Showing papers on "Power-system protection published in 1985"

Status of High Impedance Fault Detection

Abstract: This paper presents the issues associated with the detection and clearing of high impedance faults on distribution feeders. High impedance faults are those faults with current too low to be reliably cleared by conventional overcurrent protection. These faults commonly occur as fallen conductor faults and pose a hazard to the public. The status of research on this subject is reviewed, and possible improvements are evaluated. The several complex technical, legal, economic and operational problems involved in high impedance fault detection are discussed. A complete solution to the high impedance fault problem does not exist at this time, but it is important that utilities take steps to address the problem.

Development and Field-Data Evaluation of Single-End Fault Locator for Two-Terminal HVDC Transmission Lines Part 2: Algorithm and Evaluation

Abstract: A new technique for locating faults on a two-terminal HVDC transmission line which uses information from only one end of the line is developed and analyzed. The new technique uses successive reflections generated by faults. Using a differentiator and smoother the slopes of the transients are computed. Furthermore, the best estimated peaks of the slopes for the first two consecutive transients are obtained. The time interval between these two peaks is proportional to the fault location. The new technique is referred to as simple passive reflectometer (SPR). Field data obtained at the Celilo converter station of the Pacific HVDC Intertie (see the companion paper [1]) are used to evaluate the SPR. The agreement with a two-ended system is within one mile over the length of the 850-mile Pacific HVDC Intertie transmission line.

Operational and Design Considerations for Electric Distribution Systems with Dispersed Storage and Generation (DSG)

Abstract: Three studies have examined the operational and planning problems associated with connecting small power sources to an electric distribution system. In one study [ 6], the harmonic distortion produced by a subdivision of PV arrays connected through line-commutated inverters was simulated. A second study [1,2,3] exami ned the protection and safety problems associated with the operation of small ac generators and dc-to-ac inverters. A third study [11] assessed the the effects of dispersed sources on distribution planning and design. The purpose of the studies was to determine the adequacy of the electric utility industryl traditional practices, hardware, and design for the operation of dispersed power sources on electric distribution systems. The purpose of this paper is to summarize the important results of these studies and related studies, give recommendations for accommodating this new technology, and identify areas needing further research.

Circuit Breaker and Protection Requirements for DC Switchgear used in Rapid Transit Systems

Abstract: Attention is drawn to the interrupting severities encountered by dc circuit breakers on rapid transit systems and how specifications can more clearly define these conditions. The various protection equipment requirements are discussed, and it is shown that one of these requirements is difficult because of the similarity which can exist between healthy and abnormal conditions, making discrimination under certain conditions, almost impossible. A guide is given to the minimum requirements for the de switchgear which should ensure a reliable and secure power supply to the rapid transit system.

The problems posed by electrical power supply to industrial installations

Abstract: Despite the fact that electrical power is a widespread and highly flexible product, perfection cannot always be guaranteed owing to disturbances caused either by random phenomena affecting the network (lightning, network equipment faults etc.) or by the operation of certain types of equipment (are furnaces, rolling mills, electronic power equipment etc.). After a brief summary of the origins and nature of the various disturbances to which electrical networks are prone, be they public or industrial, we will deal in more detail with the problem of voltage dips and short time interruptions, these being the most problematical disturbances for the industrial customer. The principal technical solutions for correct operation of industrial installations will be described. In particular, the possibility of private generation operating in parallel with the public network will be dealt with. The need for collaboration between the user (or engineering firm representing him) and manufacturer (or installer) of electrical equipment and the electrical power distributor is stressed.

Transient Signals and Their Processing in an Ultra High-Speed Directional Relay for EHV/UHV Transmission Line Protection

Abstract: This article describes an ultra high- speed directional comparison relay (UHS relay) based on the evaluation of transient signals generated by the occurrence of a fault. The use of a replica impedance in the current circuit results in a pick-up sensitivity which is largely independent of source impedances. The discrimination between phases even in the case of long transmission lines is assured through the provision of a second measuring criterion.

