The Research And Implementation Of Online Detection Technique For Partial Discharge

With 10kV switchgear more widely deployed in high voltage substations,High voltage switchgear has become the main electrical equipment in the power grid system.Partial discharge is dielectric material’s slight discharge in electrical equipment at high field strengths,it is the important cause of insulation degradation.It is necessary to evaluate the running state of switchgear in a synthetic manner and then take the corresponding preventive measures by detecting the severity of partial discharge in switchgear.The joint detection technique that based on transient earth voltage(TEV)and ultrasonic detection technologies can effectively detect the partial discharge.The thesis makes analysis from the aspect of technology application and market demand to propose a design and implementation scheme of portable partial discharge detection system.The partial discharge detection system is based on the acoustic-electric method.The detection system consists of master control module,signal preprocessing module and human-computer interaction module.The function of master control module is to accomplish detection of partial discharge and process the data.The signal preprocessing module consists of TEV signal preprocessing sub-module and ultrasonic signal preprocessing sub-module.The function of signal preprocessing module is to precondition the signal that collected by sensor to acquire the information that useful.Human-computer interaction module visually displays the characteristics of the signal that is acquired on the monitor.It is convenient to detect and evaluate the severity of partial discharge.The main research contents can be concluded as follows:Firstly,the paper analyzes the characteristics of the ultrasonic signal and transient earth voltage and its corresponding detection methods by looking up domestic and foreign literature related to partial discharge online detection.Secondly,since the frequency range of transient earth voltage is from 3MHz to 100MHz,it is very difficult to meet the demand for the aspects of sampling rate and storage depth that converting the high frequency discharge signal from analog to digital directly.What is more,the measurement of partial discharge usually cares about peak value of the signal rather than the whole waveform.Therefore,on the module of transient earth voltage detection,the paper adopts peak-detection circuit,which is the core processing unit of the TEV signal preprocessing sub-module,to extract characteristic parameters of partial discharge.Thirdly,on the module of ultrasonic detection,the paper adopts the implicit computation of the true RMS to figure out the root-mean-square value of ultrasonic signal and then process A/D sampling.It can reduce the sampling rate of A/D converter and computing quantity of the program in this way.Fourthly,the thesis designs the software systems for partial discharge detecting instrument,completes the transplantation of the embedded system and write UI application to implement signal disposition,the extraction of signal characteristics and the design of graphical interface.Lastly,the thesis utilizes the existing testing environment to complete the performance test of the hardware modules and the integrated testing of system.The result of testing shows that the device is reliable and the interactive interface is friendly.It can detect the partial discharge of switchgear and reach the target.