Conducted Electromagnetic Disturbance Research On Secondary Equipment By VFTO

With the continuous improvement and development of China's power system,gas insulated substation has been widely used because of its compact structure,reliable operation,small footprint and other advantages.However,the very fast transient overvoltage caused by the isolation switch operation in gas insulated substation will bring serious electromagnetic disturbance to the secondary equipment nearby and affect the normal operation of the substation.Therefore,it is extremely urgent to study the electromagnetic disturbance caused by very fast transient overvoltage to secondary equipment.In order to reduce the electromagnetic interference caused by very fast transient overvoltage to secondary equipment,Scholars at home and abroad have conducted a lot of research on this,mainly embodied in the aspects of disturbance mechanism analysis,disturbance waveform measurement,shielding filtering and so on.However,there is still a lack of research on the time-frequency characteristics of the typical conduction disturbance on the side of the secondary equipment,the establishment of the conduction disturbance model and the lack of research on the immunity test device of the secondary equipment in the gas insulated substation.In this thesis,based on the actual measurement of very fast transient overvoltage to the electromagnetic disturbance of secondary equipment conducted,the above three contents are discussed and studied respectively,and some of them are combined with simulation and experimental analysis.The main contents are as follows:1.The typical conducting electromagnetic disturbance of secondary equipment in gas insulated substation is measured and analyzed.The electromagnetic disturbance mechanism of very fast transient overvoltage to voltage transformer is analyzed;A special transient measuring device was developed to measure the voltage waveform of the PT secondary side conducting electromagnetic disturbance;The time domain and frequency domain characteristics of the measured PT secondary side waveform are analyzed,and several different time-frequency analysis algorithms are compared.The time-frequency characteristics of the PT secondary side interference are obtained by the synchronous compression wavelet transform,which has the best performance.2.The typical PT secondary electromagnetic disturbance waveform is modeled.The mathematical model of secondary interference of PT is proposed by analyzing the measured results;High-order digital filter was used to filter the waveforms in different frequency bands to obtain the waveform data of each frequency band,and Evolutionary Difference Algorithm was used to extract the parameters of the proposed model,and the extracted parameters were analyzed and optimized;The proposed model was compared with the measured results,and the accuracy of the model and the feasibility of the modeling method were verified by using the value of goodness of fit R~2.3.The circuit of secondary equipment disturbance source in gas insulated substation is designed.The circuit structure of several typical conduction immunity generators is studied,and the circuit design method of the test device is determined;The circuit structures of three kinds of secondary device disturbance sources are designed and verified by simulation;Aiming at the high voltage discharge switch in the circuit of secondary equipment disturbance source,a series Si C-MOSFET switch module with single drive is proposed,and its working principle is verified by circuit simulation.4.The feasibility of the secondary device disturbance source circuit is verified through the hardware circuit experiment.Aiming at three groups of DC voltage sources in the disturbance source circuit of secondary equipment,several topological schemes of high voltage power supply were studied,and a two-stage high voltage power supply of Buck+LLC was designed and manufactured;The hardware circuit of the secondary device disturbance source was built,and the feasibility of the disturbance source circuit was evaluated by the discharge experiment combined with the high voltage power supply.