Showing papers on "Electric power system published in 1992"

Unified power-flow control concept for flexible AC transmission systems

Abstract: The author outlines the technical and economic factors which characterise the uniform, all solid-state power-flow controller approach for real-time controlled, flexible AC transmission systems. The unified power-flow controller in its general form can provide simultaneous, real-time control of all basic power system parameters (transmission voltage, impedance, and phase angle), or any combinations thereof, determining the transmitted power. The parameters selected for control can be changed without hardware alterations, e.g. the function of the controller can be changed from that of a phase-shifter to that of a series line compensator, or vice versa, with or without additional terminal voltage regulation and shunt VAr compensation, to adapt to particular short term contingencies or future system modifications. >

Voltage Stability Evaluation Using Modal Analysis

Abstract: The authors discuss the voltage stability analysis of large power systems by using a modal analysis technique. The method computes, using a steady-state system model, a specified number of the smallest eigenvalues and the associated eigenvectors of a reduced Jacobian matrix. The eigenvalues, each of which is associated with a mode of voltage/reactive power variation, provide a relative measure of proximity to voltage instability. The eigenvectors are used to describe the mode shape and to provide information about the network elements and generators which participate in each mode. A simultaneous iteration method, which is well suited to applications involving large power systems, is used for selective calculation of appropriate eigenvalues. Results obtained using a 3700 bus test system are presented illustrating the applicability of the approach. >

IEEE recommended practice for excitation system models for power system stability studies

Abstract: Excitation system models suitable for use in large-scale system stability studies are presented. Important limiters and supplementary controls are also included. The model structures presented are intended to facilitate the use of field test data as a means of obtaining model parameters. The models are, however, reduced order models and do not represent all of the control loops on any particular system. The models are valid for frequency deviations of ±5% from rated frequency and oscillation frequencies up to 3 Hz. These models would not normally be adequate for use in studies of subsynchronous resonance or other shaft torsional interaction problems. Delayed protective and control features that may come into play in long term dynamic performance studies are not represented. A sample set of data for each of the models, for at least one particular application, is provided.

Power System Relaying

Abstract: ??????????? ????? Stanley Horowitz H Power System Relaying May 13th, 2020 With emphasis on power system protection from the network operator perspective this classic textbook explains the fundamentals of relaying and power system phenomena including stability protection and reliability The fourth edition brings coverage up to date with important advancements in protective relaying due to significant changes in the conventional electric power system that will

Short-term load forecasting using an artificial neural network

Abstract: An artificial neural network (ANN) method is applied to forecast the short-term load for a large power system. The load has two distinct patterns: weekday and weekend-day patterns. The weekend-day pattern includes Saturday, Sunday, and Monday loads. A nonlinear load model is proposed and several structures of an ANN for short-term load forecasting were tested. Inputs to the ANN are past loads and the output of the ANN is the load forecast for a given day. The network with one or two hidden layers was tested with various combinations of neurons, and results are compared in terms of forecasting error. The neural network, when grouped into different load patterns, gives a good load forecast. >

A toolbox for power system dynamics and control engineering education and research

Abstract: The design concept and use of the power system toolbox (PST), a Matlab-based power system dynamics simulation and control design package, are discussed. The motivation for developing the package was to provide a flexible environment for teaching power system simulation techniques and control design concepts to advanced undergraduate and graduate students, and for graduate students to perform research and development on power systems. The authors discuss the capabilities of PST and the software development philosophy. Sample applications are given. Some potential educational usage is suggested. The future enhancement to the package is outlined. >

Fast calculation of a voltage stability index

Abstract: The minimum singular value of the power flow Jacobian matrix has been used as a static voltage stability index, indicating the distance between the studied operating point and the steady-state voltage stability limit. A fast method to calculate the minimum singular value and the corresponding (left and right) singular vectors is presented. The main advantages of the algorithm are the small amount of computation time needed, and that it only requires information available from an ordinary program for power flow calculations. The proposed method fully utilizes the sparsity of the power flow Jacobian matrix and the memory requirements for the computation are low. These advantages are preserved when applied to various submatrices of the Jacobian matrix. The algorithm was applied to small test systems and to a large system with over 1000 nodes, with satisfactory results. >

