Showing papers on "Power-flow study published in 1984"

Power Generation, Operation, and Control

Abstract: Topics considered include characteristics of power generation units, transmission losses, generation with limited energy supply, control of generation, and power system security. This book is a graduate-level text in electric power engineering as regards to planning, operating, and controlling large scale power generation and transmission systems. Material used was generated in the post-1966 period. Many (if not most) of the chapter problems require a digital computer. A background in steady-state power circuit analysis is required.

Bound Estimates of the Severity of Line Outages in Power System Contingency Analysis and Ranking

Abstract: The effect of line outages on the real power flows of a system is analyzed using the DC load flow model. It is shown that the effect of the out4ge of line jk on the power flow of an arbitrary line lm can be bounded above and below by a series of progressively tighter values which in the limit correspond to the exact DC load flow solution. The calculation of these bound estimates on the contingency line flows is progressively more computationally demanding as the limits tighten, however, the simple to compute bounds, although more conservative, still serve to filter out a large portion of the non-critical contingencies. The remaining few potentially critical outages can then be ranked and analyzed through the full DC load flow.

A generalized energy function for transient stability analysis of power systems

Abstract: In this paper, an "energy function" is derived for transient stability analysis of power systems. The main contribution of this paper is the generality of the model for the loads. The loads are modeled as constant real power loads but the reactive part of the loads are modeled as arbitrary function of the load bus voltage. This model accounts for the voltage transients of the load busses and for this general model, it is shown that the system satisfies the law of conservation of energy. An efficient algorithm for determining the stability of the system for a given disturbance is described. Results of simulation of the system studied by El-Abiad and Nagappan [2] are included and it is shown that due to the fluctuations in the system voltages, the commonly used energy function over estimates the energy of the system during system transients.

Analysis of linearized decoupled power flow approximations for steady-state security assessment

Abstract: An analytic study of various approximations of the power flow equations for electric power systems is presented. The approximate models examined are the decoupled power flow, the linearized decoupled power flow (including the dc load flow) and the adjoint network sensitivity model, all of which are commonly used in steady-state security assessment. Error bounds on the difference between the solution of each of the approximate models and the solution of the full power flow are derived. The results are applied to the steady-state contingency analysis problem, resulting in a proposed new approach to the problem.

Ampere Magnitude Line Measurements for Power Systems State Estimation

Abstract: This paper describes methods for overcoming the problems associated with utilizing ampere magnitude line measurements in Power System State Estimators. The applicability of ampere magnitude measurements to Power System observability and on-line use in Energy Control Centers is examined. A simple five bus example is presented to point out various properties of ampere solutions and further test results with the IEEE 30 bus test system are discussed.

A Generalized Circle Diagram Approach For Global Analysis Of Transmission System Performance

Abstract: The global response of a power system to variations in the node constraints is considered. The relation of specific system variables to independent node parameters is calculated using a numerical technique which provides a generalization of the elementary power circle diagram. Curves which show system performance during disturbances, tradeoffs between design parameters, voltage stability limits and multiple power flow solutions are produced. The theory of the method is presented through geometrical concepts, and its application is illustrated with several examples.

Applications of robustness theory to power system models

Abstract: The applicability of the recently developed frequency-domain, matrix-norm robustness margins for physical systems is explored in this paper using a power system example. The power system is modeled using the damping-and synchronizing-torque framework. The robustness margins evaluated at several junctions of the power system model are shown to be useful measures of the system's tolerance for unmodeled shaft torsional dynamics and variations in the effectiveness of power system controllers (e.g., multiterminal high-voltage dc modulators). In addition, the robustness margins are shown to be useful for comparing the robustness of alternate controller designs. This paper ends with general guidelines for applying the matrix-norm robustness margins to physical systems.

The Integration of HVDC Subsystems into the Harmonic Power Flow Algorithm

Abstract: This paper is an extension of recent work done in harmonic power flow studies. The extension is inclusion of HVDC subsystems. An example using six pulse converters is given. Also, a simplification to the harmonic power flow algorithm is presented based on the accuracy of the fundamental frequency solution in the absence of nonlinear loads.

The critical point analysis of electric power systems

Abstract: New results are presented on the enumeration of critical points for classical power system models involving the power flow equations and the "swing" equations. It is shown how incorporation of electrical losses into these models restricts the numbers of physically meaningful solutions to the power flow equations.

Steady-state voltage stability regions of power systems

Abstract: The steady-state voltage stability of a power system is studied via linearized dynamical equations of on-load tap changers and steady-state decoupled reactive power flow equations. A set of conditions is derived for a hyperbox of tap settings and load bus voltages to satisfy the steady-state stability requirements. The results can be used to construct steady-state voltage stability regions for the security monitoring of power systems.

