Showing papers on "Power-system protection published in 1982"

Distribution High Impedance Fault Detection Utilizing High Frequency Current Components

Abstract: This paper describes work performed by Texas A&M University on the detection of high impedance faults on distribution primary conductors. Some grounded distribution primary conductors may exhibit a very low fault current such that they may not be cleared by over-current protection. These faults may persist indefinitely, possibly causing a fire hazard or a hazard to humans by contact with an energized line. The paper begins with an examination of the high impedance fault problem from the perspective of system protection. The fault detection theory is presented next. The system utilizes a fault-generated increase in the 2-10 kHz component of feeder current for fault detection. EPRI funding enabled the verification and demonstration of this fault detection concept. Measurements were made on several faulted and unfaulted feeders to develop a representative data base of signals to which a relay would be subject. Analysis of these data provided a time and frequency domain signature of these faults. A microcomputer-based prototype relay was constructed and installed on a typical utility feeder. It successfully detected most staged faults while not indicating a false trip during a three month demonstration.

A New FFT-Based Digital Frequency Relay for Load Shedding

Abstract: A power system disturbance, or operating abnormality, can produce a severe generation and load imbalance, resulting in a rapid frequency decline. The possibility of such a disturbance has led to increased interest in the application of automatic under-frequency protection schemes to restore load/generation balance and to prevent equipment damage. In this paper a new method for detecting changes in the power system frequency, by relating it to a leakage coefficient in the FFT, is presented. The algorithm computes the deviation of the power system frequency from the fundamental component and the best estimate of its rate of change. The algorithm then predicts the percentage generation and load imbalance, and finally trips the appropriate amounts of load at the appropriate time delays.

A Microprocessor Based Three-Phase Transformer Differential Relay

Abstract: This paper presents an algorithm for digital protection of a three-phase, three-winding power transformer. Simple recursive expressions are given for the harmonics using a sampling rate of 12 times a cycle. These expressions are used as the basis for a one cycle algorithm which is compatible with proposed digital line protection schemes. The algorithm was tested on data obtained from a model transformer. Test results are given for 19 cases of energizations and faults.

A Two-Step Compensation Method for Solving Short Circuit Problems

Abstract: This paper reports on the development of a unified approach for the solution of all types of short circuit problems. The basic approach is to consider a fault condition -- a fault type or combination of fault types and associated line outages -- as modifications to the parameters of the branches of the prefault network. An extension, referred to as the two-step compensation method, of the conventional compensation scheme was developed to account for the balanced and unbalanced nature of-the modifications that networks undergo when faulted. The computationally efficient solution scheme was derived by using a decomposition of the modifications according to their balanced and unbalanced nature and exploiting the structural properties of the short circuit problem, notably sparsity. The solution approach is particularly useful for system-wide studies, in which specified fault conditions at a set of specified fault locations are analyzed sequentially, on large systems. A noteworthy feature of the proposed methodology is the natural manner in which mutuals are handled. Results of the application of this approach to investigate a variety of fault conditions on several systems, including a 2278 bus network, are presented.

Generator Ground Fault Protection Using Overcurrent, Overvoltage, and Undervoltage Relays

Abstract: This paper describes the protective relaying schemes employed by Georgia Power Company to protect synchronous generators from single-phase- to-ground faults. Three types of relays are connected in the secondary of a distribution grounding transformer. These include a conventional electro- mechanical overcurrent relay with time overcurrent unit and instantaneous overcurrent unit, a solid- state overvoltage relay (with timing module) tuned to reject frequencies near 180 hertz, and a solid-state undervoltage relay (with timer) tuned to reject frequencies near 60 hertz present at the generator neutral. The proper method of selecting the generator grounding components and protective relays is described, and detailed setting instructions for all relays are also included.

Design Criteria for an Integrated Microprocessor-Based Substation Protection and Control System

Abstract: Design requirements and approaches are described for the EPRI-sponsored development of an integrated, microprocessor-based system for relaying and control of transmission substations. The paper summarizes the architecture, hardware and software design, functional capabilities, and economics. Many important user benefits inherent in this dramatically different approach are listed.

