Showing papers on "Power-system protection published in 1983"

A New Measurement Technique for Tracking Voltage Phasors, Local System Frequency, and Rate of Change of Frequency

Abstract: With the advent of Substation Computer Systems dedicated to protection, control and data logging functions in a Substation, it becomes possible to develop new applications which can utilize the processing power available within the substation. The microcomputer based Symmetrical Component Distance Relay (SCDR) described in the references cited at the end of this paper possesses certain characteristics which facilitate real-time monitoring of positive sequence voltage phasor at the local power system bus. With a regression analysis the frequency and rate-of-change of frequency at the bus can also be determined from the positive sequence voltage phase angle. This paper describes the theoretical basis of these computations and describes results of experiments performed in the AEP power system simulation laboratory. Plans for future field tests on the AEP system are also outlined.

A New Computer-Based Flux-Restrained Current-Differential Relay for Power Transformer Protection

Abstract: The paper begins with a review of techniques for computer based protection of multi-winding three-phase power transformers. After reviewing the principles of harmonic-restraint and voltage-restraint current differential protection, the paper develops a technique which computes and uses flux-current relationship of the transformer to obtain. the restraint function. It is shown that this protection technique requires fewer computations as compared to the harmonic current computation, and hence can be implemented on a microcomputer of modest. capability. The principle has been tested. in the'laboratory on a model power transformer. The relay based on this flux-restraint principle performs well on all the system phenomena simulated in the laboratory. It is expected that a relay based on this principle will be tested in the field on a power transformer.

Composite Generation and Transmission System Adequacy Evaluation Including Protection System Failure Modes

Abstract: Protection systems are normally considered to be perfectly reliable in composite system adequacy assessment. The effect on the calculated adequacy indices of neglecting these events can be quite significant in highly redundant configurations. This paper examines some protection system models and incorporates the results in a practical application of cmxposite systemtadequacy assessment.

Computer prediction of IDMT relay settings and performance for interconnected power systems

Abstract: The application of the inverse definite minimum time (IDMT) overcurrent relay to power system protection is reviewed, and the present methods for determining its settings are briefly described. A computer program to calculate relay settings based on a generalised procedure, and therefore suitable for both radial and interconnected ring systems, is then proposed. Its application to a specific interconnected system is explained. Two further programs have been developed to be used in conjunction with the first one. These assess, by a simulated circuit breaker tripping facility, how the IDMT protection would perform on an interconnected ring power system when there occurs either a failure of the main protection or a circuit breaker on the faulted section.

Interactive security evaluation in power-system operation

Abstract: The real-time operation of power systems requires security assessment and enhancement computations to ensure that the system stays in the normal state for as long as possible. The paper describes an interactive computer package with colour graphics for power-system operational studies. The package includes load flows, fault analysis and security enhancement. A decoupled algorithm is used for security enhancement, and offers the operator a choice of feasible corrective actions to alleviate line overloads. These corrective actions include generator rescheduling, network voltage adjustments, switching of reactive compensation and the control of phase shifters. Experiments on three test systems are summarised and discussed

Microprocessor-based algorithm for symmetrical-components calculation

Abstract: This letter presents a microprocessor-based algorithm for calculating symmetrical components from the distorted transient voltage and current signals in a power system. The fundamental frequency components of the 3-phase signals are first extracted using an algorithm based on Haar functions and then "symmetrical-component transformation is applied to obtain the sequence components. The algorithm presented is computationally efficient and fast. This algorithm is better suited for application in microprocessor-based protection schemes of synchronous and induction machines.

Circuit arrangement for identifying and storing power line faults

Abstract: A circuit arrangement detects and stores power line faults. The occurrence of sporadic faults as represented, for example, by inadmissibly long network collapses, which could lead to shut-down of a current supply and, therefore, to downtime of a computer are generally difficult to detect because the faults disappear given a return of the network, as does, therefore, the prerequisite for detecting the cause of such faults. For the purpose of detecting the cause of the fault, the rectified power line voltage is supplied to a comparison circuit followed by a signal circuit. The signal circuit is connected to a memory which influences a display. As a result, power line faults remain stored despite the return of the power line input voltage. The circuit arrangement is particularly suitable for use in power supply systems for data processing devices.

High resistance grounding and selective ground fault protection for a major industrial facility

Abstract: The high-resistance grounded system offers the distinct advantage of service continuity under single ground fault conditions which is critical to many industries, such as petroleum, chemical, mining, textile, cement, pulp and paper, food, glass, utility, etc. A new major phosphate mine, with a total 120MVA electrical demand capacity, utilizes the high-resistance grounding method for the 48OV and 416OV distribution systems. A complete ground fault protection scheme that includes both first fault alarm and second fault selective tripping protection was developed for the proper protection of the system. The design of this ground fault protection system has many unique features due to the complexity of the project. Design considerations including the system leakage current, the limitation of transient overvoltage, the grounding methods, the fault detection and annunciation, and selective isolation of faults based on circuit priorities, are analyzed here.

