This paper discusses the state of the art in short-term load forecasting (STLF), that is, the prediction of the system load over an interval ranging from one hour to one week. The paper reviews the important role of STLF in the on-line scheduling and security functions of an energy management system (EMS). It then discusses the nature of the load and the different factors influencing its behavior. A detailed classification of the types of load modeling and forecasting techniques is presented. Whenever appropriate, the classification is accompanied by recommendations and by references to the literature which support or expand the discussion. The paper also presents a lengthy discussion of practical aspects for the development and usage of STLF models and packages. The annotated bibliography offers a representative selection of the principal publications in the STLF area.

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Short-term load forecasting

This text/reference presents a comprehensive, up-to-date account of computer relaying in power systems, based in part on the author's extensive experience in the field. Provides background material on current relaying practices, and covers the mathematical foundations for relaying algorithms. Each chapter contains helpful illustrations, examples, and problems.

Computer Relaying for Power Systems

A survey is presented on the currently available numerical techniques for power-system load-flow calculation using the digital computer. The review deals with methods that have received widespread practical application, recent attractive developments, and other methods that have interesting or useful characteristics. The analytical bases, computational requirements, and comparative numerical performances of the methods are discussed. Attention is given to the problems and techniques of adjustments in load-flow solutions, and the suitabilities of various methods for modern applications such as security monitoring and optimal load flow are examined.

Review of load-flow calculation methods

A survey is presented of publications in the fields of optimal power flow and dispatching. It suggests a classification of methods based on the choice of optimization techniques. The survey is summarized in a single flow-chart-type figure, which indicates the relationship between methods, their chronology, and their popularity. This figure is based on a compilation of over three hundred publications. >

A survey of the optimal power flow literature

The application of time series analysis methods to load forecasting is reviewed. It is shown than Box and Jenkins time series models, in particular, are well suited to this application. The logical and organized procedures for model development using the autocorrelation function and the partial autocorrelation function make these models particularly attractive. One of the drawbacks of these models is the inability to accurately represent the nonlinear relationship between load and temperature. A simple procedure for overcoming this difficulty is introduced, and several Box and Jenkins models are compared with a forecasting procedure currently used by a utility company.

The Time Series Approach to Short Term Load Forecasting

This paper presents a new algorithm suitable for calculating impedances from digitized voltages and currents sampled at a relay location. Each input is assumed to be composed of a decaying d.c. component and components of the fundamental and harmonic frequencies. Parameters of a digital filter determined by using the least error squares approach are then used to compute the real and imaginary components of the voltage and current phasors. Impedances as seen from a relay location are then calculated. The proposed algorithm was tested using the fault data recorded at the Regina South switching station of the Saskatchewan Power Corporation; some of the test results are included.

A New Algorithm for Digital Impedance Relays

This paper deals with the problem of alleviating line overloads in a power system by generation rescheduling and load shedding. Mathematical models based on linearized relationships between line currents and state variables, and bus injected powers and state variables are systematically developed to considerthe line overload problem. Two algorithms are described to solve the models in the Newton-Raphson and decoupled load flow programs. The techniques developed can beused to determine the generation rescheduling and load curtailment pattern to alleviate line overloads. The approaches presented in this paper shouldprove useful in system security studies and reliability studies for examining line overload alleviation with minimum computational expense. The analytical results can also serve as an operating guide to the system dispatcher. In a companion paper, the effectiveness of these techniques in alleviating line overloads in several test systems is investigated.

Generation Rescheduling and Load Shedding to Alleviate Line Overloads-Analysis

This paper presents a technique that simulates load and generation changes and outages of transmission lines and transformers. The modification of power injected into the system buses, which would simulate the outage of a transmission element, is calculated using the sensitivity matrix of the basic system state. The real and reactive power flowing in the system elements and voltages at all the system buses are then computed. The proposed technique has been applied to the Saskatchewan Power Corporation system andto the combined SPC and Manitoba Hydro systems. The power flows and bus voltages calculatedby the proposed technique are compared with those obtained from the Newton Raphson load flows.

A Fast Approximate Technique for Outage Studies in Power System Planning and Operation

This paper presents a second order load flow technique based on the Taylor series expansion of a multivariable function. An algorithm for obtaining digital solutions by the proposed approach is described. Six simplified versions of this algorithm are also discussed. The proposed algorithm and its modifications have been tested by obtaining load flow solutions of a five bus system, the 26 bus Saskatchewan Power Corporation transmission network model and the IEEE 14 bus, 30 bus, 57 bus and 118 bus test systems. The effectiveness of these algorithms is compared with the performance of the Newton Raphson approach and some of the results from these studies are presented.

A second order load flow technique

A basic mathematical model to describe the problem of line overload alleviation has been developed in a companion paper. Algorithms for solving the modeland suitable for incorporation in the Newton-Raphson and decoupled load flow programs are also described. In this paper, the effectiveness of the proposed techniques is examined using a six bus model of the Saskatchewan Power Corporation system, and the IEEE 14, 30 and 57-bus test systems. A single pass of generation rescheduling and load shedding has been found to be adequate for alleviating line overloads in almost all the systems studied. Computational time of each pass of these techniques is approximately 1/2 to 3/4th of the computational time required for the initial load flow. Storage requirements are slightly more than the requirements of the load flow technique used. The proposed techniques identify and determine the existence of a physically realizable operating condition to alleviate the line overload condition. The techniques appear attractive for security and reliability studies, and for operational planning

M.S. Sachdev

Papers

A New Algorithm for Digital Impedance Relays

Generation Rescheduling and Load Shedding to Alleviate Line Overloads-Analysis

A Fast Approximate Technique for Outage Studies in Power System Planning and Operation

A second order load flow technique

Generation Rescheduling and Load Shedding to Alleviate Line Overloads-System Studies