Protection methods for power-transistor circuits

Abstract: The paper proposes a number of protection methods which can be used with power transistors in power-control units. They give satisfactory protection against simultaneous conduction of the two devices in an inverter leg. The techniques, which are independent of the control electronics and base-drive circuits, are simple and reliable to implement. They include an instantaneous and electrically isolated method of fault indication, a fast-acting crowbar circuit and a means of diverting the current away from the power devices in the event of a fault.

Some aspects of multilevel load-frequency control of a power system

Abstract: The application of multilevel control strategies for load-frequency control of interconnected power systems is assuming importance. A large multiarea power system may be viewed as an interconnection of several lower-order subsystems, with possible change of interconnection pattern during operation. The solution of the control problem involves the design of a set of local optimal controllers for the individual areas, in a completely decentralised environment, plus a global controller to provide the corrective signal to account for interconnection effects. A global controller, based on the least-square-error principle suggested by Siljak and Sundareshan, has been applied for the LFC problem. A more recent work utilises certain possible beneficial aspects of interconnection to permit more desirable system performances. The paper reports the application of the latter strategy to LFC of a two-area power system. The power-system model studied includes the effects of excitation system and governor controls. A comparison of the two strategies is also made.

Practical Low Voltage Equipment Ground Fault Protection for Solidly Grounded Systems with Wye-Connected Source Transformers

Abstract: A low voltage equipment ground fault protection system for solidly grounded radial systems is described. The protection provides primary protection for source substation buses. It is capable of providing selective operation with downstream ground fault trip devices or phase-overcurrent devices set to detect ground faults. It also provides source transformer protection for phase-to-ground through faults to supplement transformer primary phase-to-phase and three-phase through-fault overcurrent protection.

Generator Backup Overcurrent Protection

Abstract: A concern that the characteristics and correct application of the generator backup relay are misunderstood is addressed in this report to the Power Systems Protection Committee. It is inherently a secure device, and rarely has the opportunity to operate in its intended capacity. So the question was asked, ``Do generator backup overcurrent relays really protect anything?'' In response a description of the function and operating characteristics of the backup relays, a discussion of generator fault current behavior, examples of relay settings for a typical application, and methods and criteria for determining that the relay both protects the generator and operates selectively with other protective devices are included.

Shunt Capacitor Bank Protection Methods

Abstract: A "Guide for Protection of Shunt Capacitor Banks," ANSI/IEEE Standard C37.99-1980, has been prepared recently by the, Power System Relaying Committee to assist in the effective application of relays for the protection of shunt capacitor banks used in substations. The various protective considerations along with recommended and alternate methods of protection for the most commonly used capacitor bank 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 new document, and to invite considered discussion for the purpose of improving this guide in the future.

Fault-current limiter with superconducting DC bias

Abstract: In the last decade there has been renewed interest in fault-current-limiting devices and various concepts are under active consideration. The paper describes the principle, design, manufacture and testing of a device based on one of these concepts. The possible areas of application of the device are indicated.

Earth fault protection device

Abstract: The fault protection device is based on a protection circuit in which the presence of the mains voltage is the precondition for the expected protection effect in the event of a fault (transmission of a contact voltage). The disadvantage of the known protection devices (e.g. fault protection devices with amplifiers), that they do not switch off in the case of faults involving an interruption of the centre lead, and the hazardous contact voltage thus remains, is overcome according to the invention in that the lines (2 and 3) leading to the load unit are automatically connected only when the full mains voltage is applied. This through-switching can be effected e.g. by means of two triacs (5 and 6). When the mains voltage is applied and the line has no interruption, only the ignition voltage required for through-switching is then present on a voltage divider (7, 8 and 9).