A zoom feature for a dynamic programming solution to economic dispatch including transmission losses

Abstract: An iterative dynamic programming method for solving the economic dispatch problems of a system of thermal generating units including transmission line losses is presented along with a clear explanation of modifying generator cost functions during each iteration A zoom feature is applied during the iterative process in order to converge to the economic dispatch solution with low computer time and storage requirements, Dynamic programming including a short-term load forecast is briefly discussed A three-generator example is used to illustrate the method Computer memory and time requirements are presented, along with results for a 15-unit system >

Concepts of undervoltage load shedding for voltage stability

Abstract: Undervoltage load shedding is an economical solution (or partial solution) to the voltage stability challenges facing electric utilities. Simulations for an equivalent system and for large-scale representation of the Puget Sound (Seattle) area of the Pacific northwest led to several concepts for an undervoltage load-shedding program. Application factors such as undervoltage relay settings and time delay are discussed. Pacific northwest utilities are implementing undervoltage load shedding for the 1991-2 winter operation period. >

Analytical investigation of factors influencing power system stabilizers performance

Abstract: Results of simulations, designed to illustrate the influence of power system stabilizers (PSS) on inter-area and local oscillations in interconnected power systems, are reported. It is shown that the PSS location and the voltage characteristics of the system loads are significant factors in the ability of a PSS to increase the damping of interarea oscillations. It is also shown that an interaction between modes in two distinct parts of a power system is possible, due to resonance, and that this might cause distortions in mode shape and participation factors. >

On-line power system security analysis

Abstract: A broad overview of on-line power system security analysis is provided, with the intent of identifying areas needing additional research and development. Current approaches to state estimation are reviewed and areas needing improvement, such as external system modeling, are discussed. On-line contingency selection has become practical, particularly for static security. Additional work is necessary to identify better indices of power system stress to be used in on-line screening filters for both static and dynamic security analysis. Use of optimal power flow schemes to recommend optimal preventive and corrective strategies is presented on a conceptual level. Techniques must be further developed to provide more practical contingency action plans, which include real-world operating considerations and use a reasonably small number of control actions. Techniques must be developed for costing operating variables which are not easily quantified in dollars. Soft or flexible constraints and time variables must be included in the preventive and corrective strategy formulation. Finally, the area of on-line transient and dynamic security analysis is presented. >

Voltage collapse precipitated by the immediate change in stability when generator reactive power limits are encountered

Abstract: When a generator of a heavily loaded electric power system reaches a reactive power limit, the system can become immediately unstable and a dynamic voltage collapse leading to blackout may follow. The statics and dynamics of this mechanism for voltage collapse are studied by example and by the generic theory of saddle node and transcritical bifurcations. It is shown that load power margin calculations can be misleading if the immediate instability phenomenon is neglected. >

Voltage stability conditions considering load characteristics

Abstract: It is shown that when the characteristic of the composite load of a typical utility system is taken into account, large disturbance voltage stability is assured by the existence of the stable equilibrium state of the post-disturbance system, as determined from the standard power flow model. When the load contains static components, stability limits extend considerably. The exact limit for such loads can also be determined from a power flow model, properly modified to reflect the static component of the load. In specific situations, where the bulk of the load is composed of fast response loads, a correct assessment of voltage stability would require comprehensive analyses, employing detailed dynamic models of all system components. The use of the conventional power flow model may lead to considerable error. >

A real time digital simulator for testing relays

Abstract: The structure and performance of a real-time digital simulator (RTDS) for testing relays are described. The RTDS uses parallel processing architecture based on a state-of-the-art digital signal processor (DSP) to run power system simulations in real time with a time step of 50-100 mu s. Physical devices such as relays, energy monitors for MOVs, or power system stabilizers can be fed with the appropriate signals from the RTDS and the output from the physical device can be fed back into the simulation. Examples are given of tests on a commercial distance relay. >

