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This paper proposes a method for choosing the best transmission system expansion plan considering a probabilistic reliability criterion (RLOLE). The method minimizes the investment budget for constructing new transmission lines subject to probabilistic reliability criteria, which consider the uncertainties of transmission system elements. Two probabilistic reliability criteria are used as constraints. One is a transmission system reliability criterion (RLOLETS) constraint, and the other is a bus/nodal reliability criterion (RLOLBus) constraint. The proposed method models the transmission system expansion problem as an integer programming problem. It solves for the optimal strategy using a probabilistic branch and bound method that utilizes a network flow approach and the maximum flow-minimum cut set theorem. Test results on an existing 21-bus system are included in the paper. They demonstrate the suitability of the proposed method for solving the transmission system expansion planning problem subject to practical future uncertainties. [ABSTRACT FROM AUTHOR]

This paper deals with power system restoration and discusses the connection of pumped storage loads to restoration paths. This new strategy allows avoiding any disturbance to customers during field tests of restoration paths and improves as well the reliability of restoration plans. The first application of the new strategy concerned the field test of a new path in central Italy. This paper reports the test and analyzes the main novel features of the considered path: complete separation from subtransmission and distribution networks and use of pumped storage loads during its energization. These aspects and their consequences are discussed with reference to both field testing of restoration paths and effectiveness of system restoration. [ABSTRACT FROM AUTHOR]

This paper proposes the use of an auxiliary gradient system to calculate the low-voltage solutions (LVSs) of the load flow equations of an electrical power system. It shows that the equilibrium points of that associated auxiliary dynamical system are the solutions of the load flow equations. In such a manner, the paper proposes to find the LVSs by calculating the equilibrium points of the auxiliary dynamical gradient system. The proposed method improves the classical state-space search methods by calculating a new LVS every lime the tracked one bifurcates and vanishes. It was tested on Stagg 5-bus, IEEE 39-bus, and IEEE 118-bus systems. The results are at the end of the paper and show that the proposed method presents a great tendency to find the critical LVS for the current load increase direction, as the load is slowly increased. [ABSTRACT FROM AUTHOR]

This paper presents a new method for estimating avoided transmission and distribution costs associated with small load reductions, named the one-year deferral method. It is established on the basis of the system planner's actual response to a small reduction in the forecast annual peak load. This paper has also explored the noninteger deferral time (i.e., a fraction of a year) in the present worth method, which is seemingly inconsistent with the system planning practice. In addition, as allowed by the new method, the effect of the size and type (shape) of a load reduction stream (i.e., a series of reductions in the forecast annual peak loads) on avoided costs is studied, which is important for determining generic avoided cost values intended for various applications. [ABSTRACT FROM AUTHOR]

In this paper, we address the issue of quantifying effects of model uncertainty on transmission security in a power market. The paper addresses two types of uncertainties: 1) structural (e.g., branch outages), which are modeled by contingency scenarios, and 2) perturbations of model parameters (e.g., branch impedance), which are described by sensitivity analysis. The paper embeds these considerations in an optimization procedure that checks if transmission security is maintained and, when necessary, generates minimal corrections in existing contractual transactions that ensure security. Given our interest in real-time applications, we consider problem formulations guaranteeing solution existence and global optimality. A detailed sensitivity analysis based on approximate matrix inversion and linear programming perturbation theory is performed. The paper proposes a linearized ac power flow model to describe the transmission network. The model is studied on a benchmark example of the New England/New York interconnection with 68 nodes. [ABSTRACT FROM AUTHOR]

This paper presents a reconfiguration algorithm that is specially suited to large-scale distribution systems. The algorithm uses a heuristic strategy that starts with the system in a meshed status, with all maneuverable switches closed. The choice of the switches to be opened is based on the calculation of the minimum total system losses, using a load-flow program. A refinement on this procedure, based on branch status exchange, is described. The paper includes results and comparisons on test systems utilized in three classical papers published in the technical literature. Results obtained on a real large-scale distribution system are also presented. [ABSTRACT FROM AUTHOR]

This paper presents a simulation study about the co- ordination and interaction of advanced power electronic devices working in close electrical proximity. In particular, three major power quality devices (PQDs)--an advanced static VAR compensator, a dynamic voltage restorer, and a high-speed transfer switch as well as their combined performance--are modeled and studied in detail using ATP-EMTP. The paper addresses potential problems related to the PQD's combined operation, in addition to coordination issues. Comparison between simulation results and field measurements of individual PQD's are also presented. [ABSTRACT FROM AUTHOR]