Feeder Protection and Monitoring System, Part II: Staged Fault Test Demonstration

Abstract: This paper describes the demonstration of three Texas A&M University experimental Feeder Protection and Monitoring Systems during staged fault tests at Houston Lighting and Power and at Public Service Company of New Mexico. The purpose of the experimental devices is to demonstrate improvements in the protection and monitoring capabilities of distribution relays. The Feeder Protection and Monitoring System is a microcomputer-based device installed at a distribution substation which includes arcing fault detection and overcurrent relaying. The arcing fault detector identifies many ground faults which exhibit current too low to be picked up by overcurrent devices. The digital overcurrent relay provides several enhancements over electromechanical relays. The system also demonstrates some of the advantages of computer automation of distribution protective devices by providing remote monitoring, data retrieval and adjustment of settings. These features of the Feeder Protection and Monitoring System were demonstrated during the staged fault tests. The paper includes plotted data and logs of the system performance during the fault tests.

Summary of the ``Guide for Protective Relay Applications to Power Transformers'' ANSI C37.91

Abstract: The ``Guide for Protective Relay Applications to Power Transformers,'' ANSI/IEEE Standard C37.91, has been expanded and updated recently by the Power System Relaying Committee to assist in the effective application of relays and other devices for the protection of power transformers. The various protective considerations and methods of protection for the most commonly used power transformer configurations are covered. The purpose of this paper is to review some of the highlights of the guide, to familiarize the industry with the scope and usefulness of this revised document, and to invite considered discussion for the purpose of improving future revisions of the guide.

The Continuation Method in Power System Optimization: Applications to Economy-Security Functions

Abstract: The continuation method is a powerful mathematical approach for the solution of systems of equations or of optimization problems, which tracks the (optimum) solution as a function of the varying parameter. The applications of this methodology to power system optimization problems are presented. Some implementations for the real power secure-economic dispatch, redispatching and planning are shown. The method provides the optimum trajectories of the system variables as a function of the varying parameter. This can be : system load, generation or transmission limits, generation parameters, line parameters, etc. The particular nature of power systems makes this approach very promising when solving economy-security functions. Because the continuation method proves very reliable, cases of difficult convergence with other optimization techniques may be resolved. Furthermore infeasible cases can be systematically detected.

Feeder Protection and Monitoring System, Part I: Design, Implementation and Testing

Abstract: This paper describes the development of a microcomputer-based Feeder Protection and Monitoring System at Texas A&M University. The Feeder Protection and Monitoring System includes an overcurrent relay to provide overcurrent protection for a distribution feeder and it includes an arcing fault detector which identifies some low current faults which are not cleared by overcurrent protection. The system also provides a monitoring capability which supports data storage and remote interaction with a user. The paper describes the design of the system, how the design was implemented, and the testing of three prototypes which were built for research purposes. These units properly demonstrated the overcurrent protection, arcing fault detection and monitoring functions of the system, as well as many of the features of power system automation.

Loss-of-Excitation Protection for Synchronous Generators on Isolated Systems

Abstract: Loss-of-field relays operating on an impedance-measuring principle provide an important part of the protection of a synchronous generator by minimizing possible damage to the machine and low voltages detrimental to system operation. These relays require an external source of reactive power, such as a utility tie or other in-plant generators, to insure proper operation on loss of generator field. In a multigenerator isolated system, the reactive current provided by the remaining generators may not be sufficiently large to allow proper operation of the loss-of-field relays on the generator in question. Some guidelines are provided as to the relative size of synchronous generators needed to insure proper operation of the impedance type loss-of-field relays.

Dynamic Study of an Extreme System Reactive Power Deficit

Abstract: The dynamic study described in this paper shows that relatively simple and inexpensive procedures are available that can effectively control a system reactive power deficit. By combining these procedures hierarchically, an automatic system protection is possible to enhance power system security against one of the most serious causes of breakdown.

