Showing papers on "Electric power system published in 1968"

Computer methods in power system analysis

Abstract: This book is written by authors who are well known for their pioneering work in the application of computers to power system analysis. The book concentrates on the mathematical formulation of the engineering problem and the appropriate techniques of numerical solution with simple theoretical explanations. The book is both practical and easy to read and is illustrated by many worked out examples and supplemented by engineering problems with realistic data. It also contains a comprehensive bibliography for the reader to supplement his knowledge if he so wishes.

Transmission System Reliability Evaluation Using Markov Processes

Abstract: The basic concepts of stationary Markov processes and particularly their application to transmission system reliability evaluation are discussed and illustrated. Transmission components are assumed to operate within a 2-state fluctuating environment described by normal and stormy weather conditions. Markov processes are used to determine the system failure rate and the probabilities of failure for simple configurations and to illustrate the bunching effect of storm associated failures on parallel facilities. The variation in the failure probabilities is shown as a function of the expected repair time and the degree of storm associated failures. The results are compared with those obtained using a previously published approximate method.

The Phase-Locked Oscillator - A New Control System for Controlled Static Convertors

Abstract: Static convertors for high-voltage direct-current transmission links, whether based on mercury-arc valves or thyristors, are controlled by accurately timed firing pulses from a control system. With conventional control systems it has not so far been practicable to operate a convertor on a very weak (high impedance) ac system; one principal reason is inherent harmonic instability caused by the direct dependence of the control system on ac line voltage and its distortion.

Dynamic Stability Calculations for an Arbitrary Number of Interconnected Synchronous Machines

Abstract: Describing the small signal performance of a multi- machine synchronous power system by a set of differential equations of the form [x] = [A] [x] allows standard multivariable control theory to be used in dynamic stability studies. The construction of the [A] matrix for a multimachine power system involves the application of Kron's rotational transformation to the transmission network admittance matrix, and a matrix analysis of the synchronous machines using internal flux linkages as state variables.

Optimum Control of Reactive Power Flow

Abstract: The general problem of minimizing the operating cost of a power system by proper selection of the active and reactive productions is formulated as a nonlinear programming problem in accordance with previous work by Carpentier of Electricitede France. This general problem is particularized to the minimization of transmission line losses by suitable selection of the reactive productions and transformer tap settings. An efficient computational procedure based on the Newton-Raphson method for solving the power-flow equations and on the dual (Lagrangian) variables of the Kuhn and Tucker theorem is discussed. This minimization procedure has been applied successfully to a 500-node system studied by the Bonneville Power Administration for which an effective power-flow program had been developed previously. The dual variables associated with the primary (electrical) variables are obtained in the course of the computation, and their engineering significance for power system design and tariffication is emphasized. The procedure has been extended to the general case of combined active and reactive optimization.

Frequency and Duration Methods for Power System Reliability Calculations: I - Generation System Model

Abstract: As a goal, the evaluation and computation of electric power system reliability requires that a consistent technique be used for all portions?generation, transmission, and distribution. At present, a number of different methods are used for the generation system, while the frequency and duration of outages seems to be developing as a standard measure for the analysis of the distribution system. This paper and a subsequent one will present a reliability calculation method for the generation system that incorporates the frequency and duration of unit outages and includes consideration of the loads. This method leads to calculated generation reliability measures which are the availability, frequency of occurence, and mean duration of reserve states. These are cumulative states in that they specify system reserve conditions of a given magnitude or less. This paper is concerned with the procedure for calculating the availability, frequency, and outage duration for a number of generating units connected in parallel to form a single system. Numerical data are used to illustrate the technique and make comparisons with other methods.

Method for economic secure loading of a power system

Abstract: A procedure is described for determining the most economical schedule, consistent with network security requirements, for loading plant in a power system. Conventional methods require excessive calculation time and computer storage, which render them impracticable for online computer control; these difficulties are overcome by using a linear-programming procedure utilising a modified form of the simplex method. This modified method enables the network relationships to be used to reduce the computation and storage required. With currently available computers such as the IBM 7094, the method is applicable to systems up to the size of a Grid control area.

