OF PAPER The purpose of this paper is to point out and explain some even harmonic phenomena which may attend the operation of star-star connected banks of transformers having grounded neutral on the line side only. Contrary to current opinions, the author believes the abnormal voltages and destructive effects, which often accompany star-star operation, are, in at least a large number of cases, due to even rather than third harmonics. At high magnetic densities, the third harmonic voltage may be

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... appreciable, but the indications are that the even harmonics will cause damage at nominal magnetic densities lower than those which produce appreciable third harmonic voltages. The data on which the conclusions are based include approximately one hundred and fifty oscillogram waves and a correspondingly large number of meter readings. The data are omitted from the text to a large extent, because the details could not add materially to the discussion. The tests are simple and can easily be made with an oscillograph.