On velocity skin effect — Part I: Physical principle analysis and equivalent models simulation

Velocity skin effect (VSE) is a kind of current clustering phenomenon, which occurs at the sliding contact interfaces between the high-speed armature and the stationary rails of electromagnetic railgun launchers. Serious current clustering may lead to local conductor melting, deforming, and discharge erosion, which are disadvantageous to the launching performance, but the physical principle of VSE has not been extracted and summarized so far. The typical current clustering phenomena in static conductors are classified, and the physical principle of VSE is analyzed for rail and armature respectively in this paper. The physical principle in rails is just Skin Effect because of the short risetime of the accepted pulse current, and the physical principle in armature is Clustering Near Small Source (CNSS) and Clustering Along Short Path (CASP) of steady current owing to the continuity characteristic or the voltage drop. An equivalent steady 3-dimension model has been proposed and adopted, and the quantitative distributions of current for U-shaped and cuboid armatures are simulated contrastively by Maxwell 14.0. The simulation results reveal that the current in the interface trends to cluster along the rear perimeter, and the U-shaped armature is superior to the cuboid armature. The physical principle of VSE has importance for restraining VSE.