Research On Analytical Algorithm Of Shielding Effectiveness Of Power Secondary Equipment

With the continuous development of modern power system to intelligence and integration,the high-frequency transient electromagnetic field generated in the switching operation of substation is one of the main factors leading to the failure of secondary equipment.Especially during the operation of the disconnector,the arc combustion and reburning caused by the contact will produce transient electromagnetic field on the disconnected bus and radiate the energy to the surrounding space.This will result in misoperation or system failure of secondary sensitive equipment in the substation,shortening the service life and permanent decline of performance,and even damaging electronic and electrical equipment in serious cases.The installation of metal shielding cavity usually is an effective measure to suppress electromagnetic interference.Therefore,the shielding effectiveness is defined to characterize the shielding ability of metal shielding cavity to electromagnetic wave.In practical engineering applications,the shielding cavity is not an ideal complete structure.The holes and gaps on the surface provide channels for electromagnetic coupling,resulting in the reduction of the shielding efficiency of the cavity.Therefore,the research on the prediction methods of shielding effectiveness have become the focus of many scholars.Aiming at the electromagnetic interference phenomenon faced by the secondary equipment in the substation under long-term operation conditions,and considering the weakening of electromagnetic interference caused by the installation of shielding cavity.This thesis established an analytical model to evaluate the shielding efficiency of the shielding cavity of secondary equipment,including external radiation and internal leakage.The main research contents are as follows:Firstly,considering the radiation of the interference source outside the shielding cavity of the secondary equipment,a hybrid analytical model which can quickly predict the shielding cavity with multi-aperture array was established based on BLT equation of the electromagnetic topology(EMT)theory and Dehkhoda’s model.The shielding effectiveness under the condition of electromagnetic radiation is studied,and compared with the CST simulation experiment and the analytical method in the reference.The calculation results showed that the three methods were in good agreement,which verified the accuracy of the hybrid analytical model established in this paper.Compared with CST numerical simulation,the analytic algorithm not only had fast computing speed,but also saved a lot of memory.Secondly,in practical application,in order to facilitate the installation of internal equipment,the appearance of shielding cavity was not limited to regular structure.Based on the hybrid analytical model established under the condition of external radiation,a hybrid analytical model for calculating the shielding effectiveness is established for the irregular shielding cavity structure.Compared with CST numerical calculation,the effectiveness of the extended hybrid analytical model was verified.At the same time,the characteristic law of the irregular shielding cavity under the condition of changing different parameters was analyzed,including the cavity structure parameters and the built-in lossy dielectric layer.Finally,considering the electromagnetic leakage inside the shielding cavity of the secondary equipment and the electromagnetic interference to the external electronic equipment,the analytical model of the shielding effectiveness of the leakage inside the shielding cavity was established based on the electromagnetic topology(EMT)theory,and the shielding effectiveness was studied.The simulation results were in good agreement with the reference methods.Besides the hole methods of the shielding cavity include single hole,circular aperture array and eccentric aperture array,and so on.