Optimum Load-Shedding Policy for Power Systems

Abstract: The now classical problem of optimlum dispatching miimizes the cost of production and transmission of electrical power to meet a specified demand under normal operating conditions. It appears logical and desirable to utilize and extend the methodology of optimum dispatching to problems encountered during abnormal operating conditions. This paper, as a first step in that direction, discusses a systematic approach toward minimizing the curtailment of service in a power system after a severe fault. The problem of minimizing load curtailment under a given set of emergency conditions is formulated as a problem of static optimization, subject to operational and equipment constraints. First, a feasible steady-state solution is obtained for the postfault network configuration. Starting from this initial feasible solution, the optinum (minimum curtailment) is approached by a gradient technique. An efficient computational procedure is based on the Newton-Raphson technique for solving the power flow equations, and the Kuhn-Tucker theorem for the optimization. The analytical results are verified on a 26-node example problem. Two typical emergency situations are considered: the loss of generation and the loss of an interconnection tie line. The same optimization procedure and the computed dual (Lagrangian) variables can be utilized for computer programs involving optimum service restoration, generation reserve scheduling, and system expansion studies.

Digital Simulation of Multimachine Power Systems for Stability Studies

Abstract: A digital simulation technique suitable for detailed analysis of both large and small disturbances on extensive power systems is presented. The analysis employs a hybrid reference frame for statement of the problem and for its solution. The equations of the interconnecting network are expressed with regard to a synchronously rotating common reference frame and are treated with the aid of matrix methods. Synchronous machine equations and equations of the voltage regulator and of the speed governor are solved in Park's reference frame fixed to the field of each individual machine. Provision is made for representing different machines in different degrees of detail. An efficient numerical technique for solution of the resulting complex nonlinear equations describing the behavior of the complete power system is introduced.

Influence of Excitation and Speed Control Parameters in Stabilizing Intersystem Oscillations

Abstract: Intersystem power oscillations have occurred between the interconnected utility systems of Saskatchewan, Manitoba, and Ontario (West System). Such power swings have been most evident when the power transmission angles on the interconnections or on certain internal 138-kV and 115-kV transmission have been of relatively great magnitude. The oscillations have been controlled or reduced by adjustment of the excitation of speed control parameters on various groups of machines throughout the three inter- connected systems. The analytical techniques utilized to determine the adjustments will be of considerable benefit in planning future exrtensions to the interconnections and facilities within the power systems in the three provinces.

Techniques for load prediction in the electricity-supply industry

Abstract: Considerable work has been carried out in recent years on problems concerned with load-flow analysis, economic generation scheduling and system-security checking in electrical power systems. An aspect of the overall problem which has not received much attention is that of forecasting electrical load demand. It is, however, important from the practical point of view of economic generation scheduling and security checking to be able to predict accurately load demand several hours in advance. Methods of prediction fall into two basic categories: those which use weather forecasts and meteorological information, and those which use past load data only. In the paper, the various methods which are commonly used for short-term prediction are described and their relative merits are discussed.

Dynamic Simulation of HVDC Power Transmission Systems on Digital Computers - Generalized Mesh Analysis Approach

Abstract: This paper introduces and develops a new generalized approach to the dynamic simulation of an HVDC power transmission system. The approach involved is a generalized method of mesh analysis applied to the HVDC network. The simulation of HVDC convertors is characterized by the fact that the network to be solved changes with each discontinuity, such as valve firing and end of commutation. To facilitate such an analysis, topology is used and a technique is developed for the automatic selection of the appropriate network by recognizing the state of conducting and nonconducting valves. The method is inherently suitable for following the natural process of convertor operation which may culminate in various faults. To illustrate this method a simple HVDC system consisting of one convertor at each end is considered. Essential features of the program are shown by deriving waveforms of normal operation, commutation failure, four-valve conduction, bypass valve operation, and backfire.

Generation of Abnormal Harmonics in High-Voltage AC-DC Power Systems

Abstract: The possibility of abnormal harmonic generation in an ac system feeding a converter load is examined from the standpoint of automatic control systems used in modern HVDC transmission systems. It is shown that with certain types of automatic controls, the firing angles of converter valves may sustain some errors, which in turn could generate abnormal harmonic currents in the three- phase ac system feeding the converter. A criterion for predetermining the type and extent of abnormal harmonic generation is defined, and numerical examples given. Methods of reducing abnormal harmonic generation are discussed, and some experimental data supporting the theoretical calculations are also included.

Four Methods of Power System Damping

Abstract: Techniques for damping power system swings have been studied by analog and digital simulation.

