Showing papers on "Electric power system published in 1988"

A compensation-based power flow method for weakly meshed distribution and transmission networks

Abstract: A power flow method is described for solving weakly meshed distribution and transmission networks, using a multiport compensation technique and basic formations of Kirchoff's laws. This method has excellent convergence characteristics and is robust. A computer program implementing this scheme was developed and successfully applied to several practical distribution and transmission networks with radial and weakly meshed structures. The method can be applied to the solution of both the three-phase (unbalanced) and single-phase (balanced) representation of the network, however, only the single-phase representation is treated in detail. >

An expert system operational aid for restoration and loss reduction of distribution systems

Abstract: An application of expert system techniques to the restoration of distribution systems is reported. Primary feeders are typically radial in structure. To increase system reliability, neighboring feeders are connected through a normally open tie switch. When load zones on a feeder interrupted due to a fault, system operators need to identify neighboring feeders and try to restore customers through the tie switches. To restore the maximum number of zones, several steps are followed: group restoration, zone restoration and, if necessary, load transfer. Based on the methodology, an expert system is developed which can be utilized as an online aid to system operators in a distribution SCADA (supervisory control and data acquisition) environmental. The proposed expert system is implemented in Prolog. Knowledge representation, portability of the system, and computational efficiency are discussed. Several examples illustrate the capabilities of the system. >

Optimal coordination of directional overcurrent relays in interconnected power systems

Abstract: The authors present a new methodology based upon the principles of optimization theory, to treat the problem of optimal coordination of directional overcurrent relays in interconnected power systems. With the application of the proposed technique, this coordination problem is stated as a parameter optimization problem, which in general, is of a large dimension, especially when many different system configurations and perturbations are to be considered. Several optimization procedures, including direct methods and decomposition techniques, for solving this large scale coordination problem are described, and results of optimally coordinating directional overcurrent relays in power systems with up to 30 buses are presented. >

Reliability Assessment of Large Electric Power Systems

Abstract: This book covers a wide range of relevant material related to present-day knowledge and application in power system reliability. Increasing socioeconomic pressures to create safe and reliable power systems are being exerted on utilities by government, environmental groups and society in general. The material presented in this book will play a role in finding acceptable solutions to such pressures and will encourage the increased use of reliability techniques in practical applications.

Power electronics in electric utilities: static VAR compensators

Abstract: The author deals with dynamic VAR compensation of electric power systems, applying power electronics for reactive power generation and control. After an overview of the emergence and status of modern, solid-state VAR compensators in utility and industrial applications, it is shown how dynamic VAR compensation increased transmittable power by providing voltage support, transient stability improvement, and power oscillation damping in electric power transmission systems. Methods of reactive power generation and control using thyristor-controlled reactors, with fixed and thyristor-switched capacitors or modern gate-turn-off (GTO) power converters that can function without AC capacitors or reactors, are described. A summary is included of the control structure and operation to provide the desired characteristics and performance in power systems applications. >

A posturing strategy against voltage instabilities in electric power systems

Abstract: The problem of system collapse or blackout characterized by a local severe voltage depression is generally believed to be associated with inadequate VAR support at key busses. The authors discuss techniques for improving the system security with respect to this index. The effect of adding capacitors are examined. They also present a continuation technique that redistributes the system generation to the optimal operating condition with respect to the minimum singular value index. >

Multiobjective optimal generation dispatch based on probability security criteria

Abstract: An efficient algorithm is proposed to obtain the optimal power flow in power system operation and planning phases by multiobjective optimization. The algorithm makes it possible to treat the optimal dispatch problems with multiple performance indices and to include tradeoff relations between selected indices. The effect of uncertain factors pertaining to power systems can also be taken into account. The effectiveness of the approach is illustrated with numerical examples of the IEEE 30-node, 6-generator system. >

A simple direct method for fast transient stability assessment of large power systems

Abstract: A method for online transient stability assessment of large power systems is proposed. It consists of: replacing the multimachine system by a two-machine dynamic equivalent, further amenable to a one-machine-infinite-bus system; reducing the stability problem to a sole algebraic equation, devised from the equal area criterion, or equivalently from the Lyapunov direct criterion; and using this equation to derive one-shot stability analysis strategies. A technique for system admittance matrix reduction is developed that proves efficient, especially for large systems and multiple-contingency evaluation. The method's main appeal is rapidity: it is about one order of magnitude faster than the most efficient direct criterion. Other attractive features are flexibility and ability to encompass various simulation conditions. Extensions to online sensitivity analysis and control are suggested. >

