Showing papers on "Electric power system published in 1994"

Power System Stability and Control

Abstract: Part I: Characteristics of Modern Power Systems. Introduction to the Power System Stability Problem. Part II: Synchronous Machine Theory and Modelling. Synchronous Machine Parameters. Synchronous Machine Representation in Stability Studies. AC Transmission. Power System Loads. Excitation in Stability Studies. Prime Mover and Energy Supply Systems. High-Voltage Direct-Current Transmission. Control of Active Power and Reactive Power. Part III: Small Signal Stability. Transient Stability. Voltage Stability. Subsynchronous Machine Representation in Stability Studies. AC Transmission. Power System Loads. Excitation in Stability Studies. Prime Mover and Energy Supply Systems, High-Voltage Direct-Current Transmission. Control of Active Power and Reactive Power. Part III: Small Signal Stability. Transient Stability. Voltage Stability. Subsynchronous Oscillations. Mid-Term and Long-Term Stability. Methods of Improving System Stability.

Power System Analysis

Abstract: 1 Basic Concepts 2 Transformers 3 The Synchronous Machine 4 Series Impedance of Transmission Lines 5 Capacitance of Transmission Lines 6 Current and Voltage Relations on a Transmission Line 7 The Admittance Model and Network Calculations 8 The Impedance Model and Network Calculations 9 Power Flow Solutions 10 Symmetrical Faults 11 Symmetrical Components and Sequence Networks 12 Unsymmetrical Faults 13 Economic Operation of Power Systems 14 Zbus Methods in Contingency Analysis 15 State Estimation of Power Systems 16 Power System Stability

Reliability Assessment of Electric Power Systems Using Monte Carlo Methods

Abstract: Introduction. Basic Concepts of Power System Reliability Evaluation. Elements of Monte Carlo Methods. Generating System Adequacy Assessment. Composite System Adequacy Assessment. Distribution System and Station Adequacy Assessment. Reliability Cost/Worth Assessment. Appendixes. Index.

Trends in active power line conditioners

Abstract: Active power line conditioners, which are classified into shunt and series ones, have been studied with the focus on their practical installation in industrial power systems. In 1986, a combined system of a shunt active conditioner of rating 900 kVA and a shunt passive filter of rating 6600 kVA was practically installed to suppress the harmonics produced by a large capacity cycloconverter for steel mill drives. More than one hundred shunt active conditioners have been operating properly in Japan. The largest one is 20 MVA, which was developed for flicker compensation for an arc furnace with the help of a shunt passive filter of 20 MVA. In this paper, the term of "active power line conditioners" is used instead of that of "active power filters" because active power line conditioners would cover a wider sense than active power filters. The primary intent of this paper is to present trends in active power line conditioners using PWM inverters, paying attention to practical applications. >

Integration of Distributed Generation in the Power System

Abstract: Distributed Generation (DG) reduces the amount of energy lost in transmitting electricity because the electricity is generated very near where it is used. This book introduces systematic and transparent methods for quantifying the impact of DG on the power grid. It emphasizes systematic and transparent calculation methods, allowing for a quantification of the amount of DG that can be integrated at a certain location of the grid or in the grid as a whole. It also provides an overview of the different energy sources, with emphasis on wind power, solar power and combined heat and power in the power grid.

Dynamic compensation of AC transmission lines by solid-state synchronous voltage sources

Abstract: This paper describes a novel approach in which solid-state synchronous voltage sources are employed for the dynamic compensation and real time control of power flow in transmission systems. The synchronous voltage source is implemented by a multi-pulse inverter using gate turn-off (GTO) thyristors. It is capable of generating internally the reactive power necessary for network compensation, and is also able to interface with an appropriate energy storage device to negotiate real power exchange with the AC system. The paper develops a comprehensive treatment of power flow control using solid-state synchronous voltage sources for shunt compensation, series and phase angle control. It also describes the unique unified power flow controller that is able to control concurrently or selectively all three network parameters (voltage, impedance, transmission angle) determining power transmission. Comparison of the synchronous voltage source approach with the more conventional compensation method of employing thyristor-switched capacitors and reactors shows its superior performance (including the unmatched capability of using both reactive and real power compensation to counteract dynamic disturbances), uniform applicability, smaller physical size, and potentially lower overall cost. >

