D.Ing. / Transformer design is an art which spans a century. Although the basic transformer has changed little over this period, the challenges that face high frequency power transformer designers today have grown considerably. Increasing frequency and power density and decreasing size and profile are among the most important. Eddy currents, controlling circuit behaviour and minimising losses are important aspects of design, and close attention is paid to heat removal and cooling. Modern transformers are no longer limited to certain shapes and sizes; choosing the topology and optimising the shape is often part of the design process. For each aspect of design, numerous modelling techniques exist for analysing transformer behaviour, with varying degrees of complexity. A common feature of optimisation techniques is the large number of variables and interdependent functions that relate different aspects, from the associated behavioural models, to one another. In this study, this complexity is reduced by integrating the individual analytical models for transformer behaviour. Since a convenient thermal model for high frequency transformers does not exist at present, a new thermal reference model is devised and verified. It is specifically suited to high frequency transformer applications and design, and practical sets of reference data are provided for a few ferrite materials and for copper. Transformer losses are considered next, with special attention given to eddy current analysis techniques. New formulations of eddy current solutions are given, with extensions of the orthogonality principle for skin- and proximity effects and superposition thereof. An investigation of leakage impedance design as a function of frequency scaling follows. The relationship between leakage reactance voltage drop as a function of frequency scaling by dividing a monolithic transformer into distributed elements is considered, and the results are applied to two case studies of a 35kVA transformer for a plasma burner application. A new model, the generic proportionality model, applies the thermal referenCe model to scaling of transformer parameters. A case study is also presented, demonstrating the relationships that exist between design parameters and performance functions. Another generic model, the scant model, is introduced, which integrates the thermal reference model into optimisation of transformer shape. It uses a limited number of functional and form parameters, and is applicable to a wide variety of geometries. Two case studies, demonstrate the effects of varying the shape of a rectangular configuration on derating factors.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:3426 |
| Date | 30 August 2012 |
| Creators | Odendaal, Willem Gerhardus |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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