Power electronics in electric utilities: role of power electronics in future power systems

Abstract: The role of power electronics in future power systems is considered The improvement of power semiconductors is held up as a major factor to the increased importance of this role Power electronics applications for HVDC transmission are discussed >

Influence of harmonics on power distribution system protection

Abstract: The effects of nonsinusoidal voltages and currents on the performance of static underfrequency and overcurrent relays are experimentally studied. The tests were conducted in such a way that the frequency, amplitude and phase shift of individual harmonics could be adjusted in a controlled manner by using a waveform generator with a phase-locking circuit. The relationship between the harmonic currents and voltages was modeled in terms of the power system impedance within residential distribution systems. It was found that for harmonic voltage and current amplitudes (as they occur in distribution systems), underfrequency relays and the time delay operation of overcurrent relays show a marked deterioration in performance. The instantaneous operating characteristics of overcurrent relays, however, are hardly affected by the presence of harmonic currents. >

Adaptive transmission system relaying

Abstract: The use of digital techniques to adapt transmission system protection and control to real-time power system changes is investigated. The discussion covers transmission system protection philosophy, transmission line protection, relay settings, transformer protection, and automatic reclosing. The tradeoff between dependability and security is examined, as well as the various conflicting criteria embodied in transmission line protection. Adaptive strategies that minimize the compromises required and thereby optimize system performance are presented. >

Adaptive transmission relaying concepts for improved performance

Abstract: Concepts for adaptive protective relaying of transmission lines are presented. These include changes in online relay settings, relay characteristics, or logic in response to power system or environmental changes, or as a result of operating experience. Such changes as line-out or generator-out contingencies, which affect fault current distributions and degrade the system's security level, initiate adaptive protection system responses. Adaptive relaying is shown to be capable of improving relaying reliability and power system security and of achieving better utilization of transmission facilities. Most of the concepts require a hierarchical computer system, involving front-line parallel processors, a substation host, and remote central processors, all linked by channels that transmit data or relaying changes prior to or after a disturbance. It is suggested that maximum value from adaptive relaying will result from integration with existing or planned substation control and data acquisition functions and interfacing with the central energy management system (EMS). Emphasis is placed on use of interim hardware approaches to allow evolutionary development. >

Application of superconducting magnet energy storage to improve power system dynamic performance

Abstract: The application of superconducting magnet energy storage (SMES) to the stabilization of a power system with long-distance bulk power transmission lines which has the problem of poorly damped power oscillations is presented. Control schemes for stabilization using SMES capable of controlling active and reactive power simultaneously in four quadrant ranges are proposed. The effective locations and the necessary capacities of SMES for power-system-stabilizing control are discussed in detail. Results of numerical analysis and experiments in an artificial power-transmission system demonstrate the significant effect of the control by SMES on the improvement of power-system oscillatory performance. >

Analysis and design of an active power filter using quad-series voltage source PWM converters

Abstract: The modeling, analysis, and design of an active power filter using quad-series voltage source pulsewidth modulated (PWM) converters are presented. Some instantaneous space vectors of voltage and current are used for the analysis. A vector differential equation derived in this paper makes it easy to achieve the analysis and design of the active power filter. Experimental waveforms obtained from a prototype active power filter with a rating of 7 kVA, along with simulation waveforms, are included to verify the theory presented. >

A new approach to harmonic compensation in power systems

Abstract: A novel approach to compensate for harmonics in power systems is proposed. The approach differs from conventional passive and active filters in its compensation principle. A practical system configuration to implement the approach is presented. It consists of a small-VA-rating PWM (pulsewidth-modulated) converter and a passive filter. The compensation principle is described, and compensation characteristics are examined theoretically and experimentally. The practicability and validity of the approach are experimentally demonstrated. >

10 MW GTO converter for battery peaking service

Abstract: A bidirectional 18-pulse voltage-source converter utilizing gate-turnoff thyristors (GTOs) is described. The converter, which is rated 10 MVA, was placed in service in early 1988 to connect an energy storage battery to a utility grid. The converter is rated and controlled to operate in all four quadrants (discharge, charge, leading VAr, or lagging VAr) at the full 10 MVA rating. It is capable of independent rapid control of real and reactive power with a transient response of 16 ms to changes in commanded value of real or reactive power. Thus it is usable as a reactive power controller (static VAr control), voltage control, frequency control, power system stabilizer, or real power peaking station. For use as a reactive power controller only, no battery would be needed. The design, construction, control, and application of the converter are described, and performance data taken at factory power test and at the installation are given. >

