Design And Application Of Composite Insulator Pulsed THz Imaging System

Composite insulators have the characteristics of high mechanical strength,not easy to crack,slow aging speed and so on.They are widely used in the field of electric power,making the operation of power grid more secure and reliable.In the process of manufacture and use of composite insulators,the sheathing mandrel interface is easy to generate air gap,which reduces the insulation property of composite insulators.At present,terahertz nondestructive testing technology has been proved to be effective in detecting the air gap defects at the sheath-mand-rod interface in composite insulators.However,the shape of composite insulators is cylindrical.In nondestructive testing,it is difficult to ensure the vertical incidence of terahertz waves on the surface of composite insulators,and oblique incidence will make the flight time of terahertz in testing samples of the same thickness longer.It can improve the longitudinal resolution of imaging system detection.Therefore,in this paper,a pulsed terahertz imaging system for composite insulators is designed by oblique incidence to detect the air gap defects at the sheathing interface of composite insulators,and a quantitative analysis of the thickness and area of the air gap defects at the sheathing interface of composite insulators is achieved by terahertz time-domain spectroscopy.The main work of this paper is as follows:1)Mechanical structure design of horizontal pulsed terahertz imaging system.The overall structure of the system is designed based on the etherhertz time-domain spectrum system and combined with the geometric size of composite insulators.Based on the modular design idea,the system is divided into motion support module,linear displacement module and rotating module,and the strength of each structure in the module is calculated and checked.Finally,the repeated positioning accuracy of linear displacement module of the horizontal pulse terahertz imaging system is ±0.01 mm,and the coaxiality of the driving mechanism and rotating support mechanism in the rotating module is ±0.02 mm.The levelness between the detector focus and the axis of the rotating module is ±0.02 mm.2)2)Finite element analysis of key components of horizontal pulse terahertz imaging system.According to the actual stress situation of each mechanism,the force situation of each mechanism in the motion support module,linear displacement module and rotating module is analyzed by statics analysis method.The maximum equivalent stress of each mechanism is checked by the fourth strength theory of material mechanics.In order to verify the reliability of the system built in this paper,modal analysis is carried out on the step shaft and spline shaft.In the first six orders of analysis,the natural frequency of the step shaft and spline shaft is the minimum 198.7Hz,and the natural frequency of the spline shaft is the minimum 174.68 Hz,which is far higher than the operating frequency of the rotating module 50 Hz,and no resonance phenomenon will occur in the detection process.The detection accuracy is affected.3)Control design of horizontal pulsed terahertz imaging system.Based on the performance parameters of the axial displacement mechanism,the calculation of the theoretical parameters of the stepper motor combined with the power frequency characteristic curve,the selection of the motor is realized.Appropriate drivers and controllers were selected according to the motor parameters,and Altium Designer was used to build the control circuit of horizontal pulse terahertz imaging system.On this basis,the terahertz data acquisition program was written,which provided software support for the subsequent detection of composite insulators’ air gap defects.4)Terahertz detection and quantitative analysis of composite insulator air gap defects.By means of a horizontal pulsed terahertz imaging system,the terahertz detection waveforms of composite insulators containing air gap defects are obtained,and the waveform characteristics of air gap defects are analyzed to realize the identification of air gap defects.Through the thickness analysis of the air gap defect of the standard defect simulation sample,the terahertz detection of the air gap thickness and the prefabricated air gap thickness,the detection accuracy reaches 95.48%.By using terahertz time-domain spectral imaging technology to study the terahertz imaging of standard defect simulation samples,the results show that the accuracy of the actual detection area of terahertz is 96.1%compared with the precast defect area.The practical application research of composite insulators is carried out on the horizontal pulsed terahertz imaging system designed in this paper.The research shows that there is at least 0.005 mm difference between the terahertz detection air gap thickness and the prefabricated air gap thickness,and the accuracy of the actual detection area of terahertz is 93.22% compared with the prefabricated defect area.The horizontal pulsed terahertz imaging system designed in this paper is mainly aimed at detecting the sheathing-mandrel interface.The imaging system is used to evaluate the sheathing-mandrel interface of composite insulators before they enter the network,which plays an important role in the prevention of safety accidents.