Showing papers on "Power system simulation published in 1981"

Evaluation of Dynamic Programming Based Methods and Multiple area Representation for Thermal Unit Commitments

Abstract: This paper compares the performance of four unit commitment methods, three of which are based on the dynamic programming approach. The paper also presents the modeling of inter-area flow constraints by linear flow network, so that such multi-area representation recognizes any existing transmission limitations which are normally ignored in most unit commitment methods. To assure realistic results, data for two large systems (up to 96 units) were used: EPRI Scenario System C and a midwestern utility. Unit commitment results for these two systems are presented in the paper and they demonstrate the importance of multiple area representation of a system in unit commitment. Such representation affects the schedule costs and assures the determination of realizable schedules.

Optimal short-term scheduling of large-scale power systems

Abstract: This paper is concerned with the long-standing problem of optimal unit commitment in an electric power system. We follow the traditional formulation of this problem which gives rise to a large-scale, dynamic, mixed-integer programming problem. We describe a solution methodology based on duality, Lagrangian relaxation, and nondifferentiable optimization that has two unique features. First, computational requirements typically grow only linearly with the number of generating units. Second, the duality gap decreases in relative terms as the number of units increases, and as a result our algorithm tends to actually perform better for problems of large size. This allows for the first time consistently reliable solution of large practical problems involving several hundreds of units within realistic time constraints. Aside from the unit commitment problem, this methodology is applicable to a broad class of large-scale dynamic scheduling and resource allocation problems involving integer variables.

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.

Computation of A.C.-D.C. System Disturbances - Part I. Interactive Coordination of Generator and Convertor Transient Models

Abstract: In the presence of h.v.d.c. links the conventional quasi - steady state simulation of power system disturbances is not justifiable. This paper describes a realistic solution which combines the efficiency of single-phase multimachine transient stability analysis and the accuracy of detailed transient convertor simulation. Versatility and moderate computing requirements establish the proposed solution as a viable alternative to the use of analogue simulators.

Prediction of Harmonic Voltages in Distribution Systems

Abstract: The aim of this paper is two-fold. First, it develops workable models for specific devices which are known to inject harmonics into power distribution systems, namely ac-dc converters. Second, these models are then combined with distribution system elements, and the resulting network is solved to yield harmonic voltages. An example is presented, showing the authors' application of the techniques to analyze a real-life installation.

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.

Idenntification of Parameters for Power System Stability Analysis Using Kalman Filter

Abstract: We propose that parameters on generators and the control units, used for power stability analysis, should be identified on the field data for reliable analysis in planning and operation of power supply systems. We apply Kalman filter technique in estimating the parameters. The identified data are compared with the design data and are well verified by analyzing the dynamic stability under line switching condition. Which deviation of designed values from identified values has the largest influence on the analysis, is also investigated.

Digital Simulation of Distribution System Frequency-REsponse Characteristics

Abstract: A new digital computer program developed for harmonic analysis of multi-phase networks is described. The program-the Distribution Feeder Harmonic Analysis (DFHA) Program-is designed to conveniently model distribution systems to determine frequency-response characteristics. Results of simulations performed for two different distribution systems are compared with actual harmonic measurements on the systems. Simulation accuracy is evaluated and guidelines are presented for modeling a distribution system and performing the digital harmonic analysis.

The acceleration approach to practical stability domain estimation in power systems

Abstract: We propose a systematic approach for estimating the Liapunov practical stability domain, along with some other fast techniques for transient stability analysis of power systems. The direct criterion thus derived is investigated and illustrated through a good number of simulations performed on several test systems and practical power networks. It is shown to be reliable, straightforward and computationally very fast. Besides being appropriate for conventional studies, the acceleration approach offers also another interesting possibility: the derivation of a transient stability index for on-line stability assessment and contingency evaluation.

Decentralized Power Modulation of Multiterminal HVDC Systems

Abstract: This paper appLies a new method of control design for decentralized power modulation of multiterminal hvdc systems. The feedback structure uses only local output variables which are directly available without observer action. The feedback gains are computed to assign closed loop eigenvalues of the Linearized system for any specified modes. A computer simulation of an integrated ac/dc power system demonstrates resulting control performance; for typical disturbances. Comparisons are made with centralized modulation and several designs with limited communications.

Short-term Operation Planning in Electric Power Systems

Abstract: A practical application of operational research methods is shown here for the short-term operation planning in an electric power system. Two interactive application programs are presented: a short-term load forecasting program and a unit commitment optimisation program. For the load prediction within the load forecasting program a four-component weather dependent load model is used, whereby for the weather-dependent load component an econometric model, and for the time-dependent load component a seasonal multiplicative ARIMA-model is applied. The unit commitment is optimized using dynamic programming. With this method the start-up and shut-down costs can easily be taken into consideration. Special features are necessary to allow the optimal scheduling of a large number of generators to minimize storage requirements and execution time of the program. For every cost-optimal unit commitment determined the reliability of the energy supply is then calculated.

Economic Operation of Distributed Power Systems Within an Electric Utility

Abstract: The authors evaluate the economic operation of distributed power systems within regional synthetic utilities, analyzing the interactions with the utility of customers who can both buy and sell power. These analyses utilize a linked set of economic, financial and engineering models. SYSGEN, an electric utility system operating model, optimizes annual capacity utilization. SYSGEN provides the operation and maintenance data required in ERATES, the utility rate model. ERATES calculates a set of industrial and non-industrial utility rates based on operating and capital costs. The new rates are inputs to SOLOPS and SOLIPS, which are residential, commercial and industrial load simulation models that also compute the economic value of dispersed systems to their owners. The output of SOLOPS and SOLIPS provides load reduction data as input to the SYSGEN model. The modeling cycle allows the authors to analyze the impact of increasing amounts of dispersed power system installations on utility operating and capital costs, thereby analyzing the impact on utility buy and sell rates.

