Principles of Transformer Design

by Alfred Still

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1919 Excerpt: ...sides plus one-half the area of the. lid. The cooling effect of the bottom of the tank'is practically negligible, and is not to be included in the calculations. Example. What will be the probable maximum temperature rise of the oil in a self-cooling transformer with a total loss of 1200 watts, the tank--of sheet-iron without corrugations--measuring 2 ft.X2 ft. X3-S ft. high? The surface for use in the calculations is 5 = (3.5X8) + 2 = 30 sq. ft., whence which', according to Fig. 32, indicates a 43 C. rise of temperature for the oil. The temperature of the windings at the hottest part of the surface in contact with the oil might be from 5 to 10 C. higher than the maximum oil temperature as measured by thermometer. Assume this to be 7 C. Assume also that the room tempe1ature is 35 C. and that the difference of temperature (To) between the coil surface and the hottest spot of the windings--as calculated by the method explained in Art. 23--is 13 C. Then the hottest spot temperature in the transformer under consideration would be about 35+43 + 7 + 13 = 98 C. 26. Effect of Corrugations in Vertical Sides of Containing Tank. The cooling surface in contact with the air may be increased by using corrugated sheet-iron tanks in place of tanks with smooth sides. It must not, however, be supposed that the temperature reduction will be proportional to the increase of tank surface provided in this manner; the watts radiated per square inch of surface of a tank with corrugated sides will always be appreciably less than when the tank has smooth sides. Not only is the surface near the bottom of the corrugations less effective in radiating heat than the outside portions; but the depth and pitch of the corrugations will affect the (downward) rate of flow of the oil on the insid...

80 pages, Paperback

First published November 1, 2002