Showing papers on "Power-flow study published in 1976"

A fast decoupled static state-estimator for electric power systems

Abstract: A new algorithm is described to solve the static, time-invariant weighted least-square state-estimation problem for large-scale electric power systems. The solution is obtained through P-θ and Q-V decoupling and alternately iterating the active and reactive equations using fixed, simplified submatrices of the information matrix. Thus, a much faster algorithm is obtained yielding the exact solution and requiring little computer storage. The new method is compared with the basic "Weighted-least-square" and the "Line-Only" algorithms on a practical HV network.

Probabilistic power-flow techniques extended and applied to operational decision making

Abstract: For effective control and operational decision making related to any power system, techniques are required to evaluate system insecurity risks. One such technique is to establish probabilistic load flows in the power system. The paper describes methods for extending the previously published probability and convolution techniques to powerflow studies in which the consumer demands are not totally independent (i.e. there exists some linear dependence between demands). The methods by which this can be achieved for appropriate probability density functions are described. An analysis of a power system, assuming in turn that demands are totally independent (uncorrelated), totally correlated, and partially correlated, is included and discussed, and the results for each formulation are compared. The potential use of this evaluation for risk analysis is discussed.

Long-term stability solution of interconnected power systems

Abstract: This paper describes solution and simulation techniques which result in an efficient and practical approach to long-term stability studies on digital computers. These efficiencies are derived from two algorithms used alternately to simulate large power systems. A technique for algebraization of differential equations, including the simultaneous solution of all network equations, is discussed. The results of testing the solution technique on large systems are included.

Evaluating alternative models for power system dynamic stability studies

Abstract: A dynamic stability model for detailed stability studies on synchronous power systems is presented in such a form that it can be systematically reduced to models of reduced complexity. The complete model includes representation of stator and network transient effects as well as shaft torsional oscillation effects. The family of models of reduced cemplexity span the range of models found in the literature. The general approach is applied to test cases where the effects of modelling complexity are investigated.

Qualitative indices for the system voltage and reactive power control

Abstract: Both in off-line and in on-line operation of energy systems, the computer has become an important ally of the engineer. However, results of calculations often obscure properties of steady state of the network. What will the power system network reaction be if one or more nodal voltage varies? How will these variations be reflected at certain nodes? How can one find rapidly a good operating strategy, even if not the best? Answers could be given by using non-linear programming procedures. Nevertheless, fast solutions can be found if heuristic techniques are introduced. This paper proposes to provide the power engineer with a class of indices which clears qualitatively the steady state of energy system network.

A dynamic power system model for teaching and research

Abstract: It is important to develop new laboratories for teaching and research in order to keep up with the advancement of modern power engineering1,2. This paper presents salient features of a "micro-machine" dynamic power system developed for teaching Power System Dynamics. It also has been used to develop new stabilizers to improve both dynamic and transient stabilities of power systems.

Elements of Power System Analysis, Third Edition

Abstract: The third edition of the well-known Elements of Power System Analysis consists of 14 chapters and 6 tables. The objective of the book is to present a broad range of topics related to electric power systems to electrical engineering students at the undergraduate level. Chapter 1 presents well-organized general background information: functions and structure of power systems, different types of power generating plants, voltage levels, recent growth trends, and introduction to load flow, economic load dispatch, fault, and stability studies. Chapter 2 reviews basic concepts. This chapter is new and is useful for the reader. Voltage, current, real and reactive power definitions, notations, and positive directions are given for single-phase and threephase systems. Chapters 3 and 4 discuss overhead transmission line positive sequence parameters: series resistance and inductance, and shunt capacitance for single-phase lines, three-phase single and double circuit lines, and for single and bundle conductors up to four subconductors per bundle. The treatment of series resistance, especially that of the skin effect, is significantly shorter than in the second edition of the text. Chapter 5 examines voltage and current relations on short, mediumlength, and long transmission lines, and complex power-flow diagrams in terms of ABCD constants. Chapter 6 is devoted to the representation of power systems: oneline diagrams, symbols, impedance diagrams, per-unit quantities and computations, impedance computations of three-winding transformers, and a review of dc calculating boards. Chapter 7 describes network equations and solutions for simple power-system computations, such as node elimination by star-mesh transformations, loop and node equation formulations, and node elimination technique, after a concise review of matrixes. Network bus admittance and bus impedance matrixes are also discussed somewhat briefly at the end of the chapter. Chapter 8 covers load-flow studies through the analysis of the GaussSeidel and Newton-Raphson iterative methods. Important features of digital-computer programs are also reviewed. Chapter 9 treats some principles of load-flow control. It starts with a review of synchronous machines. Then the roles of excitation and power angle of a synchronous machine are discussed. Capacitor banks, real and reactive power-flow control by regulating transformers (magnitudeand phase-shifting types) are also emphasized. Chapter 10 is concerned with the economic operation of power systems, specifically with the distribution of load between units within a plant, transmission losses, loss coefficients, distribution of load between plants, and includes an updated section on automatic load dispatching. The topic of Chapter 11 is symmetrical three-phase faults on synchronous machines. Transients in RL series circuits, synchronous machine reactances and short-circuit currents, machine internal voltages during transient conditions, and the selection of circuit breakers are covered. The use of the bus impedance matrix in three-phase fault computations is also a part of this chapter. Chapters 12 and 13 contain a discussion of relationships of unsymmetrical phasors and their symmetrical components, the phase shift of positiveand negative-sequence voltages and currents caused by wye-delta transformer banks, power in terms of symmetrical components, sequence impedances and sequence networks, and the derivation and analysis of unsymmetrical fault computations on unloaded generators and power systems. A brief review of the use of the bus impedance matrix for unsymmetrical faults is also given. Chapter 14 is entitled \"Power System Stability\" and reviews the stability problem, steady-state stability, transient stability quantities and equations (e.g., swing equation), equal-area criterion of stability, and the step-by-step solution of the swing curve for a two-machine system. Digital-computer programs for determining multimachine transient stability and some factors affecting transient stability are also discussed, although briefly. The text ends with an Appendix that contains electrical characteristics of ACSR conductors, synchronous machine constants, typical range of transformer reactances, and ABCD constants for six different networks. The value of the book is enhanced by about 65 numerical examples and about 200 problems (according to the publisher, there are 77 new problems). The reader will appreciate the abundant number of figures, the clear style and logical organization of the text, and the updated content related to modern trends in practice. Instructors of power system analysis courses or practicing engineers might miss some topics, such as the review of cables, zero sequence inductances and capacitances of transmission lines, and discussion of series faults and phasor diagrams for unsymmetrical faults. It would have been helpful to use metric and nonmetric units consistently together, following the guidelines of the IEEE. A comprehensive organized list of references at the end of the text would have been a valuable tool for further studies for the interested reader. In summary, this text is excellent, a welcome addition to the analysis of power systems, and a strong candidate for classroom use in power system analysis courses at the undergraduate level.

