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ABSTRACT: This paper enhances the observability of power networks by taking into consideration random component outages. The architecture
of wide-area measurement system (WAMS) is analyzed in order to identify components that would affect the network observability.
An iterative framework is devised to calculate a bus index in power networks equipped with phasor measurement units (PMUs)
and conventional measurements. The average of bus indices represents a system index which provides an overall insight on the
power network observability. The system index is utilized as a criterion to distinguish among multiple optimal PMU placements.
Conventional bus injection and line flow measurements and the effect of zero-injection buses are considered in the proposed
model. The numerical analyses are carried out for the proposed model and the results are discussed in detail.
KeywordsPhasor measurement units–Wide-area measurement–System observability analysis–Probabilistic assessment
04/2012; 2(1):45-65.
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ABSTRACT: This paper presents an optimization model for the calculation of the minimum number of phasor measurement units (PMUs) in electrical power networks. The problem constraint is a predefined probability of observability associated with each bus. The mixed-integer programming is used for the proposed optimization and an efficient linearization technique is proposed to convert the nonlinear function representing the probability of observability into a set of linear expressions. The PMU placement is staged in a multi-year planning horizon due to financial and physical constraints. The average probability of observability is maximized at the intermediate planning stages, subject to a limited number of PMU placements, that would satisfy the horizon year schedule. In addition, network expansion scenarios associated with intermediate stages are taken into account. Numerical studies are conducted on a nine-bus system and the IEEE 57-bus system and the results are analyzed.
IEEE Transactions on Power Delivery 05/2011; · 1.35 Impact Factor
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ABSTRACT: Transmission switching (TS) is introduced in security-constrained unit commitment (SCUC) for alleviating transmission violations and reducing operating costs. The SCUC problem is decomposed into the unit commitment (UC) master problem and the TS subproblem. The UC master problem finds the optimal hourly schedule of generating units. The TS subproblem uses this solution for transmission switching to find the optimal dispatch of units when considering network constraints. The TS subproblem also examines contingencies and identifies required changes to the UC master problem solution when contingencies cannot be mitigated in the TS subproblem. To propose a practical TS model, the standing phase angle difference limit is considered and relevant constraints are added to the TS subproblem. The case studies exhibit the effectiveness of the proposed approach.
IEEE Transactions on Power Systems 12/2010; · 2.68 Impact Factor
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ABSTRACT: This paper discusses various aspects of unified power flow controller (UPFC) control modes and settings and evaluates their impacts on the power system reliability. UPFC is the most versatile flexible ac transmission system device ever applied to improve the power system operation and delivery. It can control various power system parameters, such as bus voltages and line flows. The impact of UPFC control modes and settings on the power system reliability has not been addressed sufficiently yet. A power injection model is used to represent UPFC and a comprehensive method is proposed to select the optimal UPFC control mode and settings. The proposed method applies the results of a contingency screening study to estimate the remedial action cost (RAC) associated with control modes and settings and finds the optimal control for improving the system reliability by solving a mixed-integer nonlinear optimization problem. The proposed method is applied to a test system in this paper and the UPFC performance is analyzed in detail.
IEEE Transactions on Power Delivery 11/2010; · 1.35 Impact Factor
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ABSTRACT: Probabilistic analyses of a wide-area measurement system (WAMS) would require equivalent reliability models for its components which include phasor measurement units (PMUs). In this paper, the reliability modeling of PMU is proposed and the proposed model is extended to consider options for the PMU hardware. The Markov process is employed to analyze the proposed model and to present an equivalent two-state model of PMUs. Reliability parameters of PMU are estimated with major difficulties associated with limited and uncertain data. In this paper, uncertainties are taken into account to achieve more realistic estimates of PMU characteristics. Fuzzy sets along with reliability analyses and fuzzy importance measures (FIMs) are utilized as a means of measuring the significance of PMU components on its availability. Numerical analyses are conducted and results are discussed.
