Showing papers on "Electric power system published in 1983"

A New Measurement Technique for Tracking Voltage Phasors, Local System Frequency, and Rate of Change of Frequency

Abstract: With the advent of Substation Computer Systems dedicated to protection, control and data logging functions in a Substation, it becomes possible to develop new applications which can utilize the processing power available within the substation. The microcomputer based Symmetrical Component Distance Relay (SCDR) described in the references cited at the end of this paper possesses certain characteristics which facilitate real-time monitoring of positive sequence voltage phasor at the local power system bus. With a regression analysis the frequency and rate-of-change of frequency at the bus can also be determined from the positive sequence voltage phase angle. This paper describes the theoretical basis of these computations and describes results of experiments performed in the AEP power system simulation laboratory. Plans for future field tests on the AEP system are also outlined.

Time-Scale Modeling of Dynamic Networks with Applications to Power Systems

Abstract: Time-scales in interconnected systems.- Singular perturbations and time-scales.- Modeling of two-time-scale systems.- Dynamic networks and area aggregation.- Coherency and area identification.- Slow coherency and weak connections.- Nonlinear dynamic networks.- Reduced simulations of nonlinear power system models.

Relationship Between Voltage Instability and Multiple Load FLow Solutions in Electric Power Systems

Abstract: There have been observed several voltage instability phenomena in electric power systems where receiving end voltages oscillate remarkably or get much lower than the nominal values. Those phenomena tend to occur in heavy loaded conditions and seem to be related to the multiple load flow solution problem for the following reasons. It has been confirmed analytically and by simulations that the multiple load flow solutions are likely to appear under the heavy-loaded conditions, and that the individual solutions of the solution pair have different features from each other, from the standpoint of stability, although they are close to each other.

Dynamic Behavior of a Class of Photovoltaic Power Systems

Abstract: An important consideration in the operation of grid connected photovoltaic power systems is a means of adjusting the photovoltaic array voltage so that maximum output power is achieved for the given atmospheric conditions. The dynamic behiavior of a specific photovoltaic power system which utilizes the well known perturb and observe method of power tracking is examined. Using measured insolation data, it is demonstrated that the perturb and observe method of control migrates considerably from peak power whenever the insolation varies randomly as a result of cloud cover. An alternate method of power tracking is also examined. It is shown that the photovoltaic power system, utilizing the proposed method of power tracking, is able to track accurately peak power conditions during periods of randomly varying insolation.

Development of a Knowledge Based System for Power System Restoration

Abstract: A knowledge based system is developed for automatic control of a power system in the restorative state. System operator's heuristics seem to play a central role during the course of system restoration. So efforts are made to represent those heuristics by a set of knowledge the goal of which is to restore the power supply without overloading any transmission line. While the overload check is a numerical computation, reasoning in the knowledge based system is a symbolic computation. A method to link these two different types of computation is proposed. The knowledge based system is expected to serve managing a large scale power system in the restorative state.

Computer modelling of electrical power systems

Abstract: From the Publisher: Describes the use of power system component models and efficient computational techniques in the development of a new generation of programs representing the steady and dynamic states of electrical power systems. Presents main computational and transmission system developments. Derives steady state models of a.c. and d.c. power systems plant components, describes a general purpose phase a.c. load flow program emphasizing Newton Fast Decoupled Algorithm, and more. Considers all aspects of the power system in the dynamic state.

An AC-to-DC Converter with High Quality Input Waveforms

Abstract: An ac-to-dc converter which draws sinusoidal and inphase current waveforms from the ac power source is described. Harmonic and power factor measurements obtained from a field- effect transistor (FET) converter operating at 45 kHz for a single- phase and a three-phase connection are presented. A stability analysis and design methodology are given.

