Showing papers on "Power system simulation published in 1985"

Direct methods for transient stability analysis of power systems: Recent results

Abstract: Transient stability analysis of a power system is concerned with the system's ability to remain in synchronism following a disturbance In utility planning, transient stability is studied by numerical simulation The long CPU run times for simulation preclude their use for on-line security analysis Interest has therefore shifted toward the Lyapunov direct method of stability analysis This paper provides a critical review of research on direct methods since 1970 Considerable progress has been made on both theoretical properties of energy functions and on criteria suitable for on-line implementation Current theory provides a satisfactory treatment of voltage-dependent reactive power demand, transfer conductances, and flux decay However, it cannot incorporate the exciter control Proposed on-line criteria appear to work very well on sample examples; but, they still lack rigorous justification Finally, recent work has shown that power systems can exhibit chaotic behavior This surprising fact demonstrates that our understanding of the dynamics of power systems remains incomplete

Optimal Scheduling Of Large Hydrothermal Power Systems

Abstract: In this paper we present a new algorithm to find the optimal unit commitment and economic dispatch (UC/D) for a large hydrothermal power system. Mathematically, this is a large nonlinear, mixed integer optimization problem involving over 16,800 integer variables for a system having 100 thermal units with a 1-week scheduling horizon. We use a dual programming approach to solve a separate optimal control problem for each thermal unit and for each set of coupled hydro units. The algorithm has been tested on a 100 thermal unit/6 hydro unit system having a 168-hour scheduling period, and will find solutions that are within 0.1 to 0.25 percent of the optimal dual cost. We report computational results for a system modeled after the New York Power Pool.

A Solution of the Unit Commitment Problem Via Decomposition and Dynamic Programming

Abstract: Each day power generating units have to be selected to realize a reliable production of electric energy with the fewest fuel costs. This paper proposes decomposition and dynamic programming as techniques for solving the unit commitment problem, a high- dimensional non-linear, mixed-integer optimization problem. Experiments indicate that the proposed methods locate in less time a better solution than many existing techniques.

Generalized Method of Fault Analysis

Abstract: A generalized method is given for solving short-circuit faults of any conceivable complexity. The method efficiently combines the application of sparsity-oriented compensation techniques to sequence networks with the simulation of fault conditions in phase coordinates. All recent advances in features and modeling aspects of fault studies are incorporated in the method. Sparse vector techniques are extensively used to enhance speed and produce efficient fault solutions for any practical power system. The new algorithm has been thoroughly tested and presently is being implemented in a production- grade program.

Validation of Digital Simulation of DC Links

Abstract: A project was undertaken to test the validity of the electromagnetic transients simulation of dc links using digital computer programs. The Nelson River dc transmission system of both Bipoles One and Two were modeled on the computer using Manitoba Hydro's EMTDC program. The well known Electromagnetic Transients Program EMTP was also used for small reduced system models. Results from actual system tests were used to compare with the computer simulation of the same test. Comparisons are also made between EMTDC and EMTP as simulation tools for studying dc transmission. Computer simulation of dc links is presented as a valid option to the use of real time hard wired simulators.

A New Stabiliser Design Technique for Multimachine Power Systems

Abstract: This paper presents a new method of designing decentralised stabilisers for improved dynamic performance of multimachine power systems. The method determines the parameters of all stabilisers in the system such that some or all of its mechanical modes eigenvalues have desired locations in the complex plane. The proposed algorithm is general, effective and simple to apply. This is illustrated through three numerical examples including a three-machine and nine-machine infinite bus power systems, and with different degrees of system modelling.

Parallel Multi-Area State Estimation

Abstract: A parallel multi-area approach is presented in this paper for static state estimation of the power system. Because of a computational parallelism, the parallel multi-area approach significantly speeds up the computational process of state estimation. Furthermore this approach would help alleviate the perennial problem of insufficient computational power at the control center by down-loading most of the computational load of state estimation to relatively underused local computers. The paper also reports a summary of simulation experiments of the proposed parallel multi-area approach. The speed-up ratio and the parallel efficiency of the approach are obtained and the effects of the speed of telecommunication between computers upon these quantities are discussed.

