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The possibility of operating distributed generation (DG) in islanded mode brings several benefits but still faces some problems, especially related to the transition from a grid-connected to an islanded operating condition. When connected to the main grid, DG units operate in PQ mode. During this transition, their controls must be changed to regulate frequency and voltage. The delay for islanding detection, associated with abrupt changes in the control references, may result in large and detrimental transients. This paper proposes a new control structure for a distributed synchronous generator (DSG) to allow a smooth transition from the grid-connected to the islanded operation mode. The proposed control structure uses a compensation loop that was conceived based on the main ideas of the anti-windup bumpless transfer (AWBT) theory (although it is not, strictly speaking, an AWBT controller). The results show that the proposed structure ensures smaller excursions of the DSG variables during the transition and, therefore, the possibility of a successful formation of the islanded system is extended to a wider range of operating conditions. Moreover, with the proposed control, the success of this transition does not depend on the islanding detection time, which is the main contribution of this paper. [ABSTRACT FROM AUTHOR]

In addition to supplying electrical power to the transmission grid, nuclear generating stations rely on the grid to provide power into the facility to support critical equipment during upsets. Although backup power supplies exist, such as diesel generators, the offsite power circuits are considered to be the “preferred power supplies” and must be kept at a high state of readiness. During certain operating conditions, the nuclear unit's generator is utilized to help support the voltage of the nearby high-voltage transmission system. If the offsite power circuits are served from the same high-voltage system, events that would result in tripping of the generator could also cause a depression of voltage on the offsite circuits due to loss of this voltage support. Nuclear operators must ensure that post-trip voltage levels are adequate to support critical equipment, such as emergency pumps and valves, during extreme postulated events, such as the rupture of reactor coolant system piping. Nuclear engineers utilize analytical models of their generating station electrical distribution system to determine the switchyard voltage level needed during various scenarios, but usually rely on outside organizations, such as transmission system operators and planners, to predict the change in switchyard voltage as a result of a nuclear generator trip. These organizations utilize complex models of the transmission system to make this determination. This paper proposes a simplified approach to predicting post-trip switchyard voltage utilizing data that do not rely heavily on outside organizations. [ABSTRACT FROM AUTHOR]