Power system transient stability using individual machine energy functions

Abstract: Recent efforts to apply direct methods of transient stability analysis to multimachine power systems have used the so-called "energy functions." These functions describe the system transient energy causing the synchronous generators to depart from the initial equilibrium state, and the power network's ability to absorb this energy so that the synchronous machines may reach a new post-disturbance equilibrium state. Recent results have shown that not all the transient energy contributes to system separation. Indeed it has become increasingly evident that system separation depends on the energy of certain individual machines or groups of machines, which comprise the critical group, and which tend to separate from the rest of the machines (which make up the noncritical group). Thus there is a need for generating energy functions for individual machines (or for groups of machines). Using a center of inertia frame of reference, the energy function V_{i} for machine i is derived. A procedure for first swing transient stability assessment is developed using the energy function of individual machines and groups of machines. The method is tested extensively on two realistic power networks (the 20-generator IEEE System and the 17-generator reduced Iowa System). An analytical justification for using the critical energy of individual machines in stability assessment is provided using an invariance principle for ordinary differential equations. Power system transient stability is analyzed using the energy function of the critical group of machines. This energy function is dependent on all state variables of the power system, and satisfies the hypotheses of the invariance theorem of La Salle, enabling us to deduce the asymptotic stability of the post-disturbance equilibrium of the entire power system. It also enables us to obtain an estimate of the domain of attraction of this equilibrium of the entire power system. The methodology advanced herein, which combines computer-aided techniques with analytical tools, yields less conservative results than were obtained in previous works that used total system energy. It is to be noted that the present results are preliminary in the sense that the mechanism of separation of the critical group of machines from the rest of the system needs further investigation.

State forecasting in electric power systems

Abstract: The state vector of a power system varies with time owing to the dynamic nature of system loads. Therefore, it is necessary to establish a dynamic model for the time evolution of the state vector. The dynamic state estimation approach consists of predicting the state vector based on past estimations, followed by a filtering process performed when a new set of measurements is available. This paper presents a new algorithm for forecasting and filtering the state vector, using exponential smoothing and least-squares estimation techniques. The proposed algorithm is compared with another one based on standard Kalman filtering theory. Numerical results showing the performance for both dynamic estimators under different operational conditions are presented and discussed. Detection and identification of multiple bad data are also included. The new dynamic estimator exploiting state forecasting is extremely useful to real-time monitoring of power systems.

Electrical Power Systems

Abstract: Fundamentals of Power Systems Line Constant Calculations Capacitance of Transmission Lines Performance of Lines High Voltage DC Transmission Corona Mechanical Design of Transmission Lines Overhead Line Insulators Insulated Cables Voltage Control Neutral Grounding Transients in Power Systems Protective Relays Circuit Breakers Power System Stability Dispatch. @21 VA1

Hybrid power system for driving a motor vehicle

Abstract: A triple hybrid power system for driving a motor vehicle utilizing an internal combustion engine to drive an electric generator to charge a bank of batteries that provide electrical energy to drive an electric motor/generator that supplies power to a planetary gear set from which power is directed through a variable drive transmission to drive the wheels of the vehicle, a flywheel is used to apply periodic power through the planetary gear set to provide added power for acceleration, with a speed regulator disposed between the flywheel and the planetary gear set to maintain a substantially constant input speed that facilitates operation of the motor/generator at an optimum efficiency output. The drive transmission is operable to apply regenerative braking energy back through the planetary gear set to recharge the flywheel and, through to motor/generator, to recharge the batteries. When the vehicle is operating at a constant speed on level ground, the internal combustion engine can be applied directly to power the vehicle at optimum efficiency with the motor/generator and flywheel disengaged.

Power System State Estimation with Measurement Deficiency: an Observability/Measurement Placement Algorithm

Abstract: Measurement system failures and modeling constraints may make it impossible for the power system state estimator to estimate bus voltage magnitudes and angles at every bus in the power system from the available real-time measurements. Such a measurement deficiency may be remedied by adding pseudo measurements of estimated bus loads. This paper presents a combined observability/measurement placement algorithm that both tests the measured network for observability and evaluates pseudo measurement sites as to the desirability of their inclusion into the measurement set.

Advances in Switched-Mode Power Conversion Part I

Abstract: A new concept in the design of switched-mode power conversion circuitry is presented. Because of its extreme simplicity, flexibility, and efficiency, it has the potential to replace some conventional electrical power processing methods currently in use. A thorough discussion of the background, development, and operation of the ?uk converter and several of its extensions is included. The coupled-inductor technique further improves efficiency and reduces size and weight. The basic converter and its extensions to two-quadrant and four-quadrant operation are attractive for many applications, i.e., solar (dc) to utility line (ac) power conversion, variable speed dc or ac motor drives, switching power supplies, uninterruptible power supplies, and many others.

