The propagation of surge voltages through turbo-alternators with concentric-conductor-type windings

The study of the propagation of surge voltages in conventional types of alternator winding is modified to be applicable to the concentric-conductor type of winding used for some machines having a terminal voltage of 22 or 33kV. The theoretical analysis shows that the wave entering the winding at the machine terminal sets up series of travelling waves between each pair of adjacent conductors in the bars. The travelling waves have different velocities, which are characteristic of the conductors. The waves in the outer conductor travel slowest, owing to the presence of the iron core which forms the return circuit. The waves are reflected and refracted at the junction of the various sections of the winding. Test results on a typical machine are given, and the initial voltage distribution is explained in terms of the theoretical travelling waves. Measured values for the winding surge impedance are compared with those deduced theoretically from the various circuit parameters.