Large Electric Power Systems Research Articles

Semi-rigorous thermal unit commitment for large scale electrical power systems

The paper describes a new method developed for solving the thermal unit commitment problem in large-scale electrical power systems semi-rigorously, by using a hybrid form of the discrete decision linear programming (DDLP) [13] and heuristic techniques. It is capable of incorporating all the operational constraints of the system and obtaining fully feasible schedules. The developed algorithm has been tested on a CDC7600 computer to solve the thermal unit commitment problem in the South-Western Region subsystem of the CEGB. Simulation results have shown that various solutions with different characteristics can be obtained for the same problem, requiring modest computer time and memory. Encouraging financial savings have also been obtained due to employing an optimisation (DDLP) technique within the method.

From Computor to Electrical Engineer: The Remarkable Career of Edith Clarke

Edith Clarke's electrical engineering career had as a central theme the development and dissemination of mathematical methods that served to simplify and reduce the time spent on laborious calculations in solving problems encountered in the design and operation of large electrical power systems. As an engineer with the General Electric Company from the early 1920's to 1945, she worked during a time when power system analysis was evolving from being labor intensive to being machine intensive, with much of the labor of problem solving being shifted from human computors, often women, to electromechanical computers, such as the network analyzer and differential analyzer. This trend culminated in the development of electronic computers beginning with the ENIAC that was completed during the same year that she retired from GE. As a woman who worked in an environment traditionally dominated by men, she demonstrated that women could perform engineering analysis at least as well as men if given the opportunity. Her achievements provided an inspiring example for the next generation of women with aspirations to seek a career in electrical engineering.

Decentralized Voltage Control in Electric Power Systems

In large interconnected electric power systems the bus voltages of the feeding nodes are to be maintained at local optimum values. To avoid large information transmission networks this control task must be carried out by a decentralized control. bach control station has to ensure asymptotic regulation for the corresponding feeding node. Moreover, the controller parameters should be chosen so that the closedloop system remains stable even if several control stations are disconnected. By me ans of a necessary and sufficient condition for the existence of such controllers and the data of a real-existing power system with 20 feeding no des it is proved that vOltage control can actually be carried out in a decentralized way. As a byproduct, it is shown that this result holds for all systems with a ‘near-ideal’ voltage-reactive power behaviour.

Aggregate Feasibility Sets for Large Power Networks

An aggregate feasibility set for large electric power systems is derived. The feasibility aet consists of the set of snbstation loads that can be served in steadystate with the available generation without overloading the transmission lines or transformers. The derivation is based on an aggregate continuum model of large power systems that is obtained from the DC losad flow model.

Decentralized stabilization of large electric power systems

This paper considers the problem of stabilizing the dynamics of a large electric power system, represented by a linear time invariant system of equations, by using several decentralized (or local) state feedback control laws. The stabilization problem is formulated into a functional minimization problem which implicitly controls the closed-loop eigenvalues of the controlled system. The constraint of decentralization is tackled in the minimization algorithm by using the method of feasible directions. To illustrate the application of the algorithm, it is used to stabilize a three machine electric power system.

The Han Powell Algorithm Applied to the Optimization of the Reactive Power Generation in a Large Scale Electric Power System

In this paper the Han-Powell algorithm is proposed as a means for optimizing the reactive power generation in a large scale system. The algorithm is based upon the iterative resolution of quadratic programming subproblems. Other approaches based upon recursive resolution of linear programs seem not to be suitable for the strongly non linear characteristics of the problem.In the adopted model, a reduced and compact problem is solved with only inequality constraints.The equality constraints (load flow equations) are utilized to eliminate a large number of variables (dependent variables). In this way the optimization model is expressed only in terms of the control variables (reactive power generations or generator terminal voltages and LTC transformer tap positions). This approach allows ns to perform the reactive power scheduling of the Italian electric production and transmission system (with about 500 nodes) with reasonable computer requirements (CPU time and central core). The main advantages of the Han-Powell method are:-it is robust and reliable-it shows a sure and fast convergence-it is easy to implement provided a good quadratic programming subroutine is available.

Topologically-Partitioned Power System State Estination

Estimating the state of a large electric power system is an ill-conditioned computational task simply because of its size. This paper describes a technique which reduces the large state estimation problem to a set of smaller least-squares problems plus the solution of a square system. An observability algorithm developed earlier is used to partition the system into sub- networks whose states are estimated separately. These separate estimates are reconciled using the solution of an interconnecting subnetwork consisting entirely of measurements whose removal would render the full system unobservable. Under appropriate conditions, this partitioned state estimate is identical with the usual full least-squares estimate. Details of the implementation of this algorithm are given, and its application to the IEEE 30-bus network is described.

