Fault Transients Research Articles

Computer relaying and expert systems: New tools for detecting high impedance faults

It has long been known that certain types of faults and unacceptable operating conditions on electric distribution feeders cannot be detected by using conventional protection practices. However, advanced digital system hardware and software methods are being used to develop new techniques for protection and on-line diagnosis of system operations. This paper presents newly developed methods for the detection of high impedance, low current faults using signal processing and pattern recognition techniques in computer relaying architecture with expert systems. The characteristics of these faults are described, including the analytical methods used to separate detection parameters from the overall frequency spectrum generated by the fault transients. Fault detection parameters are identified and algorithms suitable for computer relays are presented. Elements of a digital system architecture required to implement protection algorithms are discussed. Expert system methods used in the implementation of the protection and diagnosis software are also described.

SOLUTIONS INCORPORATING MAGNETIC HYSTERESIS TO THE SUBHARMONIC PROBLEM IN POWER SYSTEMS

ABSTRACT One possibility of taking care of the subharmonics in high speed protection is to filter the fundamental frequency components from the fault transients and use them for fault detection and discrimination. This is correct only if the phases and amplitudes of fundamental components during and post-subharmonic periods remain the same in transient waveforms. An attempt is therefore made to establish this aspect by a detailed study of a typical electrical network presenting subharmonics. The Dual Input Describing Function is adopted to show the subharmonic boundaries and the influence of system parameters on subharmonic oscillations. Magnetic hysteresis is incorporated in the analysis. A fifth order nonlinearity and one-third subharmonic are assumed. The theory could be easily extended to any order of nonlinearity and to any subharmonic frequency and also to a combination of subharmonics. The analysis gives a set of nonlinear algebraic equations. These equations are solved by Newton's technique using ...

DYNA-TEST simulator: protective relaying teaching tool

The teaching aspects of protective relaying is discussed. The existing practice is to teach fault analysis and protection methods on the basis of a steady-state concept of unbalanced power systems. However teaching protection relay design requires analysis of the fault transients associated with power apparatus and instrument transformers. Appropriate tools to simulate dynamic behavior of a power system are needed in this case. A dynamic testing simulator called DYNA-TEST, to be used as a teaching tool, is proposed. The simulator can be implemented with almost any common mainframe, using readily available supplemental hardware and software. As an example, teaching experiments involving digital algorithms for distance relaying are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A method for the computation of fault transients in transmission lines

A method for the exact computation of long-line fault transients is presented. The use of a numerical inverse Laplace transform algorithm makes it possible to analyze faults on lines of any length, while the derivation of the equations in the s-domain makes it possible to represent such lines by a single two-port network for each one. For convenience, the approach is first illustrated for a single-phase representation, which is valid for symmetrical faults. Then a generalized approach for three-phase modeling is derived to simulate any type of fault. The advantages of this approach are its accuracy and simplicity as well as its inherent capability for giving the values of the different currents and voltage at different network locations at preselected time points. It is believed that one of the major applications of this method will be the testing of different digital protection algorithms and strategies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Time Delay Compensation for High Speed Digital Protection

Processing of the fault transients for eliminating the unwanted signals, is essential. for the EHV system protection. The various components which perform this function, and the filters in particular, introduce a significant delay in the operation of the protective devices. The paper investigates the various sources of time delay, and presents a digital. time delay compensation scheme, together with some test results.

Operation of a Long-Term Transient Monitoring System in a 138-KV and a 500-KV Substation

This paper describes the operating performance of automatic transient monitoring laboratories designed to capture fault and transient data on power systems. Laboratories were installed in a 138-kV and a 500-kV substation and operated for more than 25,000 hours over a three-year period. Recorded during this period were 341 events consisting of lightning, switching, and fault transients. These results provide invaluable data on actual transients in power systems to aid power system equipment designers. A summary of the transient data obtained with the laboratories is contained in a companion paper. Work described in this paper was funded by the Electric Power Research Institute under Contract RP751-1.

Operation of a Long-Term Transient Monitoring System in a 138-KV and a 500-KV Substation

This paper describes the operating performance of automatic transient monitoring laboratories designed to capture fault and transient data on power systems. Laboratories were installed in a 138-kV and a 500-kV substation and operated for more than 25,000 hours over a three-year period. Recorded during this period were 341 events consisting of lightning, switching, and fault transients. These results provide invaluable data on actual transients in power systems to aid power system equipment designers. A summary of the transient data obtained with the laboratories is contained in a companion paper. Work described in this paper was funded by the Electric Power Research Institute under Contract RP751-1.

Fracture assessment of a PWR pressure vessel

The Second Report of the Marshall Study Group [1] reviewed the design of a pressure vessel to identify those regions which were most sensitive to the expected loading conditions. The design and loading conditions, including the pressure test, were also reviewed. A stress analysis data base of sufficient detail was established to permit a full fracture analysis to be carried out. After reviewing currently available methods for fracture assessment the CEGB R6 method was adopted. Selected normal and upset, emergency and fault transients were considered. Initiation defect sizes for normal and upset transients were generally large. In the beltline and nozzle shell course, for example, the minimum initiating height for an extended line defect was approximately 70 mm. For emergency and fault conditions, providing upper shelf material properties apply, the height to initiate semi-elliptical defects exceeds 25 mm and cracks substantially larger than this will extend by only small amounts in a ductile manner and remain stable. If during the large LOCA upper shelf material properties cannot be maintained semi-elliptic defects 6 to 10 mm high may propagate transversely parallel to the inside surface of the vessel. This may be limited by warm prestressing.

