Study On Composite Insulator Detection Technology Based On Ultrasonic Guided Waves

Composite insulator is widely used in State Grid, with advantages of light weight, high mechanical strength, unbreakable and good anti-pollution performance. So, fast and accurate detection for internal defects of composite insulators is important for the safe operation. At present, guided wave ultrasonic testing technique mainly confined to the plate, pipe and rail and other common structures, for the less solid rod construction and inspection of complex components of other practical research.In this paper, a method based on ultrasonic guided wave detection for composite insulator was presented, according to the ultrasonic guided wave propagation theory, the simplified models of Fiber Reinforced Plastics(FRP) rod and composite insulator were established, relevant material parameters of FRP rod and silicone rubber were measured. The parameters of the corresponding dispersion equation was solved to obtain the frequency dispersion curve, the result showed that the L(0,1) and T(0,1) modal guided waves with frequency from 30 kHz to 150 kHz were suitable for FRP rod detection, and the smooth degree of dispersion curve for composite insulator was small, so we should choose guided wave with low frequency.The finite element numerical simulation for detecting two models with L(0,1) and T(0,1) modal guided waves at different frequencies were carried out by using ANSYS software. The simulation results of composite insulator with voltage level of 110 kV were better, guided waves’ sensitivities to various defects with different modes and frequencies were compared and analyzed by making different types of defects(Circumferential defects and axial defects. Simulation results showed that the longitudinal L and torsion T mode guided waves can perform the defect detection of FRP rod, longitudinal mode guided wave is more suitable for circumferential defect detection.Experiments for detecting composite insulator rod brittle and silicon rubber skirt damage were carried out based on the theoretical analysis and simulation results. Experimental results showed that: For the insulator with higher voltage level, in a certain range(guided wave was not completely attenuated), it was longer sensing means for sensing the better; Using 30-150 kHz low frequency L(0,1) longitudinal ultrasonic guided wave can detect the FRP rod defect of 2 mm in depth, 8 mm in circumferential length; Also, it was found out that the silicone rubber coating tend to attenuate the propagating energy and can severely degrade the performance of a guided wave test if both of excitation and receiver are positioned on the silicone rubber outside. On the contrary, if the excitation and reception point change to the FRP rod inside, using 40-100 kHz low frequency L(0,1) longitudinal ultrasonic guided wave can detect the composite insulator defect of 14 mm in depth, 40 mm in circumferential length.Based on study above, it is feasible to defect detection of composite insulator with ultrasonic guided wave technology.