In a restructured power market, the independent system operator (ISO) executes the security-constrained unit commitment (SCUC) program to plan a secure and economical hourly generation schedule for the day-ahead market. This paper introduces an efficient SCUC approach with ac constraints that obtains the minimum system operating cost while maintaining the security of power systems. The proposed approach applies the Benders decomposition for separating the unit commitment (UC) in the master problem from the network security check in sub- problems. The master problem applies the augmented Lagrangian relaxation (LR) method and dynamic programming (DP) to solve UC. The sub-problem checks ac network security constraints for the UC solution to determine whether a converged and secure ac power flow can be obtained. If any network violations arise, corresponding Benders cuts will be formed and added to the master problem for solving the next iteration of UC. The iterative process will continue until ac violations are eliminated and a converged optimal solution is found. In this paper, a six-bus system and the IEEE 118-bus system with 54 units are analyzed to exhibit the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

A two-point estimate method is proposed in this paper to assess the power transfer capability uncertainty. This paper assumes that the uncertainty of the line parameters and bus injections involved in transfer capability calculations can be estimated or measured and shows how to estimate the corresponding uncertainty in the transfer capability. Instead of using a large number of simulations as required in the Monte Carlo approach, for a system with n uncertain parameters, the two-point estimate method uses 2n calculations of transfer capability to quantify the uncertainty. The proposed method uses a numerical method to calculate the moments of the transfer capability. The moments are then used in the probability distribution fitting. Using the obtained transfer capability uncertainty information and a desired level of reliability, an adequate transmission reliability margin can be determined for each transmission service. The proposed method can be used directly with a deterministic computer program and it does not require derivatives of the transfer capability. Test results of the proposed method are compared with those obtained from the Monte Carlo simulations and a truncated Taylor series expansion method. [ABSTRACT FROM AUTHOR]

Under the deregulated environment of electric power industry, generation can be installed anywhere in the system resulting in an "imbalance" between the generation and transmission. Shortages of generation in some subregions result in "bottle- necks" within a system raising reliability concerns regarding subregional adequacy. Excess of generation capacity raises the issue of how much capacity in which location is entitled to receive payments for Stalled capacity Therefore, there is a need to determine loactional requirement for both generation and transmission such that assistance to subregions under random generator outages is not restricted. This paper presents optimization procedures for the determination of adequacy and responsibility for locational generation and transmission. The outlined procedures applicable to situations of planning to identify additional needs as well as to situations of market design for installed capacity in subregions. The paper closes by a discussion of forward auctions for the procurement of capacity in subregions. [ABSTRACT FROM AUTHOR]

This paper proposes a new method to handle distribution transformers of various winding connections in the backward/forward sweep-based power flow analysis for unbidanced radial distribution systems. The method takes advantage of available nodal admittance matrices of distribution transformers, and can automatically solve the problem of conductively isolated subnetwork to obtain their equivalent phase-to-reference voltages. In addition, this paper presents a limitation of back- ward/forward sweeps, and an extension of the power summation method for distribution power flow analysis from single-phase to unbalanced three-phase. The validity and effectiveness of the proposed method can be demonstrations by numerous examples and real systems. [ABSTRACT FROM AUTHOR]

This paper presents a new possibilistic (fuzzy) model for the multiobjective optimal planning of power distribution net- works that finds out the nondominated multiobjective solutions corresponding to the simultaneous optimization of the fuzzy economic cost, level of fuzzy reliability, and exposure (optimization of robustness) of such networks, using an original and powerful meta-heuristic algorithm based on Thbu Search. This model determines the optimal location and size of the future feeders and substations in distribution networks with dimensions significantly larger than the ones usually presented in papers on the matter. The model also allows to determine the optimal reserve feeders (location and size) that provide the best distribution network reliability at the lowest cost for a given level of robustness (exposure). The model and the algorithm have been intensively tested in real distribution networks, which proves their practical application to large power distribution systems. [ABSTRACT FROM AUTHOR]

Wind-power penetration in many cases faces significant barriers due to limited transmission capability. In Greece (and in most countries in Europe), the guaranteed access to the grid offered to wind parks, in conjunction with the existing planning practices, has led to severe limitations in wind power installed, in certain congested areas. This paper presents some simple ideas that are currently being applied to the Hellenic Interconnected System, in order to increase the wind-power penetration. The main concept is the introduction of interruptible generator contracts and the control of the power flow through congested corridors by issuing power reduction commands, whenever security limits are violated. The proposed control is implemented using common PLCs of low cost and the existing SCADA system, and is both simple and transparent. The paper presents also a methodology to assess the impact of the proposed techniques on the wind penetration achieved. [ABSTRACT FROM AUTHOR]

