Showing papers on "Power system simulation published in 1987"

Security analysis and optimization

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.

Dynamic Programming Approach to Unit Commitment

Abstract: A field-proven dynamic programming formulation of the unit commitment problem is presented. This approach features the classification of generating units into related groups so as to minimize the number of unit combinations which must be tested without precluding the optimal path. Programming techniques are described which maximize efficiency. Considerations are discussed which determine when generating units must be evaluated and when they may be ignored. The heuristic procedures described in this paper are concerned with supplying all apriori information to the program thereby minimizing its execution time. Results are presented from field testing on a medium size utility. Composite generating unit formulation is described for the economic allocation of constrained fuel to a group of units.

Transient Stability Simulation by Waveform Relaxation Methods

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.

Constrained Load Flow Using Recursive Quadratic Programming

Abstract: The present paper will discuss the efficient, practical and definitive algorithm for dealing with constrained load flow problems. Algorithms based on mathematical programming and algorithms based on the load flow calculation methods have been studied since earlier days. However, on account of numerous control variables to be determined and of inadequate calculating efficiency, the guarantee of unfailing solution is yet to be achieved. In the calculating procedure herein described the extents of adjustments are not determined simultaneously for all the control variables ; the control variables considered likely to produce greater adjusting effect are selected one by one and are adjusted successively. This adjustment method, as a consequence, is useful not only for on-line power system operation but also as simulator software for training system operators.

Coordinated Static VAR Compensators and Power System Stabilizers for Damping Power System Oscillations

Abstract: Technical advantages of coordinating static VAr compensators and power system stabilizers for damping inertial and torsional modes of steam turbine generators are demonstrated. A new control concept for Static VAr Compensators based on using modal speeds as feedback signals, is presented. The concept enables a static VAr compensator to damp all the oscillatory modes as well as controlling the system voltage. A comparison is made between the cases where either modal speeds or generator speed deviations are used as the stabilizing signals of static VAr compensators. The present study shows that coordination of static compensators and power system stabilizers can significantly increase power system dampings as compared with cases where either static VAr compensators or power system stabilizers are used to damp system oscillations. This study is performed on System-1 of the second IEEE benchmark for SSR studies, using an eigenvalue method. The analytical results are verified by detailed digital computer simulation studies, using the BPA's Electromagnetic Transients Program (EMTP).

Reduced Order Modeling of Interconnected Multimachine Power Systems Using Time-Scale Decomposition

Abstract: Time-scale decomposition is used to systematically produce improved reduced order models of interconnected multimachine power systems. The method is illustrated with two fundamental examples. The first shows that the I = YV interface equation used for studying multimachine electromechanical transients is a zero order representation of the fast network transients. As such, the time-scale theory can be used to produce improved electromechanical models without adding the network transient equations. The second example shows how linear models for small change stability analysis can be improved to virtually any degree of accuracy. The advantages of the improved models are shown with both a two- and three-machine system.

A Parallel Computation Algorithm for Static State Estimation by Means of Matrix Inversion Lemma

Abstract: This paper presents an effective parallel computation algorithm for the static state estimation of a power system. The proposed algorithm makes use of the matrix inversion lemma and assumes the use of a MIMD type computer system. The optimal block-partitioning algorithm which tears a power system into several blocks is presented and its clear difference from that for the load flow is clarified. Simulation results on systems of up to 135 nodes have demonstrated the algorithm is very promising to the speed up of the state estimation.

Power System Transient Stability Indexes for On-Line Analysis of "Worst-Case" Dynamic Contingencies

Abstract: The need for on-line analysis of power systems stability vis-a-vis postulated disturbances is felt more than ever before in modern energy control centers. The lack of a general practically implementable analytical method, makes it necessary to consider special classes of contingencies each with its own particular a priori characterization amenable to on-line analysis. In this paper a particular class of disturbances, namely faults near generator terminals, are considered; these are regarded to be "worst-case" conditions. The effects of breaker operation and the load model are taken into account. Two stability indexes are defined depending on the load model. Their computation for individual faults involves evaluation of straightforward algebraic expressions and is thus extremely fast. Simulation results are presented which demonstrate the discrimination capability of the indexes and the validity of the overall approach.