Power System State Estimation: Practical Considerations

Abstract: The current Power System State Estimator algorithm being used at Wisconsin Electric was installed in the summer of 1975. The purpose of this program was to constantly monitor system steady state security and provide system data where metering was unavailable. The solution method is a full gain matrix least-squares fit algorithm which provides line flows, voltage magnitudes and phase angles to system operators and security software modules. The purpose of this paper will be to discuss the implementation of this algorithm and the benefits and problems associated with it.

On-Line Computer Control of a Power System During an Emergency

Abstract: A control strategy to improve the performance of a power system during an emergency is presented in this paper. Immediately following a major disturbance, the future power system performance is predicted using a faster than real-time simulation. If the predicted performance is unacceptable according to a set of prespecified criteria, appropriate control actions are taken to steer the power system from the impending danger. The major problems considered in this study are abnormal frequency trajectories, transmission line overloads, and abnormal bus voltages. Test results are also included in this study.

Data Base Environmennt for Power System Simulation Models

Abstract: This paper describes the data base approach to power system analysis studies, contrasts it with the traditional stand-alone application approach and discusses the issues which should be considered in developing a data base management system. The discussion is based on the experience gained in developing and implementing a power system data base management system at the Electricity Supply Commission (South Africa). The practical use of a central data base management system, together with a library of application programs and an interactive computing environment contributed significantly to the power system planning process in which individual engineers can work efficiently and interact among themselves using common data and analysis tools.

A dynamic model of power system operation incorporating load control

Abstract: Load management, which involves tailoring electric energy use to match electric energy supply, has been frequently suggested as an alternative for increasing the efficiency of the electric energy system. However, traditional utility analysis tools are frequently inadequate for assessing the costs and benefits of alternative load management options. One such problem is the consideration of active utility load control in the unit commitment/ economic dispatch problem. A model has been developed to determine how a power system with an active load control system should be operated to make the best use of its available resources. The model uses a dynamic programming successive approximation technique called gradient dynamic programming developed during the project to solve this control problem for realistically sized systems. The development of the model and its computer implementation are presented. The use of the model is demonstrated on several case studies of current interest. The case study results indicate that the production cost savings that can be achieved through the use of direct load control are highly dependent on utility characteristics, load characteristics, storage capacity, and penetration.

Operations model for utilities using wind-generator arrays

Abstract: The report develops the effects that various combinations of wind regime, array configuration and penetrations, and system characteristics have on system variables such as area control error, frequency, interchange power and spinning reserve. The characteristics of the combinations causing system operating stress or operating problems are denoted and methods for estimating effects on a simplified and on a detailed simulation basis are reported. Methods for reducing operating problems are suggested and involve array configurations, penetration, unit commitment and dispatch changes, and wind generator controls. The limitation of the work reported is not in the utility operations simulation, which is very detailed, but in the array models which have not been verified by experimental data from large wind generator arrays.

Dynamic Simulation of Coal Mine Electrical Power Systems

Abstract: A flexible method for modeling mine electrical power systems is presented. Utilizing this simulation procedure, detailed analyses of bus voltages, transmission line power flows, and machine behavior are possible under conditions of steady-state or dynamic operation. Mining machine operation changes, as well as motor starting sequences, may be simulated. The model operates interactively, and the power system is configured as a user responds to program generated questions and requests. The theory behind the programming, as well as explanations of the models, are provided. An example is also given to demonstrate simulation capabilities.

Operations model for utilities using wind-generator arrays. Final report

Abstract: The report develops the effects that various combinations of wind regime, array configuration and penetrations, and system characteristics have on system variables such as area control error, frequency, interchange power and spinning reserve. The characteristics of the combinations causing system operating stress or operating problems are denoted and methods for estimating effects on a simplified and on a detailed simulation basis are reported. Methods for reducing operating problems are suggested and involve array configurations, penetration, unit commitment and dispatch changes, and wind generator controls. The limitation of the work reported is not in the utility operations simulation, which is very detailed, but in the array models which have not been verified by experimental data from large wind generator arrays.

A Generalized Model For Electric Distribution Systems

Abstract: A generalized mathematical model is constructed of single-phase induction machines employed within a three-phase distribution system. It is shown that this composite model retains single-phase distribution detail and describes the intrinsic characteristics of the single-phase induction generator. Power system fault(s) and circuit breaker response(s) are also modeled. Preliminary results of digital simulation indicate that a small integration step size is required to insure mathematical stability. For this reason, a dqo transformation of the generalized model is investigated and it is concluded that the presence of single-phase induction machines prevents further simplification of the system equations.

INCORPORATING UlAD CONTROL

Abstract: Load management, which involves tailoring electric energy use to match electric energy supply, has been frequently suggested as an alternative for increasing the efficiency of the electric energy system. However, traditional utility analysis tools are frequently inadequate for assessing the costs and benefits of alternative load management options. One such problem is the consideration of active utility load control in the unit commitment/ economic dispatch problem. A model has been developed to determine how a power system with an active load control system should be operated to make the best use of its available resources. The model uses a dynamic programming successive approximation technique called gradient dynamic programming developed during the project to solve this control problem for realistically sized systems. The development of the model and its computer implementation are presented. The use of the model is demonstrated on several case studies of current interest. The case study results indicate that the production cost savings that can be achieved through the use of direct load control are highly dependent on utility characteristics, load charac