Validation of Digital Simulation of DC Links - Part II

Abstract: This paper establishes the validity of digital simulation of transients in HVDC-ac power systems. For the digital simulation BPA's EMTP was used. Manitoba Hydro's Nelson River HVDC system comprising two HVDC bipoles, Bipole 1: 1668 MW and Bipole 2: 1000 MW was used for digital simulation test cases. The simulation results were compared with the field tests conducted by Manitoba Hydro.

A Linear Programming Method for Unit Commitment Incorporating Generator Configurations, Reserve and Plow Constraints

Abstract: A method of automatic unit commitment in a predominantly thermal power system is described. Linear programming techniques are used to dispatch plant at each time interval to minimise production cost over a load peak, or a daily or weekly load cycle. Generator configurations, flow constraints, functional reserve and time-limited reserve are modelled, with the capability for individual restrictions on any unit. The method has been implemented for operator usage in a control centre.

Security Assessment and Control System : Corrective Strategies

Abstract: A complete methodology for the solution of the real and the reactive subproblems of the general optimization problem that appears as part of the corrective strategies function of power system control centers is presented and analyzed. The method takes advantage of the linear behavior of the incremental relationships between the constraints and the controls. It dynamically selects a set of control variables for every iteration depending on the amount of overload to be corrected in the particular iteration. The algorithm has been used to alleviate several overloads for the IEEE 118 bus system under high and low loading conditions.

Floating Vector Processor for Power System Simulation

Abstract: This paper analyzes microprogram functions of the sparse matrix solution to obtain faster power system simulations such as the power flow calculation and transient stability analysis. The hardware structure and extended instructions of a floating vector processor (FVP) which realize simulation speed up are presented. Experimental results of a sparse matrix calculation and a power flow calculation lead to the following results: (1) the sparse matrix calculation, by the FVP is completed about 1.6 times faster than by a conventional array processor; (2) the processing speed of the FVP is ten to fifteen times faster than that of the general purpose supermini- computer Hitachi V90/50 Control Computer on the conditions that the programming style of the programs executed by the FVP is microprogramming fit to the FVP architecture, and the programs executed by the V90/50 are programmed in Fortran with simple optimization; and (3) the speed of the total power flow calculation by the V90/50 with FVP is 2.6 times faster than that by the V90/50 alone.

User-Friendly Workstation for Power Systems Analysis

Abstract: This paper presents the experimental study of advanced interactive power systems analysis using a-personal scientific computer. The personal scientific computer has new powerful displaying and operating capabilities. Our workstation, called the Advanced Analyzer of Power System (ADAPOS), intends to utilize these capabilities for power systems analysis. In addition our workstation has three features to perform effective human interaction: a supervisory system, database and graphic human interface. The supervisory system controls start and stop of application programs selected from a menu and guides a user to run them successfully according to the rules of analytical procedures. The database facilitates handling of both input and output data of application programs. The graphic human interface is the most important part of our system. Iconic and text menus, instead of a conventional command language, improve operational performance. Graphical presentations of analytical outputs, for example the color animation of power swings, aid understanding of power systems. The experimental results show that the new workstation highly contributes to effective power system analysis, although the computing speed is a little slow for large power systems.

Penetration of Wind Electric Conversion Systems into the Utility Grid

Abstract: This paper is concerned with the development of appropriate models for the interconnected operation of wind generator clusters with an autonomous power system and simulation techniques for the study of the degree of penetration of such wind electric conversion devices when operating in parallel with the utility grid. The quality of the interconnected system performance is specified in terms of operational constraints and the resultant penetration strategy is implemented via a microprocessor-based control scheme. The strategy assures a satisfactory level of system performance while optimizing the available energy transfer from the wind generators to the utility grid.

A New Real-Time Simulator for Power System Studies

Abstract: A new real-time simulator for power system studies is presented, including static VAR compensators, machines, HVDC stations, filters, lines, torsional shaft oscillation model. It is suitable for the study of the dynamic behaviour of complex systems and investigation of control problems also with real control apparatus. Mathematical models, the simulation principle, the hardware realization and experience with the simulator are described.

