Showing papers on "Electric power system published in 1970"

Power System Static-State Estimation, Part I: Exact Model

Abstract: The static state of an electric power system is defined as the vector of the voltage magnitudes and angles at all network buses The static-state estimator is a data processing algorithm far converting redundant meter readings and other available information into an estimate of the static-state vector Discussions center on the general nature of the problem, mathematical modeling, an interative technique for calculating the state estimate, and concepts underlying the detection and identification of modeling errors Problems of interconnected systems are considered Results of some initial computer simulation tests are discussed

Transmission Network Estimation Using Linear Programming

Abstract: One aspect of long-range planning of electric power systems involves the exploration of various designs for the bulk power transmission network. The use of linear programming for network analysis to determine where capacity shortages exist and, most importantly, where to add new circuits to relieve the shortages is presented. The new method of network estimation produces a feasible transmission network with near-minimum circuit miles using as input any existing network plus a load and generation schedule. An example is used to present the two steps of the method: 1) linear flow estimation and 2) new circuit selection. The method has become a fundamental part of computer programs for transmission network synthesis.

Power System Static-State Estimation, Part II: Approximate Model

Abstract: The static state of an electric power system is defined as the vector of the voltage magnitudes and angles at all network buses. The static-state estimator is a data-processing algorithm for converting redundant meter readings and other available information into an estimate of the static-state vector. Discussions center on an approximate mathematical model (related to the dc load-flow model). This model yields noniterative-state estimation equations, simplified prediction of effects of network and generation-load pattern changes on network flow, and simplified detection and identification of modeling errors. Results of some initial computer studies on the real power-voltage angle portion of the approximate model are discussed.

Power System Static-State Estimation, Part III: Implementation

Abstract: The static state of an electric power system is defined as the vector of the voltage magnitudes and angles at all network buses. The static-state estimator is a data processing algorithm for converting redundant meter readings and other available information into an estimate of the static-state vector. Discussions center on implementation problems associated with computation time requirements, dimensionality resulting from a large number of buses, and the actual time-varying (nonstatic) character of power systems. Various potentially useful approaches are discussed and compared.

A Dynamic Estimator for Tracking the State of a Power System

Abstract: The problem of real-time estimation of the state of a power system is treated from the point of view of the theory of least-squares estimation (Kalman-Bucy filtering). Since under normal operating conditions, the power system behaves in a quasi- static manner, a simple model for the time behavior of the power system is derived. This model, together with the real-time measurement system, enables the design of a tracking state-estimator algorithm. The proposed algorithm has several advantages over the previously suggested static estimator algorithm in regard to its computational aspects, real-time implementation, and the accuracy of the estimated state.

Composite Representation of a Multireservoir Hydroelectric Power System

Abstract: A composite model for multireservoir hydroelectric power systems is constructed for studying the monthly decision conceming total hydrogeneration. This is an important decision when the inflows are uncertain and when hydro, with zero marginal cost, can be used not only to satisfy firm load commitments but also to displace other firm resources or to serve secondary loads. In such a case, the tradeoff between savings at the present and expected benefits in the future is determined mainly by the total hydrogeneration. The construction of a composite representation for the multireservoir hydroelectric power system in the Pacific Northwest is described. The composite model is based on a single measure "potential energy" which is indicative of the system's generating capability. This results in a one-dam representation of the multireservoir system which, in effect, receives, stores, and releases potential energy, in a statistical model for the potential energy inflow and in a generation function which relates potential energy released to actual electric power generated. It has applications in the study of different operating policies, market structures, and investment programs through simulation or optimization. As an example, it is used to obtain the net operating revenues as a function of the excess thermal in the system.

State Estimation in Power Systems Part I: Theory and Feasibility

Abstract: State estimation is a digital processing scheme which provides a real-time data base for many of the central control and dispatch functions in a power system. The estimator processes the imperfect information available and produces the best possible estimate of the true state of the system. The basic theory and computational requirements of static state estimation are presented, and their impact on the evolution of the data-acquisition, data- processing, and control subsystems are discussed. The feasibility of this technique is demonstrated on network examples.

State Calculation of Power Systems From Line Flow Measurements

Abstract: This paper describes a new and efficient method for computing a real-time load flow solution of a power system network. The use of line flow measurements is proposed and it is shown that this measurement scheme shows superiority in speed, accuracy and numerical behavior together with advantages in error detection and identification.

