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Showing papers on "Electric power system published in 1987"


Journal ArticleDOI
01 Dec 1987
TL;DR: This paper reviews present formulations and methods, and tries to point out areas of difficulty that constitute the main challenges for successful practical on-line implementations over the coming years.
Abstract: An operationally "secure" power system is one with low probability of blackout or equipment damage. The power system control processes needed to maintain a designated security level at minimum operating cost are extremely complicated. They increasingly depend upon on-line computer security analysis and optimization. This on-line technology is still relatively new, with enormous further potential. Since security and optimality are normally conflicting requirements of power system control, it is inappropriate to treat them separately. Therefore, they are slowly becoming coalesced into a unified hierarchical mathematical problem formulation: one that is, however, far too complex to afford anything but an approximate, near-optimal solution. The practical validity of this unifying trend relies on being able to incorporate all significant security constraints within the process. The main two current computational tools in this field are contingency analysis and special operations-oriented versions of optimal power flow (OPF). Contingency analysis identifies potential emergencies through extensive "what if?." simulations on the power system network. OPF is a major extension to the conventional dispatch calculation. It can respect system static security limits, and can schedule reactive as well as active power. Moreover, the advanced versions of OPF include or interface with contingency analysis. This paper reviews present formulations and methods, and tries to point out areas of difficulty that constitute the main challenges for successful practical on-line implementations over the coming years.

533 citations



Journal ArticleDOI
01 Dec 1987
TL;DR: The various steps in constructing the model from the real-time measurements are described, including the determination of the network topology, the estimation of thenetwork state, and the approximate modeling of the unobservable (external) network.
Abstract: The use of large digital computers in control centers has made it possible to track the changing conditions in the power system with a mathematical model in the computer. This real-time model can be used to assess the security of the present system as well as to check out possible control strategies. In this paper the various steps in constructing the model from the real-time measurements are described. These steps include the determination of the network topology, the estimation of the network state, and the approximate modeling of the unobservable (external) network. This paper also discusses the checks for observability and bad measurements, and the calculation of bus load forecast factors and generator penalty factors.

183 citations


Journal ArticleDOI
TL;DR: In this paper, the status of adaptive control theory in electrical power systems control is reviewed and current mechanisms and methods of electrical power system control are examined, including adaptive generator exciter control and adaptive load-frequency control.
Abstract: Potential applications of adaptive control theory to electrical power systems control are explored. In the first part of the paper, the status of adaptive control theory is reviewed. Current mechanisms and methods of electrical power systems control are then examined. The two areas in adaptive power system control that have received the most attention are adaptive generator exciter control and adaptive load-frequency control. Nine recent papers on adaptive exciter control are described, as also are three papers on adaptive load-frequency control. Potential applications of adaptive control to other power system control problems are noted.

130 citations


Journal ArticleDOI
TL;DR: In this paper, the power system restoration task force (PSR-TF) reviewed the 1979-83 North American Electric Reliability Council (NERC) Reports on Major Bulk Power System Disturbances (2), identifying restoration problems which have been encountered during that 5-year period.
Abstract: In its second report, the Power System Restoration Task Force (PSR-TF) (1) reviews the 1979-83 North American Electric Reliability Council (NERC) Reports on Major Bulk Power System Disturbances (2), identifying restoration problems which have been encountered during that 5-year period. Generally, these problems fall into three phases of restoration activities: planning for restart, reintegration and restoration of the bulk power supply; control actions during system degradation for saving and retaining critical sources of power; and restoration after a major disturbance when the power system has stabilized. The report also briefly discusses the applicability of several existing programs to the system restoration process. The opinions and conclusions expressed in this paper are those of the authors; they are based on the referenced reports and have not been reviewed with NERC or the reporting utilities.

120 citations


Journal ArticleDOI
TL;DR: In this paper, a self-tuning proportional-integral-derivative (PID) power system stabilizer is proposed to improve the dynamic performance of a synchronous generator under a wide range of operating conditions.
Abstract: A new technique for the excitation control of a synchronous generator is presented in this paper. The proposed technique employs a self-tuning proportional-integral-derivative (PID) power system stabilizer in order to improve the dynamic performance of a synchronous machine under a wide range of operating condition. Digital simulation of a synchronous machine subject to a major disturbance of a three phase fault under different operating conditions is performed to demonstrate the effectiveness of the proposed controller. It is found that the self-tuning PID stabilizer can enhance both the transient stability and the dynamic performance of the synchronous machine.

