Effect of air temperature, barometric pressure and humidity on the temperature rise of electric apparatus

The paper discusses heat dissipation, and after citing the present Standardization Rules of the Institute in regard to “Temperature Corrections” points out that it is not only the copper resistance changes, therein assumed, which affect temperature rise, but also variations in other internal losses and heat dissipation. Then follows a discussion of the effect on temperature rise of barometric pressure, humidity and changes in resistance loss, iron loss, radiation, viscosity and thermal constants of the cooling medium, friction windage and condition of operation. It has been noted that in many cases the rise at high temperature is lower instead of higher as assumed in the Standardization Rules, and the authors made tests to determine some of the fundamentals which govern the emission of heat and temperature rise at different air temperatures. The tests made and data given cover only the direct effects of air temperature air pressure and humidity. The apparatus and methods of test are described and the results for variations in temperature and air pressure are shown graphically. The tests show that within commercial limits and at constant input the temperature rise is independent of air temperature, provided the walls or objects to which heat may be radiated are at the same temperature as the air. Barometric changes are shown to affect the temperature rise somewhat and the statement is made that humidity has no appreciable effect upon the result. The conclusion drawn is that instead of the correction specified by the Standardization Rules, no correction should be made for variation of air temperatures within the usual testing limits. This conclusion is based on the facts that there arc a number of variations, some of which are positive, some negative and some either positive or negative depending on operating conditions.