Showing papers on "Electric power system published in 1981"

Applying Power System Stabilizers Part I: General Concepts

Abstract: The general concepts associated with applying power system stabilizers utilizing shaft speed, ac bus frequency, and electrical power inputs are developed in this first part of a three-part paper. This lays the foundation for discussion of the tuning concepts and practical aspects of stabilizer application in Parts II and III. The characteristics of the "plant" through which the power system stabilizer must operate are discussed and the implications upon stabilizer tuning and performance are noted. A general approach for analyzing stabilizers utilizing an arbitrary input signal is described and applied to the frequency and electrical power input signals.

A Structure Preserving Model for Power System Stability Analysis

Abstract: A new model for the study of power system stability via Lyapunov functions is proposed. The key feature of the model is an assumption of frequency-dependent load power, rather than the usual impedance loads which are subsequently absorbed into a reduced network. The original network topology is explicitly represented. This approach has the important advantage of rigorously accounting for real power loads in the Lyapunov functions. This compares favorably with existing methods involving approximations to allow for the significant transfer conductances in reduced network models. The preservation of network topology can be exploited in stability analysis, with the concepts of critical and vulnerable cutsets playing central roles in dynamic and transient stability evaluation respectively. Of fundamental importance is the feature that the Lyapunov functions give a true representation of the spatial distribution of stored energy in the system

A Load Flow Calculation Method for III-Conditioned Power Systems

Abstract: In this paper, a load flow calculation method for ill-conditioned power systems is developed. The proposed method is very simple, has no mathematical approximations, and requires almost no additional storage and computation time when incorporated into the normal Newton-Raphson program. Using the method, the load flow solution never diverges, and also the existence of the solution from the initial estimate can be easily judged. To examine the effectivenesst two ill-conditioned power systems, i.e., 11 and 43 bus systems are studied by the method, and it is found that the solution does not exist for the 11 bus system though the given data are said to be operational, and also that the solution does exist for the 43 bus system but does not converge with the single precision due to the precision deficiency of the computer.

Excitation System Models for Power System Stability Studies

Abstract: Excitation system models suitable for use in large scale system stability studies are presented in this paper. With these models, most of the excitation systems currently in widespread use on large, system connected generators in North America can be represented.

Generalized Generation Distribution Factors for Power System Security Evaluations

Abstract: A set of Generalized Generation Distribution Factors (GGDF's) is developed to replace the conventional Generation Shift Distribution Factors (GSDF's). This model relates the line flows with generations for a given network configuration. Being in an integral form, new flows on lines can be obtained directly without running load flows when total system generation changes. Conforming load change is also demonstrated. These new factors are especially suitable for constraint formulation in mathematical programning, such as optimal generation dispatch with security contingencies considered

A Two-Level Static State Estimator for Electric Power Systems

Abstract: A hierarchical concept is used to solve the static state estimation problem for large-scale composite power systems. The solution is obtained by performing a two-level calculation. In the lower level, a conventional state estimation is carried out simultaneously for all subsystems. The coordination of these local estimations is realized in the upper level. One of the main contributions of the paper lies in the construction of an appropriate second-level algorithm. Its suitability and also the main features of the overall procedure are then explored and illustrated on the basis of the Belgian 380-220-150 kV transmission network. Comparisons with the standard "integrated" state estimation are also performed.

Probabilistic Assessment of Transient Stability in a Practical Multimachine System

Abstract: The application of probabilistic techniques in the quantitative evaluation of power system reliability is steadily increasing. Probability methods are being used extensively in the assessment of static adequacy. Their application to the evaluation of transient or dynamic phenomena has not yet, however, been widely utilized. The probabilistic nature of the transient stability problem and the inclusion of the probabilities associated with the initiating factors such as the type, location and clearance of faults in the analysis of a simple single machine-infinite bus system has been demonstrated in a recent paper.1 The present paper addresses the problem of transient stability analysis in a practical multimachine system from a probabilistic view-point. The basic concepts developed in Reference ! are applied to a simplified 33 bus model based on the Saskatchewan Power Corporation (SPC) system, to demonstrate the technique of considering the probabilities associated with the occurrence and clearance of faults. Transient stability indices for each line, for different types of faults and a single stability index for any fault are obtained. A single stability index for the overall system is evaluated for different fault types and amy fault using actual system outage statistics. The effect of fault clearing and reclosing times on the system stability is investigated for the most critical line in the system.

