Influence of the temperature, barometric pressure and humidity of the cooling medium on the temperature rise of stationary induction apparatus

For some time it has been felt that the corrections to be applied to the temperature rise of stationary induction apparatus, when operating under conditions differing from standard, needed some little revision. The theoretical considerations governing the dissipation of heat from this class of apparatus are given briefly in the first part of this paper and the influence of temperature, barometric, pressure and humidity on the emissive constants are also briefly discussed. It was expected that the presence of moisture would have considerable influence on the temperature rise of air-cooled apparatus but a theoretical analysis shows that for ordinary room temperatures, the effect can be small even if the atmosphere is saturated. Exception is made, of course, to the case of fog-laden air. The second part of the paper is devoted to a presentation of the results of some tests made to check these conclusions. Some of these tests were made under artificially produced conditions and some under natural conditions. In the last part of the paper recommendations for corrections to be applied and precautions to be taken are given. Wherever possible, apparatus should be tested under as nearly the same conditions as those under which it is to operate. In case it is impossible to maintain these conditions the following corrections should be applied: I. Variations in Room Temperature. On all classes of apparatus except air-blast no correction be applied. On air-blast the present recommendations of A. I. E. E. be followed. On water-cooled apparatus the reference be the in-going water and this temperature and that of the room should be as near 25 deg. cent. as possible. II. Variation in Barometric Pressure. For self-cooled apparatus present A. I. E. E. recommendations be followed. For water-cooled apparatus no correction be applied. For air-blast apparatus double the present A. I. E. E. recommendations be followed. III. Variations in Humidity. No corrections be applied for variations in humidity except in case of fog-laden air.