Loss of load probability evaluation based on real-time emergency dispatch

Abstract: The loss of load probability (LOLP) represents an important index in the reliability evaluation of electric power systems. The LOLP denotes the probability of customer demand curtailments due to random outages of various system components. A combined optimization/reliability technique is presented in which the system control parameters are optimized. This simulates practical contingency situations where suitable controls are invoked in order to preserve, as much as possible, the continuity of supply. A DC representation of the power network is used and the optimization problem is solved by linear programming. The active component of the net injected power and the voltage angles at all buses represent the optimization variables of the problem. The optimal solution maximizes the load power supplied subject to the power flow equations as well as upper and lower bounds on the optimization variables. A description of the computerized algorithm developed and numerical results for a test power system are also included.

Photovoltaic Power System Design for Telecommunications

Abstract: Since its inception in the 1950's photovoltaic (pv) power has been consistently applied in the telecommunications industry first as a convenient power source for satellites and recently for remote terrestrial sites. The size of economically and technically feasible systems has increased from tens of watts in the early 1970's to today's largest commercial telecommunications systems of up to 1 kW continuous power. This paper illustrates specific examples of telecommunication power system design solutions in systems supplied by BP Solar Systems. PV module construction techniques and array design methods are examined with improvements in collected insolation and other environmental data. Battery sizing, charge control, protection and power system interfacing are highlighted, along with aspects of civil/structural design. The paper concludes that reliability will be the most important parameter in further acceptance of photovoltaic power for telecommunications.

Combined control and protection system for improved performance of HVDC links in the presence of AC faults

Abstract: One of the problems of DC links is that, in the case of severe AC faults at the inverter side due to successive commutation failures, their operation is interrupted and they are unable to assist the integrated AC-DC system to recover. This is particularly true in the case of weak systems. The paper develops the theory and design of a control system which, in the case of AC faults at the inverter side, overrides temporarily the normal firing control and tries to maintain the operation of the DC link uninterrupted. The proposed control system was tested on an AC-DC system simulated on the digital computer. The model system used, the results obtained and their evaluation are presented in the paper. The simulation results show that the proposed control system is particularly effective in the case of line-to-ground faults. In the case of multiple phase faults, the control system is less effective and temporary blocking of the bridge remains the only alternative control action.

A New Fault-Interrupting Device for Improved Medium-Voltage System and Equipment Protection

Abstract: A newly developed fault-interrupting device employs radical departures in overcurrent sensing, response, and interruption techniques. It offers a large selection of time-current characteristic curves plus high continuous current ratings combined with efficient current-limiting action in a compact, self-contained package not requiring external sensing or control power. Improved protection and coordination can be provided in a wide variety of medium-voltage circuit and equipment applications, some of which cannot be properly addressed with previously available devices. Sensing and response functions of the electronic control module and operation of the interrupting module are described. Examples are presented illustrating use of the flexible response characteristics in the solution of difficult protection and coordination applications.

Coordination-Free Ground-Fault Detection for Mine Distribution Systems

Abstract: A ground-fault relaying scheme is presented that is intended to eliminate the need for time-delay relays for ground-fault detection on mine electrical distribution systems. The concept is based on pilot-relaying logic, and existing ground-check and grounding conductors are used to convey ground-fault information between adjacent relay units. The new scheme should not add any additional work during the installation of mine power systems and should minimize the expertise needed for power-system operation. To illustrate this concept, the design and development of the new relaying system is presented. The performance of a prototype relay during laboratory simulations is also given. Although the work is projected at underground coal mining, the relay appears feasible for any extensive radial distribution system.

Metal Oxide Arrester Ratings for Rotating Machine Protection

Abstract: Metal oxide arresters are ideal for protection of rotating machines against overvoltages. The absence of the gaps required in older arresters results in more consistent operation and improved protection for fast front surges. Also, the absence of gaps makes the tailoring low voltage arrester ratings to match application requirements much more practical. This paper discusses what the arrester ratings should be if they are to be established based on application requirements. After identifying arrester ratings for a wide variety of systems, a set of ratings is suggested that would provide both very good protection for the most popular machine and system voltages, and quite adequate protection for other medium voltage systems.

