This work demonstrates that the integration of variable-speed wind systems with doubly fed induction generators (DFIGs) and a four-quadrant ac-to-ac converter connected to the rotor windings increases the transient stability margin of the electrical grids, when compared with the case where the fixed speed wind systems with cage generators are used. It is due to the influence of the two dedicated rotor current regulators of the DFIG on the dynamic behavior of the other generators in the system. Besides, adequate models to represent the behavior of the DFIG in transient stability studies are presented. From the simulation results, some important conclusions can be extracted to guide the integration of the wind farms on weak or strong grids.Index Terms-Decoupled control, doubly fed induction generator (DFIG) protection, electrical grids, fixed speed wind systems, transient stability margin, variable-speed wind systems.

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Within the field of electric power systems, the study of electrical equipment can be frustrating and demotivating because of the lack of a clear vision of how this equipment functions and operates in a real environment. The use of virtual reality can provide a more concrete representation for students, who rarely have the opportunity to visit a power substation or generating plant to acquire an understanding of how the equipment operates when integrated into an actual system. This paper describes work undertaken to improve the classroom study of such equipment , and to motivate students, by providing a clear overview of the equipment, approximating theory and practical functions, and simulating real situations that would be encountered on the equipment in an actual system. A virtual reality authoring tool was developed to provide students with a visualization of an autotransformer installed in an electric power substation, and to allow them to perform virtual maintenance and operating procedures on it. The influence of the software on students' levels of motivation and their performance was evaluated using questionnaires and reports. Finally, a framework is proposed that can help others create virtual reality trainings.

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This work demonstrates that the integration of variable-speed wind systems with doubly fed induction generators (DFIGs) and a four-quadrant ac-to-ac converter connected to the rotor windings increases the transient stability margin of the electrical grids, when compared with the case where the fixed speed wind systems with cage generators are used. It is due to the influence of the two dedicated rotor current regulators of the DFIG on the dynamic behavior of the other generators in the system. Besides, adequate models to represent the behavior of the DFIG in transient stability studies are presented. From the simulation results, some important conclusions can be extracted to guide the integration of the wind farms on weak or strong grids.

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For networks with large scale integration of wind farms this paper demonstrates a significant difference between the transient behavior of Variable Speed Wind Systems that adopt doubly fed induction generators with a four quadrant acto-ac converter connected to the rotor windings @FIG) and a fixed speed wind system, where the conventional cage induction generator is used. The reason for this difference is explained, and it is shown that the phenomenon is due to the ability of the two dedicated rotor current regulators of the DFIG to control the electrical torque and reactive power quickly and accurately. This difference is clearly observed after a severe fault (short circuit) occurrence. It will be demonstrated that the adjustable speed generator (DFIG) enhances system stability in power networks.