Automatic generation control of interconnected power systems using variable-structure controllers

Abstract: The paper presents a new technique for the automatic generation control of interconnected power systems. The proposed technique is devoloped for designing the controllers, using the theory of variable-structure systems. A special feature of the variable-structure controllers is that they can greatly improve the transient performance of the system, while keeping the steady-state error at zero. In addition, when the variable-structure system is operated in the so-called sliding mode, the system response becomes insensitive to changes in the plant parameters. Results, obtained from a comparison study by digital simulations, show that variable-structure controllers can offer the control designer new possibilities for improving the quality of control for automatic generation control of interconnected power systems

Transient Stability of a Multi-Machine Power System Part I: Investigation of System Trajectories

Abstract: Direct methods of transient stability analysis of a multi-machine power system, using a function describing the system's transient energy, are discussed. By examining the trajectory of the disturbed system, the following fundamental questions are dealt with: the concept of a controlling unstable equilibrium point (u.e.p.), the manner in which some generators tend to lose synchronism, and identifying-the energy directly responsible for system separation. Resolving these issues will substantially improve transient stability analysis by a direct method.

A Fundamental Concept for High Speed Relaying

Abstract: This paper describes a fundamental approach for detecting the direction to a power system fault within the first milliseconds following the fault inception. The method is based on a combined evaluation of the voltage and current deviations generated by the fault occurrence. Design considerations and test results based on numerical simulations and on a transient network analyser are presented. The method solves several problems occurring in conventional relaying and is suitable for use in ultra high speed protection systems which employ a fast telecommunication channel between the ends of the protected network

Power System Stabilizers for Thermal Units: Analytical Techniques and On-Site Validation

Abstract: This paper reviews experience in the control design and tuning of power system stabilizers for thermal generating units. Special problems encountered in obtaining satisfactory performance at a particular generating station due to specific generator characteristics is highlighted. Analytical techniques used for establishing suitable stabilizer settings are described and their effectiveness in duplicating field measurements is demonstrated

A Robust Numerical Technique for Power System State Estimation

Abstract: It is well known in numerical analysis that the least-squares solution via the conventional Gauss' normal equation used in power system state estimation is prone to ill-conditioning problems by its own nature. Under unfavorable circumstances, this may be detrimental to the method's performance. This paper utilizes a numerically more reliable algorithm, known as Golub's method, to solve the least-squares problem as formulated in power system state estimation. Its improved numerical properties stem from the use of orthogonal transformations, which are perfectly conditioned. Details of the algorithm and its implementation are given, as well as results of its application to three different networks, including an actual 121-bus power system.

Load-Flow Studies in the Presence of Geomagnetically-Induced Currents

Abstract: Large transient fluctuations in the earth's magnetic field can produce quasi-dc currents in electric power systems. These geomagnetically-induced currents (GIC's) cause half-cycle saturation in power transformers resulting in increased transformer var requirements. This paper discusses the phenomena by which GIC's are produced in power systems, the system and transformer modeling necessary for representing the effects, and the results of load-flow studies made with GIC present in a large interconnected power system in the northern United States and Canada. Results of the studies are compared with data recorded during a geomagnetic storm.

System Restoration Plan Development for a Metropolitan Electric System

Abstract: The extended duration of recent major power system disturbances have indicated the need for development of system restoration plans (SRP), which would minimize the time required for restoration of service. This paper presents an efficient approach to SRP, from a complete collapse under peak-and light-load conditions, developed at Potomac Electric Power Company (PEPCo). The method is based on: (a) the combined effort of operating personnel and system analysts, (b) the access to data available from the on-line computer facilities, and (c) the use of an interactive load flow program. The SRP development procedure and the results described in this paper are of general interest in that they can be adopted and applied to the other electric systems.

Improvement of Transmission Capacity by Thyristor Controlled Reactive Power

Abstract: This paper shows that thyristor controlled reactive power can be used as an efficient tool to improve damping of large power systems. If thyristor switched capacitors are used there will also be positive contribution to transient stability. Examples of power systems where damping is the critical factor have been investigated. The use of supplementary control of generators and control of reactive power has been studied. Basic configurations of thyristor switched capacitors and thyristor controlled reactors are presented.