The Application of Lyapunov Methods to the Computation of Transient Stability Regions for Multimachine Power Systems

Abstract: This paper outlines a method for computing a stability region for a multimachine power system. It is shown that the dynamic equations describing this system are of the type for which some rather elegant stability criteria are known, of which the Popov criterion is the most useful. It can be proved by means of a Lyapunov function which will, together with a method for computing the domain of attraction of an equilibrium point of a dynamic system, lead to a systematic procedure for obtaining an estimate of the region of stability for a multimachine power system. The procedure is very well suited for automatic computation and can take into consideration the effects of damping and of fast governors.

Power System Dynamic Equivalents

Abstract: This paper describes a method for determining a simplified equivalent mathematical representation of portions of a power system for transient stability analysis The method leads to equations that do not correspond directly to a system composed of normal power system components Conditions under which it is possible to obtain such an equivalent are given, and the results of applying the method to the 118-bus IEEE test system are reported

State Estimation in Power Systems Part II: Implementation and Applications

Abstract: State estimation is a digital processing scheme which provides a real-time data base for many of the central control and dispatch functions in a power system. Its purpose is to permit improvements in system security and data accuracy and to reduce measurement and telemetry cost. The on-line implementation of an efficient state-estimator algorithm is discussed, and its feasibility is demonstrated on a 400-node network. The main motivations for and potential applications of on-line state estimation are listed, and the tradeoffs between measurement, estimation, and on-line load- flow computation are briefly discussed.

Power-system load scheduling with security constraints using dual linear programming

Abstract: The optimisation of power-system operating conditions is formulated as a dual linear programming problem. This suboptimal model allows fast solutions to be obtained dependably by applying the revised simplex l.p. method to the problem of minimising total generation costs subject to the constraints imposed. These constraints include the network equations, the inequalities restricting generator loading, runningspare capacity and transmission-line loading under normal and outage conditions. The fast speed of solution and low computer-storage requirements result from the reduced mathematical model developed by means of the variable eleimination and the computing strategy used. The computational procedure automatically adjusts the size of the problem to be solved according to indications obtained of the likely critical lineoutage security constraints, a small number in relation to the prohibitively large number of possible outage constraints. A sample application of the method is given for a 2700MW, 275/132kV system of 23 busbars, 30 lines and transformers, supplied by 24 generators. Using ALGOL 60 on the Atlas computer, solutions were obtained in 5s neglecting line-outage security, and 11.5s including security under all possible single-line-outage conditions. For accuracy, comparisons are also made with the network-flow technique and the full nonlinear programming solutions.

A Refined HVDC Control System

Abstract: Most commercial HVDC plants now operating are equipped with the same type of control system, the so-called individual phase control system. This system is simple and the operating experience is excellent. However, the requirements for future installations will sometimes be difficult to fulfill with the existing control system. This may be the case when the HVDC transmission is connected to a very weak ac network or to a generator station with large variations in frequency.

Improvement of Power System Transient Stability Using Optimal Control: Bang-Bang Control of Reactance

Abstract: The problem of restoring a power system to its initial steady state in minimum time after a transient disturbance is identified as a minimum time problem in optimal control theory. The optimal control obtained to achieve this objective, by use of Pontryagin's maximum principle, is bang-bang control of line reactance. The implementation of this scheme on a simple power system model is shown, along with numerical results.

Power System Operation

Abstract: Basic Principles. Transfer of Energy in Power Systems. VAR Flows. Economic Operation of Power Systems. Power System Control. Energy Accounting in Interconnected Disciplines. Power System Communication. Telemetering Methods. Supervisory Control and Data Acquisition System. Power System Reliability Factors. Power System Protection. Power System Stability. EHV Operation.

Techniques for the Real-Time Monitoring of Power System Operations

Abstract: This paper describes methods for using power system readings to compute a real-time power flow solution of the transmission network. The use of redundant data is discussed and procedures are outlined to detect, identify, and correct for data errors. Several examples are presented and the numerical behavior of the methods is discussed.

Transmission Planning Using a Reliability Criterion, Part I: A Reliability Criterion

Abstract: The utilization of a quantitative reliability criterion in long range transmission planning is proposed. The application of a conditional probability approach the determination of load point reliability indices in practical systems is discussed and illustrated by a simple hypothetical system study. Failure at a bus is defined by three planning criteria and the reliability level obtained in terms of a probability and an expected frequency of bus failure. The method requires ac load flow analysis at several load levels under possible system component outages. The technique is quite general, and any known operating conditions can be included. Planning based on acceptable load bus reliability levels results in optimum utilization of the investment placed in transmission facilities.

System for operating industrial gas turbine apparatus and gas turbine electric power plants preferably with a digital computer control system

Abstract: A gas turbine power plant is provided with an industrial gas turbine which drives a rotating brushless exciter generator coupled to a power system through a breaker. One or more of the turbine-generator plants are operated by a hybrid digital computer control system during sequenced startup, synchronizing, load, and shutdown operations. The program system for the computer and external analog circuitry operate in a multiple gas turbine control loop arrangement. Logic macro instructions are employed in programming the computer for logic operations of the control system.

