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Power Systems, IEEE Transactions on

Issue 2 • Date May 1993

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Displaying Results 1 - 25 of 47
  • A fuzzy-based optimal reactive power control

    Page(s): 662 - 670
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    A mathematical formulation of the optimal reactive power control problem using fuzzy set theory is presented. The objectives are to minimize real power losses and improve the voltage profile of a given system. Transmission losses are expressed in terms of voltage increments by relating the control variables to the voltage increments in a modified Jacobian matrix. This formulation does not require Jacobian matrix inversion, and hence it will save computation time and memory space. The objective function and the constraints are modeled by fuzzy sets. Linear membership functions of the fuzzy sets are defined and the fuzzy linear optimization problem is formulated. The solution space is defined as the intersection of the fuzzy sets describing the constraints and the objective functions. Each solution is characterized by a parameter that determines the degree of satisfaction with the solution. The optimal solution is the one with the maximum value for the satisfaction parameter. Results for test systems reveal the advantages of the approach View full abstract»

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  • A simplified approach to estimate maximum loading conditions in the load flow problem

    Page(s): 646 - 654
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    A computationally efficient and simple approach to estimate maximum loading conditions in the load flow problem is described. These operating points are known to result in a number of undesirable phenomena such as the singularity of the Jacobian, solution bifurcations, and voltage collapse. The approach presented generates precise estimates of the maximum possible amount of load increase that the system can tolerate along a specified path, as well as the corresponding voltage vector. The method is simple and efficient since it is based primarily on conventional load flow solutions. Tests on several standard power networks confirm the accuracy and efficiency of the technique View full abstract»

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  • Application of static VAr compensators to increase power system damping

    Page(s): 655 - 661
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    A theory for analyzing power system damping enhancement by application of static VAr compensators (SVCs) has been developed using the equal area criterion. Some fundamental issues, such as the effect of SVCs on a power system, how to control an SVC to improve system damping, and the differences between continuous and discontinuous control of SVC reactive power to achieve the maximum damping improvement, are discussed. A discontinuous SVC reactive power output at discrete points is determined from the power deviation on a transmission line. Time-domain simulations of the application of this approach to a one-machine system to increase swing oscillation damping and to a four-machine system to increase the damping of an interarea oscillation mode demonstrate that the theory and method can be applied to solve practical power system damping problems View full abstract»

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  • AC-DC load flow with unit-connected generator-converter infeeds

    Page(s): 701 - 706
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    The conventional AC-DC steady state formulation is modified to analyze HVDC load flows with unit-connected generator-converter infeeds. It is found that the steady state algorithm is restricted in its application to large power conditions due to the large commutation overlap caused by the extra reactance of the unit connection. Also, the results are shown to be in considerable error when the generators contain rotor saliency (probably the most common case for a remote generating plant). A concept called the equivalent inverter which uses unit-connection characteristics derived from time domain simulation is presented as a practical alternative for general load flow studies involving unit-connected schemes View full abstract»

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  • A coordinated control of voltage and reactive power by heuristic modeling and approximate reasoning

    Page(s): 636 - 645
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    A flexible approximate reasoning approach to coordinated control of voltage and reactive power in order to enhance the voltage security of an electric power system is presented. The control strategy is expressed by simple rules, which measure the proximity of system state to certain operating conditions, and utilize linear equations to obtain the effective control models. The desired control actions are determined by considering several criteria at the same time. The procedure has been applied to a model system in order to verify its effectiveness. The simulation results show the advantages of this fuzzy modeling approach over conventional expert systems for voltage-reactive-power control View full abstract»

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  • Evaluation of the transient energy function method for on-line dynamic security analysis

    Page(s): 497 - 507
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    The transient energy function (TEF) method is a direct method of power system transient stability analysis. While research work on the subject continues, questions have been raised regarding potential applications of the method for online dynamic security analysis (DSA). Some of the problems are investigated, and solutions for problems arising in the use of TEF in DSA, based on tests using real utility data, are suggested. A prerelease version of a TEF program called DIRECT (version 2.9) was used in the tests. The results indicate that TEF does have a place in DSA in conjunction with other available DSA methods View full abstract»

