Power System Control Centers Research Articles

Reactive Switching Simulation in Security Analysis at Florida Power and Light System Control Center

Reactive Switching Simulation in Security Analysis at Florida Power and Light System Control Center

Data Base Validation and Maintenance: Some Experiences During Acceptance Tests of a Large Power System Control Project

Abstract To dispose of secure and consistent data is crucial for all the functions of a modern Power System Control Center /7/. The attention of the specialists has been up to now mostly focused on the detection, the identification and possibly the suppression of bad data coming from the field via the telecommunication channels, e.g. analog measurements and statuses. In fact, it is evident the danger of such a situation, where an important monitoring function (an alarm) is misled or a wrong control action is taken, due to the false on-line information. This paper, instead, deals with a perhaps less investigated, but not less important aspect: the validation of the static part of the Data Base and the detection of lacking data. The parameters of the electrical model (derived from off-line archives), the substation and network connectivity information, the digit-to-engineer-units conversion data and many other quantities related both to the power system and to the telecommunication subsystem, have to be accurately checked and their reciprocal consistence must be verified. This side of the problem is not trivial as far as: - the dimensions of the system grow up. In this case it is important to have good offline tools in order to increase the accuracy of the static data, also because the number of people, in chargeof collecting it, is enlarged. - the control project is commissioned to a manufacturer: in this case the presence of errors in the Data Base, or in the manufacturer software or in both can make problematic the sharing of responsibility. The new Power Generation and Transmission Control (PGTC) project of ENEL meets both the above requirements: the authors describe their two-years activity in preparing, securing and maintaining static data for the on-line Data Base and in carrying out acceptance tests vis-a-vis of the manufacturer. The attention is paid to the procedures adopted in order to avoid as many as possible conflicts of responsibility and to reach the basic confidence - beyond the contractual tests merely relevantto the monitoring functions - that the delivered system is really able to support the more sophisticated controlfunctions as the security analysis and the automatic corrective actions. The experience is reported about the most frequent ej: rors detected, their nature and origin and the way of identification. An accurate description then follows of the procedures set up at ENEL for checking and validating the data, which, prepared off-line, feed the on-line Data Base. A distinctive features of such a procedure is the cross checking among different categories of data (for example the teleacquisition subsystem data and the Man-Machine Subsystem Data), which hasproved to be very effective in detecting inconsistencies. Finally the authors present some results of their experiences, in form of recommendations to companies having similar problems. One of these is the usefulness of setting up simulated, electrically coherent, error free dynamic (or variable or foreground) data for testing purposes; and of making use of the State Estimator if available - already in the initial phase of the project, say during the telemetry installation, for the off-line validation and securing of the Data Base.

Security Assessment and Control System : Corrective Strategies

A complete methodology for the solution of the real and the reactive subproblems of the general optimization problem that appears as part of the corrective strategies function of power system control centers is presented and analyzed. The method takes advantage of the linear behavior of the incremental relationships between the constraints and the controls. It dynamically selects a set of control variables for every iteration depending on the amount of overload to be corrected in the particular iteration. The algorithm has been used to alleviate several overloads for the IEEE 118 bus system under high and low loading conditions.

Modeling of External Networks for On-Line Security Analysis

The larger power system control centers of today routinely incorporate functions for on-line security analysis. In the last decade, advancement in the techniques for state estimation and static contingency analysis has made this feasible. However, the modeling of those portions of the network that are unobservable to the state estimator, but affect the contingency analysis results, remains a problem that hinders the usefulness of these functions. In this paper the state of the art for on-line external network modeling is examined. The problems with the existing methods from the point of view of practical implementation are identified. Some short term research directions are suggested to alleviate these modeling problems that introduce errors in the security analysis results.

Fast Transient Security Assessment

The growth of large interconnected power systems demands a high degree of security for normal operation. This requirement emerges from the fact that the possible disturbances in large power systems could have catastrophic results. Therefore it is the duty of power system control center to retain the operating point within secure boundaries. In order to control the security of system, one has to monitor and analyze the level of system security and enhance it in case it does not fulfill the system security requirement. The pattern recognition technique which is proposed in this paper is a method suitable for fast, on-line security assessment. Most of the literature in this area concerns the use of steady state variables for identification pruposes; the use of transient measurements, however, has been found to be better suited for the fast classification of operating points with minimal error. One of the salient conclusions of this paper is that the pattern recognition technique is a serious candidate for on-line applications. This favorable conclusion is based on the inclusion of transient state variables in the feature vector. The main objective of the pattern recognition method in transient security assessment is to reduce the computational requirement to a minimum. This is done at the expense of elaborate off-line computations. The classical methodology of pattern recognition consists of defining a pattern vector x whose components consist of all significant variables of the system.

