The thermal time constants of dynamo-electric machines

V. Karapetoff: The use of exponential expressions for heating and cooling curves of machinery is quite old. I published a complete theory of such curves in my Laboratory Notes in 1906. See also my “Experimental Electrical Engineering,” second edition, Vol. II, pp. 69 to 74. For a number of years we had at Cornell a student experiment on temperature rise in transformers using and checking exponential curves. However, the discrepancy with the observed results was so considerable that we dropped the theory and left only the measurements. As a result of study of various Institute papers on temperature rise in electrical machinery, I have come to the conclusion that the exponential theory, in the simple form used by the author, is inadequate to represent the observed facts even in simple stationary apparatus, not to speak of revolving machinery. therefore am omitting this theory from the third edition of my laboratory book.