In this paper, the problem of voltage regulation and power losses minimization for automated distribution systems is dealt with. The classical formulation of the problem of optimal control of shunt capacitor banks and Under Load Tap Changers located at HV/MV substations has been coupled with the optimal control of tie-switches and capacitor banks on the feeders of a large radially operated meshed distribution system with the aim of attaining minimum power losses and the flattening of the voltage profile. The considered formulation requires the optimization of two different objectives; therefore the use of adequate multiobjective heuristic optimization methods is needed. The heuristic strategy used for the optimization is based on fuzzy sets theory. After a brief description of the general problem of optimal control of voltage and power losses in automated distribution networks, the most recent papers on the topic are reported and commented. Then the problem formulation and the solution algorithm are described in detail. Finally, numerical results on a large distribution system demonstrate that the proposed formulation and approach are effective and feasible for finding an optimal generalized dispatching schedule. [ABSTRACT FROM AUTHOR]

This paper investigates the application of adaptive control to the Spanish load-frequency regulation scheme, Automatic Generation Control (AGC). The Spanish AGC system regulates the frequency and the power exchange between France and Spain. The system is hierarchically structured with one master regulator that coordinates four control areas. Each control area is composed of several generating units providing AGC service. Co-ordinating signals are sent to the control areas so that the global system response achieves the objective established by the System Operator. The participation of each control area in the service is set according to the rated share that it has obtained in the secondary-reserve market and its relative response speed compared to that of the rest of the control areas. Some problems, such as the lack of sensitivity to the quality of the reserve provided by the control areas, have been detected in the operation of the current AGC scheme. A new design, which is presented in this paper, has been developed in order to overcome these problems. This paper attempts to outline how this new design improves the global AGC system response and the distribution of the regulation effort among the control areas. The proposed strategy is compared with the present design by means of simulation. [ABSTRACT FROM AUTHOR]

This paper presents a low-order identification technique, which is based on standard Prony analysis. The technique has the ability to extract crucial dynamic characteristics from a system of any size (e.g., a large-scale power system), which then can be used for developing a robust controller. In this paper the proposed identification technique is coupled with a robust controller design technique based on genetic algorithm to simultaneously tune power system stabilizers (PSSs) for multiple operating conditions. To illustrate the proposed Identification and controller design techniques three case studies are presented, including a two-area benchmark system, a 50-machine test system and a large-scale (23300 bus) Eastern Interconnection power system. To allow the proposed tools to be applied té the large-Scale power system, the authors developed an Interface with a standard production grade transient stability analysis software package; PSS/E. [ABSTRACT FROM AUTHOR]

The aim of this paper is to illustrate that wide area generator speed measurements combined with Fourier analysis can be used to determine coherent generator groups. Studies are based on simulations in a 68-bus test system. Three test cases are investigated where the new method is compared to conventional methods based on the generator speed, modal analysis,. and, phasor angle measurement. The method introduced in this paper has proven to be an interesting alternative for generator coherency determination. It gives almost identical results to the offline methods based on the generator speed or modal analysis. Based on their trustworthiness the test cases indicate that the method reflects a more accurate coherency than the conventional online method based on phasor angle measurement. Moreover, compared with online applications using modal analysis the method supports real-time applications better according to its less extensive computational requirements. [ABSTRACT FROM AUTHOR]

In this paper, the authors propose a fuzzy-optimization approach to dynamic economic dispatch, considering the uncertainties in deregulated energy and reserve markets. The methodology was developed from the viewpoint of a generation company wishing to maximize its own profit and to hedge its risks as a participant In the energy market and 10-min spinning reserve market. The uncertainties in the current paper were represented with fuzzy numbers, and consist of the demand and reserves required In each market, prices cleared in each market, and the probability that reserves are called upon in actual operation. The energy and reserve markets were coordinated by the generator ramp rate limits. The optimal amounts of power. and reserve were determined by solving the optimization problem. Two reserve payment methods, payment for power delivered and payment for reserve allocated, were Investigated in this paper. [ABSTRACT FROM AUTHOR]

This paper is the second part of a two-paper set concerning a generalized modal analysis approach to the study of multiconductor nonuniform transmission-line structures. In the first part, a very detailed theoretical analysis was developed aimed at establisbing the foundations of the method. Here, numerical results are presented for the purpose of illustrating the various steps involved in the application of the new modal technique. To demonstrate the effectiveness of this new analysis method an example of a nonuniform structure, comprising the junction of two chain-connected power lines with different cross sections, is considered. The frequency-dependent propagation properties of such a structure are evaluated, the computation results revealing that important resonance phenomena take place at certain critical frequencies. [ABSTRACT FROM AUTHOR]

