Ques. Why is a high rise of temperature objectionable?
Ans. It causes rapid deterioration of the insulation, increased hysteresis losses, and greater fire risk.
Dry Transformers.—This classification is used to distinguish transformers using air as a cooling medium from those which employ a liquid such as water or oil to effect the cooling.
Air Cooled Transformers.—This name is given to all transformers which are cooled by currents of air without regard to the manner in which the air is circulated. There are two methods of circulating the air, as by
- 1. Natural draught;
- 2. Forced draught, or blast.
Ques. Describe a natural draught air cooled transformer.
Ans. In this type, the case containing the windings is open at the top and bottom. The column of air in the case expands as its temperature rises, becoming lighter than the cold air on the outside and is consequently displaced by the latter, resulting in a circulation of air through the case. The process is identical with furnace draught.
Figs. 1,961 to 1,963.—Fuse blocks for Westinghouse transformers. The fuses furnished with the transformers are mounted in a weather proof porcelain fuse box of special design. The stationary contacts are deeply recessed in the porcelain and are well separated from each other. The contacts are so constructed that the plug is held securely in place by giving it a partial turn after inserting it. When the plug is in position, the fuse is in sight and its condition can be noted which eliminates all danger of pulling the fuse while same is still intact and the transformer is under load.