Power system for a high-power burst mode pulsed load

A novel power system, recently completed and commissioned, is described. Operating directly from an ll-kV, 50-Hz public supply, it provides the electrical energy for a burst mode, pulsed load. In each burst, the minimum energy delivered by the power system is 100 kJ at a rate of 330 kW. The pulse modulator operates at a peak charge of 105 kV and is capable of switching 200 MW over a range of pulse lengths and repetition rates. The high-voltage, high-current thyratrons used as the charge, discharge, and PFN energy dump switches were specially developed, four-gap, double-ended CX 1199B thyratrons. Supply voltage stepup transformers were designed to operate over bursts of variable pulse number, length, and rate, with the rectified unfiltered transformer output directly feeding the modulator charging circuit at up to 65 kV. Polarizing effects in the transformer core caused by the use of repetition rates equal to, or harmonically related to, the supply frequency were analyzed and effectively eliminated. Special winding techniques were developed to provide the strength and insulation for withstanding fault transients. While the power supply is capable of limiting fault currents occurring in the modulator and load, normal full system protection is provided by PFN energy dumping and, in the ac supply, by fast-acting vacuum contactors. Comprehensive control, monitoring, and mode selection are based on micrologic elements. By using direct, high-voltage modulation considerable flexibility is possible. The various alternative arrangements which derive from this design concept are explained. In addition, factors which determined the major features of the equipment are reviewed. The construction, layout, and performance are illustrated.

Computation of Transients in EHV Systems (with Reference to High Speed Protective Systems)

EHV systems, being characterised by high degree of interconnections, increased fault levels and large X/R ratios, insist on fast clearance of faults with high discriminating ability. When studying the shortest times in which reliable protection measurements have to be made, it is necessary to take into account the interaction between the primary system transients transmitted by transducers, the transients induced by these transducers themselves and their effects on the decision processes of the protection schemes. Digital computer simulation can give a degree of representation that goes well beyond that feasible with laboratory analogue modelling. The purpose of the present paper is to present the results of analysis of fault transients, current and potential transducer transients and inrush currents in power transformers for a typical 400 kV system,using direct integration technique based on Dommel’s method. The computed dynamic performances of a mho and a quadrilateral type distance relays are also presented.

A new mathematical analysis of series and shunt faults on three phase power networks

A mathematical analysis of sequential fault transients due to series and shunt faults is important in the study of circuit breaker pole openings and reclosings with arc resistances. The line loading itself becomes unbalanced momentarily due to load switching. Each double fault is developed in sequence, therefore the initial currents in the second and third fault must be treated properly under transient conditions. New sequence component variables λμ0 and ρσ0 are used with αβ0 components. This study is useful for small power systems as well for large power systems. A digital simulation of various series and shunt faults is presented in a generalized manner using αβ0, λμ0 and ρσ0 components.

Stabilizing superconductors for power engineering applications

Exhibiting essentially zero resistivity at high current densities and large magnetic fields, modern superconducting materials offer intriguing possibilities in power engineering. However, in order to utilize this property in any large scale application, the superconductor must be stable during fault and overload transients in the total system. In order to know whether the superconductor itself is stable, one must understand and control the detailed mechanisms of magnetic flux motion which occur in the material. Such flux motion will give rise to a non-zero resistivity and hence will always involve heat generation, which in turn will perturb the low temperature environment necessary to sustain superconductivity. This paper discusses the essential differences between superconductors and ordinary conductors; the control of heat generation resulting from magnetic flux motion necessary to insure that the superconductor is stable; and some experiments on models of dc superconducting transmission cables which test the theoretical assumptions.

Micromachine simulation of steam power plant

Owing to the recent growth in turbogenerator size, the dynamics of the steam-power plant influence considerably the behaviour of a generating station during large transient disurbances. To study this behaviour, detailed mathematical large-signal, nonlinear models of a boiler, turbine, governor and automatic voltage regulator (a.v.r.) were developed both for digital- and analogue-computer applications. The turbine was also modelled by a d.c. motor driving a microalternator. The power plant, simulated by an analogue computer connected to a micromachine system, was tested under load rejection and pole-slipping fault transients. The results are shown to correlate satisfactorily with those obtained from the Goldington and Northfleet power-station tests. For both these tests, an explanation of the control aspects of the phenomena is attempted.

Solution of network transients using symmetrical-component techniques

The paper shows how, without any loss in generality, symmetrical-component techniques can be used to analyse power-system fault transients in static networks. The general theory is developed and formulas are given for evaluating the phase-current transients in simple and sequential shunt faults. In the case of the phase-to-phase fault developing into a 3-phase fault, it is shown that more than current doubling is possible.

Solution of network transients using symmetrical-component techniques

The paper shows how, without any loss in generality, symmetrical-component techniques can be used to analyse power-system fault transients in static networks. The general theory is developed and formulas are given for evaluating the phase-current transients in simple and sequential shunt faults. In the case of the phase-to-phase fault developing into a 3-phase fault, it is shown that more than current doubling is possible.

Fault Transients and Frequency Spectra of a D-C Generator [includes discussion

Fault Transients and Frequency Spectra of a D-C Generator [includes discussion

Fault Transients in Aircraft D-C Systems

Fault Transients in Aircraft D-C Systems