Showing papers on "Power-system protection published in 1981"

Applying Power System Stabilizers Part I: General Concepts

Abstract: The general concepts associated with applying power system stabilizers utilizing shaft speed, ac bus frequency, and electrical power inputs are developed in this first part of a three-part paper. This lays the foundation for discussion of the tuning concepts and practical aspects of stabilizer application in Parts II and III. The characteristics of the "plant" through which the power system stabilizer must operate are discussed and the implications upon stabilizer tuning and performance are noted. A general approach for analyzing stabilizers utilizing an arbitrary input signal is described and applied to the frequency and electrical power input signals.

Probabilistic Assessment of Transient Stability in a Practical Multimachine System

Abstract: The application of probabilistic techniques in the quantitative evaluation of power system reliability is steadily increasing. Probability methods are being used extensively in the assessment of static adequacy. Their application to the evaluation of transient or dynamic phenomena has not yet, however, been widely utilized. The probabilistic nature of the transient stability problem and the inclusion of the probabilities associated with the initiating factors such as the type, location and clearance of faults in the analysis of a simple single machine-infinite bus system has been demonstrated in a recent paper.1 The present paper addresses the problem of transient stability analysis in a practical multimachine system from a probabilistic view-point. The basic concepts developed in Reference ! are applied to a simplified 33 bus model based on the Saskatchewan Power Corporation (SPC) system, to demonstrate the technique of considering the probabilities associated with the occurrence and clearance of faults. Transient stability indices for each line, for different types of faults and a single stability index for any fault are obtained. A single stability index for the overall system is evaluated for different fault types and amy fault using actual system outage statistics. The effect of fault clearing and reclosing times on the system stability is investigated for the most critical line in the system.

A New Alogorithm of an Accurate Fault Location for EHV/UHV Transmission Lines: Part I - Fourier Transformation Method

Abstract: A fault location algorithm based on the Fourier analysis of a faulted network is presented. The algorithm embodies an accurate location by measuring only a local end data. Its fundamental theory is studied through digital computer simulations on a model power system. With the practical applications in mind, fast algorithms are then examined. Finally, the experimental results of a computerized fault locator applied to a laboratory system are presented.

A Fundamental Concept for High Speed Relaying

Abstract: This paper describes a fundamental approach for detecting the direction to a power system fault within the first milliseconds following the fault inception. The method is based on a combined evaluation of the voltage and current deviations generated by the fault occurrence. Design considerations and test results based on numerical simulations and on a transient network analyser are presented. The method solves several problems occurring in conventional relaying and is suitable for use in ultra high speed protection systems which employ a fast telecommunication channel between the ends of the protected network

Protection System Modelling in a Probabilistic Assessment of Transient Stability

Abstract: The application of probability methods in the evaluation of power system transient stability has been demonstrated in recent papers1-3. A probabilistic index for transient stability was developed which in addition to considering the random variations in the operating conditions, included the probabilistic aspects associated with the type, location and clearance of the system faults. It was realized during these studies that there was a need to develop stochastic models for the protection system behaviour which include the actual design aspects. The operational behaviour of the protection system is an important component in the high degree of security and service continuity associated with bulk power systems. This paper illustrates an approach used to model the protection system in the probabilistic assessment of transient stability. The probability density functions of the operating times associated with the components of the protection system such as relays, breakers, etc. are used in conjunction with the reliabilities of the main and back-up protection schemes to obtain the probability density functions of the fault clearing time for different fault locations. These density functions are used together with the critical fault clearing time for a given fault type and location to obtain a probabilities index for transient stability. A simple distance impedance protection system is used to illustrate the procedure. Continuous as well as discrete density functions for the operating times of the protection system components are used. This paper illustrates the basic probabilistic nature of the fault clearing phenomenon and its importance in transient stability assessment.

Performance of Third Harmonic Ground Fault Protection Schemes for Generator Stator Windings

Abstract: The paper shows how the normally generated third-harmonic voltage can be used to protect the lower ten to twenty percent of generator stator windings against ground faults. A method of determining the applicability of the scheme to a given machine is described which takes into account the design of the generator and its externally connected apparatus. The effects of finite resistence ground faults are also investigated and other advantages of the scheme, such as protection of the neutral, are also highlighted.

Protective relaying methods and apparatus

Abstract: The invention provides methods and apparatus for detecting a single-phase-to-ground fault on a three-phase electrical power system, and for identifying a faulted phase. A single-phase-to-ground fault is correctly distinguished from other faults, including phase-to-phase-to-ground faults, even with transmission lines which utilize series capacitors, by taking into consideration the phase-to-phase voltage which is in quadrature with the voltage to ground of the monitored phase.

