Research And Design Of Capacitive Equipment Online Monitoring System

With the continuous development of the national economy,society’s demand for electricity is increasing.Capacitive voltage transformers,transformer bushings and other capacitive equipment in substations are in large numbers,and their stable operation plays an important role in the safety of the power system.With the rise of sensors,microprocessors and other related new technologies,online monitoring technology has also been advanced and developed.In response to the current problems of low accuracy and imperfect fault diagnosis of capacitor-based equipment online monitoring,this project designs a capacitor-based equipment online monitoring system based on domestic and international research,and verifies the feasibility and effectiveness of the system.The main research contents are the following four aspects:(1)Research on the online monitoring method of capacitor-type equipment.Firstly,by analyzing the advantages and disadvantages of common monitoring methods such as the over-zero comparison method and the bridge balance method,the harmonic analysis method is chosen to measure the dielectric loss factor of capacitive equipment.The experimental results show that the improved method can effectively reduce the measurement error.Finally,the influence of five factors on the measurement of dielectric loss,such as synchronous acquisition error and interphase coupling capacitive interference,is analyzed and corresponding solutions are designed.(2)The software and hardware design of the capacitive equipment online monitoring system.Firstly,the overall structure of the distributed system and the signal acquisition device for online monitoring of capacitive devices with STM32F103ZET6 as the core are designed.Secondly,in view of the small amplitude and large span of the leakage current,a zero flux current transformer and a seven-stage adaptive amplification circuit were designed to realize the signal acquisition and processing of micro-amp to milliamp currents,and the remote communication transmission was realized through RS485 circuit,and the hardware circuit schematic design,four-layer PCB drawing and prototype fabrication of the signal acquisition device were completed.Then the lower computer software of the online monitoring system was designed,realizing the functions of signal acquisition and processing,remote communication and transmission.Finally,the upper computer operation interface based on Lab VIEW was designed to realize visual operation.(3)Establishment of fault diagnosis model for capacitor type equipment.In view of the problem of low diagnostic accuracy and poor robustness caused by the incomplete selection of fault diagnosis model features,the capacitive equipment leakage current,dielectric loss factor and temperature and humidity of the environmental factors collected by the online monitoring system are used as the input features of the model,and in view of the drawback that the BP neural network tends to fall into the local optimum,the weights and thresholds of the BP neural network are optimized and adjusted by using the global optimization capability of PSO.The PSO-BP neural network-based fault diagnosis model for capacitor-based equipment was established to realize the comprehensive fault diagnosis of capacitor-based equipment with multiple feature quantities.The experimental results show that the PSO-BP neural network fault diagnosis model has an precision rate of 97.41%,a recall rate of 98.26% and an F1-score of 97.84%,with good diagnosis results.(4)By building a test environment,the capacitor-based equipment online monitoring system was tested for function and performance.The test results show that the capacitive equipment online monitoring system designed by this topic operates stably,and in the accuracy test,the measurement errors of leakage current and dielectric loss factor are within the error range corresponding to the technical index under the two conditions of normal and harmonic interference;in the repeatability test,the maximum values of RSD for leakage current and dielectric loss factor measurement are 0.147% and 1.73% respectively,which meet the requirements of RSD of measurement value in technical index.The capacitive equipment online monitoring system designed by this research has improved the monitoring accuracy,perfected the function of fault diagnosis,and has important practical significance in promoting the development of substations in the direction of intelligent automation.