116 citations


Journal ArticleDOI
TL;DR: In this paper, a linear programming based methodology for corrective control computations is presented, which computes adjustments of unit real power output, VAR source output, transformer tap settings, capacitor/reactor switching, branch switching or line sectionalization, and if necessary, load shedding.
Abstract: This paper presents a linear programming based methodology for corrective controls computations. The methodology computes adjustments of unit real power output, VAR source output, transformer tap settings, capacitor/reactor switching, branch switching or line sectionalization, and if necessary, load shedding. A previous publication presented the basic algorithm for computing adjustments of continuous controls such as generator real power, transformer tap setting, etc. This paper addresses the problem of incorporating discrete controls such as capacitor/reactor switching and line switching/sectionalization into the overall procedure. Efficient algorithms are presented for the computation of discrete controls such as capacitor bank and transmission line switching. The methodology is illustrated with typical results obtained with the Georgia Power Company's 500 kV/230 kV/115 kV system. The network representation of this system comprises 981 buses and 1175 circuits.

115 citations


Book
01 Feb 1987

114 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a security measure to indicate vulnerability to voltage collapse in electric power systems based on expected exit time from the region of attraction for the stable operating point.
Abstract: This paper proposes a security measure to indicate vulnerability to voltage collapse in electric power systems. The voltage-collapse phenomenon is modeled as a large deviation in the nonlinear dynamics of the system, driven by small magnitude, broad spectrum disturbances in load. This model relates the collapse to shrinking of the region of attraction for the operating point. The security measure indicating vulnerability to voltage collapse is based on expected exit time from the region of attraction for the stable operating point. It is shown that expected exit time can be related to a natural Lyapunov function for the power system, and that a security measure based on this expected exit time can be calculated simply by evaluating an exponential function of the Lyapunov "energy" at a neighboring load flow solution.

109 citations


Journal ArticleDOI
TL;DR: In this article, a new method for minimizing transmission line losses and improving voltage profile in a given system by adjusting control variables, i.e., tap position of transformers and reactive power injection of VAR sources, is presented.
Abstract: This paper presents a new method for minimizing transmission line losses and improving voltage profile in a given system by adjusting control variables, i.e., tap position of transformers and reactive power injection of VAR sources. Transmission losses are considered as a function of voltage increments. The control variables and voltage increments are related by a modified Jacobian matrix. Linear Programming (LP) is used to calculate the voltage increments which minimize the transmission losses, and the adjustments of control variables are obtained by a modified Jacobian matrix. Since this method does not need any matrix inversion, it will save computational time and memory space.

101 citations


Journal ArticleDOI
TL;DR: In this article, a new method for simultaneously selecting the power system stabilizer (PSS) parameters in multimachine power systems is presented, where exact model reduction based on modal control theory is proposed to make the determination of PSS parameters highly efficient.
Abstract: This paper presents a new method for simultaneously selecting the power system stabilizer (PSS) parameters in multimachine power systems. Design of local output feedback power system stabilizer using local signal of the generator (e.g. speed or power) is formulated as a decentralized modal control (DMC) problem. Exact model reduction based on modal control theory is proposed to make the determination of PSS parameters highly efficient. Results obtained from the coordinated tuning of the parameters of three power system stabilizers equipped on a multimachine power system show that exact assignment of the eigenvalues associated with the poorly damped electromechanical modes can be achieved in a very efficient manner.

Journal ArticleDOI
TL;DR: In this article, the authors examined the various factors affecting the damping characteristics of low frequency oscillations which caused dynamic instability problem in the operation of Taiwan power system and showed that power system stabilizers can be employed as an effective means for improving dynamic stability.
Abstract: Sustained low frequency oscillations have been observed in Taiwan power system which is of longitudinal structure. It is the purpose of this paper to examine the various factors affecting the damping characteristics of these oscillations which caused dynamic instability problem in the operation of Taiwan power system. It is observed that the amount of power flow on the EHV transmission line and the characteristics of load have a significant effect on the damping of the system while the speed-governing system and the gain of automatic voltage regulator have only a minor one. Detailed investigation using both the frequency domain and time domain approaches also reveals that power system stabilizers can be employed as an effective means for improving dynamic stability of Taiwan power system.

