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The selection of a new, unused mineral transformer oil for application in transformers and related electrical apparatus normally involves an oxidation test of some type. It is also desirable, if possible, to utilize the same test procedure in order to insure consistent production or to compare similar products from different sources. Unfortunately, the length of time required to perform some of the test methods used to evaluate new oils has precluded their wide acceptance as a means of controlling the quality of repetitive shipments. Necessarily, this has resulted in the use of two types of oxidation tests: one, to evaluate and help select a new, unused oil or to compare similar products from different sources, and, second, a short-time test to control the continuity of an acceptable product. The result has been that, during the course of time, a variety of such test procedures has been proposed and has found usage both in the United States and throughout the world. Many of these methods involve the measurement of either the sludge or acidity-forming propensity of an oil or both under prescribed conditions of oxidation. A number of such methods have been investigated by Subcommittee IV on Liquid Insulation of ASTM Committee D-9 on Electrical Insulating Materials. From these investigations, ASTM has adopted as a standard test procedure, a short-time continuity control-type test, ASTM Method D 1313. A second test procedure requiring a longer test period for gaging the sludge-forming propensity of a new oil is ASTM Method D 1314. Both of these methods are limited to the determination of sludge formed under the conditions of test, although other methods under study attempt to evaluate both the acid-forming tendency and the sludging propensity. In the development of oxidation test procedures for use in selecting new, unused oil or for comparing similar products from different sources, the ASTM committee always has desired that the method developed should be backed by commercial experience and should evaluate oils in the same order as they will perform in service.
Raab, Edward L.
Manager, General Electric Co., Pittsfield, Mass.