Fig. 1966.—Section through Westinghouse ½ kilovolt ampere type S transformer. Fig. 1967.—Section through Westinghouse 50 kilovolt ampere type S transformer showing large oil ducts.
Ques. In what types of transformer is this mode of oil cooling used?
Ans. Lighting transformers.
In such transformers, the large volume of oil absorbs considerable heat, so that the rise of temperature is retarded. Hence, for moderate periods of operation, say 3 or 4 hours, the average lighting period, the maximum temperature would not be reached.
Ques. In what other capacities except that of cooling agent, does the oil act?
Ans. It is a good insulator, preserves the insulation from oxidation, increasing the breakdown resistance of the insulation, and generally restores the insulation in case of puncture.
Fig. 1,968.—Wagner 300 kva, 4,400 volt three phase oil cooled transformer. In this type of transformer the case is filled with oil and fluted so as to increase the cooling surface, an oil drain valve is screwed to a wrought iron nipple cast into the base, the duct to which is in such a position as to make it possible not only to drain all of the oil from the transformer, but when desirable, to draw off a small quantity from the bottom. Should any moisture be in the oil it is therefore drawn off first.
Ques. What is the special objection to oil?