SUMMARYRecent studies have shown that power system blackouts occur much more likely than might be expected, and their probability distribution follows power law. Cascading outages have been reported as the major cause of the large blackouts; therefore, the risk of cascading outages is significant and should be considered in operating and planning assessments of the power systems. The Oak Ridge National Laboratory, Power Systems Engineering Research Center and University of Alaska (OPA) is a model developed on the basis of self-organized criticality to study cascading outages of transmission lines. In this paper, a modified version of the OPA model is used for considering risk of cascading transmission line outages in transmission expansion planning. The proposed method finds a set of effective candidate lines having higher capability for suppressing cascading outages; then, the original OPA is exploited over the planning horizon to analyze long-term reliability of the system. The benefit of each prospective transmission line is derived by the following two innovations in calculating the risk of blackouts: (i) the power law for finding the probability of blackouts; and (ii) a nonlinear estimation of the cost of the blackouts. Accordingly, the savings associated to each candidate line is calculated. These values are used to find the optimal plan using benefit/cost analysis. Two IEEE test systems are investigated to examine the applicability and scalability of the proposed method. The investigations revealed that the proposed method provides more effective scenarios, which entail considerable saving to society.
Summary
The conventional optimal PMU placement (OPP) methods minimize the number of PMUs along with guarantying full observability of the system. However, various OPP schemes with the same number of PMUs obtained for a power system have different performances in emergency conditions. Cascading outages as the major cause of recent large blackouts cancel out full observability of the system and decrease situational awareness. In this paper, the OPA model previously developed to simulate power system blackouts is modified in order to include observability analysis through the progress of the cascading outages. The modified process is performed in turn for a given set of OPP schemes. To rank these schemes, a criterion is proposed as a monetary value using produced data by the modified OPA model. Scalability of the proposed procedure is investigated in two test systems. Simulations show that although considering N‐1 criterion in finding optimal PMU schemes decreases the consequences of transmission line cascading outages, it is not financially reasonable and does not lead to better performance of the OPP scheme. In other words, it is better to use OPP schemes in normal condition.
The endoscopic high-speed combustion photography technique was used on a four-cylinder Perkins engine to investigate spray formation and combustion events under different engine running conditions. Some tests were also carried out in a fixed-volume combustion chamber (bomb) using conditions similar to those of the engine. The major advantage of using this rig was that each parameter could be varied independently. Spray formation, penetration rate and evaporation were studied in detail. Ignition delay times were established and the location of the start of combustion was identified. Finally, in the analysis of the results the most important factors affecting combustion in a direct injection (DI) diesel engine were outlined.
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