Experiences with Grounded-Neutral, Y-Connected Potential Transformers on Ungrounded Systems

The application of Y-connected transformers to three-phase, three-wire systems, in such a manner that the third and its multiple harmonics of the exciting currents would ordinarily be suppressed, is not in accordance with the best practise. However, such applications of grounded-neutral, Y-connected potential transformers, particularly to temporarily ungrounded systems, have been made for relaying and other purposes. The resulting complications, which are of a different nature than would be anticipated from the suppression of the third and its multiple harmonics, may not be generally appreciated, so this paper outlines experiences with two such applications. The peculiar and dangerous ``saturation phenomena'' obtained and the methods of preventing their occurrence are described and considerable data thereon included. The phenomena are discussed from theoretical standpoints in companion papers by A. Boyajian and O. P. McCarty and by C. W. La Pierre.