Reliability Measure of Hardware Redundancy Fault-Tolerant Digital Systems with Intermittent Faults

Abstract: While significant results are available which allow estimation of reliability measure for systems with permanent faults, no generally applicable results are available for intermittent (transient) faults. Methods are presented here which allow reliability evaluation for systems with both intermittent and permanent faults. Two reliability measures, instantaneous and durational reliabilities, are defined and methods to compute them are given. Computed results for the durational reliability for various redundancy schemes are compared.

Power system transients caused by arcing faults

Abstract: System transients caused by fault conditions are becoming of increasing importance in system protection and insulation. Accurate prediction of such transients requires a detailed representation of all the components in the system and the development of solution methods for dealing with the resulting system equations. Of particular concern in such studies in recent times has been the representation of the arcing-fault condition and its integration into the assembled system equations. It will be the purpose of the present work to propose a suitable arcing-fault representation in system studies. Techniques will be described for assembling the faulted-system equations into a format for solution. The solution method is by Fourier transform techniques with one form of the Duhamel integral incorporated to overcome voltage-current nonlinearity problems. A simple double-ended system is considered in which transmission line is accurately represented. Representative studies directed towards high speed protection problems will be given

Stabilizing Control in Emergencies Part: 2. Control by Local Feedback

Abstract: New methods are introduced for the stabilization of the power system during violent swings after major disturbances. These techniques utilize existing or attainable measurements, computer facilities, and devices such as short rating resistors, capacitors, or fast valving. Stabilizing action is based on a new Observation Decoupled State Space which is introduced in a companion paper [1]. Components of this state space associated with individual buses can be computed locally from local conventional measurements. The origin is always the stable system equilibrium-the target of the control. In this paper methods are introduced to track this target by purely local feedback. No telemetering is involved in either the state estimation or the control. Stability of the control in a global domain was proven. Excellent performance is demonstrated by simulation on a 118 bus system with a consistent, up to ten-fold, increase in the critical clearing times.

Energy Management System Design with Dispersed Storage and Generation

Abstract: To be utilized with maximum effectiveness, the new forms of generation based on renewable resources iLtust be managed as part of existing power systems. Howevert many of these generators are by their very nature dispersed or small, so that they will be connected to the distribution part of the power system. This poses new questions of control and protection, and the intermittent nature of some of the energy sources poses problems of scheduling and dispatch. This paper assumes that the general objectives of energy management will remain unchanged, and discusses the impact of dispersed storage and generation on some of the specific functions of power system control, and its hardware.

Grounding of Generators Connected to Industrial Plant Distribution Buses

Abstract: Increasing ``energy consciousness'' in industry is causing expanded interest in in-plant generators, which are normally connected to the main plant distribution bus. Electrical system reliability requires the proper application of neutral grounding and ground fault protection for these machines. Mechanical limits on safe generator ground fault currents, possible circulating harmonic currents in multiunit installations, and the effects of internal ground faults add complexity.

Reactive compensation. Problems and concepts of static compensator control

Abstract: The paper is in three parts. In the first part, general control problems are discussed which arise whenever static compensation is used, irrespective of the applications concept chosen, e.g. variation of the closed-loop response, effects of resonances in the network impedance, maintenance of a certain reserve of power in the SVS (static VAR system) to cover faults. In the second part, a comparison is made between systems with fixed capacitor banks and systems with thyristor-switched capacitors. Here the main point is the differences from the point of view of the control techniques applied. The third part contains a summary of the structure and functional units needed for voltage control, and also the various options for VAR regulation and SVS control of switchable compensators

Fault Activity Evaluation in the Case of Electric Power Plants

Abstract: The methods to evaluate fault activity must be applicable to many kind of faults in the basement terrain, in the case of important engineering problem such as the aseismic design of nuclear power plant.In this paper, the authors have reviewed some problems which have been discussed about the activity of faults, from both scientific and engineering viewpoints home and abroad. Some characteristic features of faults have been shown through many data of dams and nuclear sites, such as fault length, distribution density, fracture thickness, texture and materials in fracture zone. Some typical methods, applicable to various kind of actual faults both inland and seabottom, are presented through the recent studies on fault activity evaluation.In conclusion, the authors have proposed a proper evaluating system of fault activity for nuclear power plant, considering the scientific and technical development and the rule required to aseismic design in the present.

Microprocessor Based Digital Relays Application in Tepco

Abstract: Two types of digital relaying systems using high speed microcomputers have been placed in service in the Tokyo Electric Power Co., Inc. (TEPCO). One is a current differential carrier relaying system for the protection of EHV (275 kV, 500 kV) transmission lines. This system will be used as the standard primary protection system for EHV transmission line. The other is a balance and directional distance relaying system for the protection of 66 kV parallel transmission lines. This system will mainly be applied around metropolitan area. This paper first describes the details of the above mentioned two digital relay systems now in service, then describes their background technology, that is, high speed microcomputer, automatic checking and other-means for higher reliability, and noise withstand capability.

