Research On On-line Detection Method Of Partial Discharge In Cable

With the development of modern industry and the improvement of urbanization level,cable as an important tool for transmission of electricity,more and more attention,the reliability of its operation directly affect the normal operation of the power system.However,the cable will inevitably encounter some failures in the operation,mainly due to the cable insulation material is prone to partial discharge phenomenon,the cable insulation material in the production due to processing technology or raw material problems,resulting in insulation after processing impurities or gas gap,air gap and impurity tip is the most prone to partial discharge phenomenon of the region.The size of the partial discharge of the cable is closely related to the insulation condition of the cable.The increase of the partial discharge quantity indicates that the insulation strength of the cable is weakened.This will damage the safe operation of the cable.Therefore,it is necessary to detect the strength of the partial discharge in advance and to avoid the cable fault.effective method.At present,the local discharge of the cable is detected at the fixed point or in the offline state.In view of the limitation of the traditional method to detect the partial discharge of the cable,the ultrasonic discharge method of cable partial discharge is deeply studied.In this paper,the three-capacitor model of cable insulation and the air-gap discharge mechanics model are used to explain the phenomenon of partial discharge and the mechanism of partial discharge to produce ultrasonic wave.The classification and cause of partial discharge are studied.At the same time,the waveform characteristics of partial discharge ultrasonic signal are studied,The test method gives theoretical support.In this paper,the propagation characteristics of the partial discharge ultrasonic signal are studied,and the frequency and amplitude information of the partial discharge ultrasonic signal and the various interference signals in the environment are analyzed.Based on this,the local discharge field Detection of ultrasonic receiver probe,design signal amplification,filtering and other processing circuits,through the calculation and analysis to select the appropriate circuit parameters,the use of STM32 microcontroller processing and storage of analog conversion signals,and the circuit was simulated and tested.Using the GUI function of MATLAB to write the user interface to process the data,can display the ultrasonic signal waveform,extract the envelope of the signal,display the maximum amplitude of the signal and the starting point of the discharge.Through the experimental study of the system,the influence of the center frequency,the intensity of the discharge and the distance from the discharge source on the partial discharge ultrasonic signal is analyzed.The results show that the partial discharge can produce an ultrasonic signal similar to AM modulation,and the signal amplitude is proportional to the discharge quantity,which is inversely proportional to the distance between the probe and the discharge source.In the local discharge signal frequency range,the low frequency band partial discharge signal The effective detection distance of the local discharge detection device is 80 cm,and the envelope of the partial discharge signal is extracted by MATLAB,and it can be intuitionistic.The optimal detection frequency of the local discharge detection device is 80 cm.When the center frequency is 27 k Hz,To analyze the signal amplitude and discharge starting point,in order to determine whether the local discharge,discharge size and location to provide an effective basis.