Physical Principle and Relevant Restraining Methods About Velocity Skin Effect

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 is disadvantageous to the launching performance. The typical current clustering phenomena in static conductors are classified, and the physical principle of VSE is analyzed in this paper. The physical principle in rails is just skin effect because of the short rise time of the accepted pulse current, and the physical principles in armature are clustering near small source and clustering along short path of steady current owing to the continuity characteristic or Laplace equation. The corresponding methods to restrain VSE are deduced and classified as follows: 1) lengthening the contact surface; 2) adding a hard and resistive cladding on the rail´s sliding surface; 3) narrowing the interface; 4) adopting a U-shaped armature instead of cuboid one; and 5) controlling the armature legs´ thickness/width distribution. An equivalent 3-D model for VSE is adopted, and simulation is carried out for a complex form of armature leg. The uniform current in the interfaces is accomplished, with which the typical uniform index is about 66%. VSE is restrained according to the simulation result. The physical principle, the relevant restraining methods, and the equivalent model are significant to railgun research work.