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Steady-state, transient, as well as dynamic analyses of self-excited induction generators (SEIGs) are generally well-documented. However, in most of the documented studies, core losses have been neglected or inaccurately modeled. This paper is concerned with the accurate modeling of core losses in SEIG analysis. The core loss is presented as a function related to the level of saturation. This relation is determined experimentally and integrated into a nonlinear model of the SEIG. The nonlinear model is solved using a mathematical optimization scheme to obtain the performance parameters of the SEIG. A new set of curves describing accurate behavior of the SEIG parameters is produced and presented in this paper. The computed parameters of the model are validated experimentally, and the agreement attained demonstrates the functionality and accuracy of the proposed core-loss model.Energies 2018, 11, 3228 2 of 12 variable function of the level of saturation in the generator. This can be extremely important, especially in the modern, well-designed SEIGs with accurate high-saturation designs. This paper derives a mathematical model for core loss as a function of saturation in the SEIG based on experimental measurements. Consequently, an accurate representation for the SEIG for advanced theoretical analysis is re-developed. The computed parameters of the model are validated experimentally, and the agreement attained demonstrates the functionality and accuracy of the proposed core-loss model. AnalysisThe system used to investigate SEIG is shown schematically in Figure 1. A three-phase synchronous motor was used as a prime mover during experimental tests.The per-phase equivalent circuit of a three-phase SEIG under R-L load is shown in Figure 2. The effect of the saturation is considered for the core loss resistance, R c , and the magnetizing reactance, X m . To determine the values of the circuit parameters, the generator is conventionally tested under DC, locked rotor, and no load [3][4][5][6][7][8]. Values of R s , R r , X s , and X r are found from the DC and locked rotor tests. The magnetization curve of the machine, which includes the relation of R c and X m against air-gap voltage (or magnetization current), is obtained from a no load test (at slip = 0), as shown in Figure 3. As clearly shown, X m and R c are variable according to the level of saturation as it is linked with the air-gap voltage. The magnetization curve of the machine in Figure 3 is redeveloped and depicted in Figure 4a, to be used with the circuit shown in Figure 2 to yield the SEIG performance measures. As the saturation level in the generator is variable, X m is obviously variable and R c must also be variable. To the best of the authors' knowledge, this fact has been ignored in all the published research concerning SEIGs [5][6][7][8][9][10][11][12][13].

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Abstruct-This paper explores the impact of six-phase transmission line faults and their subsequent fault clearing and reclosing on the torsional torques induced in turbine-generator shafts. In this context, investigations have been conducted on a large turbine-generator unit connected to a sample power system. The paper presents also a comparison between the torsional stresses induced in the turbine-generator shafts during these events with their corresponding disturbances of a threephase transmission system The results of these investigations are presented in the form of typical time responses as well as parametric studies. The EMTP is used for the simulation studies.The studies conclude that six-phase transmission line faults generally induce torsional torques in the turbine-generator shaft whose magnitudes are relatively higher than those induced due to transmission line faults in a three-phase system. This conclusion is true for both sustained faults and faults followed by clearing and high-speed reclosing operations.