Temperature rises in electrical machines with sustained variations in load and speed

A method is presented for obtaining the temperature-rise/time curve for a given machine for an arbitrary sequence of operating currents and speeds; the method is demonstrated to give results for such a run correct to about ±2° C in 60¿70° C. The method is to suppose that the equivalent thermal network of the machine is linear, its temperature/time curve thus being the sum of the temperature/time transient responses for a series of short times, ¿t, successive transients corresponding to the average operating conditions during successive intervals; and then to modify this curve to that for the actual non-linear machine by adding a correction curve which is itself composed of two series of transient responses: one of these allows for the effects of non-linearity due to temperature rise, and is based upon the succession of average temperatures, given from the first curve, during the intervals ¿t; the other allows for the effects of changes in dissipation coefficients due to changes in speed. The test-bed procedure for obtaining the temperature/time transients for the linear machine, and the corrections for non-linearity, is specified. It is recommended that this procedure, lasting, about 36 hours, should be applied to samples of appropriate types of machine.