Research On The Propagation Characteristics Of Ultrasonic Wave Of Partial Discharge Inside The Solid Medium Of Cable Accessories

In a new type of power system with new energy as its main component,the insulation safety of power equipment is crucial,and online monitoring of insulation status is a prerequisite for reliability assessment.Partial discharge is an important manifestation of insulation degradation,and real-time and accurate measurement of partial discharge is one of the most effective methods for evaluating the insulation health status of power equipment.The acoustic emission method has received much attention due to its electromagnetic immunity,and it is widely used in the detection of partial discharge in liquid and gas insulation.However,there are still problems in solid insulation such as complex propagation law of local discharge acoustic wave and unclear coupling path between sensing unit and medium,so it is of academic value and engineering significance to carry out related research.Based on the theory of solid acoustic propagation,this study derives the analytical formula for the generation and attenuation of partial discharge ultrasonic waves in viscoelastic solids and explores the relationship between the velocity of partial discharge ultrasonic waves and the intrinsic properties and density of the medium.It is clarified that the diffusion attenuation of acoustic emission is only related to the detection distance;the absorption attenuation is related to the frequency of sound waves,the sound velocity of sound waves in the medium,and the key physical properties of the medium(density,thermal conductivity coefficient,and viscosity coefficient);and the scattering attenuation is related to the frequency of the acoustic wave,the angle of incidence of the acoustic wave,the grain size of the medium,and the distribution of the grains of the medium.Based on the design and construction of an ultrasonic propagation characteristic testing platform,comparative experiments on sound attenuation of various typical crystalline polymers and amorphous polymers are conducted,and the research results show that the crystal structure in polymers would increase the absorption attenuation in sound propagation,and the attenuation of partial discharge acoustic propagation in crystalline polymers is greater than that in amorphous polymers.The storage modulus,loss modulus,and damping loss factor of insulating materials are measured by dynamic mechanical experiments,and the relationship between damping loss factor and medium sound propagation is analyzed.The damping ratio and quality factor of the material were derived through the damping loss factor,and finite element simulation models are constructed based on the measured physical properties and the structural parameters of the 220 kV cable section and the silicone rubber umbrella skirt.Based on the simulation analysis of the acoustic emission propagation law in the 220 kV cable section and the silicone rubber umbrella structure,partial discharge testing is conducted on the solid model using distributed feedback fiber laser.The simulation and experimental results show that the sound attenuation on the umbrella leaf of the silicone rubber umbrella skirt was smaller than that on the grating,and it is also verified that the propagation attenuation of partial discharge acoustic emission in cross-linked polyethylene with a crystalline structure is greater than that in amorphous silicone rubber.