Database methods in power system control centres

Historically, the electric power industry has used computer systems in energy control centres to monitor and control power system devices. Little heed was paid to the efficient management of the databases for evolving applications such as system security studies, extensive data storage and retrieval, and reporting functions. As these applications have grown in importance, however, vendors have developed and supplied ad hoc software for managing the databases, thereby increasing their practical usefulness. Current practices in database management are summarized and proposed approaches now in their early development stages are considered.

State estimation in control centres

The provision of facilities for system security or the implementation of security control is the distinguishing feature of modern power system control centres. After a rather slow beginning, the provision of secirity functions has now become virtually a standard of control centre design. The practical realization of known real-time analytical techniques for security functions has been made possible by the successful development of static state estimation methods for online application. The need for state estimation is examined and the experience of the electric power industry in the development and use of this function is discussed.

An Approach to the Design of Real-Time Database Models

The implementation of a real-time database requires the design of a database conceptual model. A new approach, based on the concepts of Entities, Links, Keys and attributes (ELKA) to the design of models is presented. A small subset of the conceptual model for the National Power System Control Center in Mexico is presented as an example of a design. The concept of metamodel is introduced, which allows to automaticaly maintain documentation of a conceptual model in a computer. The use of the ELKA approach to the design of conceptual model results in a very clear statement of database requirements.

The Role of State Estimation in Power System Operation

The security control of an electric power system requires a knowledge in real-time of the system state expressed as the vector of complex voltages at all buses of the network. The most practical way known of obtaining the system state is through State Estimation. Although introduced to the power industry about 10 years ago, State Estimation as a part of power system control centers had a very slow start until in recent years when due to the availability of cost-effective computers and the maturity of algorithms, State Estimation is now becoming more widely applied. The basic method of weighted least squares is the most widely used approach inspite of early attempts at other variations. This paper serves as an introduction to a more detailed inquiry into the subject by the interested reader.

Prospects for Security Control in Electric Power Systems

The current state of implementation of security functions in power system control centres is briefly reviewed, pointing out the particular needs for security control. Then, some promising techniques for the future in this field are presented, such as the implementation of on-line “compact” optimal power flows, the inclusion of transient stability constraints into on-line optimal power flows, the principle of a secure and economic automatic generation control, the principle of a secure and economic voltage control, the use of computer assisted changes in network topology to meet security. Conclusion includes data and computer needs necessary to perform on-line security control in the next few years.

Human Factors Survey and Analysis of Electric Power Control Centers

An electric power system generally includes a number of generating plants, substations, and high voltage transmission lines, as well as thousands of circuit breakers, switches, transformers, and other components, all spread over hundreds or thousands of square miles. Two to five system operators work at dispatch centers and use modern, computerized systems for system monitoring, information display, and operation of the power system. This paper describes the functions performed at typical dispatch centers, as well as characteristic physical facilities, group displays, operator consoles, power system controls and displays, and CRT display formats and information coding techniques. Human factors problem areas which exist within electric power system control centers are pointed out.

A Survey of Power System Control Center Justifications

This paper investigates the rationale used by utilities to justify purchasing modem Power System Control Centers. The degree which economics plays in the justification was a primary study objective. This paper may serve as a future guide to others faced with the need to evaluate benefits of upgrading power system control facilities. Criteria identified during the study as potentially able to contribute to an economic defense of such an expenditure, are enumerated for convenience.

Power/energy: System security: The computer's role: Several security-related functions can be aided by the digital computer, and linked together by a software scheme

Security functions are now incorporated into computer programs to deal with operating conditions as well as with disturbances that could lead to equipment overloads, voltage degradation, frequency decay, system instability, service interruption, or the ultimate catastrophe of a system shutdown. This article discusses how these functions fit into the overall control structure of a power system, and summarizes the extent to which they have been realized in today's power-system control centers.

An Overview of Practices and Trends in Power System Control Centers

This paper reviews the state-of-the-art of the design of control centers for the operation of electric power systems. Modern control centers are distinguished by the integration of new functions designed to enhance system security with the traditional functions of generation control and of supervisory còntrol. The emphasis therefore of the overview presented in this paper is on the practices and trends in control center design which are brought about by considerations of system security.

Power System Control Centre Display of Voltage Phase Angle

Summary The significance of voltage phase angle across important transmission lines in the New South Wales power system is discussed. A microprocessor-based unit located in a power system control centre which computes the phase angle difference between two remote locations from the data normally telemetered is described. The unit complements the role of a conventional power system static state estimator.

Alarm logger for TVA's power system control center

This paper covers basic design requirements and operating experience of the Tennessee Valley Authority's alarm logger for the communication system wire chief. Operating in the new Power System Control Center, this computerized alarm logger interfaces directly with existing remote microwave fault alarm systems, as well as local contact inputs.