Overvoltage protection scheme for d.c. generators used to power an inductive energy storage system for fusion research

The purpose of this study was to determine possible overvoltage protection schemes to be used on d.c. generators which power inductive energy storage systems. The inductive energy storage system examined is the ohmic heating circuit of an experimental fusion device known as a tokamak. The particular tokamak in question is ORMAk Upgrade, which is proposed to be built by the Fusion Energy Division of Oak Ridge National Laboratory in Oak Ridge, Tennessee. ORMAk Upgrade is to have an energy storage capability of 4.66 megajoules at a current of 20,000 amperes, and when this energy is dumped, sharp transients occur which will cause voltage spikes on the armatures of the d.c. generators which will power the system. In the study, a simple model for the ohmic heating circuit was developed. This circuit was then converted to CSMp statements so that the circuit response with different protection schemes could be determined by computer. Two feasible schemes were found, and are described in detail. Only one of these schemes, which involves disconnecting the generators from the circuit prior to the energy dump, was selected as desirable.