This thesis is concerned with the development of a prototype electromagnetic flowmeter for dielectric liquids. A initial prototype flowmeter is tested in laboratory conditions with a liquid of low conductivity, the conclusion of these initial tests being that the stability of the flowmeter is below that required for its design applications. This lack of stability is a problem reported on several occasions in similar projects involving electromagnetic flowmeters for dielectric liquids. Therefore the main body of the work is spent investigating the causes of instability and trying to redress the necessary problems in order that a viable working prototype is developed. Problems of thermal instability, electrostatic and electromagnetic shielding are addressed along with the causes and effects of all the major noise and unwanted signals experienced in such a system. A new prototype is developed incorporating stability driven improvements. This new design is rigorously tested and assessed. The stability of the meter is considered with respect to its flow related output. Several parameters of operational stability are given in the examples considered. A final assessment is then made of the flowmeters baseline performance and a account of any remaining instability is given with respect to the issue developed throughout the thesis. The conclusions indicate that the electromagnetic flowmeter for dielectric fluids does produce a linear output based on Faraday's law of induction. They also indicate that the instability experienced previously can be broken into its constituent parts and each contributor accounted for and reduced, working towards the ideal totally stable flowmeter.

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The problems of modelling the electromagnetic characteristics of vehicles and the experimental validation of such models are considered. The validity of the measurement methods that are applied in model validation exercises is of particular concern. A philosophy for approaching the validation of automotive electromagnetic models of realistic complexity is presented. Mathematical modelling of the key elements of the measurement processes is proposed as the only reliable mechanism for addressing these issues. Areas considered include: basic elements of numerical models; geometrical fidelity requirements for model elements; calibration and use of experimental transducers; the inclusion of cables in electromagnetic models; essential content for vehicle models. A number of practical measurement processes are also investigated using numerical methods, leading to recommendations for improved practices in: calibration of transducers for current measurement at high frequencies; measurement of radiated emissions from vehicles; identification of range requirements for simple methods of determining antenna gain and related characteristics in EMC test facilities. The impact of such measures on the success of model validation studies for automotive applications is demonstrated. It is concluded that experimental results are no less in need of validation than the numerical results that are, more conventionally, judged against them.

This thesis is concerned with the development of an a.c. drive suitable for directly driving the rollers of a glass conveyor at low speeds. A variable frequency three phase current source inverter has been developed, which operates on the slitwidth technique and uses power transistors as the switching elements. Open loop control of the machines was investigated initially but was rejected, due to the inadequate speed regulation obtained. Consequently, a digital speed and position measuring transducer was developed using an inexpensive, commercially available slotted disc. Strategies for controlling a.c. machines were then considered. This resulted in the development of a system which allowed a synchronous machine to be controlled with constant torque angle and an induction machine to be controlled with constant slip frequency. These control strategies allow maximum torque to be obtained from the machines over their full speed range. The synchronous machine becomes self starting and cannot lose synchronism even when large loads are applied. The control strategies developed also allow both the synchronous and induction machines' output speeds to be frequency locked to a demand input. A microprocessor interface and appropriate software was then developed to apply ramp demand speed profiles to the machine, simulating the speed profiles required by the conveyor drive. This was followed by an investigation into the speed matching of drives of similar and different types. The frequency locking nature of the control strategies allowed excellent speed matching between drives to be achieved. The same machine was used as both the synchronous and induction machine, enabling a comparison between the two different machine types to be drawn. Both machine types produced similar maximum torque outputs and speed responses. Consequently, the inexpensive and easier to control induction machine is suggested for use as the conveyor drive.

The work presented in this thesis is concerned with some aspects of power electronics largely related to the analysis and design of inverter-fed induction machines. Chapter 1 introduces the problems associated with the operation and analysis of inverter-fed induction machines, and state-of-the-art developments as highlighted in some recent publications. Chapter 2 is concerned with the development of induction machine frequency- and time-domain models and their solution methods. Methods of calculating model parameters are described. Simple and extended versions of the coupled circuit concept are developed for cage-rotor induction machines, and skin-effect is incorporated in these time domain mode is. Chapter 3 provides experimental verification for induction machine parameters and models described in Chapter 2. It also provides comparisons of measured and predicted results of dynamic tests for sinusoidal, quasi-square and sinusoidal PWM wave supply conditions. The measured and predicted results are shown to correlate reasonably well. Some specialised aspects of induction machines operation with non-sinu-soidal supplies such as peak transistor currents are also considered. Chapter 4 presents some design studies for the improvements of induction machine efficiency. Two machines are proposed; an improved 2-pole machine and an alternative 4-pole machine running at twice inverter frequency. For the same rotational speed and equal airgap magnetic and current loadings, the 4-pole version appears to have some advantage. Chapter 5 illustrates development of the time-domain induction machine models for use with the circuit analysis program ASTAP. Theoretical results of induction machine performance using ASTAP are shown to be the same as those obtained using the numerical step-by-step method, and correlate very well with experimental results. A special use of ASTAP was to model, as an equivalent circuit, the complete power-transistor inverter-induction machine system. Some examples of the interaction of the machine and inverter under fault conditions are presented.

High speed photographic and time and space resolved spectroscopic investigations have been undertaken to quantify the processes governing arc thermal reignition phenomena. A fixed nozzle and electrode geometry was used with SF6 as the host gas. A sonic flow of gas at the nozzle throat was sustained using an upstream vessel pressure of 7.8 psig. A 35.5mF capacitor bank was used to supply electrical energy for reduced and full power arcing tests using different circuit configurations. Sophisticated optical diagnostic instrumentation has enabled photographic and spectroscopic investigations with high time and space resolution to be made during the current zero period of both the full and reduced power arcing cases. The results of above experimental investigations are of value in determining the thermal structure and the processes governing thermal reignition of the circuit breaker arc of the present investigation. In particular, temperature profiles derived from the above investigations have been used to quantify the important terms of the dynamic current zero energy balance. Experimental investigations have thus been performed during the critical current zero period of a full power circuit breaker arc. The significance of these results has been realised in evaluating the current zero temperature profiles and subsequently the energy conservation equation terms for severe circuit breaking conditions

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