Probabilistic Calculations of Lightning Protection for Tall Buildings

Abstract: The analysis of the protection practices applied to tall buildings by using lightning rods or horizontal wires has shown a deficiency in defining the shape and the extent of the protective zone. The limitations in the application of the empirical protective zone defined by a conical shape below and around a lightning rod have motivated the development of new techniques for the protection of buildings against lightning. Starting from the transmission line protection practice, the protective effects of the basic lightning elements (vertical rods and horizontal wires) are studied analytically by means of the electrogeometric model developed mainly by Whitehead; as a result, we have developed a simplified shielding calculation practice, as well as a digital computer program based on Monte Carlo simulation technique. The concept of protection failure risk is introduced to characterize the effectiveness of lightning protection schemes.

Development and Field Experience of Digital Protection and Control Equipment in Power Systems

Abstract: In applying microelectronic techniques to protective and control equipment in the power system, there is an important subject to be solved, which is the assurerance of long-term reliability. From this viewpoint, countermeasures against environmental conditions, for example temperature rise, electro-magnetic interference and dust are reconsidered.

Transient Overvoltages and Overcurrents During Line Fault Tests on the Hokkaido-Honshu HVDC Link

Abstract: A series of line fault tests have been conducted at completion of Stage I of the Hokkaido-Honshu HVDC Link of Electric Power Development Co., Ltd., prior to its commercial operation, in order to study transient overvoltages and overcurrents and to confirm safety operation of system protecting devices in case of DC transmission line faults.

Relay Protection of Generator Station Service Transformers

Abstract: Generator station service transformers, also called unit auxiliary transformers, are subjected to very rigorous short circuit duty. These faults fall generally into three areas: Faults within the transformers themselves, low-side faults between the transformer and the low-side bank breakers, and faults on the station service supply buses. The purpose of this paper is to show how station service transformers should be protected, and why any protective scheme can only be effective if these transformers are properly specified for UAT service.

A Multi-Level Distributed Microprocessor System for a Nuclear Power Plant Fire Protection System Controls, Monitoring, and Communication

Abstract: All nuclear power plants must have fire monitoring and fire suppression systems. The design, construction and operation of these systems involve considerable skill and considerable cost. The instrumentation and control requirements are extensive and sophisticated. Adequate reference works for these requirements and how to achieve them are not available. This paper is an attempt to describe these instrumentation and control requirements and also to present a specific design concept. This incorporates the result of the writer's experience in working with the design review and commissioning the instrumentation and controls of the entire fire detection and suppression system in an operational nuclear power plant and his subsequent study on the subject.

Shunt Capacitor Bank Protection Methods A working-group report for the Power System Relaying Committee

Abstract: A ``Guide for Protection of Shunt Capacitor Banks,'' ANSI/IEEE Standard C37.99-1980, has bee prepared recently by the Power System Relaying Committee to assist in the effective application of relays for the protection of shunt capacitor banks used in sub-stations. The various protective considerations along with recommended and alternate methods of protection for the most commonly used capacitor bank 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 new document, and to invite considered discussion for the purpose of improving this guide in the future.

Power-system digital back-up protection

Abstract: The purpose of power-system back-up protection is to disconnt faulty primary equipment not isolated by the main protection and associated circuit breakers. Conventional back-up techniques are difficult to apply in a large power system and heavy reliance on main protection is required. In this paper, both substation-based and centrally co-ordinated back-up protection methods, using microprocessors and minicomputers, are described. In a power system with a reliable communication network between substations, a fault-directing method is proposed to perform centralised digital back-up protection. If the communication network is not available, a substation-based back-up method is suggested. Both methods can reduce back-up fault-clearance time with correct discrimination, high reliability and cost effectiveness.

Telephone Protection and Grounding

Abstract: This paper gives an overview of the various types of devices most commonly used for telecommunications protection. Gas discharge and solid state devices are discussed insofar as their application to signal line protection is concerned. Their failure mechanisms, some of their shortcomings and advantages as well as the application of combinations of both types of devices is also covered. Good bonding and grounding is extremely important to the proper operation of any protection system. A discussion of the effects of improper bonding and the resultant problems is also presented.