Journal ArticleDOI
TL;DR: In this article, the authors presented a novel methodology for feasibility analysis and design of optimal decentralized load frequency control for multi-area interconnected electric power systems, where the eigenvalue sensitivity expressions were used to determine decentralized feedback gains that will result in system transient performance similar to the one obtained with a centralized optimal control law.
Abstract: The paper presents a novel methodology for feasibility analysis and design of optimal decentralized load frequency control for multi-area interconnected electric power systems. Feasibility of the proposed decentralized control scheme is determined with a fixed mode evaluation algorithm based on eigenvalue dynamics. The eigenvalue sensitivity expressions are also used to determine decentralized feedback gains that will result in system transient performance similar to the one obtained with a centralized optimal control law. The methodology is illustrated with a two-area power system example.

Journal ArticleDOI
TL;DR: The technique known as the waveform relaxation has been extensively used in transient analysis of VLSI circuits and it can take advantage of new architectures in computer systems such as parallel processors.
Abstract: In this paper, a new methodology for power system dynamic response calculations is presented. The technique known as the waveform relaxation has been extensively used in transient analysis of VLSI circuits and it can take advantage of new architectures in computer systems such as parallel processors. The application in this paper is limited to swing equations of a large power system. Computational results are presented.

Journal ArticleDOI
01 Dec 1987
TL;DR: Why AI techniques are being used in EMS designs and the differences between knowledge-based expert systems and traditional numeric algorithm development are explored and a relay fault diagnosis system is illustrated, showing both the traditional and rapid prototyping approaches to its development.
Abstract: Power system operators often reach a cognitive barrier when information arrives too fast during a power system emergency At such times it becomes difficult to reach a correct diagnosis of the problem or to formulate the correct decision when actions must be taken Artificial Intelligence gives designers of Energy Management Systems a way to solve many of the diagnosis and decision problems so as to make the EMS more useful This paper explores reasons why AI techniques, such as knowledge-based expert systems, are being used in EMS designs and the differences between knowledge-based expert systems and traditional numeric algorithm development The differences between expert systems and the numeric approach extend to the basic conception and design of the applications This is illustrated using a relay fault diagnosis system, showing both the traditional and rapid prototyping approaches to its development Finally, issues concerned with the implementation of AI in EMS computers are explored along with the authors' predictions of possible AI applications to power system operations


Patent
20 Aug 1987
TL;DR: In this paper, a photovoltaic system controller is presented for utilization with a power system including an auxiliary generator, battery, and an array of solar cells, which is adapted to be easily field adjustable to cover a wide range of parameters.
Abstract: A photovoltaic system controller particularly adapted for utilization with a photovoltaic power system including a photovoltaic array, system battery, load and, optionally, an auxiliary generator. The controller utilizes a microprocessor to monitor various parameters of the system and to perform system control functions. The microprocessor is provided with a plurality of setpoints corresponding to desired system parameters for utilization as reference points for the conducting of control functions. The setpoints are adapted to be easily field adjustable to cover a wide range of parameters. The controller is particularly suited for adaption to an entire spectrum of system designs merely by replacing the programmable memory component of the controller. The controller derives its power from a tap off the system battery and is designed to withstand the harsh environment associated with remote site locations. All of the control functions are temperature compensated. The controller is provided with timing control means which allows the controller to be inactive between operating cycles so as to reduce power requirements.

Journal ArticleDOI
TL;DR: The total life-cycle cost of stand-alone photovoltaic (SAPV) power systems is mathematically formulated and a new optimal sizing algorithm for the solar array and battery capacity is developed.