On the phase portrait of a class of large nonlinear dynamic systems such as the power system

Abstract: Complete results are presented on the phase portrait of a class of large nonlinear dynamic systems that includes the power system The connection between the constant energy surface and the stability boundary of the power system is explored This gives valuable insight into classical stability tests, which are based on the constant energy surface An approach to stability monitoring of the power system derived from these results is outlined >

An efficient technique for reliability analysis of power systems including time dependent sources

Abstract: A method of reliability analysis of electric power systems with time-dependent sources, such as photovoltaic and wind generation is introduced. The fluctuating characteristic of unconventional generation units affects the reliability of the generation system in a different manner than the conventional units. The method proposed by the authors groups the units into several subsystems. One subsystem contains the conventional units and the remaining subsystem consist of unconventional units. A generation system model is built for each subsystem. The outputs for the unconventional units and the load are treated as correlated random variables. Using a clustering procedure states are identified wherein for a given value of load there are specific mean values of the outputs of the unconventional units. Reliability analysis is performed by combining the conventional subsystem with the unconventional subsystems in each state. The output from all the states is combined to compute the loss of load expectation and expected unserved energy. >

Electric Power Transmission System Engineering: Analysis and Design

Abstract: Part I: Electrical Design and Analysis Transmission System Planning Introduction Aging Transmission System Benefits of Transmission Power Pools Transmission Planning Traditional Transmission System Planning Techniques Models Used in Transmission System Planning Transmission Route Identification and Selection Traditional Transmission System Expansion Planning Traditional Concerns for Transmission System Planning New Technical Challenges Transmission Planning After Open Access Possible Future Actions by FERC References Transmission Line Structures and Equipment Introduction The Decision Process to Build a Transmission Line Design Tradeoffs Traditional Line Design Practice Transmission Line Structures Subtransmission Lines Transmission Substations SF6-Insulated Substations Transmission Line Conductors Insulators Substation Grounding Ground Conductor Sizing Factors Mesh Voltage Design Calculations Step Voltage Design Calculations Types of Ground Faults Ground Potential Rise Transmission Line Grounds Types of Grounding Transformer Classifications Environmental Impact of Transmission Lines Transformer Connections Autotransformers in Transmission Substations Transformer Selection Transformer Classifications References Fundamental Concepts Introduction Factors Affecting Transmission Growth Stability Considerations Power Transmission Capability of a Transmission Line Surge Impedance and Surge Impedance Loading (SIL) of a Transmission Line Loadability Curves Compensation Shunt Compensation Series Compensation Flexible AC Transmission Systems (FACTS) Static Var Control (SVC) Static Var Systems Thyristor Controlled Series Compensator (TCSC) Static Compensator Thyristor-Controlled Braking Resistor Superconducting Magnetic Energy Systems (SMES) Subsynchronous Resonance Use of Static Compensation to Prevent Voltage Collapse or Instability Energy Management System Supervisory Control and Data Acquisition (SCADA) Advanced SCADA Concepts Substation Controllers Six-Phase Transmission Lines References Overhead Power Transmission Introduction Review of Basics Constant Impedance Representation of Loads Three-Winding Transformers Autotransformers Delta-Wye and Wye-Delta Transformations Transmission Line Constants Tables of Line Constants Equivalent Circuits for Transmission Lines Short Transmission Lines (up to 50 mi or 80 km) Medium-Length Transmission Lines (up to 150 mi or 240 km) Long Transmission Lines (above 150 mi or 240 km) General Circuit Constants Bundled Conductors Effect of Ground on Capacitance of Three-Phase Lines Environmental Effects of Overhead Transmission Lines Additional Solved Numerical Examples for the Transmission Line Calculations References Problems Underground Power Transmission and Gas Insulated Transmission Lines Introduction Underground Cables Underground Cable Installation Techniques Electrical Characteristics of Insulated Cables Sheath Currents in Cables Positive- and Negative-Sequence Reactance Zero-Sequence Resistance and Reactance Shunt Capacitive Reactance Current-Carrying Capacity of Cables Calculation of Impedances of Cables in Parallel EHV Underground Cable Transmission Gas-Insulated Transmission Lines Location of Faults in Underground Cables References Problems Direct Current Power