Temperature Rise of Ventilated Railway Motor Armatures

The calculation of temperature rise and of time-temperature curves of a railway motor for which only preliminary design data are available, usually presents considerable difficulty. Modern railway practise demands increasingly large power units in a limited space, so that accurate methods are necessary for the predetermination of temperature rise as a basis for guaranteed ratings and of time-temperature curves for the application of a motor to a complicated service cycle. For calculating the temperature rise of the armature in a new design of motor for any time interval and load condition, the author presents a method which is shown to give consistent results when applied to motors of widely varying size. A brief outline is given of the method by which the equations are derived from the usual theory of heat flow between related bodies. It is shown that by making certain assumptions the armature can be reduced to a simple equivalent model consisting of two conducting bodies separated by an insulating wall, and that the equations resulting from an analysis of this thermal system form a practical method of calculating time-temperature curves of an armature from preliminary design data. A detailed mathematical treatment is presented in an appendix. By substitution of existing test data into part of the formula it is shown how a curve can be obtained which renders the equations applicable to a very wide range of motor sizes.