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In this work, a WAMS-Based Voltage Stability Indicator considering real time operation conditions is proposed. The indicator considers operational limits, such as reactive power reserves, transmission constraints, generating capacity, and voltage limits. The proposed indicator is based on a combination of the reactive margin and the actual demand at each busbar of the system. The reactive margins are obtained from an optimization problem. Applications on a test system show that the indicator is able to identify the proximity to voltage collapse, successfully. It also provides a reliable measure to assess the system security of real time operation in power grids.

SUMMARYThis paper investigates the sensitivity of the long-term performance simulations of solar energy systems to the degree of stratification in both liquid and packed-bed storage units. The degree of stratification is controlled by the number of nodes used in a finite-difference approximation of the storage system temperature distribution. Short-and long-term simulations of typical water heating and solar thermal power plant systems are conducted. The results indicate that the long-term performance of these systems is far less sensitive to the number of nodes used to represent the degree of stratification than expected based on short-term simulations or experimental data. An explanation is offered for this non-intuitive result.

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