Research On Partial Discharge Localization Method Of Transformer Based On Pulse Current And Ultrasonic Detection

With the continuous increase of power system capacity and voltage classes,the operation of transformer,the core equipment of power transmission and transportation in power system,has direct influence on the security of power network.Large-scale power failure may happen due to fault caused by partial discharge of insulation structure.So a method based on pulse current and ultrasonic detection is proposed in this thesis to reasonably arrange the positions of ultrasonic sensors on the transformer box,which plays a vital role on the early prevention of transformer faults as well as provides the support for operators maintenance.The main thesis are as follows:Firstly,the basic theory of partial discharge on transformer is introduced,the mechanism of pulse current signal and ultrasonic signal generated by partial discharge is analyzed,and the reception of the two signals is studied.On this basis,a laboratory experimental platform is built to analyze the propagation path of ultrasonic signal in pure transformer oil and dielectric transformer oil in transformer oil tank.The attenuation of ultrasonic signal in different media is analyzed,and the propagation speed of signal wave in pure insulating oil and insulating oil with other media is measured as well.Secondly,the detection system for transformer partial discharge is designed,including hardware and software.The detection system initially is applied in examining mechanical watch to verify the feasibility of the system in practical application.Then the detection system is applied to transformers in laboratory to detect the terminals and pulse current signals on the grounding line by ultra-wideband high frequency pulse current sensor,and then to analyze the magnitude and polarity of the signals to determine the positions of partial discharge in the end.The ultrasonic sensors are arranged outside at this position.After detecting the representative positions with partial discharge sources,the ultrasonic signals of those positions can be obtained.Finally,the wavelet threshold de-noising method is used to remove the disturbance for ultrasonic signals.By extracting the arrival time of each first wave to the sensor,calculating the time difference of them,the non-linear problem of TDOA is converted into a linear problem by applying CWLSA.The aim of locating partial discharge source is achieved.