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  • Windfarm layout as a senior electrical engineering student design project

    Page(s): 753 - 758
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    A proven senior design project from a wind engineering course is described. Students select equipment, make economic choices, and write a report for a windfarm electrical distribution system. Using topographical maps of potential sites increases realism, helping to make the design project well liked by students View full abstract»

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  • Incorporating sources of uncertainty in forecasting peak power loads-a Monte Carlo analysis using the extreme value distribution

    Page(s): 730 - 737
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    The extreme value distribution (EVD), in conjunction with Monte Carlo simulations, is used to analyze sources of uncertainty in forecasting annual peak power loads. The methodology is applied to 1984-1986 load and weather data for a public utility district near Spokane, Washington. The methodology embodies a four-step approach: estimate a weather-sensitive daily peak load model, simulate historical peak loads, estimate the parameters of an extreme value distribution, and predict the probability points associated with different forecast horizons. Monte Carlo analysis is used to incorporate the uncertainty of the disturbances in the estimated daily load model. A separate EVD is estimated for each Monte Carlo simulation, and then the estimated EVDs are used to derive a composite distribution. Corrections are made for the small couple bias in maximum-likelihood estimates of the EVD parameters. A bootstrapping technique extends the procedure to examine the uncertainty of the daily load model's structural parameters View full abstract»

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  • Bulk transmission system loss analysis

    Page(s): 405 - 416
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    A hierarchical approach to capacity and energy loss evaluation in bulk power transmission systems is presented. The approach consists of two levels or hierarchies: a higher level, aimed at producing accurate but relatively slower active capacity and energy loss evaluations, and a lower level, which yields fast but relatively approximate evaluations. This structure allows the users to interactively control the level of accuracy of the calculation, and the relative speed by which it is performed. Results of testing the performance of an implementation of the approach for accuracy, convergence, and speed (using systems with up to 530 buses) are also presented View full abstract»

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  • On the nature of unstable equilibrium points in power systems

    Page(s): 738 - 745
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    The application of direct methods for transient stability analysis of stressed power systems is considered. One of the most important issues in this area is to find the controlling unstable equilibrium point for the disturbance under consideration. A conceptual framework for discussing stable and unstable equilibrium points in power systems based on simple topological arguments is provided. It is shown that every conceivable case of system separation can be related to a specific unstable equilibrium point (UEP) in an unloaded system. This result can be seen as a verification of the soundness of the often-used corrected corner point approximation and ray point approximation, since these two approximations would give the same unstable equilibrium points in an unloaded system. Moreover, an example is given to show that some of the unstable equilibrium points can disappear when the loading of the system increases. The implications of the findings are discussed for the so-called MOD method of finding the controlling UEP, which is used in some software packages. A method based on a combination of the MOD method and the BCU method is outlined and proposed as the subject of future investigation View full abstract»

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  • Voltage-dependent model for teaching transformer core nonlinearity

    Page(s): 746 - 752
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    A voltage-dependent model for transformer core nonlinearity suitable for undergraduate instruction is proposed. The model is based on Fourier series representation of the excitation current, and its parameters are determined with the aid of computer software and measured data. Laboratory experiments are performed to determine the model and verify its validity. The experiment shed light on transformer nonlinearity when used as part of the classical experiment on transformer saturation in the undergraduate energy conversion/power systems laboratory course View full abstract»

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  • Observability and bad data analysis using augmented blocked matrices [power system analysis computing]

    Page(s): 426 - 433
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    Observability and bad data analysis in the context of the recently developed blocked sparse approach are discussed for power system analysis. The factorization-based observability analysis is extended to this method. Important statistical derivations involving the blocked augmented matrices are presented. The computational aspects of performing bad data analysis as well as guidelines for computing residual variances and sensitivity matrices are discussed. An efficient implementation of a bad data analysis algorithm based on normalized residuals and nonlinear residual computations is described View full abstract»