A New Method of Determining Loss Coefficients

Abstract: A new method is presented for finding B coefficients expressing loss in a power system as a function of power input. The computer program necessary to find these loss (B) coefficients is very simple, and transformations of variables are not required. The method takes advantage of the fact that partial derivatives of voltage phase angles with respect to any plant power output are independent of system generation schedules and load levels, as shown in a previous paper. Many of the usual assumptions in calculating B coefficients are eliminated.

Shunt regulation electric power system

Abstract: A regulated electric power system having load and return bus lines. A plurality of solar cells interconnected in power supplying relationship and having a power shunt tap point electrically spaced from the bus lines is provided. A power dissipator is connected to the shunt tap point and provides for a controllable dissipation of excess energy supplied by the solar cells. A dissipation driver is coupled to the power dissipator and controls its conductance and dissipation and is also connected to the solar cells in a power taping relationship to derive operating power therefrom. An error signal generator is coupled to the load bus and to a reference signal generator to provide an error output signal which is representative of the difference between the electric parameters existing at the load bus and the reference signal generator. An error amplifier is coupled to the error signal generator and the dissipation driver to provide the driver with controlling signals.

Application Considerations for SCR DC Drives and Associated Power Systems

Abstract: A rapid growth of silicon controlled rectifier (SCR or Thyristor) dc drive applications has resulted from the many benefits derived by these equipments where adjustable speed of drive is required. These are areas normally served by conventional Ward Leonard M-G sets as well as eddy-current couplings. However, SCR drives are not exact equivalents of M-G sets and special considerations requiring some fundamental knowledge of this conversion technology must be made. This paper presents some of the application considerations regarding successful utilization of SCR drives. The paper will be divided into two parts: The first deals with the static power conversion equipment itself, its characteristics and benefits, as well as its effect on the dc drive motor. The second part deals with the effects of the SCR power conversion equipment on the power distribution system, with suggested approaches to certain problems that may arise, particularly as related to kilovar supply.

Large Signal Dynamics of Load-Frequency Control Systems and Their Optimization Using Nonlinear Programming: II

Abstract: The first part of this paper deals with the response of a large load-frequency control system (power system) when subjected to a major disturbance. If the system becomes unstable, upon the occurrence of a disturbance, incidents like the great blackout of 1965 in the Eastern United States and Canada can occur. This paper differs from much previous work in the respect that the assumption that the system be linear is not made. A numerical method is presented to solve for the nonlinear system. The linear case can be treated as a degenerate case of the more difficult problem. Since it is possible to find an exact solution for a linear system, examples are presented to show good agreement between the exact solution and the solution obtained by the numerical method.

Automatic load scheduling in a multiarea power system

Abstract: In the paper an algorithm is described for solving the problem of secure economic load scheduling on a large power system. The method is an extension of that of Wells, which solves the problem as a linear program by means of the dual simplex algorithm. A dual form of the decomposition principle of Dantzig and Wolfe is used in order to reduce the size of the problem, so that it can be solved efficiently on a computer system. This is correlated with a corresponding decomposition of the power system into autonomous areas, co-ordinated by the specification of recommended boundary transfers and spinning spare capacity. Further levels of decomposition are incorporated in a similar fashion, allowing three or more levels, say, for the CEGB supply system. Although the entire problem can be solved on a single computer, for application to online control a more complex computing system is anticipated.

An energy storage system

Abstract: Part of Oklahoma State University's program of energy storage research in the School of Electrical Engineering involves the use of unconventional energy sources such as wind and sunlight.1 This energy must be used when available or stored until needed. Since the energy supply and demand are usually independent, some type of storage is needed to act as a buffer to match the two.2 The storage system currently under study uses an electrolysis cell to convert electrical energy into hydrogen and oxygen under high pressure and stores them until they are used either in a fuel cell or in an internal combustion engine or steam turbogenerator.5,6,7Two slightly different power system configurations are prominent in our research efforts. For small systems the design is kept simple; for the larger systems the efficiency of operation becomes important enough to warrant additional switching and control devices. The two situations to be modeled using GPSS are the simple case shown in Figure 1-(A) wherein all energy passes through storage and the more complex situation shown in Figure 1-(B) wherein a direct path exists between the generator and the load in parallel with the storage system. The objective of the simulation is both to provide design information and to provide information for the economic optimization of the systems.