Critical Survey of Hierarchical Methods for State Estimation of Electric Power Systems

Abstract: This paper intends to give a unified survey of methods appropriate for solving the state estimation problem in large-scale electric power systems After a first overview of the various approaches proposed up to now, the most suitable among them are described, examined and compared The comparisons are carried out on the basis of selected criteria evolving estimation properties of the resulting algorithms, along with their organization possibilities and their capabilities of handling some important satellite functions

30-MJ superconducting magnetic energy storage system for electric utility transmission stabilization

Abstract: A superconducting magnetic energy storage (SMES) system has been built to damp power oscillations on the Western U.S. Power System, particularly on the Pacific AC Intertie that is used to transmit power from the Northwest to southern California. The 30-MJ superconducting inductor that stores energy for this purpose is contained in a nonconducting dewar and is supported by a helium refrigerator and a gas-handling system mounted on trailers. Energy flows in and out of the inductor at frequencies from 0.1 to 1.0 Hz with power amplitudes up to 11 MW. The principal oscillation to be damped has a characteristic frequency of 0.35 Hz. The superconducting coil maximum current is 5 kA with terminal voltages up to 2.2 kV. The coil interfaces with the Bonneville Power Administration 13.8-kV bus at the Tacoma Substation through a converter and transformers. The system can be operated with the converter either in parallel-bridge mode or for constant VAR control with the bridges in buck-boost mode. The program for the design, fabrication, installation, and the preliminary experimental operation of the system is reviewed.

Self-Tuning Controller for Generator Excitation Control

Abstract: It has long been recognized that the generator excitation control is an effective and low cost means for improving the power system stability. Recent developments in control theory and digital technology suggest an extension of the results obtainable through analog control to derive potential improvements through the use of digital control. There has been reluctance to apply real time digital control in electric power engineering, perhaps this is due to lack of experience and confidence in this technology. In addition to advances in technology, motivation for investigating the control of a generator at the end of a long transmission line comes from the common occurrence of generation being remotely located. Such is the case, for example, at Liu Jia Xia in the People's Republic of China where a 330 KV, 332 mile single circuit line connects a 400 MW station with the main grid. It is reasonable to attempt to use excitation control to permit line loading to the transmission limit. Much work has been done with many interesting results by applying linear optimal feedback control theory to the excitation control. Most of the results are based on the assumption that an explicit deterministic mathematical model of the system to be controlled is available. The system model is then linearized around some fixed operating point with the system parameters assumed constant. By numerous off-line simulation studies, suitable weighting factors involved in an index of quality can thus be found by trial and error.

A Probabilistic Approach to Power System Stability Analysis

Abstract: Power system stability analysis is usually performed in a deterministic framework in which the time domain response of the power system is studied for certain specific disturbances to determine the adequacy of the system. However, the occurrence of disturbances and their attendant protective switching sequences are random processes and it would be more meaningful to determine the probability of stability for a power system. An approach for such a determination is presented in this paper. The probability of steady state stability is relatively easier to determine because of the linearization of the system equations. The probability of transient stability, on the other hand, is much more difficult to obtain analytically because of the nonlinear transformations required. However, a Monte Carlo simulation method to determine transient stability probability is shown to be feasible.

Tuning of Stabilizers in Multimachine Power Systems

Abstract: This paper proposes a novel approach for simultaneously selecting. the parameters of all the stabilizers in multimachine power systems. The parameter optimization problem is cast into an eigenvalue. assignment formulation and. an algorithm enabling exact assignment of selected system modes is presented. The proposed algorithm is used to design the stabilizer loops for a three machine-infinite bus dynamically unstable power system.