Patent
01 Jun 1987
TL;DR: An improved signaling system for command and information signaling over a power system interconnection comprising the utilization of pseudo-random binary pulse code with frequency modulation to overcome the extraordinarily high noise ambient while providing a way of achieving practicable transmission within the constraints typically inherent in a large interconnected power system is presented in this article.
Abstract: An improved signaling system for command and information signaling over a power system interconnection comprising the utilization of pseudo-random binary pulse code with frequency modulation to overcome the extraordinarily high noise ambient while providing a way of achieving practicable transmission within the constraints typically inherent in a large interconnected power system.

Journal ArticleDOI
TL;DR: In this article, an adaptive, weather sensitive, short term load forecast algorithm was developed for two South Carolina Power Systems: CEPCI (Central Electric Power Cooperatives, Inc., Central for short) and Combined System.
Abstract: This paper introduces an adaptive, weather sensitive, short term load forecast algorithm that has been developed for two South Carolina Power Systems: CEPCI (Central Electric Power Cooperatives, Inc., Central for short) and Combined System. The model is based on a State Space formulation specially tailored for this application. A detailed correlation study is performed to identify the most relevant weather variables. Different models are used for Summer and Winter, since different weather variables are found to be relevant in both seasons. Adaptivity is attained through careful usage of Kalman filtering and Bayesian techniques. An appropriate methodology is developed to identify and correct anomalous load data and to model nonconforming loads. A new technique is introduced for "filling in" weather forecasts. The model has been sucessfully implemented using state-of-the-art data-base and man-machine techniques. Implementation results are reported. This model benefits from the experience gained using a variety of tools and represents important enhancements over existing methods.

Patent
15 Dec 1987
TL;DR: A computer power system comprises an AC-to-DC power supply for providing DC power to the computer during the presence of AC line power and a backup power supply that provides DC power from batteries directly to the DC operated components of the computer system, completely bypassing the AC to DC power supply when AC line voltage is absent or low.
Abstract: A computer power system comprises an AC-to-DC power supply for providing DC power to the computer during the presence of AC line power and a backup power supply for providing DC power from batteries directly to the DC operated components of the computer system, completely bypassing the AC to DC power supply, when AC line voltage is absent or low.

Journal ArticleDOI
TL;DR: In this article, a systematic procedure is developed to locate reactive power devices in a power system based on a set of indices, that are based on overall system conditions, and after identifying the desired locations, the cost of installation and number of reactive power device, subject to any required practical and real economic constraints, are minimized.
Abstract: A systematic procedure is developed to locate reactive power devices in a power system based on a set of indices, that are based on overall system conditions. After identifying the desired locations, the cost of installation and number of reactive power devices, subject to any required practical and real economic constraints, are minimized. Existing controllers are fully utilized before adding any new devices. Linearized sensitivity relationships of power systems are used to obtain an objective function for minimizing the cost of installation. The constraints include the limits on dependent variables (reactive powers of the generators, load bus voltages) and control variables (generator voltages, tap positions, switchable reactive power sources). A parametric linear programming technique based on active set analysis is proposed to solve the reactive power allocation problem.

Patent
20 Mar 1987
TL;DR: In this paper, a method and apparatus for monitoring an energy management system which controllably drops load in response to preselected conditions is presented, where the apparatus periodically interrupts the EH system to restore full load.
Abstract: A method and apparatus are provided for monitoring an energy management system which controllably drops load in response to preselected conditions. The apparatus periodically interrupts the energy management system to restore full load. The apparatus monitors energy usage immediately prior to interrupting the energy management system and also monitors the energy usage during interruption when the load is restored. The information gathered at these two times represents the actual energy used when the energy management system is conserving energy, and when the energy management system is disabled and full energy usage is realized. The difference between the two energy usages represents the energy savings realized by using the energy management system.

Journal ArticleDOI
TL;DR: In this article, a generalized probabilistic model of harmonic current injection and propagation is presented, which takes into account random variations of both the operating modes as well as the configuration of nonlinear loads connected to a distribution feeder.
Abstract: A generalized procedure to obtain the probabilistic model of power system harmonic current injection and propagation is presented. The model takes into account random variations of both the operating modes as well as the configuration of nonlinear loads connected to a distribution feeder. The method is illustrated by an example of a bus having linear as well as nonlinear loads of different types. Potential applications of the model are also discussed.

