Excerpt from Transformers for Single and Multiphase Currents, Vol. 33: A Treatise on Their Theory Since the first edition of this book appeared, now twelve years ago, enormous improvements have taken place in the construction of transformers. Apart from the general development of the science of electrical engineering, which has affected all branches alike, these improvements were mainly due and rendered possible by three causes: the more general appreciation of oil as a cooling and insulating medium, the advent of alloyed iron, and last, but not least, the growing demand for large unit in connection with power transmission. Whilst only a few years ago a transformer of 200 or 300 kw. was considered a very large unit, now-a-days units of 1000 and more kw. have become quite usual. At the same time the efficiency has been raised, the regulation improved, and the price reduced. It has been my aim in the present edition to show how by a careful study of the thermic condition the output of a transformer of given weight and cost may be increased. I have also considerably enlarged the part dealing with the testing of transformers and iron samples. Some readers might perhaps think that I have given too much space to the treatment of ballistic and similar methods, since these belong rather to a treatise on physics than to an engineering handbook. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.