Travelling waves in high-voltage alternator windings

The security of the windings of an alternator generating at 22 kV or above and connected directly to a network depends mainly on the ability of the insulation to withstand surge voltages. The distribution of surge voltages in the various types of stator winding hitherto adopted in commercial practice is examined, together with the relation of this distribution to that of the effective insulation available. As alternators nearly always operate with the neutral point of the windings unearthed, the voltage stresses on the insulation near the neutral in these circumstances are determined and the danger of the use of graded insulation is discussed. In no case does there appear to be an inherent tendency for all transient voltages to be distributed over the length of the stator winding in the same proportion as the generated voltage of the machine.