Surge Protection for AC Motors-When Are Protective Devices Required?

Abstract: AC motors require surge protection. However, rotating machinery arresters and capacitors are not required on the terminals of all ac motors. Often the distribution system parameters provide inherent surge protection. A simplified method is provided for determining when additional surge protection equipment is required at motor terminals.

Probabilistic Approach for Lightning Protection of Structures: Application Criteria for Protective System Design

Abstract: The problem of lightning protection for structures is treated from a probabilistic point of view. A criterion is suggested to evaluate the exposure of the structure, exposure being defined as the number of direct lightning strokes received., The influence of landform and of surrounding structures is considered. An approach is discussed for selecting the basic characteristics of the system suitable for ensuring protection of the structure compatible with the admissible risk fixed by codes. The influence of the characteristics of the protective system on protection performance is evaluated and discussed.

Reliability Calculations for Electrical Transmission Systems on the Basis of Mean Failure Indices

Abstract: In an electric power transmission network, a fault occurring on any one of its components sometimes causes an' active event' as a result of interaction between the power system and its protection system. An outage of sections adjacent to the faulted one for a small duration is characteristic of these events. In this paper, the mean failure indices (mean probability-of-failure and mean frequency-of-failure) of a network are defined as functions of the failure indices at various load points. Several types of active events including those caused by failure of protection system are considered and their contribution to the mean failure indices of the network evaluated. The effectiveness of providing normally open paths in reducing the mean failure indices of the network is explained. The points are illustrated by examples.

Application Criteria for High-Speed Bus Differential Protection

Abstract: Specific application criteria for high-speed bus differential protection are discussed, in addition to substitute protection arrangements and limitations involved System arrangements for which high-speed bus differential protection usually cannot be justified are also described

Computerised in-situ testing of feeder protections

Abstract: A description is given of the general arrangement of the overall feeder protection systems used by the CEGB. It is shown how this arrangement is only designed to accommodate protection relay failure when this failure leads to nonoperation under power-system fault conditions. The increasing importance of ensuring relay failures do not cause incorrect tripping is highlighted and existing methods of preventing this are discussed. A new approach to overcome this problem is described; that of computerised maintenance testing. A computerised protection test set specificaly developed for this purpose is described. Details are given of the hardware, software and mode of operation of the equipment, and test results produced by it are used to demonstrate the tests which the equipment can perform.

Arcing Fault Protection on Vepco's 480Y/277 Volt Secondary Spot Networks

Abstract: This paper reviews the problems encountered by this utility in finding a reliable and economical protection scheme to protect spot networks from arcing ground faults. We have also shown the various methods that we have implemented to resolve this problem on old spot network installations and on new installations through the use of ground relays, ultraviolet detectors and continuous line thermal detection systems.

Discriminative response of distance protection in reverse-fault operation

Abstract: The paper provides a detailed investigation of the principal properties of distance protection response, for the particular conditions of faults immediately behind the intended zone of protection coverage, and against which the protection is required at all times to discriminate. Based, first, on a nontransient evaluation model and stability indices defined for each earth- and phase-fault element of a complete protection terminal, the combinations of conditions for which reverse-fault stability margins are likely to be lowest are identified. The dependence of the margins on the fault level at the protection location, protection forward-reach settings, the crosspolarising level, and the power transfer at the instant of fault inception are examined. From this basis, the extent to which stability margins might be impaired by the presence of transients in comparator input signals is investigated using extensive dynamic simulation facilities. Of principal concern in close-up reverse-fault operation is the transient response of capacitor-voltage transformers, from which protection signals are derived, but the paper shows that, for all asymmetrical fault conditions, dynamic stability margins remain high. Protection discrimination is most severely tested by symmetrical 3-phase-to-earth faults, for then all primary input voltages to capacitor-voltage transformers collapse, and the subsequent protection response is determined mainly by their residual transients. In this extreme fault condition, all earth- and phase-fault comparators are close to an operating threshold, but the paper gives the form of capacitor-voltage-transformer response which guarantees stability.

Service Supply-Line Protection - An Industrial Plant User's View

Abstract: Since electrical service supply to an industrial plant is very important, it deserves a careful examination of power-supply requirements, such as quality and reliability. The protection of the service supply line is more important to the plant operator than to the supplier of electrical power. A close engineering coordination between the plant operator and the power service supplier is necessary. for increased quality and reliability at optimum cost. Industrial plant power-supply requirements, system disturbances and their effects, and protective measures needed to meet plant electrical power supply requirements are presented.