Point of collapse methods applied to AC/DC power systems

Abstract: The authors describe an extension of the point of collapse method developed for studies of AC systems to the determination of saddle-node bifurcations in power systems including high voltage direct current (HVDC) transmission. Bus voltage profiles are illustrated for an AC/DC test system. They significantly differ from the profiles of pure AC systems for typical system models. In particular, voltage dependent current order limits are shown to affect the voltage profiles and the loadability margin of the system. It is also shown that Hopf bifurcations, which are possible in purely AC lossless systems with second-order generator models, become plausible when the dynamics for the HVDC system are included. >

Transient Stability Test Systems for Direct Stability Methods

Abstract: The aim of this paper is to present a standard set of power system data with benchmark results against which direct stability techniques to assess transient stability could be compared and tested. The test systems have been selected to display a wide range of dynamic characteristics to provide a robust test of the efficacy and accuracy of the various analytical techniques to analyze transient stability. Transient stability test system data and benchmark results obtained from two commercially available time domain stability analysis packages are presented in this paper.

Present and future of distributed power systems

Abstract: The current stage of development of distributed power systems is presented. Various DC-bus and AC-bus distributed power system architectures are discussed. System integration issues related to paralleling and cascading of DC/DC converters are explained. Benefits and challenges of distributed power systems in various applications are summarized. >

Parallel processing in power systems computation

Abstract: The availability of parallel processing hardware and software presents an opportunity and a challenge to apply this new computation technology to solve power system problems. The allure of parallel processing is that this technology has the potential to be cost effectively used on computationally intense problems. The objective of this paper is to define the state of the art and identify what the authors see to be the most fertile grounds for future research in parallel processing as applied to power system computation. As always, such projections are risky in a fast changing field, but the authors hope that this paper will be useful to the researchers and practitioners in this growing area.

Benefits of GTO-based compensation systems for electric utility applications

Abstract: The performance of reactive compensation systems based on gate-turnoff thyristors offers potential benefits compared to conventional compensators. The authors describe these benefits in applications involving increased steady-state loadability of heavily stressed systems; in improving the security of systems with heavy motor loads; in improving the transient stability of systems experiencing large power swings; and in adding damping to power swings. These performance benefits lead to the ability to solve specific application problems with less rating and with better stability than with conventional devices. >

Voltage collapse proximity indicator: behaviour and implications

Abstract: With the increased loading and exploitation of the power transmission system, the problem of voltage stability and voltage collapse attracts more and more attention. A voltage collapse can take place in systems or subsystems, and can appear quite abruptly. Continuous monitoring of the system state is therefore required. This paper is concerned with the problem of voltage stability, and investigates a proposed voltage collapse proximity indicator applicable to the load points of a power system, based on the optimal impedance solution of a two-bus system. This indicator is generalised and applied to an actual system. The performance of this new indicator is investigated over both the stable and the unstable regions, as the load at a particular node or the system load increases. Tests show that the indicator can provide useful information at any operating point.

Computing an optimum direction in control space to avoid stable node bifurcation and voltage collapse in electric power systems

Abstract: Given a load power forecast, the sensitivity with respect to controls of a load power margin measuring proximity to voltage collapse is computed. The computation is simple enough to contribute to the practical planning and control of a power system to avoid voltage collapse blackouts. The computation applies to avoiding saddle node bifurcation instability of a general dynamical system. >

High quality electrical power distribution system

Abstract: The system comprises a central module supplying a distribution network, for example formed by a bus, with permanent DC power. Terminal modules, located near the loads, convert the DC power distributed by the distribution network into DC or AC electrical power adapted to the requirements of each load. A communication bus enables data communication between the various modules.

