External axial magnetic field excitation system in intermediate-frequency current interruption experiment

An external axial magnetic field (AMF) excitation system applied in the intermediate-frequency current interruption experiment is designed. In the system, an intermediate-frequency current transformer (CT) is designed to induct the current in the main circuit and the secondary current is used to excite the Helmholtz coil. So that the AMF which is synchronous with the primary current and regulated by the transformation ratio is generated in axes center of the Helmholtz coil. In this way, the axial magnetic field generated by the contact coil in the current breaker can be simulated. Firstly, the relationship between the inducted magnetic intensity in the axes center of the Helmholtz coil and secondary current is theoretically established. And the designing process for the essential parameters is introduced in detail. Secondly, the equivalent circuit is simplified based on the high magnetic permeability and low leakage inductance of CT. It is proved by calculation that the iron core would not reach saturation when the current root mean square (RMS) value in the circuit is maximal. The phase-difference between the primary current and the secondary current is also verified to be in a reasonable range. Finally, the experiment is implemented to test the excitation system. The magnetic induction intensity is calculated according to the supposed mathematic model of the circuit and the experimental data in the AC experiment. The calculation result of B/I turns out to be consistent with that of the theoretical value, which verifies the effectiveness of this excitation system.