Influences of Generator Parameters on Fault Current and Torque in a Large-Scale Superconducting Wind Generator

Due to higher magnetic flux density, larger effective magnetic air gap, and lesser use of ferromagnetic materials, large-scale direct-drive superconducting (SC) wind generators have a very high peak fault current and torque, which pose a challenge for their armature windings and mechanical supports. Understanding the behavior of the SC generators under faults is important for their application and commercialization. In this paper, a 13.2-MW direct-drive SC wind generator is analyzed under the three-phase symmetric short circuit using 2-D finite-element analyses. The key differences in the short-circuit behavior between SC generators and conventional machines are explained. The effects of a high fault torque on the cost and weight of a generator are also discussed. It is found that the higher fault current and torque in an SC generator are mainly caused by low reactances and nonnegligible armature resistance. Generator parameters, including the use of ferromagnetic materials, the value of magnetic loading, the pole number, the number of turns per armature coil, and the number of armature winding sets, have a significant influence on reactances, fault current, and torque. The influences of these parameters on fault current and torque under the three-phase symmetric short-circuit are analyzed in detail. Moreover, several ways to decrease the fault current and torque in terms of machine design are proposed.