Multi-Area Reliability -- A New Approach

Abstract: Transmission interconnections can improve power system reliability, and this reliability improvement can be measured by the change in loss of load probabilities (LOLP's) . This paper presents a new method for evaluating loss of load proba bilities for an interconnected multi-area system. This method is based upon a reduced set of demand-supply feasibility conditions. This reduced set of feasibility conditions are used to directly define the infeasible region without iterative state space decomposition. LOLP's are then evaluated by attributing the probabilities of infeasible states to the appropriate reliability indices. The simulation results of a sample four-area system with 9,068,544 capacity states are presented in this paper. The computational efficiency of the proposed method is also illustrated in this paper.

Real-time power system simulation

Abstract: This paper describes the theoretical basis and application of a simulation package for electrical generation, transmission and distribution systems. The software provides an environment for the development and testing of online analysis and control algorithms, and also has potential for application in operator training. Dynamic and algebraic models of power system elements are described which are appropriate for study time scales of up to one day. Numerical techniques are presented which obtain solutions with acceptable accuracy in real time for medium sized networks using minicomputer hardware. Typical results are given for a test network of 30 substations which illustrate the dynamic behaviour of the network under emergency conditions.

A Multi-Micro-Computer based Dual-Rate Self-Tuning Power System Stabilizer

Abstract: A dual-rate self-tuning control technique, in which the system identification and control calculation are performed separately, is proposed in this paper. This greatly increases the control rate. A self-tuning power system stabilizer (DSPSS) making use of this technique is developed and implemented using multi-micro-computers. Simulation and experimental results with DSPSS show that the increase in the control rate can considerably improve the system performance.

Benefit Assessment of Finite-Element Based Generator Saturation Model

Abstract: The accuracy with which power system transient stability limits can be calculated by computer simulation depends on the synchronous machine model. The saturation representation in the machine model can be improved now by non-linear magnetic finite element analyses of the machine. This paper describes steps taken to incorporate a saturation algorithm, based upon finite element analyses, into an 1100 bus power system stability program. Power transfer capability of a hypothetical system is compared using the finite element based algorithm versus the conventional algorithm based upon the manufacturer's open circuit saturation curve.

The Energy Systems Research Center Electric Power System Simulation Laboratory and Energy Management System Control Center

Abstract: The increasing complexity of the systems that monitor and control a modern power grid require of the power engineer and system operator a correspondingly greater fundamental understanding of phenomena occurring in the system from a system point of view. With the objective of giving the engineer and operator this increased understanding, the Energy Systems Research Center is now in the process of constructing a model electric power system coupled with a commercially available Energy Management System control center. The combination of EMS and realistic power system model make this a unique laboratory in which can be performed studies in stability, system control, power system load modeling, etc. The paper gives an overview of the design of the realistically scaled down, three phase model power system, and it's integration with the EMS control center. The paper concludes with a discussion of how the laboratory is to be used.

A Methodology for Dynamic Utility Interactive Operation of Dispersed Storage and Generation Devices

Abstract: This paper is introducing a new methodology for the dynamic integration of dispersed storage and generation devices into the electric utility distribution network operations. The dispersed source is viewed as an active device contributing towards the regulation of real and reactive power flows while improving the stability of the power system. Conceptual means are developed for an effective DSG-utility grid interface. Computer models of appropriate interconnection and control equipment are used in simulation studies to test the effectiveness of control strategies and optimize design parameters. Simulation results indicate that load frequency control and voltage regulation may be effectively accomplished with dispersed generators within a fraction of the time required for conventional regulating units. Appropriate modulation and conditioning of the DSG-output power can assist in damping out undesirable power oscillations. Implementation of the proposed policies may result in reduced load following requirements for conventional power generating units, increase the value and acceptability of new energy technologies, and improve power quality and stability of the interconnected system.

An algorithm for transient simulation of power electronics systems

Abstract: The development of a general algorithm, which constructs the state equations of switching systems as a function of the state of their switching elements, is presented. Although the algorithm is developed primarily for transient simulation of power electronics systems, it can be applied to any system that can be modeled by an equivalent circuit consisting of linear ERLC elements and ideal switches.

Application of the Two-Step Compensation Method to Line-Out and Line-End Fault Calculations

Abstract: This paper presents an application of the two-step compensation method to the most commonly performed line-out and line-end fault calculations, demonstrating the use, generality and flexibility of the algorithm. The paper is aimed at both computer applications engineers who might implement the algorithm described herein in software packages, and protection engineers who might use the paper's heuristics to efficiently guide their analyses. The compensation-based scheme is extremely powerful for solving problems involving large-scale power systems. Detailed, step-by-step numerical computations are carried out for five examples in this application paper. The examples include calculations for a line-end fault with ensuing line outages. Mutual couplings are included in the network.

