It is generally recognised that insulation constitutes the most vulnerable part of electrical machinery, and manufacturers and users alike are confronted with the problem of how to ensure the maintenance of electrical service while dependent on materials known to be of an unreliable character. The extremely unmechanical nature and general unsuitability of the commercial insulating materials for withstanding the high temperatures and stresses occurring in service, has discouraged any wide-spread scientific investigations of directly practical application. As a result, therefore, insulation problems have in the past been solved largely by process of trial and error. The necessity for greater attention to these problems has been forced upon engineers by the advent of high voltages and larger and more costly units. Modern scientific research has thrown much light on the electrical behaviour of dielectrics, and much scattered data has been published dealing with the properties of insulating materials. This information, however, has not been available heretofore in a co-related form whereby it can be used as a fundamental basis for the practical insulation of electrical apparatus. In this treatise the authors have endeavoured to set forth the underlying principles and methods whereby the design of insulation can be carried out with precision and have embodied the results of many years of practical experience in connection with insulating problems.
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