Analysis of the magnetic field distribution of the reactor and its coupling to the shielding box under short-circuit condition of flexible DC converter station

With the rapid development of primary and secondary fusion, more and more secondary devices are installed nearby the strong magnetic field sources. In the past, secondary equipment was generally not arranged around the reactor. Nowadays, the high requirement of compact development for space utilization makes it necessary to arrange secondary equipment around the reactor. Since the reactor is a strong magnetic field source in the flexible DC converter station, especially in short circuit, the secondary equipment arranged around it is easy to be disturbed by the strong magnetic field. Thus, the magnetic field distribution of the reactor needs to be studied. The existing studies about the magnetic field distribution are mostly based on highly simplified model. The existing studies about the shielding efficiency of the shielding box are mainly carried out in the high frequency band, and based on simple geometric models. In this paper, Theoretical derivation and simulation calculation of the magnetic field distribution of the unsimplified model are completed. Furthermore, the effects of the orientation of the shielding box with complex structure on the shielding effect are studied. In particular, the frequency of the short circuit current of the reactor measured in the field is analyzed and the self-inductance and mutual inductance parameters are calculated according to the unsimplified reactor structure. The magnetic field distribution around the bipolar reactor is calculated by using Biot Savart's law under the condition of quasi-static state. In addition, the calculation model of the bipolar reactor's magnetic field and the shielding efficiency of the shielding box are established in the electromagnetic field simulation software comsol. The results show that the main frequency range of the short-circuit current is DC- 180kHz, the theoretical calculation of the magnetic field distributionof the reactor is in good agreement with the finite element simulation results, the relative error is within 5%, and the best orientation of the shielded box is that the door is perpendicular to the magnetic field. The research results can provide reference for the layout of secondary equipment and the establishment of immunity standard for protection and control equipment under the condition of short circuit fault in converter station.