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 generat ion 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°C as the allowed maximum core hot spot temperature under sustained worst conditions of load, core — excitation and ambient temperature.
Transformer diagnostics using dissolved gas analysis and polarisation and depolarisation current measurements — A case study
This paper presents analysis of the measurements carried out on three distribution substation transformers. Dissolved Gas Analysis (DGA) and Polarisation/Depolarization Current (PDC) measurements were carried out on three transformers. DGA analysis is carried out using Ratio methods and Duval's triangle. In addition, furan and moisture analysis are done from the oil samples. Then, PDC results of the same transformers are used to calculate paper/oil conductivity. Furthermore a discussion on the results of DGA and PDC measurements is presented.
Observations of nearshore infragravity waves: Seaward and shoreward propagating components
[1] The variation of seaward and shoreward infragravity energy fluxes across the shoaling and surf zones of a gently sloping sandy beach is estimated from field observations and related to forcing by groups of sea and swell, dissipation, and shoreline reflection. Data from collocated pressure and velocity sensors deployed between 1 and 6 m water depth are combined, using the assumption of cross-shore propagation, to decompose the infragravity wave field into shoreward and seaward propagating components. Seaward of the surf zone, shoreward propagating infragravity waves are amplified by nonlinear interactions with groups of sea and swell, and the shoreward infragravity energy flux increases in the onshore direction. In the surf zone, nonlinear phase coupling between infragravity waves and groups of sea and swell decreases, as does the shoreward infragravity energy flux, consistent with the cessation of nonlinear forcing and the increased importance of infragravity wave dissipation. Seaward propagating infragravity waves are not phase coupled to incident wave groups, and their energy levels suggest strong infragravity wave reflection near the shoreline. The cross-shore variation of the seaward energy flux is weaker than that of the shoreward flux, resulting in cross-shore variation of the squared infragravity reflection coefficient (ratio of seaward to shoreward energy flux) between about 0.4 and 1.5.