A bottom-up approach to residential load modeling

Abstract: A model of electric residential end-use is proposed for establishing the load diagram of an area by a process of synthesis. The model follows a "bottom-up" approach, allowing construction of the relative load shape of the area, starting from knowledge of its most relevant socioeconomic and demographic characteristics, unitary energy consumption and the load profiles of individual household appliances. Several probability functions have been introduced in order to cover the close relationship existing between the demand of residential customers and the psychological and behavioral factors typical of the household; the model makes frequent use of the latter through a Monte Carlo extraction process. The model has been applied for the simulation of a residential area where field measurements of power demand had been made at 15-minute intervals and a combined mail survey had been conducted to investigate household energy usage. The paper reports the results of a comparison between recorded and predicted load profiles. >

A summary of environmental/economic dispatch algorithms

Abstract: Traditionally electric power systems are operated in such a way that the total fuel cost is minimized regardless of emissions produced. With increased requirements for environmental protection, alternative strategies are required. This paper presents a summary of algorithms of environmental-economic dispatch in electric power systems since 1970. The algorithms attempt to reduce the production of atmospheric emissions such as NO/sub x/ and SO/sub x/ caused by the operation of fossil-fueled thermal generation. Such reduction is achieved by including emissions either as a constraint or as a weighted function the objective of the overall dispatching problem. >

Modelling and identification of nonlinear dynamic loads in power systems

Abstract: This paper describes an approach for experimental determination of aggregate dynamic loads in power systems. The work is motivated by the importance of accurate load modeling in voltage stability analysis. The models can be expressed in general as nonlinear differential equations or equivalently realised in block diagram form as interconnections of nonlinear (memoryless) functions and linear dynamic blocks. These components are parameterized by load indexes and time constants. Experimental results from tests in Southern Sweden on the identification of these parameters are described. >

Modern Power System Planning

Abstract: This work provides a comprehensive approach to the planning and reliability calculations for the expansion of power generation systems, transmission networks and plant maintenance scheduling The mathematical and statistical theory required by the reader is introduced and explained by means of examples at the beginning of the text and particular emphasis is given to operational research and reliability calculations This should provide the reader with a means to become familiarized with the mathematical techniques before applications are introduced Detailed case studies based on practical power engineering examples are presented in each chapter The work should be of interest to both students and practising engineers The techniques discussed in the text are particularly appropriate for the power utility structures being set up throughout western economies

A BCU method for direct analysis of power system transient stability

Abstract: A boundary of stability region based controlling unstable equilibrium point method (BCU method) for direct analysis of power system transient stability is presented. Features distinguishing the BCU method from the existing direct methods are that it consistently finds the exact controlling unstable equilibrium point (UEP) relative to a fault-on trajectory and that it has a sound theoretical basis. Moreover, the BCU method appears to be fast. This method is based on the relationship between the boundary of stability region of a power system and that of a reduced system. The BCU method finds the controlling UEP of the original system via a reduced system whose controlling UEP is easier and cheaper to compute. Effective numerical schemes to speed up the presented method are also proposed. This method has been tested on several power systems with very promising results. Simulation results on a 50 generator, 145 bus system are presented along with a comparison between the results obtained using the BCU method and another existing method. >

A comparison of high power DC-to-DC soft-switched converter topologies

Abstract: Many industrial and military applications are arising that require high power DC-DC conversion. These applications include shipboard, spaceborne, and transportation power systems. By employing new high voltage, high power IGBTs, along with modern soft-switching techniques, the switching frequency can be significantly higher than obtained using GTO devices, which in turn can lead to smaller, lighter weight, and potentially more cost effective equipment. The purpose of this paper is to compare the properties of several soft-switching converter topologies when used to achieve DC-DC conversion at high power and high voltage levels. As an example, a 100 kW transformer isolated converter with 700-1400 V DC input is designed with an estimated weight in the 200 pound range and an energy efficiency of 95%. >

Static var compensator models for power flow and dynamic performance simulation

Abstract: The static var compensator is now mature technology that is widely used for transmission applications. Electric utility industry standardization of basic models is needed, and is recommended in this paper. Description and model requirements for more detailed representations, including supplementary function modules, are included. In addition to transient stability program modeling, requirements for power flow and longer-term dynamics programs are given.