Transmission Basic Definitions Introduction Overhead High Voltage DC Transmission Comparison of Power Transmission Capacity of High Voltage DC and AC High Voltage DC Transmission Line Insulation Three-Phase Bridge Converter Rectification Per-Unit Systems and Normalizing Inversion Multibridge (B-Bridge) Converter Stations Per-Unit Representation of B-Bridge Converter Stations Operation of Direct Current Transmission Link Stability of Control Use of FACTS and HVDC to Solve Bottleneck Problems in the Transmission Networks High Voltage Power Electronic Substations Additional Commends on HVDC Converter Stations References Problems Transient Overvoltages and Insulation Coordination Introduction Traveling Waves Effects of Line Terminations Junction of Two Lines Junction of Several Lines Termination in Capacitance and Inductance Bewley Lattice Diagram Surge Attenuation and Distortion Traveling Waves on Three-Phase Lines Lightning and Lightning Surges Shielding Failures of Transmission Lines Lightning Performance of UHV Lines Stroke Current Magnitude Shielding Design Methods Switching and Switching Surges Overvoltage Protection Insulation Coordination Geomagnetic Disturbances and Their Effects on Power System Operations References Problems Limiting Factors for Extra-High and Ultra-High Voltage Transmission Introduction Corona Radio Noise Audible Noise Conductor Size Selection References Problems Symmetrical Components and Fault Analysis Introduction Symmetrical Components The Operator "a" Resolution of Three-Phase Unbalanced System of Phasors into its Symmetrical Components Power in Symmetrical Components Sequence Impedances of Transmission Lines Sequence Capacitances of Transmission Line Sequence Impedances of Synchronous Machines Zero-Sequence Networks Sequence Impedances of Transformers Analysis of Unbalanced Faults Shunt Faults Series Faults Determination of Sequence Network Equivalents for Series Faults System Grounding Elimination of SLG Fault Current by Using Peterson Coils Six-Phase Systems References Problems Protective Equipment and Transmission System Protection Introduction Interruption of Fault Current High Voltage Circuit Breakers Circuit Breaker Selection Disconnect Switches Load-Break Switches Switchgear The Purpose of Transmission Line Protection Design Criteria for Transmission Line Protection Zones of Protection Primary and Backup Protection Reclosing Typical Relays Used on Transmission Lines Computer Applications in Protective Relaying References Problems Transmission System Reliability Basic Definitions National Electric Reliability Council Index of Reliability Section 209 of PURPA of 1978 Basic Probability Theory Combinational Analysis Probability Distributions Basic Reliability Concepts Systems with Repairable Components Reliability Evaluation of Complex Systems Markov Processes Transmission System Reliability Methods References Problems Part II: Mechanical Design and Analysis Construction of Overhead Lines Introduction Factors Affecting Mechanical Design of Overhead Lines Character of Line Route Right-of-Way Mechanical Loading Required Clearances Type of Supporting Structures Mechanical Calculations Grade of Construction Line Conductors Insulator Types Joint Use by Other Utilities Conductor Vibration Conductor Motion Caused by Fault Currents References Problems Sag and Tension Analysis Introduction Effect of Change in Temperature Line Sag and Tension Calculations Spans of Unequal Length: Ruling Span Effects of Ice and Wind Loading National Electric Safety Code Line Location Construction Techniques References Problems Appendix A: Impedance Tables for Overhead Lines, Transformers, and Underground Cables Appendix B: Methods for Allocating Transmission Line Fixed Charges Among Joint Users Appendix C: New Trends and Regulation Appendix D: A Guide to the FERC Electric Transmission Facilities Permit Process Appendix E: Standard Device Numbers Used in Protection Systems Appendix F: Order No. 1000 of Federal Energy Regulatory Commission Appendix G: Unit Conversions from the English System to SI System Appendix H: Unit Conversions from the SI System to English System Appendix I: Classroom Example to Select Conductors for an EHV Transmission Line Design Appendix J: Additional Solved Examples of Shunt Faults Appendix K: Additional Solved Examples of Shunt Faults Using MATLAB(R) Appendix L: Glossary for Transmission System Engineering Terminology Index

MW/voltage control in a linear programming based optimal power flow

Abstract: A functional improvement to the linear-programming-based optimal power flow technique is reported. The new feature allows the rescheduling of the active power controls to correct voltage-magnitude-constraint violations. It preserves the reliability and speed characteristics of the traditional linear programming approach. Results demonstrating the effectiveness of the method on a small and a large power system are presented. >

Practical reactive power allocation/operation planning using successive linear programming