A Power System Stabilixer Using Speed and Electrical Power Inputs-Design and Field Experience

Abstract: Further development of a power system stabilizer based on measurement of unit accelerating power, where the mechanical power component is derived from speed and electrical power signals, is described. Techniques to facilitate the implementation of such a controller are discussed and the ability of this type of stabilizer to remove some of the limitations inherent in other stabilizer designs is demonstrated. The design, testing and commissioning of this stabilizers is covered and field experience with it on large fossil-fired and nuclear units is documented.

Computer-aided dispatch for electric power systems

Abstract: This paper provides a review of the subject of electric power dispatching. In Section I we show where dispatching fits into the hierarchy of power system operating and planning problems. Section II provides an overview of the issues, concerns and practices of dispatching. Sections III-V are devoted to the algorithmic aspects of dispatching. Finally, in Section VI we highlight the conclusions reached in the proceeding sections and identify a number of research needs.

Discrete Convolution in Power System Reliability

Abstract: This paper describes a general method for convolving discrete distributions using Fast Fourier Transforms. It can be used in evaluating reliability of any system involving discrete or discretised convolution. It has been used in power system studies to deduce capacity-outage probability tables and to solve probabilistic load flows. These studies have shown it to be much less time-consuming and more efficient than the conventional direct methods. The method is used in the paper to evaluate the loss of load probability of a generating system in order to demonstrate the method's application and inherent merits.

Transient Stability Analysis of Multi-Machine AC/DC Power Systems Via Energy-Function Method

Abstract: In this paper, the direct method of stability analysis using energy functions is applied for single and multi-machine AC/DC power systems. The system loads including the terminal characteristics of the DC link are represented as constant current type loads, and their effects on the generators at the internal nodes are obtained as additional bus power injections using the method of distribution factors, thus avoiding transfer conductance terms. Using the center of angle formulation, a modified form of the energy-function method is used for the swing equations and the DC link dynamical equations to compute the critical clearing time for a given fault. Numerical results of critical clearing time for a single and multi-machine system using the energy-function method agree well with the step-by-step method.

Hybrid D.C. power controller

Abstract: A hybrid D.C. power controller of the relay/circuit breaker type that uses a hybrid arrangement of hard contacts (4) and power FET's (18, 20) in cooperative functional combination as the arc quenching means for 270 volt D.C. power systems in low atmospheric pressure environments such as at 80,000 feet altitude in aircraft applications. Also, the relay is provided with arc horns (44c, 48b, 48c, 46c), magnetic field amplifiers (60, 62) looped stationary contacts (44, 46), arc splitters (64, 66), and gas ablating insulating members (60b, 62b, 72, 74, 64b, 66) to enable the relay to interrupt the power circuit if necessary without the help of the power FET's. The power FET's are controlled in both opening and closing the power circuit to afford arcless contact operation in normal load make-break situations. Current and voltage sensing (28, 32) and sampling (CS, VS) circuits determine when to turn the power FET's on after contact arcing has provided the required values. The power contacts (4) can be closed and opened by manual switch (TS) control and opened automatically under overload or short circuit conditions by instantaneous trip detector (ITD) control. Isolation contacts (2) in the power circuit are controlled by delay means (MMV4, MMV8) to close last and open first with respect to the power contacts.

Measurement and Modeling of Pacific AC Intertie Response to Random Load Switching

Abstract: In recent years spectral analysis of system response to random load changes has become a standard engineering tool at the Bonneville Power Administration. Analysis of random fluctuations in power on the Pacific AC Intertie has provided information about the influence of system operating conditions upon the effectiveness of Pacific HVDC Intertie modulation, and about dynamic behavior of the western power system generally. This technique has also been used to estimate the required size for a superconducting electromagnetic storage device which will provide backup to HVDC Modulation, and has detected a major system mode 6 months before it was first observed in a transient disturbance

Analysis of Grounding Systems

Abstract: A general methodology for the analysis of electrical grounding systems is presented. Earth is represented as a two layer semiinfinite region. An equivalent circuit model of the earth embedded electrodes and conductive soil is developed via numerical lution of Laplace equations. The equivalent circuit model, together with the electric power system network, represents a large scale network which is solved via the modified nodal analysis method. The procedure enables accurate analysis of complicated grounding systems and computation of touch, step and transfer voltages. Effects of tower footing resistance, counterpoised wires, types of system faults (phase to ground, line to line, etc.) can be analyzed. Practical grounding systems can be easily analyzed because model reduction techniques can be incorporated in the analysis method. The methodology is demonstrated with the study of a nontrivial grounding system analysis problem.