Innovations in power distribution in cement plants

Abstract: A few of the many new product applications and protection methods first used in the decade between 1971 and 1981 for cement plant power distribution systems are surveyed. References noted in each brief discussion contain application details as well as equipment descriptions, ratings, and application advantages of the innovations discussed. Transformers: Transformer designs, transformer through fault protection. Motors: Thermal tracking motor protection wound rotor motor protection, dual drive protection, high efficiency 460 V motor design, large horsepower SCR-DC fan drives, medium voltage load commutated inverter drives. System: Medium voltage vacuum circuit breakers, pilot wire tie line protection, transformer ground differential protection, zinc oxide station class surge arresters.

A Controlled-Capacity Power Unit for High-Density Backplane Protection

Abstract: Signal-carrying conductors located near power conductors can be damaged by fault currents. Previously, these signal conductors have been protected in high-density backplanes by segmenting the load and limiting the current available per segment to a safe level using one of three methods: current-limited power supplies, electronic monitors in the power distribution network, or distribution fuses. This paper describes a system that uses a controlled-capacity power unit to protect signal conductors without the inherent expense of segmentation.

An Electronic Replacement for Thermo-Mechanical Load Protection Devices

Abstract: An electronic replacement for the thermo-mechanical overcurrent protection devices for ac loads is sought. The proposed scheme works on a principle of integrating certain width- and amplitude-controlled line current ``error'' signals and it is shown to be capable of having variable overload protection characteristics. Facility for protection of loads against unbalance is also incorporated in the scheme. A simple hardware implementation is given and the results obtained thereof are found to be satisfactory. It is concluded that such a scheme would be commercially viable.

AC Service Protection in Unattended ESS Telephone Equipment Buildings

Abstract: Unattended ESS telephone equipment buildings present different considerations than those presented by the older electromechanical Central Dial Offices. The planning and design of the AC service protection system in these buildings is now directed toward the building environment and ancillary mini-microcomputers as well as the exchange switching equipment. This paper describes the equipments, circuits and economical considerations used when planning the protection system with its associated administrative alarms. Included are sketches for "do-it-yourself" unitized equipments fabricated to provide economical protection with space saving concepts.

Novel fail-safe earth-fault protection schemes for underground coalmines using restricted-neutral system of power supply

Abstract: The paper reports the development of two novel fail-safe sensitive earth-fault protection schemes for coal mines using restricted-neutral system of power supply. Minimisation of earth leakage current for an underground coal mine's power-supply system is of great advantage in reducing hazards like electrical shock from exposed metal works, fire and methane explosion. Restricted-neutral system of power supply can effectively limit earth-fault currents to a very low limit (100-200 mA) as compared to that of 500-1000 A in solidly earthed neutral system. With such drastic reduction of earth-fault current, the earth-fault relay design becomes quite complex and requires application of electronic circuits, because the weak output voltage of the core balance transformer can no longer operate a conventional relay directly during an earth fault. Most of the existing earth-fault protective devices used for this purpose are either nonfail-safe or partially fail-safe, and to the author's knowledge no attempt has been made, so far, to study their fail-safe characteristics in a systematic manner. This leaves a scope of doubt about their degree of fail-safety feature. The new protection schemes developed by the authors use two novel circuits with fail-safe features, such that in case of failure of most of the circuit components the circuit breaker is tripped off thereby offering additional safety for underground application. The fail-safe feature of the protective devices developed have been critically ascertained by typical laboratory simulation of component faults. The protection schemes developed offer good reliability for earth-fault setting of 100mA and above.

Protection and Supervision of DC-DC Converters for Electronic Telephone Switching Systems

Abstract: Power conversion equipment in electronic switching systems require protection against faults that may cause damage to the equipment. The most severe faults which must be protected against are those that would cause an electrical fire. Basic protection techniques such as fusing and current limiting are well known and widely utilized. Enhanced protection is provided by an automatic shutdown technique which monitors the outputs of a converter for both high and low conditions and causes a shutdown in the event of a fault. Typical fault conditions and the protection provided by the automatic shutdown circuit are analyzed. Supervision of DC-DC converters in electronic telephone switching systems is required to implement local power control zones and to achieve configuration control. A power supervision circuit is described which provides a flexible means of linking independent converters in common local power control zones. The manual and system interfaces which contribute to configuration control are also described.