Ollgopolistic equilibrium models are widely used in electricity market analysis, among which the supply function equilibrium model has been chosen as the basis of many power market models. A nonlinear complementarity approach has been proposed in this paper to calculate the Nash supply function equilibrium for a bid-based-pool generation market with a dc transmission model, A mixed nonlinear complementarity problem (NCP) is presented by combining the Karush-Kuhn-Tucker conditions of all strategic generating firms. Using a special nonlinear complementarity function, the mixed NCP is reformulated as a set of nonlinear algebraic equations and thus can be. solved by an inexact Levenberg-Marquardt algorithm. Numerical examples are presented to verify the effectiveness of the proposed method. The results show that the generating firms could exercise their market power by over-production under congestion, or by capacity withholding In case of power shortage. The approach developed in this paper provides an efficient way to the solution of large-scale, complicated equilibrium models for electricity markets. [ABSTRACT FROM AUTHOR]

Traditional methods for regulating electricity distribution grids have several weaknesses hi terms of incentives, risk allocation, consumer preferences, and the value of reliability. Rate of Return and Performance Based Regulation do not provide incentives for both cost efficiency and quality of service. These regulatory structures also allocate the risk of outages almost entirely to consumers and fail to Incorporate consumer preferences for reliability/service quality Additionally, investments in system reliability are not explicitly valued. This paper proposes an insurance scheme for reliability as a possible solution. Reliability Insurance provides economically efficient investment incentives and alleviates consumers' reliability risk. Consumers provide economic signals to the distribution provider for their desired quality of service through insurance contracts. The value of reliability to consumers is thereby made transparent, allowing Distribution Companies (DisCo's) to make efficient investment decisions. Insurance also allocates outage risk to the DisCo (which controls the system), instead of consumers (who have little or no control over reliability). Reliability insurance effectively unbundles delivery and reliability services and enables consumers to receive differentiated reliability based upon their value for this service. This paper describes the potential for reliability insurance to improve both efficiency and risk allocation compared to conventional regulatory structures. [ABSTRACT FROM AUTHOR]

Many problems have appeared with the practical implementation of restructured electrical business in the U.S. and European Union such as lack of generation, network constraints, etc. A good example of these problems is the scarce participation of the demand in the electricity markets-energy, reserve, and other ancillary services-problems that could be solved through new demand responsive programs, aimed to replace the traditional demand side management programs into voluntary demand participation programs. A methodology for the generation of demand side bids and offers in large customer facilities and a real application to a university customer is presented in this paper. The methodology is based on the knowledge of the physical processes involved in the electricity consumption and on the flexibility of the required supply. The result of the methodology proposed is a set of demand packages that can be used to participate in different electricity markets, whose possibilities-in the market arena-will be explored in a consequent paper. [ABSTRACT FROM AUTHOR]

This paper addressed some theoretical and practical issues relevant to the problem of power system load modeling and identification. Two identification techniques are developed in the theoretical framework of stochastic system identification. The identification techniques presented in this paper belong to the family of output error models; both techniques are based on well-established equations describing load recovery mechanisms having a commonly recognized physical appeal. Numerical experiments with artificially created data were first performed on the proposed techniques and the estimates obtained proved to be asymptotically unbiased and achieved the corresponding Cramér-Rao lower bound. The proposed techniques were then tested using actual field measurements taken at a paper mill, and the corresponding results were used to validate a commonly used aggregate load model. The results reported in this paper indicate that the existing load models satisfactorily describe the actual behavior of the physical load and can be reliably estimated using the identification techniques presented herein. [ABSTRACT FROM AUTHOR]

A method is proposed in this paper to select the input signals for both single and multiple flexible ac transmission system (FACTS) devices in small and large power systems. Different input- output controllability analyses are used to assess the most appropriate input signals (stabilizing signal) for the static var compensator (SVC), the static synchronous compensator (SSSC), and the unified power-flow controller (UPFC) for achieving good damping of interarea oscillations. The study presented in this paper is carried out on one small system with one FACTS device at a time; and one large system equipped with the SVC, the SSSC, and the UPFC. [ABSTRACT FROM AUTHOR]

Dynamic equivalents have been widely used to reduce computational efforts when a large number of scenarios have to be studied to evaluate the stability of interconnected power systems. Most coherency methods developed for model reduction do not consider the effect of voltage variations on the coherency of generators due to weak coupling between real power and voltage. In reality, however, the coherency of generators can be influenced by voltage related factors such as location and speed of AVR controls, generator terminal voltage variation, and load bus voltage variation. The reduced dynamic equivalent is not accurate if the voltage characteristics of the original system are not included in the model. This paper presents coherency identification techniques incorporating rotor and voltage dynamics in order to improve the accuracy of dynamic equivalents. This paper also presents a new method to match the power flow conditions for generator aggregation. This new technique is shown to be critical for the accuracy of aggregated dynamic models. Numerical results based on the model of an actual power system in Asia are presented to demonstrate the performance of the proposed method. [ABSTRACT FROM AUTHOR]

