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Power Systems, IEEE Transactions on

Issue 4 • Date Nov. 1997

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Displaying Results 1 - 25 of 58
  • Author index

    Publication Year: 1997 , Page(s): 1 - 21
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  • Subject index

    Publication Year: 1997 , Page(s): 21 - 75
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  • Equivalent optimization model for loss minimization: a suitable analysis approach

    Publication Year: 1997 , Page(s): 1403 - 1412
    Cited by:  Papers (7)
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    Any OPF (optimal power flow) tool used in on-line minimum loss calculation requires an accurate representation of the external or unobservable parts of the network. This paper proposes an optimization model of both internal and external network represented explicitly. Although requiring only external network data, any available information about the external state may be used to improve its response. A general methodology for the performance analysis of equivalent OPF models is also proposed. On one level, the robustness of equivalent models for the production of accurate control actions in the internal system is analyzed. Accurate control actions are those that are as close as possible to the controls obtained through a hypothetical OPF solution of the complete system. On a second level, the capacity to react accurately, when such control actions are set in the internal system, is investigated. The proposed model and the Extended Ward equivalent have been tested through the presented methodology. The proposed model has been capable to take into account the information related to the optimization “status” (under optimization or not) of external system. This is an important information since it affects considerably the internal control action calculation. This information cannot be incorporated in the reduced equivalent models. Computational test results with the Brazilian South-Southeast 810 bus real system are presented View full abstract»

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  • UPFC application on the AEP system: planning considerations

    Publication Year: 1997 , Page(s): 1695 - 1701
    Cited by:  Papers (26)
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    In 1995, American Electric Power (AEP), an investor owned electric utility company, completed detailed planning studies to resolve voltage and thermal loading concerns in parts of its Kentucky/West Virginia service areas. These studies led to the initiation of a project including a unified power flow controller (UPFC), which is currently being developed through a tailored collaboration by AEP, Electric Power Research Institute (EPRI), and Westinghouse Electric Corporation (Westinghouse). This paper describes the planning concerns, the study objectives, and the UPFC function in resolving these concerns. It also provides information on the UPFC modeling for system studies and its technical parameters that would be of interest to transmission system planners and other prospective users of this new technology View full abstract»

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  • Dynamic modeling of a TCSC with application to SSR analysis

    Publication Year: 1997 , Page(s): 1619 - 1625
    Cited by:  Papers (27)
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    Conventional subsynchronous resonance (SSR) study methods such as eigenanalysis require a linear dynamic model of each device. FACTS devices such as thyristor-controlled series capacitors (TCSC) are difficult to model due to their nonlinear switching behaviour. Linearizing the TCSC steady-state average model is inadequate as this does not model the passive damping associated with the open-loop operation of a TCSC. The proposed approach exploits the fact that the thyristor controlled reactor associated with the TCSC is switched in a regular pattern. A linear model is obtained by linearizing the half-period map associated with sampling the TCSC capacitor voltage twice every cycle. Such an approach models the passive damping which varies with the steady-state conduction angle of the TCSC. It is shown that passive damping has a significant effect on the modal damping of the torsional modes associated with subsynchronous resonance phenomena View full abstract»

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  • Parametric variations in dynamic models of induction machine clusters

    Publication Year: 1997 , Page(s): 1549 - 1554
    Cited by:  Papers (1)
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    This paper presents a probabilistic approach to the characterization of dynamical models of induction machine clusters. The authors' method derives bounds on eigenvalue variations for linearized models expressed in terms of stochastic norms. In their examples of the modeling of power system loads, this characterization tends to be less conservative than alternative deterministic approaches. They consider examples of induction machines with different ratings (classes), and allow for wide variations of electrical and mechanical parameters. They describe a stochastic norm approach to: (1) efficiently describe the dynamical model variations for a cluster of similar machines without having to perform repeated eigenvalue calculations, e.g. in a wind farm application; and (2) suggest the order of the reduced model in power system load modeling where the tightness of the bounds of eigenvalue variations is used for guidance in decisions regarding the number of different classes that would efficiently represent a given composite load View full abstract»

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  • Combined quadratic-separable programming OPF algorithm for economic dispatch and security control

    Publication Year: 1997 , Page(s): 1682 - 1688
    Cited by:  Papers (1)
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    This paper presents a new algorithm for optimal power flow (OPF), which is based on P/Q decomposition of OPF problem and on combined application of quadratic and separable programming methods. Initially the unit cost curves are approximated by the quadratic functions and the quadratic programming algorithm is applied as a starting method. This gives a good initial point for optimization and reduces the total computation time. The modification of a separable programming (SP) algorithm with generation of approximating intervals is considered. A new quadratic-separable algorithm for OPF is proposed, which combines the main advantages of quadratic and separable programming methods. A bi-criterion formulation of security control problem on the base of economic and security objective functions (OF) is proposed. The numerical results of OPF for large-scale power systems are given for different methods View full abstract»