Power System Long-Term Planning in the Presence of Uncertainty

Abstract: The determination of the least costly long-term expansion of a power system in the presence of uncertainty about future loads is formulated as a mathematical optimization problem. It is recognized that more information about these future loads will be acquired with time. The objective is to find an expansion policy such that the investment decision is based on an up-to-date estimate of the system requirements.

Instrument Transformers

Abstract: Instrument transformers serve an important role in the protective circuits of industrial and commercial electric power systems. They are auxiliary devices that are used in the measurement of current and voltage. They reproduce in their secondary circuits, in a definite and known proportion suitable for use in protective devices, the current or voltage of their primary circuits with the phase relations substantially preserved. They are used to protect personnel and apparatus from high voltages and to permit the use of reasonable and standardized insulation levels and current-carrying capacities in the protective device circuits. The high degree of accuracy required for meters and instruments is not essential for protective purposes. Since system protection and coordination is the subject, the aspects of high accuracy for metering are not covered. The two general types are 1) current transformers, used in current measurement; and 2) potential transformers, used in voltage measurement.

Electrical apparatus with frequency controlled load compensation

Abstract: A wound rotor motor and a flywheel are provided on a shaft with speed control of the motor by frequency control on its secondary applied by means such as a cycloconverter that is responsive to pulsating load conditions on the system. Power flows from the flywheel into the system during periods of high load and into the flywheel during periods of low motoring load or a regenerative load. The invention permits use of equipment, such as large excavators, that have sharply varying loads in their duty cycles, in locations where there are small, otherwise inadequate, power systems.

Stability Analysis of a DC Power System

Abstract: A stability study of a dc power system is performed by applying Nyquist stability criterion to a mathematical model that describes the behavior of the system during small disturbances about a steady-state operating point. The operating-point stability, as predicted by this linearized model, is compared with the response of the hybrid computer simulation of the actual system. Regions of instability for various system parameters, including the impedance of the ac system and the transmission line length, are established by a digital computer study. The delay and attenuation of the transmission line as well as the action of the converters with typical controllers are accurately taken into account. The linearized model presented should be helpful in the design and development of converter control systems for two-terminal dc power systems. Moreover, this method of analysis may be readily extended to include multiterminal dc power systems.

A Digital Computer Program for the Calculation of Switching and Lightning Surges on Power Systems

Abstract: A digital computer program for the calculation of switching and lightning surges on three-phase power systems is presented. It is designed for fast operation, statistical processing of results, and high versatility in network representation. Network elements can be symmetrical or asymmetrical, linear or nonlinear. Transmission lines can be transposed or nontransposed and may have frequency-dependent damping.

A Method of Improving Power System Transient Stability Using Controllable Parameters

Abstract: Controllable parameters in a power system include generator terminal voltage, generator input power, and network admittances. These parameters can be controlled to damp mechanical rotor oscillation in the generators and thereby improve system transient stability. Explicit equations are derived for the control of these parameters to introduce damping uniformly throughout a large power system. These equations are derived on the basis of minimizing a positive definite error function. Decision functions are included which inhibit damping action when it leads to system instability. This method can be used to coordinate the application of locally based damping techniques.

Power System State Estimation

Abstract: A computer program that calculates the steady-state voltages, phase angles, and shaft phases from measured power flows has been written. The weighted difference between measured power flows and computed power flows was a scalar error that was minimized using a modified Newton's method and a second-order method. The admittance matrix was revised following a system change, and the changes in shaft phases were calculated for control purposes. In the event that the power flows were not balanced or the system was unstable, optimum spinning reserve allocation and load shedding was calculated. New algorithms for fast ac load flows were developed.

Power System Stability Considerations with Dynamically Responsive DC Transmission Lines

Abstract: An evaluation is made of the effectiveness of a dynamically responsive dc line in improving the steady-state and transient stability of a power system. A control system, incorporated into the Edison Electric Institute (EEI) 700-kW model, is described. Studies also reported compare the performance of a simple system consisting of two ac transmission lines with the same system when one of the ac lines is replaced by an equivalent dc line.

Probability of Loss of Load for Three Areas

Abstract: A three-area loss-of-load probability theory is presented which forms the basis of a practical working computer program. The method applies specifically to electric power systems within which transmission limitations exist. Existing single-area techniques assume no transmission limitations. A method recognizing tie-line limitations between two areas was published in 1963 [1].