Software design reuse has been discussed in the past at the component level through Design Patterns. A software framework is an approach to achieve software reusability for an entire domain. This paper presents architectural design concepts of a framework for power distribution system analysis. The commonalities of distribution system analysis, including components, topologies, and algorithms are considered. A layered architecture with strict top-down dependency is proposed to decrease software couplings. Inter aces are used to hide the internal structure of each layer. The Composite and Iterator design patterns are used in the framework design. This paper also presents practical examples of developing customized applications that reuse and extend the framework. [ABSTRACT FROM AUTHOR]

A multiple-frequency three-phase load-flow model was developed in this paper. There are two new submodels including the fundamental power flow (FPF) and harmonic frequency power-flow (HPF) model. In FPF, models of electrical elements and PV buses were treated in the form of current injections in a transmission system. The standard Fourier analysis was used to deal with the harmonic loads to get injection currents. With harmonic currents as equivalent current sources, the HPF can be derived. Besides, the decoupled fast version of FPF and HPF, called DFPF and DHPF, were also proposed in this paper. Test results show that the proposed general-purpose methods are better performers than conventional power-flow solutions and are very robust. [ABSTRACT FROM AUTHOR]

System reliability models typically use average equipment failure rates. Even if these models are calibrated based on historical reliability indices, all-like components within a calibrated region remain homogeneous. This paper presents a new method of customizing failure rates using equipment inspection data. This allows available inspection information to be reflected in system models, and allows for calibration based on interruption distributions rather than mean values. The paper begins by presenting a method to map equipment inspection data to a normalized condition score, and suggests a formula to convert this score into failure probability. The paper concludes by applying this methodology to a test system based on an actual distribution system, and shows that the incorporation of condition data leads to richer reliability models. [ABSTRACT FROM AUTHOR]

This paper presents a new method for optimal reconfiguration of radial distribution systems (RDS). Optimal reconfiguration involves selection of the best set of branches to be opened, one each from each loop, such that the, resulting RDS has the desired performance. Amongst the several performance criteria considered for optimal network reconfiguration, maximizing loadability is an important one. Owing to the discrete nature of the solution space, a fuzzy adaptation of the evolutionary programming algorithm for optimal reconfiguration of RDS to maximize loadability is proposed in this paper. This method maximizes a fuzzy index developed using a maximum loadability index. A 33-bus RDS is optimally reconfigured by the proposed method and the results are presented. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to solving the short-term unit commitment problem using an evolutionary programming-based tabu search (TS) method. The objective of this paper is to find the generation scheduling such that the total operating cost can be minimized, when subjected to a variety of constraints. This also means that it is desirable to find the optimal generating unit commitment in the power system for the next H hours. Evolutionary programming, which happens to be a global optimization technique for solving unit commitment problem, operates on a system, which is designed to encode each unit's operating schedule with regard to its minimum up/down time. In this, the unit commitment schedule is coded as a string of symbols. An initial population of parent solutions is generated at random. Here, each schedule is formed by committing all of the units according to their initial status ("flat start"). Here, the parents are obtained from a predefined set of solutions (i.e., each and every solution is adjusted to meet the requirements). Then, a random decommitment is carried out with respect to the unit's minimum downtimes, and TS improves the status by avoiding entrapment in local minima. The best population is selected by evolutionary strategy. The Neyveli Thermal Power Station (NTPS) Unit-II in India demonstrates the effectiveness of the proposed approach; extensive studies have also been performed for different power systems consisting of 10, 26, and 34 generating units. Numerical results are shown comparing the cost solutions and computation time obtained by using the evolutionary programming method and other conventional methods like dynamic programming, Lagrangian relaxation, and simulated annealing and tabu search in reaching proper unit commitment. [ABSTRACT FROM AUTHOR]

This is a follow-on paper to "A New Thermal¹ Governor Modeling Approach in the WECC²" [1]. The paper describes the steps being taken to obtain validated data for the new governor models. It was recognized that the developmental database [1] that was created to prove the new thermal governor model should not be used to perform operation or planning studies. Invalid governor data for real-lime operation simulations gives rise to risks and liabilities in the determination of intertie limits. Due to the large number of governors involved (about 1100 units) and the short timeline for obtaining data in critical 2003 summer operation studies, a concerted effort is being made to assist generator owners to select and validate the appropriate governor model codes for their units. This effort includes a workshop and the issue of detailed guidelines aid validation methodologies for governor modeling. [ABSTRACT FROM AUTHOR]

