Research On Modeling And Suppression Method Of Electromagnetic Interference Of Electronic Transformer In Strong Electromagnetic Environment

With the development of intelligent power system,more and more electronic devices are integrated into the gas insulated substation（GIS）system.As the main measurement equipment in substations,electronic transformers have good dynamic characteristics and frequency response characteristics,and gradually replace traditional electromagnetic transformers.However,when the isolation switch in the substation is operated,transient electromagnetic interference with high amplitude and high frequency will be generated,which will be coupled into the low-voltage circuit unit composed of integrated circuit chips,resulting in extremely high failure rate of electronic transformers.Therefore,this thesis studies the electromagnetic interference and suppression methods of electronic transformers in GIS,mainly including the following aspects.Firstly,the transient process during the operation of the isolation switch is analyzed,and the principle of very fast transient over-voltage（VFTO）and very fast transient overcurrent（VFTC）are studied.First,an equivalent model of GIS is carried out and verified by experiments to study the electromagnetic interference characteristics and influencing factors.Secondly,the output signal of the primary sensing unit of the electronic transformer under different voltage levels is measured,and the interference characteristics of the electronic transformer under the operation of the isolation switch are analyzed.Secondly,taking the acquisition unit of a voltage and current combined electronic transformer of a manufacturer as an example,the electromagnetic interference problem in the strong electromagnetic environment generated by the isolation switch operation is studied.First,based on the actual structure of the electronic transformer,a simulation model is built to obtain the electromagnetic field distribution inside the transformer pipeline and the collection room.Then,the electromagnetic interference inside the acquisition unit is further analyzed,including the radiation interference of the electromagnetic field coupled into the shielding shell to the PCB and the conduction interference of the induced voltage on the equipment line to the key circuit.Finally,the problems of board-level resonance and microstrip line crosstalk of the acquisition unit are studied.Thirdly,the methods of suppressing electromagnetic interference of electronic transformers are studied.The electromagnetic interference of electronic transformers is suppressed from the perspectives of interference source,coupling path and susceptible equipment,including adding ferrite magnetic rings and wave traps to the system to suppress interference sources,improving the shielding structure to block the coupling path,and improving the anti-interference performance of the acquisition unit by filtering and adding decoupling capacitors,and then the effectiveness of the above suppression methods is verified by simulation.The results shows that the maximum over-voltage of the isolation switch is between1.2 and 1.9 p.u.,and is affected by the system input and output capacitance,the residual voltage of the bus and the speed of the switch.The generated transient electromagnetic interference will affect the electronic transformer by means of radiation interference,conduction interference,board level crosstalk and resonance.And the reliability of the operation of the electronic transformer can be improved by restraining the interference source,blocking the coupling path and improving the anti-interference performance.