A model-referenced controller for stabilizing large transient swings in power systems

Abstract: This short paper deals with a control strategy which is considered reasonable for on-line stabilization of the large transient swings that occur in power systems following a major system disturbance. The strategy is compared to other similar strategies both in terms of philosophy and physical application. The example shows the benefit of on-line coordinated application of a dynamic brake and network switching to the transient stability problem when control decisions are implemented using a proper coordinating control strategy.

High-Resistance Grounded Power Systems--Why Not?

Abstract: Many systems could be high-resistance grounded--with the traceable signal to locate the first ground fault--to result in a safe, economical, reliable, and uncomplicated method of grounding of 480-. 2400-, and 4160-V delta or wye 3-wire systems--with these benefits

Improved power system state estimation with constant gain matrices

Abstract: An earlier paper described an algorithm for power system state estimation exploiting decoupling between active and reactive equations and including an estimation of regulating transformer ratios. An improvement which avoids repeatedly calculating the gain matrices is described. Execution times are decreased by up to 80 percent.

Generator and power system performance with the GENERREX excitation system

Abstract: Increasing pressures to limit transmission facilities while increasing the utilization of remote coal reserves and generating station sites is proving a challenge to the nation's utilities. Delays in obtaining construction permits, intervener actions, and difficulties in obtaining the required capital for financing have added to the challenge. The generator excitation controls can play an important role in achieving the goal of high service reliability under conditions which tend to reduce stability margins. High initial response excitation systems with high ceiling voltage capabilities can produce significant performance improvements, particularly in conjunction with power system stabilizer controls. A new concept featuring a high initial response excitation system has been developed which combines the excitation system power supply as an integral part of the generator design, utilizing common parts and cooling systems. Analytical prediction of the on-line performance of this new excitation concept is a vital requirement for both detailed design of the equipment and confirmation of power system design. Correlation of analytical results with factory test data on the prototype unit, The Montana Power Company Colstrip No. 1, establishes a measure of confidence in the ability to predict performance of this new equipment.

The Fletcher-Powell approach for large power system optimization

Abstract: The application of non-linear programming techniques to optimal power system planning and operation problems has been demonstrated in the recent literature. The Fletcher-Powell technique appears to be more efficient with regard to the computer time requirement compared to the other available approaches. The technique, however, fails to provide convergence for optimization studies of large power systems. This paper presents a decomposition approach for the extension of the Fletcher-Powell technique to large power system studies. The application of the technique has been demonstrated by a sample system study. The suggested decomposition approach also requires less computer memory and time and provides a better stability of convergence than the earlier techniques.

Discussion of "Generator and power system performance with the GENERREX excitation system"

Abstract: Increasing pressures to limit transmission facilities while increasing the utilization of remote coal reserves and generating station sites is proving a challenge to the nation's utilities. Delays in obtaining construction permits, intervener actions, and difficulties in obtaining the required capital for financing have added to the challenge. The generator excitation controls can play an important role in achieving the goal of high service reliability under conditions which tend to reduce stability margins. High initial response excitation systems with high ceiling voltage capabilities can produce significant performance improvements, particularly in conjunction with power system stabilizer controls. A new concept featuring a high initial response excitation system has been developed which combines the excitation system power supply as an integral part of the generator design, utilizing common parts and cooling systems. Analytical prediction of the on-line performance of this new excitation concept is a vital requirement for both detailed design of the equipment and confirmation of power system design. Correlation of analytical results with factory test data on the prototype unit, The Montana Power Company Colstrip No. 1, establishes a measure of confidence in the ability to predict performance of this new equipment.