Applications of Dynamic Models in Dispatcher Training Simulator and in Other System Dynamic Performance Studies

Abstract: A number of steam turbine prime-mover models for extended system dynamics simulation has recently evolved and been documented from planning type of studies. Significant effort has been expended in the development resulting in some general awareness of this applicability. However, the effective model structure as affected by limited data, and individual dynamic response characteristics of these state-of-the-art models remain to be considered. It was not known how these models individually respond dynamically in terms of closed-loop response time and nonlinear effects such as dead-bands and limits. It was also not known how well these models can be used in a dispatcher training simulation. This paper presents computed results of individual unit dynamic responses of two such models out to several minutes. Computations simulating load following and breaker opening are included. The responses show nonlinear effects due to dead-bands in series with major control paths. The closed-loop response times are found to be not directly related to any single time parameter of the model. Effects and limitations of integration time steps and integration methods are illustrated. The results of the computational study show that the models can be adapted for dispatcher training simulation, and time steps can be as long as two seconds with appropriate choice of integration algorithm. Computational interface consideration for these models in other power system studies is also included in this paper.

Production Simulation for Power System Studies

Abstract: Predicting expected generation for different power plants as well as the system's total expected production cost is an integral part of quantitative power system analyses. Numerous publications presenting "exact" as well as "approximate" methods of solving stochastic production simulation problem exist in the literature. However, there is no one publication where a comprehensive review of this extremely important topic is presented. Such a review is the subject of this paper.

Development of Time Constant Regulator for Micronmachine

Abstract: Micromachines are small machines specially designed so that their parameters, on a per unit basis, are similar to those of large generators in power systems, and they are widely used to study the performance of these large machines under abnormal operating conditions through physical modeling and simulation.

The Application of Dynamic Programming in a Discrete Supplementary Control for Transient Stability Enhancement of Multimachine Power Systems

Abstract: This paper considers the use of a discrete supplementary control for transient stability enhancement of multimachine power systems. The principle advantage of the method presented in this paper is that off-line compuations are used. This permits the application of the supplementary control of a ``multimachine'' power system. The designation ``multimachine'' is used in this context to denote systems of up to three machines; for practical systems containing more than three machines, appropriate model order reduction is suggested. Supplementary controls differ from primary controls in that they are only used during disturbances rather than continuously. Attention is focused on the insertion of braking resistors and a specially designed dynamic programming algorithm is described for optimal resistor switching. The switching strategy is computed off-line so that the online computational requirements are minimal. The contribution of this paper is in the area of multimachine control and, in particular, a power system emergency state control. Topics concerning control models, optimization criteria and characteristics of discrete supplementary controls have been addressed. Control strategies are evaluated through digital and analog simulation involving a ten machine test system. A systematic approach to the optimization of multi-stage decision processes, called dynamic programming, was introduced by Bellman in the 1950' s [1-2]. Dynamic programming principles provide a perspective for examining optimization problems which lead to iterative functional equations. These equations are efficiently solved by using a digital computer and employing a dynamic programming computational procedure described by Larson [3].

A New Real Time Simulatro for Power System Studies

Abstract: A new real-time simulator for power system studies is presented, including static VAR compensators, machines, HVDC stations, filters, lines, torsional shaft oscillation model. It is suitable for the study of the dynamic behaviour of complex systems and investigation of control problems also with real control apparatus. Mathematical models, the simulation principle, the hardware realization and experience with the simulator are described.

Stability and security assessment of a class of systems governed by Lagrange's equation with application to multi-machine power systems

Abstract: In recent studies, it has been verified heuristically and experimentally (via simulations) that instability in power systems due to a fault occurs when one machine or a group of machines, called the critical group, loses synchronism with the remaining machines. Using energy functions associated with a critical group (rather than system-wide energy functions), transient stability results which are less conservative than other existing results, have recently been obtained. The existence and identity of a critical group is ascertained in these studies by off-line simulations. In the present paper, we establish some general stability results for a large class of dynamical systems (which are arrived at via a Lagrange formulation). We then show that our stability results can be used to establish analytically the existence and the identity of the critical group of machines in a power system due to a given fault. The applicability of the present results is demonstrated by means of a specific example (a 162-bus, 17-generator model of the power network of the State of Iowa).