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  • Optimum control strategies for transient as well as oscillatory instability of power systems

    Page(s): 491 - 496
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    A coordinated dynamic braking strategy and excitation control for arresting the first swing instability as well as subsequent oscillations in a power system is proposed. Comparison is made between braking resistor, resistor-reactor and resistor-capacitor strategies with and without excitation control. The control strategies are obtained in terms of system states and other measurable quantities. Assumptions that the reference machine is large and that it is not equipped with dynamic braking lead to a simpler control strategy. The excitation strategy can also be significantly simplified by relaxing the constraints on the rotor angle. Computer simulation of a multimachine power system shows that a coordinated application of braking resistor-capacitor and excitation strategies controls the transients effectively View full abstract»

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  • Power oscillation damping using controlled reactive power compensation-a comparison between series and shunt approaches

    Page(s): 687 - 700
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    How controlled reactive power compensation can be used to damp power system oscillations is described. This is of particular interest in the case of weakly coupled networks. A comparison is made between two kinds of controllable reactive power elements, namely, the CSC (controlled series capacitor) and the SVC (static VAr compensator). Efficiency in terms of damping effect per installed MVAR and the dependence of equipment location are considered. The influence of connected loads is investigated to some extent. Basic relationships for the CSC and the SVC approaches are shown View full abstract»

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  • A transmission network model for multi-area reliability studies

    Page(s): 459 - 465
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    A transmission network suitable for use in multiarea power system reliability models which utilize a Monte Carlo simulation approach is presented. The transmission network model utilizes the REI equivalent, which permits accurate modeling of transmission ties between areas while reducing computational burden and permitting variations in area generating capacity and loads as required in reliability studies. A computationally efficient approach to generation redispatch as required to model mutual assistance between areas in multiarea reliability studies is presented. Sample results are given for the IEEE Std 118-bus test system and a large power pool with 13 areas View full abstract»

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  • Configuration management in an open architecture system power system control

    Page(s): 441 - 444
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    The hardware and software operating environments for power system automation are described. Software portability and distributed databases are discussed. It is seen that in order to configure a system of computing elements that share information in an open architecture environment, a common system manager with respect to configuration, database and failover must reside at the system level, with elements residing at each logical node View full abstract»

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  • Multicommodity network flow model for long-term hydro-generation optimization

    Page(s): 395 - 404
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    A model for long-term hydrogeneration optimization based on multicommodity network flows is presented. The problem of optimizing hydrogeneration with partially dependent water inflows in the reservoir systems is also addressed. The results obtained are consistent with the operating experience for the reservoir systems and meet expectations. The optimal results obtained for volume and discharge for one of the reservoirs is shown graphically. The same type of result can be obtained for any of the reservoirs. These graphs show that water use policies are specific for each commodity; thus it is worth optimizing simultaneously the different types of water use with common constraints in a single program as the model proposes View full abstract»

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  • Time domain modeling of external systems for electromagnetic transients programs

    Page(s): 671 - 679
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    A time domain method for accurate modeling of external power systems in electromagnetic transients programs (EMTPs) is presented. The time domain response of the external system to a multisine excitation signal is utilized to identify a discrete-time model for the external system. The identified model parameters are determined by least-squares estimation. The details of building both single-phase and multiphase equivalents are given. The validity of the equivalents is verified by comparing the electrical transients generated due to the energization of an open-ended line using the full and the equivalent external system. The method is being extended to multiport equivalents View full abstract»

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  • On modelling iron core nonlinearities

    Page(s): 417 - 425
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    An algorithm is presented for the computation of the saturation characteristics of transformer iron cores based on supplied conventional Vrms-Irms curves and no-load losses at rated frequency. Laboratory measurements on a steel sample were carried out. It is shown that the iron core losses are a nonlinear function of the applied voltage. Taking these losses into account improves the nonlinear flux-current characteristics View full abstract»

