Analysis on Ultrasonic Guided Wave Detection for Scale Layer of Equalizing Electrode on Valve Section
At present,the detection of the thickness of the scale layer on the equalizing electrode in the converter station is carried out by shutting down the transmission system and manually disassembling,which has significant time,labor costs,and blind screening of the equalizing electrodes with the scale layer.There is an urgent need for a non disassembly online detection method for the scale layer on the equalizing electrode.Ultrasonic guided waves have the advantages of high detection efficiency and low energy attenua-tion.Therefore,based on ultrasonic guided waves,a non disassembly online detection method for the thickness of the scale layer on the equalizing electrode is proposed,and its effectiveness is verified through the simulation and experimental analysis.Firstly,by drawing the dispersion curve of polyvinylidene fluoride(PVDF)filled water pipeline,the approximate excitation frequency range of ultrasonic guided waves is determined to be 40～100 kHz,and the longitudinal L(0,2)mode is also determined.Then,a finite element model of the axial longitudinal section of the PVDF water filled pipeline is further established,and the optimal excitation frequency is determined to be 60 kHz through calculation.Based on this model,the variation patterns of scale layer thickness and received signal amplitude and time are analyzed.At the same time,an experimental platform is built to verify the ultrasonic guided wave detection method of the equalization electrode.The research results indicate that using longitudinal L(0,2)ultrasonic guided waves to detect the scale layer on the equalizing electrode has advantages such as fewer modes and weaker frequency dispersion,and has good discrimination ability for the equalizing electrode with different thickness of scale layers.This method provides a certain application basis for non-destructive testing of the scale layer on the equalizing electrodes.
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