Transactions section: Field testing of generator insulation EEI subject committee on generator insulation and testing

I — Introduction NEED for a practical as well as a reliable nondestructive test that will determine the condition of generator insulation has long been recognized by the industry. Simple methods now in general use, the high voltage proof test and the insulation resistance test, do not accurately or positively disclose the overall condition of windings, indicate the degree of deterioration, or necessarily locate weak spots. This lack of suitable insulation tests has been emphasized recently by the return to service of a number of machines either after long shutdown periods during the depression years or from standby service to low pressure elements used in connection with topping units; in these cases knowledge of insulation condition is vital. As a result of this situation the Edison Electric Institute electrical equipment committee undertook active work on the problem in 1935.¹ In 1937 a special subject committee was appointed on “Generator Insulation and Testing,” with the ultimate object of developing a reliable test procedure for determining the condition of generator insulation. The investigation has been carried out by various member companies of the EEI and others in the industry interested in the problem, under the guidance of the subject committee. Close contact has also been maintained with the manufacturers who have made many valuable suggestions, assisted in testing, and given aid in analyzing data. The study is by no means complete and this paper should not be construed as a final report with definite conclusions, but rather as a progress report on an investigation still under way.