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  • Dynamic modeling and parameter estimation of a radial and loop type distribution system network

    Page(s): 483 - 490
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    An identification approach to three-phase power system modeling and model reduction taking the power system network as multi-input, multi-output (MIMO) process is presented. The model estimate can be obtained in discrete-time input-output form, discrete- or continuous-time state-space variable form, or frequency-domain impedance transfer function matrix form. An algorithm for determining the model structures of this MIMO process is described. The effect of measurement noise on the approach is also discussed. This approach has been applied to a sample system. Simulation results are presented View full abstract»

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  • Frequency dependent eddy current models for nonlinear iron cores

    Page(s): 588 - 597
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    Frequency dependent representations of eddy currents in laminated cores of power transformers are developed. One representation is based on a continued fraction expansion for the frequency dependent magnetizing impedance while the other is based on a discretization of flux distribution within the lamination. Both models are low order and reproduce the frequency characteristics of the transformer magnetizing branch up to 200 kHz with less than 5% error. The importance of modeling the frequency dependence of eddy currents for the calculation of the transient recovery voltage across a low voltage transformer breaker interrupting a nearby fault is demonstrated View full abstract»

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  • Transient stability enhancement and voltage regulation of power systems

    Page(s): 620 - 627
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    Improvement of the transient stability and voltage regulation of a single-machine-infinite-bus power system under the effects of a symmetrical three-phase short-circuit fault is detailed. The dynamical model of the system is described. A design strategy for nonlinear controllers is considered, and the design of a nonlinear variable-structure excitation controller is described. Simulation results obtained using the nonlinear excitation controller are given, and a new nonlinear coordinated controller is proposed. Simulation results obtained by using the nonlinear coordinated controller are presented View full abstract»

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  • Development of an emergency generation assistance system for Taiwan Power Company

    Page(s): 534 - 540
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    The necessity of emergency generation control (EGC) is explained. A new approach for power system recovery is described. Three, hydro electric power plants are selected for this task at the first stage due to the simplicity of their output control. Field tests conducted prove the feasibility of this approach are described View full abstract»

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  • Reliability differentiated real-time pricing of electricity

    Page(s): 548 - 554
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    Optimal resource planning and power dispatch models (from a societal welfare point of view) imply an optimal pricing policy, which is referred to here as reliability differentiated real-time pricing or, in short, reliability differentiated pricing. This pricing scheme combines real-time pricing and priority pricing with reliability differentiation based on consumer outage costs. This pricing policy is analyzed. The model used in the analysis is developed with particular emphasis on consumer behavior and welfare effects. The implications of the model for the pricing of spinning reserve and firm capacity, as well as for revenue reconciliation, are examined. It is concluded that such a pricing scheme will in general result in greater attainable welfare than either the real-time pricing or priority pricing paradigms. Moreover, it results in the maximum attainable welfare for the system with revenue reconciliation and provides an optimal pricing scheme for spinning revenue and firm capacity View full abstract»

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  • Refinement of conventional PSS design in multimachine system by modal analysis

    Page(s): 598 - 605
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    The design of the lead/lag network in a conventional power system stabilizer (PSS) is intended to provide the correct compensation in order to obtain an electrical torque component in phase with the speed variation. It is shown that, for a multimachine system, the conventional design analysis and synthesis tend to oversimplify the system representation and hence the interaction effects. A more rigorous approach that considers four torque (or power) components instead of the conventional single component is discussed. Using a modal analysis, the significance of these other components is revealed, the more comprehensive treatment using a generalized multimachine representation is justified and a reliable means for optimizing the PSS parameters is presented View full abstract»

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Aims & Scope

Covers the requirements, planning, analysis, reliability, operation, and economics of electric generating, transmission, and distribution systems for general industrial, commercial, public, and domestic consumption.

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Editor-in-Chief
Antonio J. Conejo
The Ohio State University