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.
Calculation of spatial loss distribution in stacked power and distribution transformer cores
This paper describes an analytical solution to use a generic 2D finite difference method to accurately calculate the quasi 3D spatial distribution, components, and total core losses in transformer cores. The solution takes into account: (1) magnetic anisotropy and nonlinearity of the core material; (2) all components of iron losses of the core material, including losses in directions other than the rolling direction; and (3) joint model and localized losses due to the distorted flux distribution in the joint regions (due to core gaps) across the core-stack. The results are used to: (1) calculate very accurately the total core losses of a transformer at the design stage every time, for all core materials, at all operating inductions, for all core geometries, for both 50 Hz and 60 Hz; (2) understand the contribution of cross losses, harmonics, and joints to the total losses of a core; (3) evaluate the impact of various joint attributes, such as, type of joint, number of steps, number of laminations per step, size of gaps, and lamination thickness on the total performance of the core; and (4) improve the core loss performance of transformers by optimizing core design and core material parameters. This paper presents the analysis as applied to 3-phase, 3-limb cores. The paper also presents the results of the extensive experimental/test verification performed on a number of model cores in the lab as well as on a large number of actual commercial transformer cores with excellent agreements. The results have been used to calculate core losses of stacked power and distribution transformers with consistent accuracy.