Computer Applications in Power System Analysis at the Ohio State University

Abstract: This paper will review the use of the computer (both main-frame and micro) as a tool in electric power system engineering education at The Ohio State University.

A Real-Time Digital Simulation of Synchronous Machines: Stability Considerations and Implementation

Abstract: The study of the transient behavior of a large power system has been difficult and time consuming even on mainframe computers. One way to obtain real-time studies is to configure digital simulation modules in a parallel processing network that corresponds to the physical system. The focus of this work is on the creation of a generator module that is compatible with such a digital simulation network. To approach operation in real time, a fast and accurate state equation integrator is required. Investigation has revealed that the load imposed on the simulated generator plays a major role in the stability of the integration routines. The linearized stability limits of forward difference, modified Euler, fourth-order Runge-Kutta and Adams-Bashforth-Moulton integration methods were calculated for an impedance terminated generator. These were found to agree closely with the corresponding experimentally determined nonlinear limits. The TMS32010 digital signal processor was chosen as the heart of the generator simulator module, and fixed-point arithmetic routines were developed to make it a high-speed state equation integrator. Operation in real time was achieved for an infinite bus-type termination, but an impedance load led to a somewhat slower simulation.

A Unique Method of Evaluation of System Damping in Simulations of Large Power Systems

Abstract: This paper documents a practical numerical method of evaluating damping of slow oscillations in computer simulations of large power systems. This technique has been tested and improved over the last two years. The damping coefficients can assist in evaluation of acceptable transfer limitations. The proposed method also provides a means to evaluate the sensitivity of various transfer path loadings and transmission and generation facility contingencies on system damping.

Simulation for electrical characteristics of superconducting generator connected to a power system

Abstract: This paper describes simulation studies on the electrical characteristics of a superconducting generator (SCG) connected to a power system. In the system for the simulation studies, the SCG is connected to an infinite bus through two transmission lines in parallel. The equation describing the SCG is the so-called Park's Equation, which is derived from electro-magnetic analysis. The characteristic of the driver of an SCG is taken into account, which affects the transient behaviors of the SCG. The initial values when the system changes (e.g. the system fault) are considered. The simulation results agree well with the experimental results. The torque and the Joule heating of the cold and warm dampers during transient states are calculated.

Multi-microprocessor power system simulation

Abstract: This thesis presents the results of research performed into the simulation of electrical power systems using a set of microprocessors operating in parallel , The uses and methods of simulation on analog and single processor computers are discussed as well as on multiple processor machines . It then considers various methods already used in the field of simulation for both the dynamic and network sets of equations in detail and the problems of using them on parallel processors . Several possible methods of parallel simulation are proposed and the best of these developed into a detailed algorithm for simulating both the dynamic and network portions of the power system .The different types of multiprocessor system are looked at , both in terms of physical configuration and the type of hardware used to implement the different types of system .The problems inherent in parallel computing are discussed and a form of multiprocessor, suitable for the simulation algorithm, is then developed taking these problems Into account. The hardware is developed using widely available hardware and the algorithm Is then Implemented upon this hardware .The results obtained using the simulator show that the proposed system provides a more economical solution, both in terms of the time taken in producing results and in the cost of the system, when compared with a conventional single processor computing system such as a mini computer.

Concurrent architectures for power system control

Abstract: Electric energy systems require powerful and flexible computer structures for on-line control at different levels. This paper briefly discusses control requirements and computer architectures, proposing some new research areas according to past experiences and future developments of computer technology. Design and test of efficient, concurrent algorithms for power system simulation is one of the most important tasks.

Long Term Power System Simulation for Real-Time Training with a Reduced Size Program

Abstract: This paper presents a brief description and discussion of the results of a reduced size computer program for long-term power system simulation. It includes detailed models of a hydro, a coal-fired and a pressurized water reator (PWR) generation plant. Typical data taken from operating records have been used. Since the simulation runs faster then real-time, the program can be used as a power system simulator operator training.

Correspondence: experience with economic dispatching for a rapid developing power system

Abstract: This paper presents a method to solve unit commitment and economic dispatching problems for rapid developing power system of moderate size. The method is simple and can be used by system engineers without requirement of sophisticated expensive commercial computer codes. In spite of that the main goal of these rapid growing systems is to satisfy their demand securely, yet using this method will reduce the production cost even with one type of generation. The heat rate models for the different units have been obtained using two sets of data, the designers and the on site test data indicating the importance of site test data.