Integration of Nonutility Generating Facilities into the reliability assessment of composite generation and transmission power systems

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Integration of Nonutility Generating Facilities into the reliability assessment of composite generation and transmission power systems (EN)

Papakammenos, DJ (EN)
Koskolos, NC (EN)
Dialynas, EN (EN)

N/A (EN)

Non-Utility Generating Facilities (NUG) are among the most important supply-options available to utilities for generating least cost energy plans. The task of quickly and accurately evaluating the merits of this supply option is becoming an important function of utility system planners and operators. Furthermore, the reliability performance of the composite generation and transmission system together with the reliability indices of service supplied to customers constitute one of the major aspects that are taken into account in the power system planning and operating phases. North American Electric Reliability Council has developed a reference document containing the planning and the minimum operating considerations that both the utility and nonutility generating facilities must follow to assure the continued reliability of the bulk electric system. The most important considerations that affect the reliability assessment of the composite generation and transmission power system are the load-following capability, generation schedule, fuel supply and storage capabilities, maintenance requirements, emergency availability and restoration procedures. An improved computational method has been developed considering the main features of the Monte-Carlo sequential approach and its objective is to calculate an appropriate set of indices that quantify the operational and reliability performance of a power utility system incorporating NUG facilities together with the respective indices for each NUG facility under consideration. The basic improvements of this method are die following: 1) The generation rescheduling and branch overloading techniques have been extended to include the particular operating characteristics of NUG units. 2) A fuel supply control technique has been developed incorporating all the operating characteristics of two alternative models (constant order size or time interval). A particular model is assigned to each NUG plant by the user indicating the fuel order policy being applied. 3) The overall performance of the power system being analyzed is quantified by calculating the following indices: • Expected total energy supplied by all system generating units. • Expected energy supplied by all NUG units. • Expected average production cost of all system generating units. • Expected average production cost of all NUG units. • Expected total cost of energy purchased by the utility. • Expected damage cost of interruptions due to failures in the entire system. • Expected damage cost of interruptions due to failures in the NUG plants. 4) The operational performance of NUG plants is quantified by taking into account the events which occur when the NUG units fail to produce their output capacity agreed due to limitations existing in the NUG plants (failures, maintenance, fuel supply limitations) and utility system (split system, overloaded branches). Another category of events is also considered which cause the operation of NUG plants outside of their agreed time schedule (over-supply while in operation, continue to supply, start to supply while not in operation, continue to supply while there are fuel supply limitations). The following four indices are calculated for all the above categories of events: • Frequency of events being occurred. • Expected annual duration of events being occurred. • Expected energy not supplied (or supplied accordingly) during the events being occurred. • Penalty charges paid by the NUG plants (or the utility accordingly). 5) A technique has been developed that calculates the Long-Run Marginal Cost (LRMC) of integrating a NUG plant into a utility system for the time period under study. This cost is related to the expected energy supplied by the NUG plant and takes into account the capital cost of the investment and the operating cost of the plant units. 6) The Interrupted Energy Assessment Rate (IEAR) for the entire system (SIEAR) is calculated by taking into account the IEAR indices of all system load-points and their contribution to the total system load demand. The method developed has been implemented efficiently into the self-sufficient and easy to use computer program RANUG which can be used for analyzing alternative system configurations and establishing the impact of various system parameters. The data required for both the utility power system and the NUG facilities are inputted in a very simple way considering the respective single line diagram and the operating features being applied. Furthermore, the paper presents the results obtained from the analysis of a system based on the IEEE Reliability Test System and incorporating NUG facilities that were added at selected buses. (EN)


cogeneration (EN)
Non-Utility Generation (EN)
reliability (EN)
power systems (EN)
Monte-Carlo simulation (EN)

Εθνικό Μετσόβιο Πολυτεχνείο (EL)
National Technical University of Athens (EN)

IEEE Power Engineering Review (EN)



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