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This investigation deals with the modelling of turbogenerators when submitted to small disturbances in a region around steady-state operation. A preliminary investigation, mentioned in the paper, concerned two particular cases, namely, nonlinear steady-state and linear transient performances; results of both a theoretical and experimental nature have been given in previous reports. Consideration of a general dynamic operation involves linked effects due to eddy-currents and saturation. These are investigated in the paper and their description is provided by a linearized model of the machine. Experimental results are discussed and compared with theoretical ones; test data refer to a 370 MVA unit, and specify frequency responses for small departures.

It has been pointed out by several authors that the influence of impurity particles on dielectric phenomena in non-solid dielectrics can be significant in some cases, especially for technical liquids. In order to get information on such impurity influence, a computer-aided study of the motion of a charged spherical particle under general transient conditions, and with unrestricted conductivity and permittivity of both the medium and the particle has been carried out. To verify the model consistency, a set of tests in n-hexane with sphere-plane electrode geometry have been carried out using different experimental techniques, including high-speed-photography, and satisfactory agreement has been observed. On this basis, a model of the low-field conduction process by impurity particles has been developed assuming negligeable interactions between particles. A computer-aided procedure for the evaluation of impurity convection currents under different conditions has been implemented. The results obtained are compared with tests carried out on n-hexane with controlled pollution. Finally, a detailed discussion of the results obtained is given.

In recent years, growing attention has been paid to frequency response techniques for identifying turbogenerator models. A large amount of experimental results provided by frequency response tests carried out on a 107 MVA turbogenerator, is shown in this paper. The direct and quadrature axis transfer functions of the generator are experimentally identified over a frequency range up to 100 Hz; specifically, experimental results obtained from measurements at standstill and with rotating generator are carefully compared in order to investigate rotation effects. Additionally, low order models for use in stability studies are considered; proper parameters are identified by optimal fitting of test data and compared with design values

An analysis of the electromagnetic stresses on a hard superconductor wire has been performed by the critical state model. A theoretical approach has been carried out by taking into account both the field produced by the current flowing in the wire and an external field orthogonal to the wire axis. Owing to analytical difficulties, mainly depending on the non-linear hysteretical feature of the field penetration, a general solution cannot be found. Nevertheless, under some restrictive conditions, an approximate solution is obtained, allowing us to compare the various force components of different origin acting on the wire.

It has been pointed out by several authors that the influence of impurity particles on dielectric phenomena in non-solid dielectrics can be in some cases significant, especially for technical liquids.