Journal ArticleDOI
TL;DR: In this article, an alternative approach for power system stabilization based upon the tuning of the existing generator controllers, both governors and A.V.R.'s, is presented, where the sensitivities of the eigenvalues to the controller parameters are evaluated and an optimization technique is developed to maximize the dynamic stability.
Abstract: Dynamic stability problems are usually overcome through the application of Power System Stabilizers. This paper presents an alternative approach for power system stabilization based upon the tuning of the existing generator controllers, both governors and A.V.R.'s. The sensitivities of the eigenvalues to the controller parameters are evaluated and an optimization technique is developed to maximize the dynamic stability. Application of the parameter optimization method on a realistic model of the Hellenic Interconnected System has proved an efficient way to stabilize a number of unstable oscillatory modes by relatively small parameter variations. The results are tested with a nonlinear simulation program and the achieved stabilization, as shown by the rotor angle swings, is found to be significant.

Journal ArticleDOI
01 Dec 1987
TL;DR: In this paper, the authors summarized the system characteristics associated with AGC, as well as current practices of program design and operation, and discussed current issues such as fuel scheduling, dispersed generation technologies, and advanced load management schemes may change the nature of the AGC problem in the future.
Abstract: Within an Energy Management System, the Generation Scheduling and Control function controls the electrical power output of generators so as to supply the continuously changing customer power demand in an economical manner. This function is largely provided by an Automatic Generation Control (AGC) program operating within the control center computer. Power system dispatchers also play an important role, interacting with the program to incorporate current operating conditions. This paper summarizes the system characteristics associated with AGC, as well as current practices of program design and operation. Topics of current interest are also discussed. Current technology in this area is fairly mature, and existing performance is good over-all. Current issues such as fuel scheduling, dispersed generation technologies, and advanced load management schemes may change the nature of the AGC problem in the future.

Journal ArticleDOI
TL;DR: In this article, a steady-state turbogenerator saturation algorithm suitable for inclusion in power system stability codes has been devised under EPRI sponsorship, which was constructed to fit reactances resulting from nonlinear finite-element calculations of steadystate load points covering the operating range (V,P,Q) of the generator.
Abstract: Under EPRI sponsorship, a steady-state turbogenerator saturation algorithm suitable for inclusion in power system stability codes has been devised. The algorithm was constructed to fit reactances resulting from nonlinear finite-element calculations of steady-state load points covering the operating range (V,P,Q) of the generator. Saturation functions were derived for two generators: Cholla 4, owned by the Arizona Public Service Company, and Bull Run (HP unit), owned by the Tennessee Valley Authority. The owners of these generators measured steady-state load data for these machines, and the measured load angles and excitation currents were compared with those calculated using the algorithm. Agreement within 2 degrees in angle (max. 3 degrees), and 2 percent in excitation was obtained. This paper describes the fitting process and the comparisons of the results to test data. A companion paper describes increases in power transfer found from coding the algorithm into an existing stability program, and testing the prototype code on an 1100 bus stability study.


Journal ArticleDOI
TL;DR: An overview of the analytical and computational problems encountered in the large scale application of the TEF method is presented, and approaches used to overcome the problems are provided.
Abstract: This paper deals with the demonstration of the Transient Energy Function (TEF) method in large, realistic power networks. Documented examples of application in power system operation and associated software development for systems up to 228-generators and 1644-buses are given. An overview of the analytical and computational problems encountered in the large scale application of the TEF method is presented. Approaches used to overcome the problems are provided, and the relevant improvements and modifications to the TEF software are discussed.

Journal ArticleDOI
TL;DR: In this article, the authors describe an approach to service restoration which should speed up the process of restoring service to customers while at the same time limiting the risks of damage to equipment.
Abstract: Service restoration following a major power failure can occasion voltage problems on weak EHV systems from the point of view of both steady-state and temporary operation. This is due to the use of long EHV transmission links between the production sites and the load centres, which can cause large amounts of reactive power to be generated, and low short-circuit level, leading to low-frequency resonance, further excited by the presence of transformers. This paper describes an approach to service restoration which should speed up the process of restoring service to customers while at the same time limiting the risks of damage to equipment.