Microprocessor-Based Architecture for a Modular Process Protection Upgrade System

Abstract: The Westinghouse Process Protection Upgrade System (Eagle 21TM) is a functional replacement for the existing analog process protection equipment used to monitor nuclear generating stations and actuate the reactor trip and engineering safeguards systems as required. However, the Eagle 21TM system does more than merely replace the existing analog hardware; it exploits the power of a functionally decentralized architecture with multiple independent microprocessorbased subsystems to increase plant availablity, reduce test time, reduce reconfiguration time, and increase the amount of information available to the operator and to new diagnostic systems. The architecture of the system is described and the major benefits are highlighted.

Interactive Computation System for Relay Setting and Simulation of Relay Operation in a Large Scale EHV Power System

Abstract: This paper explains the interactive computation system for setting for the main and back-up protective relays used on the 500 kV and 275 kV power systems of the Tokyo Electric Power Co.. The object of the interactive system and the major calculations involved in the main protective relay setting and relay operation simulation are described. For the main protective relay setting calculations, this paper explains the basic theory and methods of relay setting; and in the relay operation simulation, it explains the basic theory, function and methods of calculation as well as the man-machine interfaces.

Diesel Generating Sets Control Cubicles

Abstract: Power supply of digital switching systems asks for a primary stand by power to mains. The stand by power is usually made of high reliability diesel generating systems, since the primary stand by power has to supply the air conditioning system of the telephone exchange rooms, essential for the exchange operation. In order to achieve high reliability levels, the performances of the control and supervision cubicle are the most important. SIP, the Italian Telephone Operating Company, has specified and ITALTEL has developped a new series of diesel generating sets control and supervision cubicles for power ratings up to 1000 KVA. Dimensions of the new cubicles are 600×600×2067 (mm) and each cubicle consists of: - electronic control, and supervision device - power circuit and ancillary circuits switching, breaking and protection device - battery charger - instruments. Highlighting features of the system are: - electronic overload protection of sincronous generators from 150 up to 1000 KVA - control and supervision device for all the diesel generating set functions, operating from the strater battery of the diesel engine and therefore with a DC voltage from 8V up to 30V DC - high diagnostic capacity for the diesel generating set - possibility of manual by-pass of the cubicle - interface for information management at higher level maintenance centres, through a processor system. The paper describes the features of the diesel generating set control cubicle, of the electronic control and supervision device and the results of tests and field operation.

Development and Application of Fault-Withstand Standards for Power Transformers

Abstract: After five years of effort, a working group of the IEEE Transformers Committee completed work on one of the most important new electrical standards to be developed in recent years, the Transformer Through Fault Current Duration Guide. This document defines the exposure limits of liquid-immersed transformers to short circuit currents, and establishes fault withstand guidelines for all conditions of service. This paper provides a description of these new standards and a brief history of how and why they were developed.

Protective Relaying for Tapped High Voltage Transmission Lines

Abstract: It is Ontario Hydro's practice to provide a dual supply to subtransmission or distribution buses supplying loads in excess of approximately 45 MVA A typical supply station of this type utilizes two transformers which are normally operated in parallel on the low voltage side through circuit breakers, and connected to separate high voltage supply circuits via air break switches A multi-tapped supply line may cause protection difficulties and the required solutions deviate from the conventional two-ended line protections In this paper typical protection problems, their solutions and operating experience of the multi-tapped high voltage transmission lines are described

Protection Techniques for Telecommunication Power Systems

Abstract: NTT has been developing various techniques to protect telecommunications power supply systems against natural disasters, such as earthquakes, heavy rains, and lightning, because Japan is hit every year by such natural disasters. As a result of examinations in this area, NTT has intensified certain of its protection techniques in the area of earthquake-proofing, flood protection, and lightning protection. This paper outlines these protection techniques for telecommunication power supply systems.

DC Power Distribution and Grounding in the 5ESS TM Switch

Abstract: This paper describes the 48-volt dc power distribution system for the 5ESSTM digital switching system This distribution system includes duplicate feeder lines for increased system reliability Each of the feeders serves half of the Power Control and Distribution Frame (PCDF) The PCDF incorporates fuses to protect the load from voltage transients and a capacitor to limit the transients generated during fuse clearing The 5ESS switching system has a single point grounding system ("ground window") This method of grounding is found to be the most ideal for controlling the external fault or lightning currents to which the switching system is exposed