Decision trees for real-time transient stability prediction

Abstract: The ability to rapidly acquire synchronized phasor measurements from around the system opens up new possibilities for power system protection and control. This paper demonstrates how decision trees can be constructed offline and then utilized online for predicting transient stability in real-time. Primary features of the method include building a single tree for all fault locations, using a short window of realistic-precision post-fault phasor measurements for the prediction, and testing robustness to variations in the operating point. Several candidate decision trees are tested on 40,800 faults from 50 randomly generated operating points on the New England 39 bus test system. >

Voltage stability analysis using generic dynamic load models

Abstract: This paper investigates the dynamic nature of voltage stability. Using a generic load model representing the dynamic behaviour of aggregate loads, the mechanism of voltage collapse is revealed by examining the interaction of load dynamics with the supply network. The relationship between power flow based static techniques and time simulation based dynamic techniques for voltage stability analysis is established. Guidelines for voltage stability control are developed. >

Computation of closest bifurcations in power systems

Abstract: Voltage collapse and blackout can occur in an electric power system when load powers vary so that the system loses stability in a saddle node bifurcation. This paper computes load powers at which bifurcation occurs and which are locally closest to given operating load powers. The distance in load power parameter space to this locally closest bifurcation is an index of voltage collapse and a minimum load power margin. The computations are illustrated for several power systems. Monte-Carlo optimization techniques are applied to obtain multiple minimum load power margins. The use of load power margin sensitivities to select system controls is discussed. >

A power flow measure for unsolvable cases

Abstract: As power systems become more heavily loaded, there will be an increase in the number of situations where the power flow equations have no real solution, particularly in contingency analysis and planning applications. Since these cases can represent the most severe threats to viable system operation, it is important that a computationally efficient technique be developed to both quantify the degree of unsolvability, and to provide optimal recommendations of the parameters to change to return to a solvable solution. Such an algorithm is developed in the paper. The distance in parameter space between the desired operating point and the closest solvable operating point provides a measure of the degree of unsolvability, with the difference between these two points providing the optimal system parameter changes. The algorithm is based upon a Newton-Raphson power flow algorithm, which provides both computational efficiency and compatibility with existing security analysis techniques. The method is demonstrated on systems of up to 118 buses. >

Robust Optimization for Power Systems Capacity Expansion under Uncertainty

Abstract: We develop a robust optimization model for planning power system capacity expansion in the face of uncertain power demand. The model generates capacity expansion plans that are both solution and model robust. That is, the optimal solution from the model is ‘almost’ optimal for any realization of the demand scenarios (i.e. solution robustness). Furthermore, the optimal solution has reduced excess capacity for any realization of the scenarios (i.e. model robustness). Experience with a characteristic test problem illustrates not only the unavoidable trade-offs between solution and model robustness, but also the effectiveness of the model in controlling the sensitivity of its solution to the uncertain input data. The experiments also illustrate the differences of robust optimization from the classical stochastic programming formulation.

Economic emission load dispatch with line flow constraints using a classical technique

Abstract: An attempt is made to explore the feasibility of developing an approach to solve the power system economic emission load dispatch (EELD) problem with line flow constraints using a classical technique based on co-ordination equations. The inability of the classical technique to handle the line flow constraints so far is circumvented innovatively by expressing the line flows in terms of active power generations through distribution factors. These distribution factors are elegantly developed from existing load flow information using a perturbation technique. The proposed model based on the classical technique for EELD is tested on IEEE 14- and 30-bus test systems and the results are compared with those obtained by quadratic programming, the Hessian method, the Ricochet gradient method and the linear programming method.

Method for modeling a physical system of elements using a relational database

Abstract: An information model based on a physical system, such as the physical equipment in a power system. An object-oriented information model provides a generic power system model that may be applied to any of several specific applications. In the invention, physical pieces of equipment are represented as objects with attributes that can be verified (primary data) and relations including connectivity, grouping, and location. The model handles all known configurations of power systems and is extensible to new configurations. Attribute input is supported from primary sources and is used to calculate data required by applications programs. A window-based graphical user interface uniquely simplifies operation of the database. Thus, the present invention provides a single, easy to use, source for all proprietary application databases at a utility.

Damping of power system oscillations by use of controllable components

Abstract: This paper deals with damping of power system electromechanical oscillations using controllable series compensators (series capacitors and phase shifters) and controllable shunt capacitors. The study is based on investigation of the eigenvalues of a simple linearized power system model. The controllable series components are located on the transmission line connecting two areas and the controllable shunt capacitor is located close to a load. It is shown that the level of transmission line loading, load characteristics and inertia of the two areas influence the damping achieved by the controllable components to different degrees. The contributions of the controllable series components to the enhancement of power system damping for the same rating of the controllable components are compared. Numerical examples are provided to verify the theoretical findings. The purpose of this paper is to provide an insight and understandings in the basic characteristics of the damping effects of the studied devices. This insight is obtained by study of a simple power system that exhibits power oscillations. The understandings and findings can facilitate the analysis of realistic, and more complex power systems. >

Ramp-rate limits in unit commitment and economic dispatch incorporating rotor fatigue effect

