Approximate Expressions of Maximum Values of Transient Magnetic Fields and Electromagnetic Forces Imposed on Windings in Superconducting Generator

Abstract

As superconducting generators have a number of advantages, the investigations for such machine have been actively carried out throughout the world.
In the superconducting generator, it is very important to support the field winding and to protect it from quenching. On the other side, as the armature winding is of air core, the evaluation of eddy current loss in the winding and the way of its support are inevitable. Thus, we should know the magnetic fields and the electromagnetic forces acting on both the field and the armature windings at the early stages of the machine design.
We have partially discussed in previous papers the transient behavior of magnetic fields and electromagnetic forces acting on the windings of a superconducting generator based on a computer simulation for a sudden 3-phase fault. However, the behavior of magnetic fields and electromagnetic forces during transient period is very complicated and many calculations are required in order to find their maximum values.
In this paper, for practical use at the early stages of the machine design, we derived approximate expressions to calculate the maximum values of the magnetic fields and electromagnetic forces on the windings in the case of a 3-phase fault. In order to numerically check these expressions, we conceptually designed a 1, 000 MVA superconducting generator. The numerical results obtained by using these expressions agree well with the computer simulation results.