Coherency identification for large electric power systems

An important problem associated with contingency and reliability studies for large-scale electric power systems is the use of dynamic equivalent models to represent the behavior of aggregable parts of the system. Fundamental to the aggregation process associated with any coherency-based approach is an ability to identify groups of coherent generators or generators that swing together in response to a contingency. Coherency identification is thus a key step in the reduction process. In this paper, an analytical process is examined which permits identification of coherent groups based upon the closed-form solution of a linearized power system model and the use of the Cayley-Hamilton theorem. The result is an algebraic characterization of coherency. Computationally practical coherency indices are developed which do not require significant computer storage. A physical interpretation of this characterization is discussed which suggests that coherency depends not only of the electrical distances between generators but also on generator inertia constants. The method of coherency identification developed in this paper is evaluated on a detailed model of a 39-bus test system.

Eigenvalue Analysis of Synchronizing Power Flow Oscillations in Large Electric Power Systems

A new computer program is described which permits eigenvalue analysis of the oscillations associated with synchronizing power flow in large electric power systems. The program has been given the acronym AESOPS, for the Analysis of Essentially Spontaneous Oscillations in Power Systems. The program is the principal product of a research project funded by the Electric Power Research Institute. This project was recommended by the Westinghouse Advanced Systems Technology Division and the MAPP/MARCA Dynamic Device Operating Task Force.

Present State of the Art and Prospects for On-line Security Control in Large Scale Electric Power Systems

Present State of the Art and Prospects for On-line Security Control in Large Scale Electric Power Systems

Ultra fast state estimation for the large electric power system

A reorganized solution of the state estimation problem is proposed which takes advantage of dedicated microprocessors at the local buses to circumvent interacting solutions of the power flow equations. The latter makes conventional state estimation much too time consuming for on-line use in emergencies.

Hierarchical state estimator: A new way for large power systems estimation

We propose a new concept suitable for performing static state estimation in large scale electric power systems. It consists in decomposing the over-all system into sub-systems and in carrying out a two-level calculation. In a lower hierarchical level, a standard state estimation is at first performed in parallel for all sub-systems and independently from each other. A coordination of these local estimations is then realized at the second (upper) hierarchical level which, by this means, receives and treats only a small number of variables. It may therefore obey various requirements, such as goegraphical, economical, etc. The advantages of this hierarchical procedure over the standard “integrated” one are drawn in the Conclusions.

Uncertainties in large scale electric power systems

Uncertainties in large scale electric power systems

A New Approach to Transient Stability Analysis of a Large Scale Electric Power System

A new approach to transient stability analysis of a large-scale electric power system based on the two-level structure of a power system has been suggested. At the superior level comprising the EHV network with connected controlled power station nodes, the state vector is estimated using the new static state estimation method presented here. This estimated vector is used by the lower level, comprising controlled synchronous machines to the fast transient stability analysis of a large power system.

Prospects for Dynamic Security Monitoring in Large Scale Electric Power Systems

Prospects for Dynamic Security Monitoring in Large Scale Electric Power Systems

Power System State Measurements for Transient Control Augmentation Using Digital Techniques

Any strategy, considered reasonable for the control of transient modes which occur as the result of a major disturbance in a large electric power system, will require fast and reasonably accurate measurements of at least two states per machine, namely, rotor speed deviation and torque angle. Since any control strategy will probably require an on-line digital computer for decision, computation, and execution, minimal computation time for the determination of state is imperative. Such a computer based technique along with the pertinent hardware for implementation is presented in this paper.

Use of computer model of interconnected power system to assess generation control strategies

This paper describes the development, validation and use of a non-linear dynamic model developed for the study of automatic generation control and economic dispatch structures within a large multi-company interconnected electric power system. The model constitutes a unique tool for the realistic evaluation of the dynamic performance of newly developed system control and dispatch strategies. The improvements obtainable with these strategies and the determination of sufficient response reserves are demonstrated.

Simplified model for dynamic stability studies

The study of dynamic stability of large interconnected electrical power systems is time consuming and requires large storage capacity of the digital computer memory. A simplified model is developed to reduce the storage space required for the system matrixA which represents the generators field, amortisseur windings, voltage regulators, speed governers, and the interconnected power net work. This is done by transforming theA matrix, which is almost full matrix to sparse one so while the storage requirement is reduced, the time of computation is minimized.

State Estimation of Large Scale Electric Power Systems by Decomposition Methods

This paper deals with the computational methods for the state estimation problem of a large-Scale electric Power system. This state estimation problem can be defined as the power flow problem which has overdetermined boundary conditions, and non-linear function minimization techniques can be used to solve the problem. The mathematical foundation of proposed methods is based upon the perturbed Newton method which includes as special cases standerd function minimization techniques such as Newton-Gauss method, Fretcher-Powel1 method and steerest descent method.The proposed methods in this paper are considered as decomposition methods for the reason that the coefficient matrices of iteration schemes are decomposed into block diagonal forms from the view joints of a power system configuration or a sersitivity between variab1es.These methods are suitable for the state-estimation problem which has many state variables for the simplicity of the coefficient moatrix in non-linear function minimization techniques.

Meteorological Diversity-Load Diversity, A Fresh Look at an Old Problem

Abstract A method is developed which can be used to produce estimates of electric power load diversity from samples of ambient daily mean temperature observations from a large interconnected power system. This method has several advantages, the most important of which is the comparative case with which homogenous samples of temperature data can be located. The method is believed to have important applications in long-term planning of large interconnected electric power systems.