Effect of Geometry Change on Armature Behavior

Diffusion-controlled erosion of armatures, which is accentuated by the velocity skin effect, gives rise to nonuniform current conduction and consequent nonuniform heating. Earlier computational studies have highlighted the role played by armature geometry in current density and temperature distribution. Recently, we designed modified C-shaped armatures, called saddle-shaped armatures, to study the effect of geometry change on armature erosion and its consequent effect on rail deposits. The trailing edge and the throat of the armature were curved to better align with the magnetic field, thus reducing the nonuniformity of current density distribution. A front tab was also provided to reduce current concentration and heating at the leading edge of the contact area. Low-speed tests, in which armatures were recovered and compared with recovered conventional C-shaped armatures, were conducted. Similar experiments at speeds above 2 km/s were conducted and compared with corresponding C-shaped armature experiments. It was found that in conformation with our hypothesis, the saddle-shaped armatures recovered from low-speed shots showed less erosion both on the contact surface and in the throat area. The high-speed tests showed that the contact voltage for saddle-shaped armatures was significantly lower than that for conventional C-shaped armatures. This implies less energy loss at the rail-armature interface and potentially less lateral force generated during contact arcing