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  • Damping of electro-mechanical oscillations in a multimachine system by direct load control

    Publication Year: 1997 , Page(s): 1604 - 1609
    Cited by:  Papers (5)
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    Electric utility-controlled customer loads as actuators present new possibilities for power system control. The use of active loads controlled by local bus frequency is proposed for the damping of power system electromechanical oscillations. The viability of the idea is studied for one load in a three-machine power system with a meshed network. Active power mode controllability and phase angle mode observability are determined from the eigenvectors of a differential algebraic description of the uncontrolled system. The geographical variations in the entire network of controllability and observability are shown to be identical. It is presented graphically on a 3-D view of the network topology and is used as a generalization of the term mass scaled electrical distance. System zeros limit the maximum damping. An electromechanical mode pendulum analog is introduced that explains this. Time simulations verify the final controller design View full abstract»

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  • Features that influence composite power system reliability worth assessment

    Publication Year: 1997 , Page(s): 1536 - 1541
    Cited by:  Papers (5)
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    Reliability worth assessment using customer interruption costs is an important element in electric power system planning and operation. This paper deals with two features that affect the composite generation-transmission system reliability worth assessment. One feature is the incorporation of temporal variations in the cost of interruption. This paper illustrates the effect on the expected annual system outage cost of temporal variation in the interruption costs for the residential, agricultural, industrial, commercial and large user sectors. The other aspect considered in this paper is using a probability distribution approach to represent the cost of interruption model. The conventional customer damage function approach utilizes average customer costs while the probability distribution approach recognizes the dispersed nature of the customer outage data. These two methods of cost evaluation are applied to reliability worth assessment in this paper. A sequential Monte Carlo approach incorporating time varying loads is used to conduct all the studies. Case studies performed on two composite test systems show that incorporating time varying costs of interruption for the industrial sector resulted in a significant reduction in the expected outage cost. A comparison of the reliability worth obtained using the customer damage function method (CDF) with the probability distribution approach suggests that using the CDF method may significantly undervalue the reliability worth by a factor of three to four View full abstract»

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  • A fast-computation Hopfield method to economic dispatch of power systems

    Publication Year: 1997 , Page(s): 1759 - 1764
    Cited by:  Papers (30)
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    This paper develops a direct-computation Hopfield method for solving the economic dispatch (ED) problems of thermal generators. The method employs a linear input-output model for neurons. Formulations for solving the ED problems are explored. Through the application of these formulations, direct computation instead of iterations for solving the problems becomes possible. Unlike the usual Hopfield methods which select the weighting factors of the energy function by trials, the proposed method determines the corresponding factor using formulation calculation. Hence, it is relatively easy to apply the proposed method. The effectiveness of the developed method is identified through its application to two example power systems. Computational results show that the method has excellent performance, and that it is superior to other methods in many respects View full abstract»

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  • Applicability of simple expressions for electrical breakdown probability increase in vacuum and gas

    Publication Year: 1997 , Page(s): 1455 - 1460
    Cited by:  Papers (5)
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    Simple analytical expressions for the law of breakdown probability increase are suggested. They are tested by comparing with experimental data obtained by impulse and DC breakdown. The pressure 10-4 Pa and interelectrode gaps d<0.1 mm are used for vacuum, and the pressure 1 bar-5 bars and the interelectrode gaps 1 mm-50 mm are used for gas breakdown. The insulation gas was a SF6, N2 and gas-mixture: SF6-N2. It is concluded that such a simplified approach is not appropriate for vacuum. It is also concluded that, for gas, the BPI (breakdown probability increase) law, in the form of a simple expression, is valid in the considered range of relevant experimental parameters View full abstract»

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  • Network equivalents and expert system application for voltage and VAR control in large-scale power systems

    Publication Year: 1997 , Page(s): 1440 - 1445
    Cited by:  Papers (16)
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    This paper presents an application of the steady-state network equivalents and an expert system for voltage and reactive power (VAr) control in large-scale power systems. A steady-state network equivalencing technique is used to construct the “three-tier” subsystem which is adequate to solve voltage violation problems. An expert system utilises the sensitivity tree method to select the optimal set of control actions to alleviate the voltage problem. The expert system was developed using the VP-EXPERT system shell. VP-EXPERT interacts with the power system analysis software providing analysis of the network sensitivity matrix and data for the knowledge base. Practical application of the developed expert system is demonstrated on the example of the Hydro-Electric Commission (HEC) power system of Tasmania, however the proposed approach is not limited by the system size View full abstract»