A modern power system simulation laboratory: A power system engineering lab should be a priority for universities updating their facilities. One is currently being built at Virginia Tech.

Abstract: A description is given of a modern laboratory for power system engineering being developed at Virginia Polytechnic Institute and State Univ. Some of the considerations that have gone into designing the laboratory are summarized. These include: phenomena for simulation; simulation techniques; role of physical models; system size needed; transmission modeling techniques; transformer modeling techniques; machine modeling techniques; instrumentation, protection, and control; and scale factors.

Interactive Computation System for Relay Setting and Simulation of Relay Operation in a Large Scale EHV Power System

Abstract: This paper explains the interactive computation system for setting for the main and back-up protective relays used on the 500 kV and 275 kV power systems of the Tokyo Electric Power Co.. The object of the interactive system and the major calculations involved in the main protective relay setting and relay operation simulation are described. For the main protective relay setting calculations, this paper explains the basic theory and methods of relay setting; and in the relay operation simulation, it explains the basic theory, function and methods of calculation as well as the man-machine interfaces.

On the Mechanism of Transient Instability of Power Systems: Improved Results

Abstract: In recent studies, using energy functions associated with a critical group of machines, transient stability results which are less conservative than other existing results, have been obtained. The existence and identity of a critical group is ascertained in these studies by off-line simulations. In the present paper, we establish stability results for a multi-machine power system with non-uniform damping, and use these to establish the identity of the critical group of machines in a power system due to a given fault. The applicability of the present results in obtaining an estimate of the domain of attraction of an asymptotically stable equilibrium of a power system is demonstrated by means of a specific example.

Power System Simulation by Parallel Computation

Abstract: The concept of parallel processing is applied to power system simula­ tion. The Component Connection Model (CCM) and appropriate numerical methods, such as the Relaxation Algorithm, are established as a conceptual basis for the parallel simulation of small power networks and individual power system components. A commercially available multiprocessing system is intro­ duced for the power system simulator, and the system is adapted to facilitate high-speed parallel simulations. Two separate strategies for controlling the parallel simulation, synchronous and asynchronous relaxation, are introduced, and their performances are evaluated for the parallel simulation of an induction motor drive system. The performances of the parallel methods are also com­ pared to a similar simulation run on a single processor, and the results show that considerable simulation speed-up can be obtained when parallel processing is employed.

Adjoint modeling of electrical networks based on generalized tellegen's theorem

Abstract: The method fo r consistent adjoint siniulation of various e lec t r ica l systems (e.g. , lumped or distributed c i r cu i t s , power systems) i s introduced i n the paper. Sens i t iv i t ies of any function of system vdriables are obtained via adjoint aridlysis. The method presented i s bdsed on a generalized form o f Tellegen's theorem and i t uses the concept o f system secondary variables in the derivation of adjoint models. Adjoint elements are not defined in a unique way. A particular form of an adjoint element depends on the selection of secondary variables describing the original element. The method includes the case O F coniplex secondary variables as well as the case o f real seconddry vdriables. Adjoint models of some elements a re developed in t h e pdper t o i l l u s t r a t e the method.

Effect of accuracy of wind power prediction on power system operator

Abstract: This research project proposed a modified unit commitment that schedules connection and disconnection of generating units in response to load. A modified generation control is also proposed that controls steam units under automatic generation control, fast responding diesels, gas turbines and hydro units under a feedforward control, and wind turbine array output under a closed loop array control. This modified generation control and unit commitment require prediction of trend wind power variation one hour ahead and the prediction of error in this trend wind power prediction one half hour ahead. An improved meter for predicting trend wind speed variation is developed. Methods for accurately simulating the wind array power from a limited number of wind speed prediction records was developed. Finally, two methods for predicting the error in the trend wind power prediction were developed. This research provides a foundation for testing and evaluating the modified unit commitment and generation control that was developed to maintain operating reliability at a greatly reduced overall production cost for utilities with wind generation capacity.