Abstract: In this study, a rigorous mathematical method is proposed for dealing with the ramp-rate limits in unit commitment and the rotor fatigue effect in economic dispatch An iterative procedure is employed to coordinate the unit commitment and the power dispatch for obtaining an economical solution within a reasonable time The Lagrangian relaxation method is used to generate the unit commitment schedule with relaxed power balance constraints A network model is adopted to represent the dynamic process of operating a unit over the entire study time span, as the required unit commitment schedule can be achieved by searching for the shortest path in the network In order to find the global optimal solution for the economic dispatch problem within personal computer resources, a piecewise linear model is used for thermal units Furthermore, linear programming is used in optimizing the benefits of ramping the units, with low operating cost against the cost of shortening the service life of the turbine rotor In this regard, linear programming is used to dispatch the power generation among committed units by considering a ramping penalty for the fatigue effect in rotor shafts, while preserving the operational constraints of the system as well as the generating units >

Bifurcations, chaos, and crises in voltage collapse of a model power system

Abstract: Bifurcations occurring in power system models exhibiting voltage collapse have been the subject of several recent studies. Although such models have been shown to admit a variety of bifurcation phenomena, the view that voltage collapse is triggered by possibly the simplest of these, namely by the (static) saddle node bifurcation of the nominal equilibrium, has been the dominant one. The authors have recently shown that voltage collapse can occur "prior" to the saddle node bifurcation. In the present paper, a new dynamical mechanism for voltage collapse is determined: the boundary crisis of a strange attractor or synonymously a chaotic blue sky bifurcation. This determination is reached for an example power system model akin to one studied in several recent papers. More generally, blue sky bifurcations (not necessarily chaotic) are identified as important mechanisms deserving further consideration in the study of voltage collapse. >

A Canadian customer survey to assess power system reliability worth

Abstract: A common approach used in quantifying the worth or benefit of electric service reliability is to estimate the customer costs (monetary losses) associated with power interruptions. Customer surveys are often used to determine interruption costs. The IEEE Power Systems Research Group has conducted surveys of Canadian electric utility customers in the residential, commercial and industrial sectors. These surveys were sponsored by the Natural Sciences and Engineering Research Council and seven participating utilities. This paper presents the overall results of these surveys with emphasis on the cost results. >

Harmonics: the effects on power quality and transformers

Abstract: The use of nonlinear devices such as rectifiers or converters, power supplies and other devices utilizing solid-state switching has increased in industry during. Unfortunately, the effect of harmonic distortion has also increased on the industrial power system as a direct result. This paper is based upon actual harmonic studies on 480 V, three-phase, variable speed drives and the effects of harmonics on transformers in those systems. It also includes the recommendations for correction of the problems resulting from harmonic distortion. >

Dynamics models for combines cycle plants in power system studies

Abstract: This paper is the third of a series of papers prepared by the Working Group on Prime Mover and Energy Supply Models for System Dynamic Performance Studies. It describes various aspects of combined cycles made up of gas turbine, waste heat recovery boiler and steam turbine and develops models designed to simulate the response of the combined cycle plant for use in system dynamic performance studies

Power system harmonic state estimation

Abstract: A power system state estimation based on (a) multiphase model, (b) voltage and current waveform measurements, (c) synchronized measurements and (d) multifrequency model (i.e. the approach accounts for waveform distortion or harmonics) is formulated. The paper focuses on the following: (a) modeling, (b) implementation, (c) observability and (d) performance. Sensitivity analysis is used to show how transmission line modeling and measurement schemes affect the performance of harmonic state estimation. The overall performance of the system is described in terms of confidence level versus error. These concepts are illustrated with simple systems. The overall harmonic measurement system is scheduled for installation and field evaluation on the NYPA/New York Power Pool transmission system by the end of 1993. >

The influence of motor re-acceleration on voltage sags

Abstract: The assumption that a voltage sag is rectangular is not correct in a power system with large induction motor loads. The motors decelerate during the short circuit. After fault-clearing, they will accelerate again, drawing a high reactive current from the supply, causing a prolonged postfault voltage sag. This is aggravated by the removal of branches by the protection. The resulting shape of some voltage sags in an example power system is shown and discussed. For the example power system, a stochastic voltage sag table is determined. This table gives the expected number of sags of different depth and duration. The influence of faster protection and of reduced transformer impedance on the table is presented. A simple motor model is implemented in a method for including interruptions due to voltage sags in the reliability analysis of power systems. This model is presented briefly and used to show the influence of motor parameters on the number of sags that lead to an interruption of plant operation. >