The paper addresses practical capabilities of artificial neural networks (ANNs) in developing measurement-based continuous-time dynamic equivalents for power systems. Our method is based on a set of measurements at boundary nodes between a subsystem that is to be modeled in detail ("retained" portion of the system) and the part that is to be replaced by a simplified ("equivalent") model. We are particularly interested in combining standard physics-based models with signal-based models derived from measurements. We utilize a color-coding scheme to distinguish between physics-based models (clear or white box) at one end, the signal-based models (opaque or black box) at the opposite end, and mixed (gray box) models in the middle. The paper also proposes a way for combining classical and ANN-based equivalents in a hybrid model implemented in a standard software environment for transient analysis (in this case, ETMSP). Our conclusions are based on simulations performed on a model of a benchmark multimachine power system derived from the WSCC system. [ABSTRACT FROM AUTHOR]

The paper investigates the possibility to use relative gain array (RGA) for power system small-disturbance stability analysis. The RGA has been successfully used in the past as steady state measure of interactions for multivariable, decentralized control in chemical and process engineering. The effectiveness of the RGA in identifying electromechanical modes and selecting the optimal location for placement of PSSs is compared with the conventional, approach that uses transfer function residues, eigenvalues and participation factors Two different multimachine power systems are used for the case studies. Limitations and advantages of the use of RGA in this purpose are clearly indicated in the paper. [ABSTRACT FROM AUTHOR]

This paper addresses the allocation of electrical losses in distribution networks with embedded generation, in a liberalized environment. The nonlinear nature of the issue, the loss changes due to voltage variation and, specially, the contribution of embedded generation to loss variation are considered. The proposed method is based on tracing the real and imaginary parts of the currents and has two steps. First, the loses in the distribution network, in the absence of embedded generation, are allocated to the consumers (or their providers). Second, the variations in the losses that result from the influence of embedded generation are allocated to the generators. These variations are a measure of the avoided or added costs related to losses. In the allocation process, made in a branch basis, both real and reactive powers ate considered. The methodology presented in this paper can be used to evaluate embedded, generation incentives or to design tariffs for the use of the distribution network. [ABSTRACT FROM AUTHOR]

A detailed AC OPF-based formulation for procuring, pricing, and settling energy and ancillay service in simultaneous auctions by integrated market systems is presented. The paper provides clear definitions of locational marginal prices for energy and ancillary service marginal prices in terms of Lagrange multipliers. The characteristics of the prices are analyzed especially when economic substitution among ancillary services is required. The paper also evaluates the conditions under which opportunity costs are incurred to units that provide ancillary services. It is particularly shown that the intuitive belief that the provision of regulation down service does not incur opportunity cost to the provider, in general, is not true. [ABSTRACT FROM AUTHOR]

This paper deals with the calculation of a sparse network equivalent (SNE) for the analysis of electromagnetic transients in large systems. The methodology and the mathematical details are presented in the companion paper [1]. The sequel presents application examples to demonstrate the accuracy and computational efficiency of the SNE. Equivalents for networks composed of 12, 50, and 100 transmission lines are derived and the results are discussed. [ABSTRACT FROM AUTHOR]

The problem of exchanging data between two or more organizations in a format that is accessible and under-standable by each is a universal problem. Furthermore, the problem of translating or accessing data in the correct format for applications using proprietary data formats is challenging. Legacy software applications may endure, for some time given, regulatory expenditure pressures on electricity system operators and these require data translators (importer/exporter) and access facilities. The basis of this paper is that the Electric Power Research Institute (EPRI) common information model (CIM) in eXtensible Markup Language (XML) represents the first stage a revolution of data exchange and manipulation for power systems. This paper explores the problem of translating data in the CIM XML format to the required format for such legacy power system analysis applications. This paper discusses solutions some of the challenges in data translation, and illustrates how these solutions can be implemented. [ABSTRACT FROM AUTHOR]

This paper resulted from the research aimed at introducing modeling and simulation as a major methodological approach for enhancing power engineering education. The reasons for such an approach an explained first. Different options and uses of the modeling and simulation tools are discussed next. Several implementations of the teaching examples ate outlined. The paper ends with the conclusions reached based on the study. [ABSTRACT FROM AUTHOR]

This paper is concerned about the accurate representation of transmission lines for electromagnetic transients simulation studies. The frequency dependent (FD) line model (also known as the J. Marti model) which is currently used in most electromagnetic transient programs [1], has been a major contribution to the power system transient simulations. However, despite its accuracy and computational efficiency for most simulation cases, it still requires improvement due to the approximation it makes in choosing the modal transformation matrix T[SUBv]. This matrix is, in general, frequency dependent and used in transforming variables between the phase and modal domains at each simulation time step. Currently, it is approximated as a constant matrix which may not hold true for certain tower configurations and/or conductor types where line parameters vary drastically with frequency. In this paper, a wavelet-based alternative solution, which incorporates frequency dependence of transformation matrices into the simulation process, is proposed. Simulation results, illustrating the effects of using the proposed model versus the existing FD line model, are also presented. [ABSTRACT FROM AUTHOR]

