Prevention of transient voltage in windings

This paper relates to windings such as are used in transformers, reactors and the like, with particular reference to the characteristics which determine internal distributions of suddenly impressed voltages or sudden voltage changes, and the resulting internal oscillations. Ordinary lightning arresters, which limit the maximum voltages reaching the winding terminals, but cause rather than prevent the occurrence of sudden voltage changes, certainly give no protection against excessive voltages between turns or between coils. After describing the production of these transient voltages in ordinary windings, and pointing out that the treatment of symptoms by the addition of extra insulation tends to defeat itself by augmenting the cause, this paper explains these phenomena as due to faulty arrangements of inherent capacitance with the inductance of the winding. A fundamental principle is evolved indicating the constitutional remedy, which, if perfectly applied, would give only uniform internal voltage distributions, however abrupt or frequent the voltage changes at the terminals might be. Methods of application are described for the ordinary windings, by supplementing the faulty arrangements of inherent capacitance with auxiliary capacitances or condensers. Methods are given, also, for the construction of windings with the ideal distribution of inherent capacitance called for by the principle. Two alternative statements of the fundamental principle upon which the ideal distribution of capacitance is based are emphasized in the paper, and the application of the principle is adequately illustrated in the figures, of which Fig. 2 is a simplified diagrammatic representation of the arrangement of inherent capacitance with the inductance of that certain type of ordinary windings shown in Fig. 1, Figs. 3 to 5 illustrate methods of correcting this faulty arrangement by means of supplementary condensers, Figs. 6 and 7 show two typical forms of a general method of constructing windings with the ideal distribution of inherent capacitance, and the remaining figures illustrate practical modifications of this method. With the ideal distribution of capacitance with inductance called for by the fundamental principle here enunciated, sudden and erratic changes in voltage at the terminals of the winding, or impressed wave trains of any frequency, result only in voltage distributions which are at every instant uniform. With practical arrangements approximating the ideal one, it is only necessary to insulate between turns and between coils, with ordinary factors of safety, for the proportional part of the maximum voltage which may appear at the terminals.