sloshing damping than the position of the plate.(4)A spherical dome is proposed to take the place of the original cylindrical one,which is more suitable for the inclined busing.The design of the spherical tuned liquid damper(STLD)for the composite bushing is carried out based on the dynamic characteristics of liquid linear sloshing in the spherical tank.Then,the effect of liquid depth in the spherical dome on the dynamic response of the composite bushing is further studied under strong earthquake excitations.The numerical results reveal that the STLD is more efficient in utilizing liquid sloshing than the ATLD,and it can provide a wider bandwidth for reduction.When the liquid filled depth ratio in the spherical tank is 0.6,the liquid nonlinear sloshing in the spherical dome provides the best seismic reduction ratio for the composite bushing and the corresponding reduction ratio can reach more than 20%. |
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