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Investigation of variable transformers by finite element modelling

El-Shawish, J. M. (2004). Investigation of variable transformers by finite element modelling. (Unpublished Doctoral thesis, City, University of London)


The prime topic of research presented in this thesis is the development and use of computer-based modelling methodologies for design and performance modelling of key industrial components in the electrical industry, exemplified in variable transformers used in voltage regulation and control. Despite the recent introduction of the solid-state devices variable transformers, which are adjustable autotransformers, are still widely used as voltage regulators in many applications. Although originally developed as voltage regulating and testing devices for use in the laboratory, variable transformers have since found countless applications in many key industries with significant importance in UK exports.

Although conventional transformers are well covered in the literature, very few studies have been carried out so far that concern variable transformer and, to our knowledge, none concerning the modelling, design and validation of variable transformers. This research addresses these issues.

Detailed methodologies for mathematical modelling and performance-analysis of variable transformers have been developed. These have been realised in detailed 3D finite element (FE) models of commercial variable transformers using a general-purpose electromagnetic (EM) FE package Opera-3d running under Unix on Sun workstations. The core activities have included the accurate modelling and computation of magnetic field in the complex topology in and around the transformer core taking into account various nonlinearities (e.g. saturation, eddy currents, etc.).

Validation of modelling results constitutes an essential and integral part of any modelling work. In order to validate the above modelling methodologies and refine the FE models developed, experimental investigations of one of the designs of commercial variable transformers TS1225 were carried out in industry. The experimental results obtained in terms of flux density values were compared with corresponding data obtained from FE modelling. This showed good agreement which validated the modelling methodologies developed and established confidence in the results of further more extensive modelling investigations.

Having validated the modelling methodologies, investigations were carried out to quantify and evaluate the effects of various design and operational regimes on magnetic field distribution in commercial variable transformers. This included the detailed investigation of field distribution in air above the transformer core which contributes to eddy current losses in the transformer top plate. This was also investigated to quantify the effects of higher harmonics. The results of the modelling studies to establish the effects of operational regimes determined by various brush and tap positions gave a vital insight into the design of the transformer core for a given output power. The detailed investigation of flux density distribution in the core and its variation with its geometric parameters quantified the effects of these parameters on the core design.

The modelling methodologies developed and the investigations carried out using the FE models developed constitute an integral part of computer aided design (CAD) and analysis of variable transformers. The same modelling strategies could be equally used for the design and analysis of similar electromagnetic devices.

Publication Type: Thesis (Doctoral)
Subjects: Q Science > QA Mathematics > QA75 Electronic computers. Computer science
T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments: School of Science & Technology > Engineering > Electrical & Electronic Engineering
School of Science & Technology > School of Science & Technology Doctoral Theses
Doctoral Theses
Text - Accepted Version
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