Numerical Analysis on the Transient Inductance Gradient of the Resistive Overlay Rail on the Sliding Electrical Contact

Abstract

A resistive overlay rail for an electromagnetic launcher was tested and its inductance gradients were analyzed using 2-D and 3-D finite-element methods (FEMs). The overlay rail was consisted with outside copper rail for good conduction of current and inside steel one for the prevention of rail wear. When the armature slides along the steel rail, electrical current flows mainly through the copper rail before it reaches the armature tail and it penetrates the steel rail at the armature tail due to the velocity skin effect. The rail inductance gradient $L^{\prime }_{R}$ is obtained with 2-D FEM in both frequency and time domains without an armature and the propulsive inductance gradient $L^{\prime }_{P}$ are obtained with 3-D transient FEM with a moving armature. A C-shaped aluminum armature was launched with the velocity over 2 km/s on the resistive overlay rail and gouging was not induced, while it appeared in the experiment with a copper rail. Using the two obtained inductance gradients, the circuit simulation was conducted and it explains the experiment result with a good agreement.