Increasing penetration of variable loads and renewable generation will cause the conventional operation strategy of the distribution system to become less certain and effective. This paper presents a method of determining the minimum loss network configuration of a distribution system with uncertain load and renewable generation. A robust optimization model is proposed wherein the optimal decisions on network configurations and losses are derived in two subsequent steps. The first step enforces the radiality constraint before knowing the actual system loads and output level of renewable generation. Power flows are computed next to achieve minimum network losses considering the worst operating conditions over the uncertainty sets. A mixed-integer two-stage robust optimization formulation and a decomposition algorithm in a master-slave structure are proposed to solve the problem. Results of an illustrative example and two test systems are presented to demonstrate the proposed method. [ABSTRACT FROM PUBLISHER]

This paper considers future distribution networks featuring inverter-interfaced photovoltaic (PV) systems, and addresses the synthesis of feedback controllers that seek real- and reactive-power inverter setpoints corresponding to AC optimal power flow (OPF) solutions. The objective is to bridge the temporal gap between long-term system optimization and real-time inverter control, and enable seamless PV-owner participation without compromising system efficiency and stability. The design of the controllers is grounded on a dual \epsilon-subgradient method, while semidefinite programming relaxations are advocated to bypass the non-convexity of AC OPF formulations. Global convergence of inverter output powers is analytically established for diminishing stepsize rules for cases where: i) computational limits dictate asynchronous updates of the controller signals, and ii) inverter reference inputs may be updated at a faster rate than the power-output settling time. [ABSTRACT FROM PUBLISHER]

This paper proposes a multi-agent control strategy to coordinate power sharing between heterogeneous energy storage devices distributed throughout a DC microgrid. Without requiring a central controller, the proposed control strategy extends the benefits offered by hybrid energy storage systems to DC microgrids with batteries and ultracapacitors spatially distributed at different levels of the power distribution hierarchy. The proposed control strategy has the following advantages. 1) The high frequency microgrid load is provided by the ultracapacitors. 2) The low frequency load is provided by batteries used for bulk energy storage during islanded mode, and the main grid during grid connected operation. 3) The ultracapacitor voltages are regulated at a desired reference. 4) State of charge balancing is provided between the batteries. 5) The energy storage systems cooperate based on neighbor-to-neighbor output feedback over a sparse communication network. The only communication requirement is a spanning tree from the ultracapacitor leaders and battery leaders to their respective followers. Simulations are presented demonstrating the performance of the proposed control strategy for a 380 VDC datacenter during grid connected and islanded operation. [ABSTRACT FROM PUBLISHER]

Motivated by several recent incidents, this paper investigates the impact of wind farm spatial distribution and shunt compensation levels on triggering system-side sub-synchronous oscillations (SSO) in wind-integrated power systems. Quantitative analysis on system eigenvalue sensitivities with respect to wind farm and transmission line parameters as well as system operating conditions is performed systematically to understand the multi-wind-farm-induced SSO. Coupling relationship for wind turbines with identical and different parameter settings on the studied SSO modes is investigated. Electro-magnetic simulations are performed on a multi-machine wind farm model derived from a practical wind-integrated power system, in order to verify the proposed study. [ABSTRACT FROM AUTHOR]

This paper presents a planning framework to find the minimum storage sizes (power and energy) at multiple locations in distribution networks to reduce curtailment from renewable distributed generation (DG), specifically wind farms, while managing congestion and voltages. A two-stage iterative process is adopted in this framework. The first stage uses a multi-period AC optimal power flow (OPF) across the studied horizon to obtain initial storage sizes considering hourly wind and load profiles. The second stage adopts a high granularity minute-by-minute control driven by a mono-period bi-level AC OPF to tune the first-stage storage sizes according to the actual curtailment. Congestion and voltages are managed through the optimal control of storage (active and reactive power), on-load tap changers (OLTCs), DG power factor, and DG curtailment as last resort. The proposed storage planning framework is applied to a real 33-kV network from the North West of England over one week. The results highlight that by embedding high granularity control aspects into planning, it is possible to more accurately size storage facilities. Moreover, intelligent management of further flexibility (i.e., OLTCs, storage, and DG power factor control) can lead to much smaller storage capacities. This, however, depends on the required level of curtailment. [ABSTRACT FROM AUTHOR]

