Study On Propagation Of Ultrasonic Guided Waves In Composite Insulators

Composite insulators have been widely used in high voltage transmission lines because of their many advantages.On account of manufacturing process,long running time and natural environment,different kinds of defects will be formed,which have brought great security risks to power grid.Owing ot its fastness,accuracy and high efficiency,ultrasonic guided wave has been applied to the non-destructive testing of various fields.In this paper,the propagation characteristics of ultrasonic guided wave in composite insulators was mainly studied by finite element simulation and experiment,which provided the basis and guidance for application of the technology to the detection of composite insulator defects.Firstly,the dispersion equation of T mode and L mode guided wave in single core and bilayer composite insulator model was deduced based on guided wave theory,and the dispersion curves were drawn according to the relevant parameters.The influence of section size,axial dimension and time step to simulation results in finite element simulation was discussed,which provided guidance for parameters setting in the simulatuion.Secondly,with the diameter of 18 mm FRP(Fiber Reinforced Plastics)rod and 220 KV composite insulator as an example,propagation of different frequencies of L mode and T mode guided wave were simulated separately by using ANSYS Workbench.The simulation results showed that 50KHz-60 KHz L-mode guided wave and 40KHz-80 KHz T-mode guided wave were suitable for FRP rod detection.20 KHz or 50 KHz L mode guided wave and 60KHz-90 KHz T-mode guided wave were suitable for composite insulator detection.Finally,the experimental system was built,and the propagation of the guided wave in the composite insulator was studied experimentally.The experimental results showed that there were different degrees of attenuation and modal transformation in the propagation process of different frequency and mode guided wave,and it was suitable for detecting defect in the FRP rod by observing the defective echo.The metal structure of composite insulator had a certain attenuation influence on guided wave propagation.The attenuation of L-mode and T-mode guided waves with different diameters of umbrella skirts did not show much difference.Because silicone rubber had a serious attenuation influence on guided wave propagation,so it was not suitable for detecting defect by motivating and receviving on silicone rubber.When partial silicone rubber was removed,motivating and receviving were located on the FRP rod inside,the waveforms reciewed were relatively clear to identify,which was suitable for detecting defect in FRP rod.