Distributed Power Architecture Concepts

Abstract: For critical electronic equipment applications such as PBXs (Private Branch Exchanges), system reliability is as important an index of performance as equipment first cost To minimize the effects of power failures on overall reliability, duplicate systems may be used to power the same loads However, in today's tight economy, such redundant configurations are often not a cost-effective alternative Distributed power architectures are designed to meet this dual challenge of low cost and high reliability A distributed powering arrangement divides the system load into several groups, each powered by its own power conversion unit, to limit the effect of isolated power component failures on total system operation The result is an economical fault-tolerant system This paper discusses cost and reliability factors for distributed power architectures

Wind and Solar-Powered Hybrid Prime Power Systems

Abstract: During the past five years, there has been rapid development in the field of wind and solar-powered hybrid prime power systems. This paper will discuss the following three aspects of this development: A review of accepted techniques for designing and installing a hybrid alternative energy system and also the possible pitfalls one might encounter. System controllers. System controllers play a dynamic role in the reliability of hybrid prime power systems. New developments in these controllers will be discussed, focusing on both accuracy and heightened reliability, including a discussion on the latest methods of amp-hour accumulation and subsequent signalling of control circuits and telemetry outputs. System sizing. System sizing plays an important role in the effectiveness and economics of a hybrid prime power system. A discussion of both the worst-case scenario as well as life cycle costing techniques will be presented. A step by step example will illustrate present techniques for optimization of wind and photovoltaic resources and battery capacity.

Energy-like Lyapunov functions for power system stability analysis

Abstract: In this paper, a concept of strong stability of an equilibrium point of an electric power system is introduced. It is shown that almost all stable equilibria of the standard transient stability model are strongly stable and that strong stability is a necessary and sufficient condition for the existence of a local energy-like Lyapunov function for all small perturbations of the nominal system. Such a Lyapunov function is explicitly constructed. A complete local analysis of the stability of power system equilibria in the presence of transfer conductances is given.

Distributed Rectifier Loads in Electric Power Systems

Abstract: Modern literature on power system harmonic problems, analysis, and solution is mostly of the case history type [1]. When the harmonic signal strength is low, the assumption of sinusoidal bus voltages is usually made, thereby simplifying analysis considerably. Since interest is often restricted to distribution circuits, simple radial circuit configuration is frequently assumed, and band (frequency) limitation of harmonics is also assumed. The proliferation of rectifier and other nonlinear loads, however, particularly in localized regions, suggests a renewed look at harmonic signals, especially at high harmonic content, near resonance, and cases of considerable bus voltage distortion. Xia and Heydt [2-3] have modified the Newton-Raphson power flow study algorithm to accommodate nonlinear loads without the assumption of superposition, radial circuitry, or sinusoidal bus voltage. Grady [7] has extended the Xia-Heydt algorithm to include nonlinear resistive loads (e.g. fluorescent lamps) and zero sequence signals. One of the primary reasons for the increased deployment of nonlinear loads is the successful development of high power semiconductor switching devices. Nonlinear loads are often characterized by either widespread distribution (such as the case in fluorescent lighting loads and electronic loads and such is the potential in the case of electric vehicle loads [4-6]). Also, the use of large industrial rectifiers directly on the subtransmission voltage system is not unusual in applications of large dc motors, electro-deposition installations, and induction furnaces. Static var devices are new electronic localized sources of harmonic signals.

Optimal reactive power planning

Abstract: A new method is presented for optimal long-term reactive power planning. The planning problem is divided in two parts: short-term and long-term planning. In the short-term reactive power planning problem, the real and reactive power is optimally dispatched for the economic operation of a power system. As in other methods, the problem is decomposed into a P-optimization module and a Q-optimization module, but in this method both modules use the same generation cost objective function. The control variables are generator real power outputs for the real power module and generator reactive power outputs, shunt capacitors/reactors, and transformer tap settings for the reactive power module. The constraints are the operating limits of the control variables, power line flows, and bus voltages. The long-term planning is to determine the required investment in reactive power compensation devices. The method economically determines the required compensation to keep system voltage profiles within a prescribed range which may change due to load increase over a number of years. This goal is achieved by reducing the operation cost (fuel cost) and investment cost in the system. The algorithm uses discrete optimal control theory to optimally determine the required annual investment in new reactive power compensation.

A Method to Analyze Voltage Resonance in Power Systems

Abstract: While the appearance of nonlinear devices as loads in electric power systems is not a new phenomenon, this sector of the total demand is significantly increasing and has reached substantial levels in many areas. Experience has shown that the configuration of the power system to which these devices are attached can be such as to cause a resonance condition to develop [1], [2]. This paper proposes a method to readily evaluate a system configuration so that an evaluation of possible problems due to harmonic voltage resonance can be made. This method will produce results with enough accuracy to reduce the need to run multiple modified Newton-Raphson power flow studies [3], [4].

