Showing papers on "Power-system protection published in 1975"

An improved method for the digital protection of high voltage transmission lines

Abstract: This paper explores the accuracy of the digital methods for protection of high voltage transmission lines under transient fault condition on a long line and describes an improved method for future digital protection schemes. With this method it is possible to calculate R and L of high voltage transmission lines so that any number of harmonics on the current and voltage waveforms can be eliminated and it is shown to be suitable for distance protection during the first cycle of fault occurrence.

Series capacitors in power systems

Abstract: The paper reviews the experience obtained with series-compensated power systems, particularly in Sweden, where internally fused capacitor units and simple system designs have contributed to the the good results. It also introduces new approaches for meeting future demands, e.g., optronic protection and a high-speed flip-flop reinsertion system.

Extensive field measurements support new approach to protection of arc furnace transformers against switching transients

Abstract: Recent investigations of systems involving vacuum switching have forced a reappraisal of the traditional protection methods necessitating major changes in protection philosophy. The new philosophy has been developed on industrial systems supplying are furnace transformers where the exceedingly large number of switchings makes such systems particularly sensitive. This paper discusses a new transient voltage protection system which has been developed in response to these recent investigations. In support of the development of the new protection system, transient voltage measurements have been made on 14 are furnace systems at various locations within the United States and abroad. This paper also documents the instrumentation used to monitor transients on these systems and describes its application. Typical oscillographic records are presented as indications of the performance of the system with and without the new transient voltage protection system.

A Cause-Consequence Chart of a Redundant Protection System

Abstract: A cause-consequence chart is applied in analysing failures of a redundant protection system (a core spray system in a nuclear power plant). It is shown how the diagram provides a basis for calculating two probability measures for malfunctioning of the protection system. The test policy of components is taken into account. The possibility of using parameter variation as a basis for the choice of test policy is indicated.

Reliability analysis of substations with automatic modelling of switching operations

Abstract: This paper reviews some of the problems related to the evaluation of substation and switching station reliability and introduces an improved computing method. In particular, it describes a computer program which, from basic data only, classifies all momentary interruptions according to the time of switching required to restore service. The method is based on a Failure Mode and Effect Analysis and is illustrated by the analysis of a practical substation configuration.

Ground Fault Protection for Electric Utility Generating Station Medium Voltage Auxiliary Power Systems

Abstract: Many generating station 480-volt auxiliary power systems employ a WYE distribution system with the source neutral solidly grounded. Because of the arcing nature of some ground faults, the ground fault currents developed on these systems are often too low to operate phase overcurrent protective devices. As WYE systems became more popular, a more sophisticated approach to protection was needed, resulting in the development of many new protective devices for ground fault protection. This paper reviews the application of such ground fault protective devices for use in 480-volt auxiliary power systems of generating stations. In addition, some modifications to existing products are suggested.

Unconventional Methods of Current Detection and Measurement in EHV and UHV Transmission Systems

Abstract: The use of optical and electromagnetic current transformers for protection and measurement in EHV transmission systems is outlined along with salient specifications imposed by diversification of present-day applications. Basic principles of operation and typical applications of optical and electromagnetic current transformers are presented.

Problems Involving Industrial Plant-Utility Power System Interties

Abstract: One of the most important considerations in the development of the overall protection scheme in an industrial plant is the special relaying requirements of the industrial plant-utility power system intertie. The proposed revision to IEEE Red Book Chapter III includes a description of typical intertie relaying practices for industrial plants both with and without in-plant generation. The application of this relaying will be reviewed and several problem areas that must be recognized and dealt with for satisfactory system performance will be discussed.

A Megawatt Converter with Ride-Through Fault Capability

Abstract: Protecting thyristors by means of fuses in electro-chemical rectifiers where more than 100 devices are used in a single unit may cause considerable service interruption when fuses open during temporary faults. This paper considers the thyristor and fuse ratings in conjunction with gate suppression techniques to achieve a protective system which allows a 17.5 MW rectifier to ``ride through'' momentary faults without service interruptions.

Fast response overload protection relay - uses logic circuits which discriminate between faults and switching surges

Abstract: The circuit is for use in power system protection, and relies on the fact that switching surges decay very rapidly although their peak value may be the same as that for a fault. Protection current transformers are loaded onto a resistor which is followed by an integrator to eliminate any d.c. component. The integrator output is fed to logic gates and a trigger circuit is used to control a flip-flop element. Alternate positive half cycles of the measured current are applied to the logic gates and their analog stores, and the stored values are measured in a comparator. If the second positive half wave is less than the first there is no fault and therefore no output. If equal or greater a fault is indicated and the remaining logic elements and amplifiers respond to trip the circuit breaker.

Coordinating Overcurrent Protective Devices with Automatic Transfer Switches in Commercial and Institutional Power Systems

Abstract: Emergency and standby power is fast becoming a major consideration in commercial and institutional buildings and complexes. In fact, emergency power is a National Electric Code mandatory requirement for health care facilities and places of assembly. Transfer switches are a vital link in the portion of a distribution system that must provide power and illumination essential to life and property. Overcurrent protection is of equal importance. It is the purpose of this paper to objectively define and analyze important transfer switch functions and application criteria. Of these, the coordination of overcurrent protective devices to match the transfer switch ratings, under fault conditions, is perhaps the most important application aspect in providing reliable operation of a standby or emergency power system.