A security based approach to composite power system reliability evaluation

Abstract: An electric power network containing generation and transmission facilities can be divided into several states in terms of the degree to which adequacy and security constraints are satisfied in a reliability evaluation of the composite system. The composite system is classified into different system states for which probabilistic indices are calculated. Both annualized and annual indices using a seven-step load model are presented for two test systems. Selection methods are used to detect problem-creating contingencies. A linear programming model for generation rescheduling and minimization of the amount of load shed is presented. A linear programming model for correcting the voltage problem is presented. >

Effect of superconducting magnetic energy storage on automatic generation control considering governor deadband and boiler dynamics

Abstract: A comprehensive digital computer model of a two-area interconnected power system including the governor deadband nonlinearity, steam reheat constraints, and the boiler dynamics is developed. The improvement in automatic generation control (AGC) with the addition of a small-capacity superconducting magnetic energy storage (SMES) unit is studied. Time-domain simulations were used to study the performance of the power system and control logic. Optimization of gain parameters and the stability studies were carried out by the second method of Lyapunov. Suitable methods for the control of SMES units are described. >

Neural network for estimation of harmonic components in a power system

Abstract: The paper presents a novel approach to the estimation of harmonics in the power system. The proposed method uses the optimisation neural network theory and its implementation in an analogue form. As is proven in the paper, this formulation, and its practical implementation, leads to the correct solution of the problem in real time. The solution presented is inexpensive and suitable for use with the solid state compensating systems to improve the quality of delivered energy.

Back-up uninterruptible power system

Abstract: A back-up uninterruptible power system has a power supply path from input terminals connected to AC power system lines to normally supply power to a load. Upon the occurrence of a line fault, a static switch in the power supply path interrupts the connection between the AC power lines and the load and an inverter is turned on to provide power derived from an auxiliary battery through a transformer to the power supply path to supply AC power to the load. By using the static switch, switching from line connection to backup power can be done quickly, within a half cycle, so that substantially no interruption of the output waveform is observed. The inverter can be operated to provide a commutation pulse to the SCRs in the static switch to commutate an SCR which might otherwise continue conducting after the triggering signals to the gates are cut off and before the inverter supplies the AC power to the load. A relay connected between the input terminals and the static switch is controlled to open relay contacts after the static switch has interrupted the current flow to the load, thereby providing positive electrical isolation of the AC power system from the uninterruptible power system while allowing the mechanical relay contacts to switch only during times of no current. Line fault detection is carried out by creating a digital waveform composed of an average of prior cycles of the AC input waveform, converting the stored waveform to an analog signal, and comparing it with the present input signal in phase lock therewith to detect deviation of the input signal from the reference waveform.

Method of autonomously reducing power consumption in a computer sytem by compiling a history of power consumption

Abstract: Power consumption in an electrical system, particularly a battery powered computer system, may be reduced by a method in which the performance of the system's power consuming assets (e.g., I/O devices, memory, processors, etc.) is monitored during the operation of application programs. The performance metrics (e.g., time on, processing assets, instruction density, etc.) for each of the application programs is stored in a look-up table below the application program software level that is accessible to the basic input/output system and/or disk operating system. The look-up table may be dynamically updated each time an application program is run. The data in the look-up table are used to remove all or part of the power from those assets that require no or less power during operation of a particular application program. The method is transparent to the application programs and may use a terminate and stay resident programs.

Design of a stand alone system with renewable energy sources using trade off methods

Abstract: The authors present an application of recent theoretical advances in multiobjective planning under uncertainty, in the design of a stand-alone system with renewable energy sources. The system under design consists of a wind energy plant, a solar plant, and an storage battery. Time series data on wind, insolation, and load for the site of interest are assumed to be available. The developed design methodology systematically selects the size of the various components of the system so as to give a robust design, i.e. a design that is a reasonable compromise between the conflicting design objectives under most foreseeable conditions. >

The application of network objective functions for actively minimizing the impact of voltage harmonics in power systems

Abstract: The impact of voltage harmonics on a power system can be minimized by using active filters to inject distortion-canceling currents. However, a network objective function must be specified before the optimum filter injection currents can be determined. The authors illustrate the application of a distortion-minimizing procedure with each of the following four network correction strategies, total harmonic voltage distortion, telephone influence factor, motor load-loss function, and single-bus sine wave correction. It is also pointed out that, as with any active device, care must be taken when sitting and controlling an APLC (active power line conditioner) to ensure maximum improvement in network distortion. If a network approach is not used, a poorly located APLC could have an overall negative impact. >