Power system transient stability: The critical clearing time

Abstract: Energy and Lyapunov methods, termed direct methods, have been developed for the study of transient stability of power systems. Although they reduce the amount of computations involved, they have been found to be conservative, i.e. the critical clearing time predicted by these methods is found in most cases to be too small compared to the critical clearing time obtained via the conventional integration routines. Here we address the conservativeness problem and seek to remedy the direct methods approach to remove this obstacle. First we restate and prove a theorem upon which the analysis of the Lyapunov methods in the power system context have been based. The theorem originally is due to Willems but for which there has been no proof in the literature. We discuss the existing methods such as the controlling UEP and the PEBS (Potential Energy Boundary Surface), identify the sources of conservativeness in these methods and carefully illustrate these issues using a one machine-? bus example. A new view that aims at resolving the pessimistic (sometimes over optimistic) results of direct methods is presented, then a new approach which is based on parameterizing a "piece" of the boundary associated with the "Controlling" UEP is introduced. The concept of Controlling UEP appears to offer a feasible approach that can be made analytically sound. Finally, the new approach is applied to the one machine-? bus for the purpose of an illustration.

A Simple Approach to the Solution of the ac-dc Power Flow Problem

Abstract: The advent of inexpensive and reliable high-power SCR's has led to the reemergence of dc power systems for industrial and utility applications. Calculations of the voltage profile for these systems require that the ac-dc power flow problem be solved. While many texts treat the ac power flow, none to date have incorporated the ac-dc power flow. Presented in this paper is an approach for simultaneously solving the ac and dc systems equations which constitute the ac-dc power flow problem. The approach is valid for multiterminal HV dc links as well as industrial dc networks. The use of Newton's method in this approach allows the ac-dc power flow to be presented as a generalization of the ac power flow.

Disturbance decoupling control of the swing equations

Abstract: This paper initiates an investigation of the application of nonlinear disturbance decoupling theory to the emergency control of electric power systems. The nonlinear classical swing equation model for a network of generator buses is employed. A complete characterization of the set of decoupling feedback controllers is presented. The disturbances considered are generation and load loss, and the control mechanism employed is variation of mechanical input power.

A new efficient method for integrated control of voltage and reactive power in power systems

Abstract: This paper presents an efficient method for the integrated control of voltage and reactive power in power systems. This method is able to maintain the bus voltages in their permissible limits while simultaneously realizing well-balanced operation of VAR sources and a reduction in active transmission losses. The proposed method has the following features compared with the conventional methods. (1) Voltage and reactive power control is divided into two parts: control of the switchable VAR sources and control of the load tap-changing transformers. This decomposition technique can realize well-balanced operation of VAR sources.

Electrical power systems for Space Station

Abstract: Major challenges in power system development are described. Evolutionary growth, operational lifetime, and other design requirements are discussed. A pictorial view of weight-optimized power system applications shows which systems are best for missions of various lengths and required power level. Following definition of the major elements of the electrical power system, an overview of element options and a brief technology assessment are presented. Selected trade-study results show end-to-end system efficiencies, required photovoltaic power capability as a function of energy storage system efficiency, and comparisons with other systems such as a solar dynamic power system.

Design of the electrical power system

Abstract: The objectives of the power system design and choice of equipment are to ensure maximum security of supplies with operational flexibility at an acceptable cost. The paper describes the development of the design, from the conceptual pretender stage to the completion of manufacture of equipment ready for shipment to the site. In the development of the design a number of problems are identified, relating to the constraints of fault levels and voltage regulation on power systems with large induction-motor loads. Alternative solutions are examined, and reasons given for the solution adopted. The importance of computer modelling is emphasised in the analysis of power system design, not only for the solution of technical problems, but for optimisation to realise any cost advantages available. Finally, the authors indicate their views on future trends in system design for large power stations, and conclude that the objectives of supply security, operational flexibility and acceptable cost have been achieved at Castle Peak B.

A Discrete Model Approach to Power System Transient Performance Simulation

Abstract: A novel discrete model approach is presented for the integration of the differential equations involved in power system transient performance simulation. The models can be derived directly and analytically from the differential equations of the system dynamic elements, and the approach offers more precise and accurate solution than methods such as the implicit trapezoidal. Results obtained via the discrete model approach are compared with those using the implicit trapezoidal method and itemized breakdowns of the computational demands of power system simulation calculations are analyzed along with limitations on numerical stability.

The Formation of the Bus Impedance Matrix and the Solution of Power System Networks

Abstract: This note deals with the computation of the impedance matrix and the solution of the voltages of a power system, by adding one branch at a time. The technique is straightforwardly derived from general matrix theory results or from circuit theory concepts.