IEEE Transactions on Power Delivery 11/2010; · 1.35 Impact Factor
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ABSTRACT: Transmission switching (TS) is introduced to add flexibility to the transmission and generation capacity expansion planning problem. TS could improve the performance of the capacity expansion planning model and reduce the total planning cost. The capacity expansion planning problem is decomposed into a master problem and two subproblems. The master problem utilizes the candidate set for additional generating unit and transmission capacity investments to find the optimal plan throughout the planning horizon. The subproblems use the optimal plan, apply transmission switching to relieve any transmission flow violations, and calculate the optimal dispatch of generating units. The transmission network contingencies are also considered in the subproblems. The case studies exhibit the effectiveness of the proposed expansion planning approach.
IEEE Transactions on Power Systems 09/2010; · 2.68 Impact Factor
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ABSTRACT: The intermittency and volatility of wind generation (WG) would require additional upward and downward reserves, as well as enhanced ramping capabilities in power systems. This study investigates the optimal expansion planning of fast-response generating capacity (e.g. gas-fired units) to accommodate the uncertainty of WG. The study utilises a mixed integer programming-based security-constrained unit commitment for analysing operational and reliability issues related to the proposed optimisation problem. Numerical experiments signify the effectiveness of the proposed method.
IET Generation Transmission & Distribution 09/2010; · 1.20 Impact Factor
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ABSTRACT: A proper investment mechanism is required in restructured power systems to secure the adequacy of installed capacity by encouraging investments on generation and transmission expansions. In this study, the authors propose a locational capacity price (LCP) model along with multi-level load bidding curves, which reflect the effectiveness of the market-based capacity payment and at the same time, prohibits the capacity withholding and the exercising of market power. The purpose of capacity expansion decision is analysed and compared with three other market design options, that is, energy-only, capacity payment (CP) and installed capacity (ICAP). The case studies show that the proposed LCP method provides proper investment signals in capacity-constrained locations. The proposed LCP method also provides signals to system operators to alleviate transmission congestions economically using proper operation strategies in power systems.
IET Generation Transmission & Distribution 04/2010; · 1.20 Impact Factor
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ABSTRACT: In this paper, a model for the optimal placement of contingency-constrained phasor measurement units (PMUs) in electric power networks is presented. The conventional complete observability of power networks is first formulated and then, different contingency conditions in power networks including measurement losses and line outages are added to the main model. The communication constraints which would limit the maximum number of measurements associated with each installed PMU is considered as measurement limitations. The relevant formulations are also proposed to make the model more comprehensive. The IEEE standard test systems are examined for the applicability of proposed model. The comparison of presented results with those of other methods is presented which would justify the effectiveness of proposed model with regards to minimizing the total number of PMUs and the execution time. A large-scale system with 2383 buses is also analyzed to exhibit the applicability of proposed model to practical power system cases.
IEEE Transactions on Power Systems 03/2010; · 2.68 Impact Factor
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ABSTRACT: When there are transmission service requests for a specific sink/source pair in a transmission system, the ISO must allocate the available transfer capacity (ATC) of that pair to the requests. Since the requests could have different types, tariffs and time frames, the allocation must be accomplished in a sound and fair manner that incorporates various aspects of the requests. This paper proposes a comprehensive approach to allocation of ATC to transmission service requests. The proposed method considers types, tariffs, and priority of requests in a mixed-integer nonlinear optimization which incorporates the allocation rules. The solution to the optimization problem gives the amount of accepted requests and their priority to the system operator while an emergency could result in the curtailment of certain transmission services. The proposed method is applied to a test system and its performance is evaluated and compared with that of existing methods through a series of studies.
IEEE Transactions on Power Systems 06/2009; · 2.68 Impact Factor
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ABSTRACT: This paper demonstrates how a probabilistic criterion could be explicitly integrated in the unit commitment (UC) formulation. Both spinning reserve and interruptible load are taken into account as the operating reserve facilities. Incorporating the interruption notice time of interruptible load involves some complexities in the evaluation procedure and problem formulation which is considered in this paper. The expected energy not supplied (EENS) is considered as a probabilistic criterion and a new method is proposed to calculate this index in the presence of interruptible load. The reliability-constrained unit commitment (RCUC) problem is formulated based on the mixed-integer programming (MIP) method that can be solved using large-scale commercial solvers. The effectiveness of the proposed formulation is examined using the IEEE-RTS. Numerical results are presented and the implementation issues are discussed. A number of analyses are examined to evaluate the impact of some important factors on the problem solution.
IEEE Transactions on Power Systems 03/2009; · 2.68 Impact Factor
