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Although parametric devices have been known for many years, very little attention had been paid to the possibilities of exploiting the principles involved for low frequency power conversion purposes, until tfie recent advent of the parametric transformer. The theory of this device is developed in the thesis, and the unusual performance characteristics are explained. Possible application areas are discussed, for an assessment of the future potential of the device as a power-control element. The operation of the parametric transformer is considered initially on the basis of the Mathieu-Hill equations. The stability chart for these equations is extensively used to permit graphical interpretation of the behaviour and characteristics. As no complete theory exists for non-linear systems with time-varying parameters, other analytical methods are also considered, although since all of these regard the device as a parametric oscillator they throw little light an the inherent transformer action. By considering the parametric-transformer as a conventional saturable reactor with a capacitor connected across the load winding and the control winding driven from an alternating source, it can be placed within the perspective of non-linear magnetic devices already known. Many possible magnetic constructions with parallel and/or orthogonal flux. interactions are investigated, with special attention paid to the bridged magnetic core analogue of the two-C-core construction. The illustration of parametric coupling as a result of flux interaction in saturable reactor devices leads to a derivation of the overall equations directly from the physical system. The functions representing the magnetic structure of the parametric transformer are first evaluated graphically, ard using various analytical representations of the B/H curve their explicit expressions are then formulated for different magnetic configurations. The introduction into the study of the concept of a relative magnetisation curve is invaluable in explaining the current waveforms and many other aspects of the device. A mathematical model is established for the parametric transformer and the system equations are solved numerically by a digital computer. The voltage and current waveforms and performance characteristics are demonstrated, and the correctness of the theory is ascertained by comparison with experimental results. Based on considerations of losses and efficiency, the advantages and disadvantages of parametric transformers are discussed. Possible applications in such areas as power supplies, inverters and converters are viewed and examples are given.

Mathematical models of varying complexity for representing turbo- generators and associated excitation and prime mover control systems are developed. Special reference is made to the application of these models for digital computer solution to determine turbogenerator transient performance-under large system disturbances. A parametric study, of the effect of differing generator designs and control systems configurations, on the transient behaviour is performed, using the digital computer model, In particular, the capabilities of the latest high speed control systems, such as, thyristor exciters and electrohydraulic governors, are assessed, Novel methods of stabilisation of these systems and the effects of both single and combined control action are investigated. In choosing the most appropriate computer-model, the aim was to achieve the highest possible complexity, taking into account the limitations on available machine data, A full account of the results of fault tests on a full scale turbogenerating system with thyristor excitation, in which the author participated, is given, These were intented to verify some of the control policies developed, and provide an accuracy check on the computer programme to give confidence in the modelling technique for future simulkations. Fast response instrumentation for obtaining specialised feedback signals for the site tests is described, together with a full set of equipment for laboratory investigation on a model power system. Although a number of difficulties with the instrumentation were encountered in the tests, the results serve to illustrate the capabilities of fast thyristor excitation systems, and the high degree of accuracy obtained by the digital computer simulation techniques.

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