Application of Power Transistors to Residential and Intermediate Rating Photovoltaic Array Power Conditioners

Abstract: An investigation into power conditioners that interface with photovoltaic arrays and utilities has been recently completed. The ratings for this investigation include residential systems (5-30 kW) that interface with a 240-V single-phase utility connection and intermediate systems (30-200 kW) that interface with a 480-V three- phase utility connection. Both systems mandated that an isolation transformer be provided between the array and the utility interface. A trade-off study was performed for many transistor and thyristor circuits and configurations. The weighting criteria included full- and part-load efficiency, size, weight, reliability, ease of control, injected harmonics, reactive power requirements, and parts cost. As the result of this study, a 10-kW high-frequency PWM transistor inverter feeding a high-frequency isolation transformer with a sinusoidally shaped current wave was selected. The output of the transformer is rectified with a diode bridge rectifier. Four thyristors, used as 60-Hz switches, reverse the polarity of the rectified current on every other half-cycle of the utility voltage. This reversal is accomplished slightly before the natural zero crossing of the voltage, thereby providing commutation for the thyristors. The results in the intermediate rating study targeted on a 100-kW design using power transistors in a full-bridge circuit connected to a 60-Hz three-phase transformer. Three bridge circuits are provided to interface with the polyphase utility. The switching strategy for the power transistors is based on a sine wave shape of current with a controlled deadband.

Probabilistic dynamic security assessment of power systems-I: Basic model

Abstract: A comprehensive framework for power system security assessment which incorporates probabilistic aspects of disturbances and system dynamic responses to disturbances is presented. Standard mathematical models for power system (steady-state) power flow analysis and transient stability (dynamic) analysis are used. A linear vector differential equation is derived whose solution gives the probability distribution of the time to insecurity. The coefficients of the differential equation contain the transition rates of system structural changes and a set of transition probabilities defined in terms of the steady-state and the dynamic security regions. These regions are defined in the space of power injections. Upper and lower bounds on the time to insecurity distribution are obtained.

Wind turbine generator interaction with diesel generators on an isolated power system

Abstract: The Block Island Power Company (BIPCO), on Block Island, Rhode Island, operates an isolated electric power system consisting of diesel generation and an experimental wind turbine. The 150-kW wind turbine, designated MOD-OA by the U. S. Department of Energy is typically operated in parallel with two diesel generators to serve an average winter load of 350 kW. As part of an experimental program to evaluate wind turbine generator performance on the isolated diesel power system, the recordings from an extensive data measurement effort were reviewed and analyzed to define the nature of the dynamic interaction effects. The data were collected over a three-month period on the system to which the DOE/NASA experimental wind turbine was connected. During this time, the diesel units were lightly loaded resulting in up to 60 percent of the total load demand being supplied by the MOD-OA in periods of severely gusting winds. In three of the modes of normal MOD-OA operation. startup???synchronization, shutdown/cutout, and continuous fixed pitch running???power, frequency and voltage transients were comparable with those produced by typical load changes on the diesel system alone. In the fourth mode, variable pitch (constant power) control, a significant reduction in system damping sometimes occurred which gave rise to increased frequency and voltage perturbations under gusty wind conditions. Based on a linear model of the system it is shown that changes in control system settings could be made to improve damping.

Large Scale Reactive Power Planning

Abstract: A new methodology for planning future reactive compensation for large scale systems is presented. The planning technique is based on a restructuring of the network model and a special formulation of the revised simplex method. A preprocessor is incorporated for correcting systems which are not able to converge using conventional power flow or optimal power flow programs. A 600 bus example is provided which considers 285 transmission contingencies.

A New Power System Stabilizer Synthesis In Multimachine Power Systems

Abstract: A simple synthesis method of a power system stabilizer (PSS) was developed by combining the frequency response method and the pole assignment method. This method enables synthesis in a multimachine system and is easily incorporated into an eigenvalue program for the power system. Although there are limitations of the model accuracy, the damper winding, the governor system and the load characteristics can be considered in the synthesis.

Monte Carlo Simulation of Power System Stability

Abstract: This paper presents a Monte Carlo simulation of the transient stability of a power system. The simulation time is in the order of years in which the occurrence of disturbances and the subsequent protective action are considered to be stochastic processes. The objective is to obtain a probabilistic measure of transient stability for a power system instead of just its particular response to an individual disturbance. The latter is the usual output of deterministic transient stability programs that are used for present day worst case analysis. A probabilistic analysis is needed if such worst case design criteria is to be replaced by (probabilistic) reliability criteria. This paper describes a computer program that has been developed for such a Monte Carlo simulation and presents some results of its application to representative systems.