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Investigation of No-load and on-load performance of a model three-phase transformer core operating under sinusoidal and PWM voltage excitation

Dgali, Nabiel 2019. Investigation of No-load and on-load performance of a model three-phase transformer core operating under sinusoidal and PWM voltage excitation. PhD Thesis, Cardiff University.
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Abstract

The iron losses in transformer laminated cores is higher than the nominal losses of the material itself by a factor known as the building factor. Reduction of the building factor of a transformer core is as important as the improvement of the basic properties of the material. In this investigation grain oriented 100 kVA three-phase distribution transformer core was investigated in order to obtain detailed study of losses. The core used in this study has overall dimensions of 540 mm in length and 520 mm in width. The core was built of 120 laminations as single joint three lamination per stacking layer with length of overlap shift of 3 mm and density of 7650 kg/m3. The core has the [011] [100] texture which is known as the Goss texture or Cube-on edge texture. This study considers four aspects of losses and localised magnetostriction on transformer core. Firstly, the power loss under sinusoidal and PWM excitation in the three-phase transformer core which was made up of 3% silicon Highly Grain-Oriented material (HGO) was measured. Also, the power loss of Epstein strips at various flux density and frequencies was measured. In addition, localised and overall flux density distributions in depth under sinusoidal and PWM excitation conditions in the transformer core at core flux densities of 0.4T, 0.6T and 1.0T under load and no-load conditions were measured. Secondly, the effect of the clamping pressure on overall and localised power loss was determined under sinusoidal and PWM voltage excitations. The results showed that the loss under PWM voltage excitation increased by 10-30% as the flux density is increased. Further, the shape of the excitation voltage as well as the switching frequency spectrum and modulation index values also played a major role in the power loss. Thirdly, the influence of localised magnetostriction on the three-phase transformer core was investigated under sinusoidal and PWM voltage excitations by measuring the mechanical strain distribution in the transformer core under different peak flux densities. The investigation showed that increasing the peak flux density from 0.4T to 1.0T increased localised magnetostriction where the largest localised magnetostriction was obtained at the T-joints. Investigation of No-load and on-load performance of a model three-phase transformer core operating under sinusoidal and PWM voltage excitation iv Finally, using MATLAB environment comparisons have also been made between the results obtained from sinusoidal and PWM inverter. These results showed that the localised and overall power loss increased considerably under PWM voltage excitation. Comparisons have also been made between practical core and the simulated model magnetic core results. These results showed that lower power losses occurred under simulated results because the model core had zero flux leakage.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: PWM inverter and sinusoidal voltage excitation; Three-phase transformer measurements; Losses measurements under PWM voltage excitation; Load and No-Load measurements; localised magnetostriction measurements.
Date of First Compliant Deposit: 20 March 2019
Last Modified: 20 Mar 2019 10:38
URI: http://orca.cf.ac.uk/id/eprint/120910

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