3 research outputs found
Investigation of the influence of material and manufacturing parameters on the flux distribution and noise of transformer cores
Flux distribution in transformer core has a significant effect on vibration-born-noise of the ferromagnetic core. The grade of electrical steel and the geometry of the core joints as well as the manufacturing and utilisation parameters affect the flux distribution in the core, mainly in the joints. Understanding the effect of materials and the manufacturing parameters on flux density distribution would enable transformer design engineers to improve the core performance.
In this study, localised search coils were used to measure the flux density distribution in a linear joint assembled from different grades of electrical steel and the results were verified using COMSOL Multiphysics software with a 2D model. The flux density distribution was also measured in a mitred corner joint and the effect of the variability of the airgaps was investigated. A 3D laser scanning vibrometer was deployed to measure the vibration of the mitred joint and the results were compared with the flux density distribution. The front surface of a three phase three limb production transformer core was scanned using the 3D laser scanner and the emitted noise was measured in the same induction level to find a correlation between the noise and vibration.
The flux in the limb is non-uniform due to the longitudinal airgaps in the joints and the length of this non-uniformity greatly depends on the airgap length and the permeability of electrical steel. The peak value of the interlaminar flux density was found to be higher in NO steel than GO and the flux density in the rolling direction in the NO assembly was more uniform than GO. The flux in the outer layers of the stacked transformer core was found to be higher than in the central layers and increasing the height of stack made the flux more uniform. The calculated Maxwell forces and mechanical deformation in the joint had a good correlation with flux distribution and the scanned vibration data. A reasonable correlation was found between the surface vibration acceleration and the emitted noise of the production transformer core with frequency domain analyses
Comparison between measured and computed magnetic flux density distribution of simulated transformer core joints assembled from grain oriented and non-oriented electrical steel
The flux distribution in an overlapped linear joint constructed in the central region of an Epstein Square was
studied experimentally and results compared with those obtained using a computational magnetic field
solver. High permeability grain-oriented (GO) and low permeability non-oriented (NO) electrical steels
were compared at a nominal core flux density of 1.60 T at 50 Hz. It was found that the experimental results
only agreed well at flux densities at which the reluctance of different paths of the flux are similar. Also it
was revealed that the flux becomes more uniform when the working point of the electrical steel is close to
the knee point of the B-H curve of the steel