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  • Cascaded artificial neural networks for short-term load forecasting

    Publication Year: 1997 , Page(s): 1524 - 1529
    Cited by:  Papers (22)
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    An application of artificial neural networks (ANNs) to short-term load forecasting is presented in this paper. An algorithm using cascaded learning together with historical load and weather data is proposed to forecast half-hourly power system load for the next 24 hours. This cascaded neural network algorithm (CANNs) includes peak, minimum and daily energy prediction as additional input data for the final forecast stage. These additional input data are predicted using the first (ANNs) model. The networks are trained and tested on the electric power system of Kuwait. The absolute average forecasting error is reduced from 3.367% to 2.707% by applying CANNs as compared to the conventional ANNs. Simulation results indicate that the developed forecasting approach is effective and point to the potential of the methodology for economic applications View full abstract»

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  • Fast calculation of a voltage stability index of power systems

    Publication Year: 1997 , Page(s): 1555 - 1560
    Cited by:  Papers (6)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    The minimum singular value of the Jacobian matrix of the load flow equation may have been preferred as an indicator of voltage collapse when the static voltage stability of power systems is studied. In this paper, the authors propose a highly efficient algorithm to calculate the smallest singular value of a Jacobian matrix of the load flow equation by employing the noniterative characteristic of an incremental condition estimation (ICE) method and the sparsity characteristic of large scale power networks. Both theoretical bases and computation costs of the algorithm are also detailed in the context. Finally, a practical application example is also given for demonstration View full abstract»

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  • A new dual-type method used in solving optimal power flow problems

    Publication Year: 1997 , Page(s): 1667 - 1675
    Cited by:  Papers (10)
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    In the framework of the sequential quadratic programming (SQP) method for optimal power flow (OPF) problems, the authors propose a new dual-type method for solving the QP subproblems induced in the SQP method. Their method achieves some attractive features; it is computationally efficient and numerically stable. The computational formulae of their method are simple, concise and easily programmed. The authors have tested their method for OPF problems on several power systems, including a 2500-bus system View full abstract»

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  • An optimization-based algorithm for scheduling hydrothermal power systems with cascaded reservoirs and discrete hydro constraints

    Publication Year: 1997 , Page(s): 1775 - 1780
    Cited by:  Papers (26)  |  Patents (1)
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    An optimization-based algorithm is presented for the short-term scheduling of hydrothermal power systems using the Lagrangian relaxation technique. This paper concentrates on the solution methodology for hydro subproblems with cascaded reservoirs and discrete hydro constraints. Continuous reservoir dynamics and constraints, discontinuous operating regions, discrete operating states and hydraulic coupling of cascaded reservoirs are considered in an integrated fashion. The key idea is to substitute out the reservoir dynamics and to relax the reservoir level constraints by using another set of multipliers, making a hydro subproblem unit-wise and stage-wise decomposable. The optimal generation level for each operating state at each hour can be obtained simply by minimizing a single variable function. Dynamic programming is then applied to optimize the operating states across the planning horizon with a small number of well structured transitions. A modified subgradient algorithm is used to update multipliers. After the dual problem converges, the feasible solution to the hydropower subsystem is obtained by using a network flow algorithm, with operating states obtained in the dual solutions, and possibly adjusted by heuristics. Numerical testing based on practical system data sets show that this method is efficient and effective for dealing with hydrothermal power systems with cascaded reservoirs and discrete hydroelectric constraints View full abstract»

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  • Short-term load forecasting in an autonomous power system using artificial neural networks

    Publication Year: 1997 , Page(s): 1591 - 1596
    Cited by:  Papers (8)
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    This paper presents the development of an artificial neural network based short-term load forecasting model for an autonomous power system. Problems encountered in data preparation, network structure definition and the model's sensitivity to temperature, together with suggested solutions, are discussed. The proposed model can provide next week's load forecasts. Experiences obtained during the application of the model to predict daily load curves in the autonomous power system of the Greek island of Crete are presented View full abstract»

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  • Investigation into an artificial neural network based on-line current controller for an HVDC transmission link

    Publication Year: 1997 , Page(s): 1425 - 1431
    Cited by:  Papers (8)
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    An artificial neural network (ANN) based current controller for a HVDC transmission link is described in this paper. Different ANN architectures and activation functions (AFs) are investigated for this ANN controller. Small (set current change) and large (DC-line fault) signal perturbations are applied to optimize the learning parameters for the controller. Performance evaluation of the ANN controller under noise conditions is studied. A comparison between a traditional PI and the proposed ANN controller is made for various system contingencies and it is shown that the latter has many attractive features View full abstract»

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  • An energy based approach to evaluate optimum interruptible load carrying capability in isolated and interconnected systems including well-being constraints

