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Investigation of the influence of material and manufacturing parameters on the flux distribution and noise of transformer cores

Shahrouzi, Hamid 2018. Investigation of the influence of material and manufacturing parameters on the flux distribution and noise of transformer cores. PhD Thesis, Cardiff University.
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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.

Item Type: Thesis (PhD)
Date Type: Submission
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Transformer Core vibration; Transformer core noise; Magnetic flux density distribution in transformer core joints; Flux distribution in mitred and linear joint; Magnetic Search coils; Electrical steel.
Funders: Shanghai Baosteel Group Corporation
Date of First Compliant Deposit: 24 January 2019
Last Modified: 11 Dec 2020 02:50

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