In the field of electric machine design, a trend in many applications has been to design machines with increasing torque density. When machines fail to meet torque density requirements or are simply incapable of matching load torque, gears are commonly used. Magnetic gears have been proposed as a means of increasing torque density within electromechanical systems, while avoiding problems associated with traditional mechanical gears. While the idea behind magnetic gears goes back to early patents, their study and use in industry has been very limited to date. This study looks into variations of the gear which could lead to more industrial use. The effect of pole count upon torque ripple is investigated with finite element analysis (FEA). The analysis is extended to new magnetic layouts which borrow from permanent magnet machine design. One of the most critical components of the gear, the stator pole pieces, are also investigated for variations which aid in construction while maintaining the performance of the gear. As a means of supplementing analysis of the gear, winding function theory (WFT) is used to analyze the gear. Winding function theory has enjoyed success with induction, synchronous, and even switched reluctance machines in the past. This study is the first of its kind to apply winding function theory to a device devoid of windings altogether. It is shown that this method is capable of generating the stall torque and steady-state torque ripple waveforms which have been commonly attempted with FEA. While magnetic gears enjoy distinct advantages over mechanical gears such as inherent overload protection, they are not as torsionally stiff as their mechanical counterparts. As such, the use of damper windings for the purpose of stiffening the gear against transient oscillations is also investigated. Several competing designs are investigated for their performance, and a final design is studied which is capable of arresting transient oscillations in less than a second. In addition, a prototype has been fabricated and will be used to verify the analysis undertaken. The prototype is used to verify variations of the stator pole pieces as well as the inner rotor magnetic layout. A dynamometer has been assembled to test the performance of the prototype. A new design is also proposed for future work.

After decades of routine operation, the hydropower industry faces new challenges. Large-scale integration of other renewable sources of generation in the power system accentuates the role of hydropower as a regulating resource. At the same time, an extensive reinvestment programme has commenced where many old components and apparatus are being refurbished or replaced. Introduction of new technical solutions in existing power plants requires good systems knowledge and careful consideration. Important tools for research, development and analysis are suitable mathematical models, numerical simulation methods and laboratory equipment. This doctoral thesis is devoted to studies of the electromechanical interaction between hydropower units and the power system. The work encompasses development of mathematical models, empirical methods for system identification, as well as numerical and experimental studies of hydropower generator and power system interaction. Two generator modelling approaches are explored: one based on electromagnetic field theory and the finite element method, and one based on equivalent electric circuits. The finite element model is adapted for single-machine infinite-bus simulations by the addition of a network equivalent, a mechanical equation and a voltage regulator. Transient simulations using both finite element and equivalent circuit models indicate that the finite element model typically overestimates the synchronising and damping properties of the machine. Identification of model parameters is performed both numerically and experimentally. A complete set of equivalent circuit parameters is identified through finite element simulation of standard empirical test methods. Another machine model is identified experimentally through frequency response analysis. An extension to the well-known standstill frequency response (SSFR) test is explored, which involves measurement and analysis of damper winding quantities. The test is found to produce models that are suitable for transient power system analysis. Both experimental and numerical studies show that low resistance of the damper winding interpole connections are vital to achieve high attenuation of rotor angle oscillations. Hydropower generator and power system interaction is also studied experimentally during a full-scale startup test of the Nordic power system, where multiple synchronised data acquisition devices are used for measurement of both electrical and mechanical quantities. Observation of a subsynchronous power oscillation leads to an investigation of the torsional stability of hydropower units. In accordance with previous studies, hydropower units are found to be mechanically resilient to subsynchronous power oscillations. However, like any other generating unit, they are dependent on sufficient electrical and mechanical damping. Two experimentally obtained hydraulic damping coefficients for a large Francis turbine runner are presented in the thesis.