Equivalents for Security Analysis of Power Systems

Abstract: This paper describes a procedure to generate an adaptive Dimo equivalent. Fictitious nodes aggregate buses belonging to the same class of REI equivalence. As a result, an equivalent that preserves the physical characteristics of the power system is obtained. The reduced model is updated by using a realtime calibrating procedure. The resulting adaptive Dimo equivalent is suitable for subsequent use to reliably perform the security analysis function in a multi-area power system environment. Shunts are found to be of fundamental importance, and their treatment in network analysis algorithms is assessed. Numerical results are also discussed in this paper.

On The Formulation of Power Distribution Factors for Linear Load Flow Methods

Abstract: Fast linear load flows used in contingency analysis, interchange studies and many optimization schemes often utilize power distribution factors. The success of many of these methods has hinged greatly on the use of the Z matrix reference to swing or an arbitrary ground tie. This paper furnishes a mathematical basis for these heuristic methods.

Load Characteristics of Synchronous Generators by the Finite-Element Method

Abstract: In developing synchronous machine models for power system stability studies, it is essential that the magnetic saturation of the machine is adequately represented and that its internal state on load operation prior to the disturbance is accurately predicted In this paper an iterative method employing the finite-element analysis techniqueis presented for determining the load operating point, which is defined by several quantities such as the field current, the d- and q-axis components of the stator current, and the load angle The procedure developedin the-analysis is applied to a 50-MVA turbine-generator for determining the no-load and rated load operation and the evaluation of steady- state reactances

Transient Stability of a Multi-Machine Power System. Part II: Critical Transient Energy

Abstract: This paper deals with transient stability analysis of a multi-machine power system using direct methods based on the transient energy of the system when subjected to a large disturbance. The component of the transient energy that does not contribute to system separation is identified, and is corrected for in the computation of the critical transient energy at clearing. The technique is validated by computing critical clearing times for two test systems and comparing the results with those obtained by time solutions.

1981 Analysis and Control of Harmonic Current in Systems with Static Power Converters

Abstract: In the last 50 or 60 years, the development of rectifier and semiconductor technology has led to new products and applications for drives in all industries. These semiconductor converters produce harmonics in the ac power system. With the widespread application of these economical power supplies, problems are arising that should be approached from a logical standpoint and preventive measures taken. The theory of the problem and the solution to it is discussed.

Simulation-Based Load Synthesis Methodology for Evaluating Load-Management Programs

Abstract: A physically-based methodology for synthesizing the hourly residential heating, ventilation, and air-conditioning (HVAC) load was developed and tested against the data from a utility. The method, which is coded in FORTRAN IV, is currently operational. It involves a simulation model and a newly-developed load-diversification? model. The simulation model captures the thermodynamic principles of building structures. The load-diversification model estimates the diversified load from a limited number of load shapes of individual households. Because of the physically-based nature of the method, it could be used to analyze the resulting changes in load shapes due to load- management technologies (e.g. cycling of air-conditioners, water storage heating and cooling system, ceramic brick storage system). The load-synthesis method also provides an efficient procedure to analyze the effect on the system load due to different penetrations of load-management technologies. Resulting load shapes could be led into a generation (G) expansion model and a transmission and distribution (T&D) model to assess the impacts on the utility's planning. This methodology, which has been validated against the metered data of a midwestern utility, is a cost- effective tool with predictive capability for evaluating load-management programs.

Large Scale Induction Generators for Power Systems

Abstract: Induction generators coupled with controlled static var sources can replace the function of synchronous alternators. They can operate in systems composed exclusively of induction generators or in mixed systems of induction and synchronous sources.