Abnormal Voltages in Transformers

This paper deals with the electrical behavior of transformer windings when subjected to steep wave fronts and high-frequency wave trains. The dependence of the internal voltages produced, upon the distribution of capacity with the inductance of the winding, is discussed. Practical windings are divided into two general classes, one in which inductance and capacity are practically uniformly distributed, and the other in which the capacity is more or less concentrated at certain points, with relatively concentrated portions of inductance intervening. Neglecting the effects of the high-frequency dielectric losses in the insulation at high frequency, distinct mathematical analysis is given to these two classes of winding to determine the ratios of the internal voltages to the voltage of the external wave or wave train. The resulting internal voltage distributions are plotted for various frequencies, and curves are plotted for the relations of maximum internal voltages to frequency. These curves show that some frequencies are dangerous, while others are not, but it can not be said that one of these types of winding is better than the other from the standpoint of the possibility of excessive internal voltages. The analysis is by no means complete, but an examination is made of the facts and fundamental principles involved which will enable us to insulate for and guard against excessive internal voltages in a more scientific manner.