Thermal Analysis of a Small D-C Motor; Part II. Experimental Study of Steady-State Temperature Distribution in a D-C Motor with Correlations Based on Dimensional Analysis [includes discussion]

A research program has been under way to study systematically the combined thermal and electrical processes in small rotating electric machines. The previous paper in this series was limited to the application of dimensional analysis to such processes in a small d-c shunt-wound motor.1 This paper presents the results of extensive measurements of steadystate temperatures within such a motor, made with the aid of about 130 thermocouples. The details of the test motor, the procedures followed, the variables measured, and the results are described. For reasons of space, only eight selected temperature distributions are given from a total of 33 runs. The results for all the other important variables are shown in tabular form. The validity of the entire body of data was investigated in terms of a first-law balance or energy-flux balance for all processes occurring in the motor. The excellent balances obtained give great weight to the validity of the data. The experimental data in terms of the dimensionless parameters are fitted to simple empirical equations. The results are discussed from the point of view of prediction of size reduction for motors of the same design as the test motor, geometrically similar, and made from materials identical to those used for the test motor.