    Publication Year: 1997 , Page(s): 1676 - 1681
    Cited by:  Papers (5)
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    A generation system is considered to be capable of serving a target firm load that is consistent with accepted operating criteria. This target is referred to as the firm load carrying capability of a system. The same generation system may be capable of supporting a limited amount of interruptible load on top of the firm load without violating the operating criteria. This capability is defined as the interruptible load carrying capability (ILCC) of the system. This paper presents a probabilistic technique to evaluate the ILCC of isolated and interconnected systems. The objective is to determine the amount of interruptible load and the corresponding interruption time that can maximize the expected energy supplied while satisfying the operating criteria. The operating criteria are defined using a well-being framework. Study results are illustrated using the IEEE-RTS View full abstract»

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  • Strategic bidding in an energy brokerage

    Publication Year: 1997 , Page(s): 1729 - 1733
    Cited by:  Papers (43)
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    This focus of this paper is to present a framework in which strategies may developed for the individual participants in an energy brokerage. Such a framework is expected to be important with the increasing interest in electricity market structures, such as the energy brokerage, that deregulation has produced. To illustrate the process of strategic bidding, a simple suboptimal bidding strategy is presented with the aid of a numerical example. The bidding strategy must be suboptimal because of the amount of unknown information about the other bidders. Further tuning of this strategy will be required before application to realistic scenarios View full abstract»

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  • Artificial neural network based dynamic load modeling

    Publication Year: 1997 , Page(s): 1576 - 1583
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB)  

    The aim of this research is to investigate the use of artificial neural networks (ANN) with feedback loops for the modeling of power system dynamic loads using field data. In addition to the power demand before the transient, only the phase voltages are assumed available at the recall stage. It is found that the load dynamics can be identified using the ANN developed for the season and the location of the load being emulated. The frequency response of the tested load is also obtained using the achieved ANN model View full abstract»

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  • Energization transients of shunt reactors

    Publication Year: 1997 , Page(s): 1626 - 1631
    Cited by:  Papers (3)
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    This paper investigates the impacts of energization transients of large shunt reactors on the operation of HVAC and HVDC/AC power systems. The Electromagnetic Transients Program for DC systems (EMTDC) is used for these simulation studies. The studies conclude that shunt reactor energization can result in undesirable response of power system apparatus and even interruption of power flow, e.g. commutation failure of HVDC power converters. The studies also indicate that the energization transients can be adequately alleviated based on the use of pre-insertion resistor and/or controlled energization strategies View full abstract»

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  • Fast estimation of voltage and current phasors in power networks using an adaptive neural network

    Publication Year: 1997 , Page(s): 1494 - 1499
    Cited by:  Papers (33)
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    A new algorithm for the estimation of parameters of voltage or current waveform of power networks contaminated by noise is proposed. The problem of estimation is formulated by using an adaptive neural network consisting of linear adaptive neurons called adaline. The learning parameters of the adaline are adjusted to force the error between the actual and desired outputs to satisfy a stable difference error equation, rather than to minimize an error function. Illustrative computer simulation results confirm the validity and accurate performance of the proposed method. Laboratory test results are also presented in this paper to support the effectiveness of the proposed approach in tracking the waveforms in real-time View full abstract»

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  • Methods for calculating oscillations in large power systems

    Publication Year: 1997 , Page(s): 1639 - 1648
    Cited by:  Papers (25)
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    The authors present algorithms to calculate the Hopf bifurcation related segment of the feasibility boundary for a realistically large power system model. The algorithms are used by calculating the Hopf-related segment of the feasibility boundary, for the well-recorded June 12, 1992 disturbance on the midwestern segment of the US interconnected power system for analyzing the resulting oscillations. The computational results confirm that this event was indeed related to a Hopf bifurcation. This proposed method clarified the operational perspectives of the low frequency power oscillation that occurred. It also demonstrated the value of the proposed computational approach in assessing the security of an operating point in an area of the parameter space View full abstract»

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  • Basic control of unified power flow controller

    Publication Year: 1997 , Page(s): 1734 - 1739
    Cited by:  Papers (47)  |  Patents (1)
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    A unified power flow controller (UPFC) is a typical FACTS device capable of instantaneous control of three power system parameters. This paper presents a basic control system which enables the UPFC to follow the changes in reference values of the active and reactive power supplied from the outer system controller. The analysis is based on the transformation of the three-phase power system to the rotating reference frame. As a step closer to a practical application of the UPFC, a modified control structure with a predictive control loop and precontrol signal for a DC-voltage control was designed. The new control system offers better stability and transient performance in comparison with the classical decoupled strategy, especially considering the harmonic distortion of the current being controlled. The derived basic control of the UPFC was tested with the NETOMAC program system 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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Meet Our Editors

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