State space analysis of electric power systems

Abstract: The dynamic analysis of a balanced three-phase electrical power system comprised of a finite set of: (1) synchronous generators, (2) induction and/or synchronous devices, (3) transmission line networks, (4) RL (or RLC)-loads, and (5) mechanical loads is analyzed by use of the state variable approach. Each component of the electric power system is described by its own state model. These constituent component state models are then interconnected as dictated by the topology of the power system at hand, and the state model for the total system is derived. The resultant state model can then be solved on a digital computer. The state models of the energy converters, the RL-load, and the mechanical load are borrowed from [6, 7 and 8], and the state model of the transmission line is borrowed from [1]. Finally, the algorithm GEBVEM, developed in [1] is used to formulate the state model of the power system at hand and to provide solutions for the desired state variables.

Stability of flows of a dynamic flow network

Abstract: The need for a network model for the purpose of study of stability of flows is first discussed. A dynamic flow-network model is then presented. It has applications to power networks. A two-matrix transformation method is used to find a suitable Liapunov function. Stability conditions are then obtained when some constraints are imposed on the dynamic components and on the connectivity of the network. The conditions are like a circle criterion, which are on the bounds of the conductances, the memoryless components of the network.

Stabilization of a power system through output feedback

Abstract: The optimal stabilization of a power system using the state variable feedback has the drawback that all the state variables are not available for measurement. A suboptimal control policy for stabilization of a power system is proposed, using the available output variables and employing the pole assignment technique. The proposed scheme is illustrated with an example.

Digital computer calculation of power system short circuit and load flow utilising diakoptics and sparsity techniques

Abstract: In part A a non-singular connection matrix is used to combine the self and mutual impedance matrix of a group of mutually coupled elements with a network bus impedance matrix; the resulting impedance matrix is then reduced by eliminating rows and columns if necessary, to give the bus impedance matrix of the interconnected network. The self impedances of the mutually coupled group of elements are added to the network bus impedance matrix in the same way as uncoupled elements, then the mutual impedances Are added followed by matrix reduction. By considering examples of the connection matrix applied to adding a single element, then to adding groups of uncoupled and coupled elements to a network, rules are devised for combining the celf impedances of branch and loop elements and group mutual imped-ances with the network bus impedance matrix. From the bus impedance matrix of power system sequence networks fault parameters are derived by simple arithmetic operations. It is shown that rules for adding a group of mutually coupled loop elements can be applied to modify a bus impedance matrix when element self and mutual impedances are changed. The derivation of an equivalent network from the bus impedance matrix is noted; the addition of two network bus impedance matrixes is considered and shown to be a special case of the more general problem of adding a self and mutual impedance matrix to a bus impedance matrix. A numerical example involving the calculation and modification of the bus impedance matrix, deriving an equivalent circuit and adding bus impedance matrixes is included. An outline of a digital computer power system short circuit programme which calculates fault parameters from the bus impedance matrix derived from randomly ordered lists of network element self and mutual impedances is given. The inverse of the connection matrix discussed in part A is used in part B to combine a network bus admittance matrix with the self and mutual admittance matrix of a group of mutually coupled elements. From this the Well known method of forming the bus admit-tance matrix from uncoupled element self admittances follows and is extended to cover self and mutual admittances of coupled elements. For a group of mutually coupled elements, the diagonal terms of the group admittance matrix are added to the bus admittance matrix in the same way as self admittances of uncoupled elements while the off-diagonal terms are added in a matrix operation either before or after the diagonal terms. A relationship is indicated between the admit-tance connection matrix and the group element bus incidence matrix. Although the presence of mutual coupling results in some loss of spal-sity, it is shown that for power systems the bus admittance matrix still has a large proportion of zero terms. By eliminating terms below the main diagonal in an optimal order, a "factored inverse" of the admittance matrix is derived which has considerably fewer non-zero terms than the corresponding bus impedance matrix. Terms of the Impedance matrix can be obtained from the inverse as required. The numerical calculation of the bus admittance matrix of a power system zero sequence network is set out and derivation of fault impedance and current distribution factors included. A digital computer programme using the bus admittance matrix and factored inverse method for power system short circuit studies is described and a tabulation indicates the affect on computer storage requirements of the optimal factoring procedure. In part C Newton's method of power system load flow calculation using Gaussian elimination to solve the voltage correction equations is discussed. The network and problem parameters are specified in rectangular cartesian co-ordinates. As the voltage correction equation matrix has the same form as the bus admittance matrix, a preferred order for the Gaussian elimination which preserves sparsity is devised by analogy with network reduction. A digital computer load flow programme is outlined and a tab-ulation included which shows that, for typical power system networks, the preferred elimination order retains sparsity in the matrix. Algol listings of the digital computer short circuit and load flow programmes are included in the supplement with data and corresponding calculated results for power system studies.