A computer circuit analysis investigation into stray subplate capacitance effects during the discharge of an MHD magnet

A computer model has been constructed to evaluate the contribution of stray subplate capacitance to the generation of overvoltage transients to the anticipated value of the emergency discharge voltage levels. The model includes voltage tap location and effects of adding resistors between the subplate and the magnet conductor. Order-of-magnitude approximations were used to obtain values for capacitances, resistances, and inductances. The first two subplates of fifteen were modeled, together with the circuit breaker, dump resistor, and power supply. The model consisted of 26 resistive elements, 19 inductive elements, and 22 capacitance elements. Results show no overvoltage transients were generated during discharge. In addition, there were no local channel bundle overvoltages, although the bundle did generate damped oscillations at approximately 500 kHz, for approximately 20 microseconds. The addition of a current-limiting resistor between each subplate (ground) and the magnet conductor, has beneficial effects on oscillations observed in the channel bundles and across the voltage taps, in that oscillation damping is increased with the resistor added.