Eddy-current losses computation in the armature slot- bars of a turbogenerator fitted up with superconducting field winding

Abstract

This paper describes a fast computing method of determining the losses due to the eddy currents which take place in the armature slot-bars of a turbogenerator provided with superconducting field winding. Since in such kind of machines there is no need for an iron structure in the rotor and in the stator, the tangential component of magnetic flux density in the armature winding air space turns out to be of the same magnitude as the radial one. By using the magnetic vector potential formulation, a computer program worked out by the authors is used to determine both the radial and tangential component of the magnetic flux density due to the excitation current. It is found that the total Joule losses can be expressed in the form of the asymptotic series replacing the resulting Kelvin functions and an approximate formula is derived by truncating the asymptotic series to the first term. The total amount of Joule losses per unit length in an elemental armature conductor of a two-pole three-phase turbogenerator is computed employing this technique which takes into account both magnetic flux density components along with their harmonic content. The eddy-current losses are found by comparing the actual Joule losses with their computed d.c. value.