[Electric engineering.] . certain amount of loss in every trans-former, owing to the resistance of the coils and the resistancethat the core offers to the changing magnetism, i. e., owingto the hysteresis loss. These losses all reappear in the formof heat, and this heat must be gotten rid of by radiation. Ifthere is an air space between the coils and the iron case ofthe transformer, the heat is conducted away with difficulty; S14 ELECTRIC TRANSMISSION. 57 but if the case is filled with oil, the oil circulates more orless and serves as a conducting medium for carrying theheat from the coils and
[Electric engineering.] . certain amount of loss in every trans-former, owing to the resistance of the coils and the resistancethat the core offers to the changing magnetism, i. e., owingto the hysteresis loss. These losses all reappear in the formof heat, and this heat must be gotten rid of by radiation. Ifthere is an air space between the coils and the iron case ofthe transformer, the heat is conducted away with difficulty; S14 ELECTRIC TRANSMISSION. 57 but if the case is filled with oil, the oil circulates more orless and serves as a conducting medium for carrying theheat from the coils and core to the case, where it is radiatedto the surrounding air. Very often, when the transformersare large, they are unable to get rid of the heat by radiationalone, without becoming so hot that there is danger of dama-ging the insulation, and it is necessary to provide some arti-ficial means for cooling them. This is usually accomplishedeither by mounting the transformer so that air may be fr/mary Ma//7S Suspension JiooAs. FIG. 19. circulated through it by means of fans or by immersing thetransformer in oil, which is kept cool by water circulatingin coiled pipes. As stated above, these precautions are onlynecessary in the case of large transformers, such as thoseused in substations. Transformers of ordinary size, such asare placed on poles, are able to get rid of the heat generatedwithout any special cooling devices, because the area exposedto the air is much larger in proportion to the output in thecase of a small transformer than in the case of a large trans-former. 58 ELECTRIC TRANSMISSION. 14 71. Primary Fuses.—Transformers are operated onconstant-potential circuits almost exclusively; hence, if ashort circuit occurs on either primary or secondary, therewill be a heavy rush of current, which will do damageunless the transformer is instantly disconnected from thecircuit. This is accomplished by inserting fuses in the pri-mary between the transformer and the line. These fus
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