. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . sportation, and againby carelessness in leaving the cover offduring installation. When installingtransformers first make sure that thereis no water in the bottom of the case andtest the water coils for leaks. It is a verygood plan to dry out the transformerthoroughly before filling the case withoil. One method of doing this is to applya low voltage to the windings for severalhours, taking care that their tempera-ture does not rise above the boiling pointof water. If, however, either water orm
. Railway and locomotive engineering : a practical journal of railway motive power and rolling stock . sportation, and againby carelessness in leaving the cover offduring installation. When installingtransformers first make sure that thereis no water in the bottom of the case andtest the water coils for leaks. It is a verygood plan to dry out the transformerthoroughly before filling the case withoil. One method of doing this is to applya low voltage to the windings for severalhours, taking care that their tempera-ture does not rise above the boiling pointof water. If, however, either water ormoisture is found to be present in thetransformer oil, llie best plan is to drawoff the oil, dry out the case and refill thecase with pure, dry oil. The necessity for having perfectly dryoil is shown by the fact that even such asmall amount of moisture as four partsin 10,000 lowers the insulating value ofthe oil one half, and as there are innumer-able ways in which the oil may collectmoisture, its treatment for the removalof water is of prime importance. Thereare a number of methods for the separa-. 9-tg O*.....^ iiMDTnE FOR llii. TLNNKL. glass. Moisture is that portion that isintimately mixed with the oil, and its pres-ence cannot be determined by this test. Ifwater is found, moisture is also present,but the converse is not true. The simplestand at the same time a very good testis to remove a sample of oil in a an iron nail to a dull red heat andthrust it into the cup. If a cracklingsound like that of flying grease is heardmoisture is present. It does not makeveo much diflference as to the amount ofmoisture, as even a very small amountwill ruin the value of the oil.• There is nothing for which an opera-tor must be more on his guard than toprevent moisture getting into high tensiontransformers. The writer has known two22,000-volt transformers to fail from noppparent cause. Upon investigation thenail test disclosed the presence of mois-ture in the transformer o
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