This paper proposes a probabilistic power flow analysis technique based on the stochastic response surface method. The probability distributions and statistics of power flow responses can be accurately and efficiently estimated by the proposed method without using series expansions such as the Gram-Charlier, Cornish-Fisher, or Edgeworth series. The stochastic continuous input variables following normal distributions such as loads or non-normal distributions such as photovoltaic generation and wind power and their multiple correlations can be easily modeled. The correctness, effectiveness and adaptability of the proposed method are demonstrated by comparing the probabilistic power flow analysis results of the IEEE 14-bus and 57-bus standard test systems obtained from the proposed method, the point estimate method, and the Monte Carlo simulation method. [ABSTRACT FROM AUTHOR]

This paper presents a new mixed-integer linear programming (MILP) model to solve the multistage long-term expansion planning problem of electrical distribution systems (EDSs) considering the following alternatives: increasing the capacity of existing substations, constructing new substations, allocating capacitor banks and/or voltage regulators, constructing and/or reinforcing circuits, and modifying, if necessary, the system's topology. The aim is to minimize the investment and operation costs of the EDS over an established planning horizon. The proposed model uses a linearization technique and an approximation for transforming the original problem into an MILP model. The MILP model guarantees convergence to optimality by using existing classical optimization tools. In order to verify the efficiency of the proposed methodology, a 24-node test system was employed. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of the overexcitation limiters (OELs) on the stability margin of a power system which is operating under stressed conditions. Several OEL modeling approaches are presented and the effect of their action has been examined in model power systems. It is realized that, more often than not, OEL operating status goes undetected by existing dynamic security assessment tools commonly used in the industry. It is found that the identification and accurate representation of OELs lead to significantly different transient stability margins. Unscented Kalman filtering is used to detect the OEL activation events. In the context of stressed system operation, such quantitative assessment is very useful for system control. This understanding is further reinforced through detailed studies in two model power systems. [ABSTRACT FROM AUTHOR]

Cascading outages in power systems can lead to major power disruptions and blackouts and involve a large number of different mechanisms. The typical development of a cascading outage can be split in two phases with different dominant cascading mechanisms. As a power system is usually operated in N-1 security, an initiating contingency cannot entail a fast collapse of the grid. However, it can trigger a thermal transient, increasing significantly the likelihood of additional contingencies, in a “slow cascade.” The loss of additional elements can then trigger an electrical instability. This is the origin of the subsequent “fast cascade,” where a rapid succession of events can lead to a major power disruption. Several models of probabilistic simulations exist, but they tend to focus either on the slow cascade or on the fast cascade, according to mechanisms considered, and rarely on both. We propose in this paper a decomposition of the analysis in two levels, able to combine probabilistic simulations for the slow and the fast cascades. These two levels correspond to these two typical phases of a cascading outage. Models are developed for each of these phases. A simplification of the overall methodology is applied to two test systems to illustrate the concept. [ABSTRACT FROM AUTHOR]

In this paper, a new procedure based on a backward/forward sweep (BFS) algorithm for solving power flows in weakly meshed dc traction networks is presented. The proposed technique is able to consider the trains as nonlinear and nonsmooth (nondifferentiable) voltage-dependent loads or generators. This feature permits the inclusion of the trains’ overcurrent protection and the squeeze control. With the use of the mentioned controls, the conventional power flow problem becomes a voltage constrained power flow problem, and the interaction between the trains and the network can be accurately modeled. However, the train control induces a highly nonsmooth voltage-dependent load characteristic, causing convergence problems in most of the derivative-based algorithms. The proposed algorithm is faster, more robust, and more stable than the derivative-based ones. In addition, the authors present all of the formulation in a compact matrix-based form by means of the graph theory application and the node incidence matrix. [ABSTRACT FROM PUBLISHER]

This paper proposes a new multi-objective framework for primary distribution system planning (DSP). Further consideration is devoted to early DSP formulations in order to assess the risk imposed by probabilistic customer choices on reliability (CCOR). The CCOR is a buy/sell strategy that permits customers to pay the electricity price equiponderant to the reliability level provided by the distribution utility over the contract period. A Monte Carlo-based simulation is carried out to examine the effects of the probability of a customer's interest in adopting the CCOR on profit-at-risk. Furthermore, the DSP was conducted to simultaneously minimize both total planning cost and profit-at-risk. The resultant optimization problem is solved through the non-dominated sorting genetic algorithm (NSGA-II) accompanied by a fuzzy decision making method to select the best result among the obtained Pareto optimal set of solutions. The developed method is applied to an actual large-scale distribution system with about 140\thinspace000 customers, followed by a discussion on results. [ABSTRACT FROM PUBLISHER]