The overall aim of this thesis is to provide a systematic procedure designed to assess the impact of voltage sags on continuous industrial processes. The study initially introduces voltage disturbances, industrial processes, and the cost of downtime. It presents a critical review of relevant past studies and their shortfalls and sets a framework for the research.

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Experimental and theoretical studies are made of small snap-action switches designed for use in thermostatic controls operating on a.c. at 240 volts r.m.s., 50Hz. The performance of the silver cadmium oxide contacts (Ag. CdO, 85/15%) is evaluated over a range of currents from 1 to 10 amps, for make and break operations. The arc at break is found to be the predominant factor contributing to the erosion of the contacts for the range of currents used. Tests using a high speed camera show that the energy dissipated in the arc between the contacts can be evaluated from equations describing the arc in terms of its voltage, current and length as functions of time. Subsequently work is carried out to develop the relation between arc energy and contact erosion, with specific regard to the distribution of energy between the two contact surfaces and the arc column. This is related to the power dissipation in the two electrode fall regions, and the resulting direction of net material transfer is thought to be influenced by the length achieved by the arc before extinction. Erosion is generally in the form of anodic loss and cathodic gain and the reasons for the directional bias in this type of switch are suggested. Ways of reducing the amount of erosion per operation by changing the switch opening characteristic are discussed and supported with experimental results.

The efficient generation of relatively large quantities of electrical energy in vehicles is becoming an increasingly important issue, as a result of increasing demands of ancillary equipment and the emergence of hybrid power-train vehicles. An attractive solution to meeting these demands is to extract the electrical energy by means of a generator driven by a high-speed exhaust mounted turbine, a technology that is beginning to emerge commercially. This thesis is concerned with the design of a system, which extends this concept to enable both electrical generation and highly flexible air-management. The heart of the system is a high-speed switched reluctance machine, the rotor of which is located on a common shaft with the turbine and compressor wheels of a standard commercial turbocharger. The design synthesis of a -switched reluctance machine capable of meeting the required performance specification is particularly onerous given the harsh environment in which it operates, specifically in terms of the restricted space envelope, the high ambient temperature and the very high rotational speeds. This thesis describes the design of a switched reluctance machine for a prototype system, a procedure that encompasses the detailed analysis of centrifugal stress in the rotor, aerodynamic losses, iron loss, rotordynainic performance and dynamic performance. The design and analysis of the system is supported by experimental evaluation at both component and system level.

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The thesis describes new methods of determining control schemes for multimachine power systems by using Linear Multivariable Control Theory. The initial stages of the work include a review of the different modelling techniques available for studying the performance of synchronous machines by analogue or digital computation. Based on this review a non linear digital program that describes any multimachine power system is produced. For control work a linearised version of this program is available. A review of the mathematical theory behind Linear Multivariable Control methods is given emphasising its link with the classical approach of Nyquist Analysis. The control theory is interfaced with the digital model of the power system to produce a series of designs by which control is achieved by either: (i) Impedance switching (ii) Fast valving (iii) Field Excitation The different control designs are compared both with each other and with control schemes suggested by other authors, forking, from a purely mathematical basis control schemes are postulated that produce improved operation to both small and large disturbances. The advantages of fast valving as a control method is outlined and suggested as the most advantageous method of overall control for both single - and multimachine power systems.

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