The operation of vacuum interrupters when tested at abnormal voltages/currents

Abstract: The behavior of 15-kV, 28-kA vacuum interrupters, when subjected to fault duty operations at voltages up to 30 kV, or currents up to 80 kA, is explored. Insight into the physical factors governing this behavior is presented as are the consequences of subjecting the vacuum device to such abnormal duty conditions.

Considerations of Ground Fault Protection as Influenced by the Occupational Safety and Health Act and the Mining Enforcement and Safety Administration

Abstract: The first step in recognizing the necessity of low voltage ground fault protection was taken by the 1971 National Electrical Code (NEC), Section 230-95. With the passage of the Occupational Safety and Health Act (OSHA) of 1970, more emphasis has been placed on adherence to the code. Since the establishment of OSHA, questions have been raised as to the jurisdiction between the Occupational Safety and Health Administration and the Mining Enforcement and Safety Administration (MESA). This has resulted in both agencies considering and deciding on design standards for cement plant electrical systems. Indications are that in the future, MESA standards will also recognize the necessity of adequate ground fault protection. Since the introduction of ground fault protection in the codes, there have been arguments for and against the methods of applying ground fault protection. It is for this reason that the present code requirements are minimal. In order to provide the electrical service reliability required by modern cement plants, more extensive protection is required. The intent of this paper is to evaluate the new requirements of ground fault protection. It also examines how we, as engineers concerned with electrical power systems in cement plants, approach the problems of providing safe reliable electrical systems which meet applicable code requirements and which also function satisfactorily in relation to plant operation.

The PWR Protection System - Present and Future

Abstract: In a nuclear power generating station, the system used to protect the reactor and its containment is the plant protection sytem. The pressurized-water-reactor (PWR) protection systems encompass all electrical and mechanical devices and circuitry (from sensors to actuated device input terminals) involved in generating those signals associated with the protective function. These signals include actuation signals for the Reactor Protection System (RPS) and Engineered Safety Features System (ESFS) such as Safety Injection Actuation System, Containment Spray Actuation System, Main Steam Isolation System, Auxiliary Feedwater Actuation System, and Recirculation Actuation System. This paper deals with the present status and future development of the Plant Protection Systems utilized by Combustion Engineering, Inc. (C-E) and Kraftwerk Union (KWU) for their Pressurized Water Reactors. The latest techniques of signal processing, logic design, reactor trip and engineered safety features actuation circuitry, automatic testing, isolation and interfacing, are discussed. Current system design criteria, which as a result of the dynamic national and international licensing atmospheres influence system design philosophies, are highlighted.

Process Control Protection Against Power Line Interruptions

Abstract: Power dips, interruptions, and disturbances occur frequently throughout a plant power distribution system that adversely affect plant lighting, computers, process controls, and drive systems. Critical processes that must operate continuously require an uninterruptible power supply to protect against both long-and short-term interruptions. However, most industrial processes are not critical and need only be protected against power transients and short duration outages. Process equipment with properly supplied ride-through capability can prevent waste and downtime. It is the intent of this paper to discuss short duration power line disturbances; the type of , control and stored energy system available to protect against these disturbances; and the advantages and disadvantages of the various approaches available to ride through power line disturbances.

Application of microcomputers to the protection and control of power system substations

Abstract: The use of digital computers for power system protection and control has been studied for the past decade. However, economic considerations, reliability problems, and system constraints have prohibited the actual use of computers in substation protection schemes. Recent advances in microcomputer technology have provided power system protection engineers with a new tool. A distributed microcomputer protection scheme is introduced and compared to present substation protection techniques. Speed, reliability, and operating advantages as well as the adaptive control possibilities of the proposed system are pursued.

The measurement of substation ground resistance and its use in determining protection for metallic communication circuits

Abstract: The increased use of metallic communication circuits in electric substations requires that adequate protection be provided for personnel and equipment during fault conditions. The design of such protection requires a knowledge of the behavior of ground systems, ground rise calculations, and communication techniques. This paper discusses the problem in three parts: I. A development of the characteristics of and measurement techniques for groundbeds and a discussion of how interconnections affect the measurement problem. A new measurement technique is developed which is capable of accurately measuring the resistive part of the grounding impedance of interconnected groundbeds. II. A discussion of the proper use of fault study and ground resistance information for the calculation of ground potential rise. III. A description of the metallic communication circuit protection techniques used by Northern States Power Company.

Protecting CATV Equipment Against the Effects of Longitudinal Sheath Currents

Abstract: The advantages and disadvantages of various protection devices which are used in CATV systems are explored. The interrelated effects of other components related to system reliability, such as time-delay relays, standby power supplies, and system grounds are then discussed.

Staged fault and laboratory tests on a cable pair protection system designed to serve power stations

Abstract: Cable pairs entering power stations may be subjected to ground potential rise (GPR) and/or induction of several thousand volts during power system faults. A cable protection system designed to give a high degree of reliability is described, and the results of staged fault and laboratory tests are discussed. An analysis of neutralizing transformer transient performance shows how the transformer's behavior during fault conditions is determined by its volt-time capability.