Performance of a predictive automatic load-dispatching system

Abstract: This paper describes the experimental use of a predictive automatic load-dispatching system, and discusses the experience gained. The objectives of control were the economic dispatch of active power only, while maintaining the security of the power system against loss of generation and transmission capacity. The control system used a digital computer, which allocated loads to individual generators for various times in the future, and transmitted instructions to the power stations, where they were automatically implemented by special machine controllers. The system was operational for about ten months. The aspects of control considered in the paper are prediction, the dynamic performance of the loading program, power-system security, frequency control, and operating economies. Other subjects treated in companion papers are the influence of machine-controller parameters on system stability, the performance of the machine controllers, and operator work load. Although it was only possible to examine the behaviour of a control system employing predictive techniques and regular instruction of generation, it was concluded that prediction of system conditions about 10min ahead was optimal for executive control of generation, but that regular instruction had serious drawbacks. Operating economies of a few tenths of one per cent seem feasible, but are markedly influenced by the way in which the constraints of the power system are quantified and handled.

A Hybrid Computer Study of a DC Power System: II

Abstract: In this paper the hybrid computer-is-used-to-study dc power system consieing-of a 2-wire transmission system and two 12-phase converters with ground return. This work is an extension of the hybrid computer study of a 6-phase, 2-wire dc system which was reported in Part I of this paper.[2] Several features of a dc power system are presented including a comparison of results obtained from the hybrid computer study and those obtained using the University of Wisconsin ac/dc system simulator for a line-to- ground fault. It appears that the hybrid computer may be used to advantage in studying the effects of ac or dc system disturbances as well as the feasibility of any type of converter control system. Moreover, the simulation techniques presented in this paper may be extended to include a 3-phase transmission system whereupon the hybrid computer may be used to study electrical transients in ac power systems.

An Improved Method of Determining Incremental Loss Factors from Power System Admittances and Voltages

Abstract: A method is presented for reducing the many complicated calculations of partial derivatives involved in the exact expression for incremental loss factors (that is,) needed for economic load dispatching. Calculations of the partial derivatives of voltage phase angles with respect to plant power output, which comprise the major obstacle to use of the exact expression, are avoided by digital-computer simulation of the mode of operation implied by the partial derivatives. These partial derivatives are investigated and are shown to be independent of system generation schedules and load levels. Their values may be determinied for one particular set of operating conditions and used thereafter (with the partial derivatives of total power loss with respect to voltage phase angles) to determine the most economic schedule of generation. The method gives very accurate values for the incremental loss factors for a Voltage-controlled system. For a non-voltage-controlled system, the values appear to be as accurate as those determined by B coefficients calculated by the usual tensor method.

Network-Flow Method Applied to Load-Flow Calculation

Abstract: This paper aims to apply a network-flow method for the load-flow calculation in electric power systems and to discuss a computer handling technique from the computational aspects. An attractive feature of the new method is its ability to handle calculation rapidly without requiring so large an amount of computer memory. The program based upon the proposed method has been developed, and a flow diagram for the algorithm is presented. A numerical example for the calculation is also described as well as the convergence characteristics of the solution of computational processes. The method is compared with a conventional one from viewpoints of computation time and data storage space.

Power System Voltage Control by Using a Process Control Computer

Abstract: Kyushu Electric Power Company (KEP) already has the automatic load dispatching control system by using a digital computer for process control In addition to the existing computer control system, KEP put into service the control of power system voltage and reactive power early in 1968 The necessity, principle, and method of the centralized control system of system voltage and reactive power in KEP is discussed

Transient response and transient stability of power systems

Abstract: The paper presents a case for correlating transient response with transient-stability limit of power systems. An elementary power system provided with fast acting voltage regulators using various feedback signals is analysed in detail. The effect of varying regulator gains on transient response is investigated with the help of gain-locus diagrams on a gain plane. The Runge-Kutta method with fourth-order approximation is used to determine the transient-stability limit of the same system for various gains. The gains which give good transient response are compared with those which give high stability limit. Efforts have thus been made to see whether it is possible to correlate good transient response with high transient-stability limit.

Experience with high-speed rectifier excitation systems

Abstract: Excitation systems which utilize controlled rectifiers supplied directly from the generator terminals for the main exciter are in service at four remote generating stations. Due to the nature of the power system, these excitation systems were designed to withstand high ac overvoltages and to provide simultaneous control of a number of parallel generators. Experience in testing and operating these excitation systems is described.