Abstract: A method for reactive power planning is presented that it finds an optimal solution for both allocation and operation planning in large systems using linear programming (LP). The method utilizes calculated linear sensitivities including active power and voltage phase angle in the formulation. Although the overall method includes these relations, the number of constraints and variables are not augmented in its first procedure, APPROACH-1. Its second procedure, APPROACH-2, overcomes numerical problems caused by a dense constraint matrix. This is achieved by retaining untouched sparse sensitivities in the constraint matrix and by eliminating any calculations related to the inverse matrix. The results of applying this method to a practical 224-bus system and the IEEE-30 bus system verify its robustness and fast convergence. >

IEEE Recommended Practice for Electric Power Distribution for Industrial Plants

Abstract: A thorough analysis of basic electrical-systems considerations is presented. Guidance is provided in design, construction, and continuity of an overall system to achieve safety of life and preservation of property; reliability; simplicity of operation; voltage regulation in the utilization of equipment within the tolerance limits under all load conditions; care and maintenance; and flexibility to permit development and expansion. Recommendations are made regarding system planning; voltage considerations; surge voltage protection; system protective devices; fault calculations; grounding; power switching, transformation, and motor-control apparatus; instruments and meters; cable systems; busways; electrical energy conservation; and cost estimation.

Fast contingency screening and evaluation for voltage security analysis

Abstract: The authors describe a fast security-analysis technique for voltage security assessment in an energy-management system. The proposed method identifies the location of buses with potential voltage problems and thereby defines a voltage-sensitive subnetwork for contingency screening. This allows the evaluation of a large number of contingencies. The efficiency of this method is derived from the use of a voltage subnetwork to drastically reduce the number of bus voltages to be solved; and subsequently from the use of compensation techniques and sparse-vector methods (including adaptive reduction) for screening and final solution of contingencies. Results demonstrating the effectiveness of the method on a small and a large power system are presented. >

High power electronics and flexible ac transmission system

Abstract: During the last decade, higher energy costs, the difficulty in building new power plants and improved converter technology provided an increased Market for HVDC transmission. However, HVDC, due to the high cost of converters, will play a limited role in the overall ac power system. The author discusses the potential of thyristors in ac power systems. The concept of a thyristor-assisted ac power system, called Flexible AC Transmission System is introduced and discussed.

Secondary voltage control using pilot point information

Abstract: The authors study the minimal information structure needed for monitoring and control of the voltage profile and the reactive power flow of a power system. Emphasis is on the minimum amount of information (data) required for reliable decision-making. An effort is made to work with fewer voltage data and therefore make the real-time monitoring and control more manageable. An annealing algorithm for selecting pilot points is presented. These are the load buses at which the voltage is to be measured in real time. Simulation results obtained with the algorithm for the Central Illinois Light Company system are presented. >

Integrated security control using an optimal power flow and switching concepts

Abstract: A synthesis of methods is presented which combines security analysis and optimal power flow in order to achieve n-1 security. The concepts of corrective switching are used to model outages, making it possible to generate constraints to be attached to the optimal power flow. A distinction is made between the secure state (conservative) and a state which is achieved by postcontingency rescheduling. Results for an 80-node system show the dispatch of control variables for the source states, the losses and the CPU-times. >

Determination of voltage stability limit in multimachine power systems

Abstract: A method of determining the load limit and the critical state of a general multimachine power system is presented. In the method, the search for the load limit is formulated as an optimization problem. With this formulation, difficulties related to singularity of the load-flow-equations Jacobian matrix, and convergence of the load-flow solution around the voltage stability limit, are avoided. Modification to the basic formulation to allow consideration of load-voltage characteristics is also shown. A voltage stability margin is defined which may serve as a measure of the security of a given operating condition from voltage instability or collapse. Results of application of the proposed method to the AEP 14-bus network are presented. >

Loss reduction by network switching

Abstract: Systematic and fast switching for the purposes of reducing losses in power transmission networks is treated as an optimization problem whereby switching is to be understood in a general and comprehensive way. Injected currents applied to a base network are used to model the switching operation. These currents are used as variables in a linear programming (LP) problem formulation. The objective function, i.e. the change in losses, can be expressed by the injected currents, taking into account that all nodes are constrained by constant active powers except for the slack node. The change of power of the slack node is the change in losses, which is obtained by a two-step approximation. Each single optimal switching operation is obtained by an LP-like operation followed by a load-flow update. The interaction between LP and AC load-flow leads to a sequence of optimal switching operations whereby losses are reduced to a minimum subject to the given constraints. >