Factors affecting insulation resistance of large D-C machines

INSULATION RESISTANCE of rotating machines was considered by many to be a haphazard collection of unrelated numbers. One reason for this view was that insulation resistance readings rarely were taken under the same conditions. Many of the factors which greatly affect insulation resistance were not known. In the past decade, significant contributions have been made toward a better understanding of the problem.^1–4 The influence of insulation temperature, time of application, and magnitude of test voltage, moisture, and machine size were recognized.