Directional Characteristics of Distance Relay Mho Elements: Part II - Results

Abstract: The directional characteristics of mho elements in a 6 element distance protection are examined using a new method described in a companion paper. The results show the effect of polarizing, load angle and fault resistance on the response of mho elements that are either in or out of the faulted loop. Some mho elements are shown to become non-directional at normal reach settings and load angle, indicating the requirement for consideration of supervision by directional elements to prevent incorrect operations on reverse faults. Certain type of polarization in mho elements is also shown to lessen the likelihood of incorrect operations in reverse faults.

Digital simulation of fault autoreclosure sequences. With particular reference to the performance evaluation of protection for EHV transmission lines

Abstract: The successful development of EHV transmission-line protection increasingly depends on a detailed simulation of power-system faulted responses. In consequence, increasing use is being made of programmable test equipment in which the primary-system responses are simulated digitally. Previous work on digitally simulating faulted-system responses has been concentrated very largely on the initial faulted period prior to the initiation of an autoreclosure sequence. The implications of incorrect operation of protection at any time throughout the process of fault clearance are, however, often serious, and the paper is therefore concerned with detailing methods of frequency-domain simulation which have been developed to greatly extend the capability of computer-based simulation methods in their application to protective-gear testing. Problems associated with the simulation of various network time nonlinearities are overcome, and the new methods enable both 3-phase and single-pole autoreclosure to be simulated. The paper concludes with a presentation of some simulation studies relating to a short 500kV interconnection which is subjected to various transient and sustained fault conditions

Instantaneous Circuit Breaker Settings for the Short-Circuit Protection of Three-Phase 480-, 600-, and 1040-V Trailing Cables

Abstract: Present Federal regulations which specify maximum instantaneous circuit breaker settings for the short-circuit protection of coal mine trailing cables are discussed. The characteristics of mine power systems that limit short-circuit current in three-phase trailing cables are analyzed and minimum expected short-circuit currents for three-phase 480-, 600-, and 1040-V trailing cables are tabulated. New maximum instantaneous circuit breaker settings, based on minimum expected short-circuit currents and typical breaker tolerances, are proposed with emphasis on safety. Finally, atypical mine power systems are discussed and field tests cited.

Polyphase distance protection characteristics

Abstract: The paper considers the steady-state performance of existing schemes of polyphase distance protection for high-voltage systems and introduces new polyphase schemes for phase and earth-fault protection. Differences in the performance of various schemes are highlighted and a comparison is given for close-up faults and zone 1 boundary faults. A new approach is suggested to assess the high-speed tripping characteristic of a polyphase unit and a method is given to establish whether or not high-speed protection is possible during close-up faults. Results of computer studies indicate that prefault load and power swings have a less marked effect on the reach of the new scheme during resistive faults, than is the case with a conventional 6-element scheme. Comparisons are also made with five switched-distance schemes supplied by relay manufacturers in Western Europe and the advantages and disadvantages of the polyphase approach are listed

Microprocessor-Aided Instruction in Power-System Protection

Abstract: Supplementary use of microprocessors in electrical engineering education can provide an effective learning environment for introductory as well as advanced studies In addition, sufficient exposure to microcomputers as a design and analysis tool is consistent with the ever expanding industria applications of these devices Presented is an approach to the creation of such a situation through interactive application of a low-cost microcomputer system The procedure given applies to the instruction of power system analysis and overcurrent relaying techniques, but it is evident that these analytical and graphic approaches could also be applied in other areas of electrical engineering

Radio Interference with the Operation of Static Utility Protective Relays

Abstract: Controls used in electric power distribution systems are generally tolerant of the high level of interference signals found in that environment. Recently, however, increased power demnds have required a new class of solid state controls which are more sensitive to RFI. In order to delineate the problem this report examines the magnitude and distribution of RF fields in a small power substation during an incident of radio transmission. RF electric field strengths were of the order of 10 V/m. Exposure of cormercial distribution relays to such fields are shown to produce considerable interference with normal operation. Radio frequencies from 20 to 500 MHz were employed

Multiple Levels and Classifications of Emergency Electrical Power Systems

Abstract: Today, designers are faced with the challenge of ensuring that all important facility functions are protected from power failures both externally and internally by providing one or more backup supply to the primary source (typically utility service). Each application has its own unique requirements of the Emergency Electrical Power Systems (EEPS) for performance, reliability, and speed to assume the load, and the length of time it must be able to provide emergency power. Lack of industry-wide definitions and standards are severely limiting the availability of equipment and services from which the users can make the best choice for his particular needs. To solve these problems, organizations such as IEEE, EMA, UL and NFPA are now, through representatives of users, the insurance industries, consulting engineers, inspectors, and manufacturers, engaged in an effort to develop definitions and guidelines. Some of the basic problems are explored, the rationale behind the present industry efforts to find a solution is given, and an approach using multiple levels and classifications of Emergency Electrical Power System is suggested.