Hydrogen gas generation due to moderately overheated transformer cores

This paper first presents an overview of this phenomenon from its initial discovery to the stage of the factory/laboratory investigations performed to confirm this new mechanism of gas generation in power transformers. This is followed by an overview of the increased significance of developing accurate calculation of the core hot spot temperature. The paper then presents the detailed accurate diagnosis performed on a 600 MVA transformer that had this issue in the field, the improvement made, and the calculation of the predicted gas generation performance of its loading cycle throughout a year of operation. The paper then presents the basis for the additions/changes proposed to be implemented in the IEEE Standards as a result of the discovery of this new gas generation mechanism. The paper also provides the basis for recommending to the IEEE Standards the selection of 130 degC as the allowed maximum core hot spot temperature under sustained worst conditions of load, core - excitation and ambient temperature.