Phenomena accompanying transmission with some types of star transformer connections

The purpose of this paper is to demonstrate the phenomena attending the operation of star-star transformers with grounded neutral on the line side. Contrary to current opinions, the author believes the abnormal voltages and destructive effects, which often accompany star-star operation, are due to even harmonics, at least in a large number of cases. At high magnetic densities, the third harmonic voltage may be appreciable, but the indications are that´ the even harmonics will cause damage at nominal magnetic densities lower than those which require appreciable third harmonic exciting current. The data on which the conclusions are based, include approximately 150 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 to made with an oscillograph in any laboratory or substation. One precaution must be kept in mind, namely that the observations should start at low voltages, which may be increased gradually until the various phenomena are observed. Unless this is done, the equipment may be wrecked.