Showing papers on "Power-system protection published in 1999"

Condition monitoring and fault diagnosis of electrical machines-a review

Abstract: Research has picked up a fervent pace in the area of fault diagnosis of electrical machines. Like adjustable speed drives, fault prognosis has become almost indispensable. The manufacturers of these drives are now keen to include diagnostic features in the software to decrease machine down time and improve salability. Prodigious improvement in signal processing hardware and software has made this possible. Primarily, these techniques depend upon locating specific harmonic components in the line current, also known as motor current signature analysis (MCSA). These harmonic components are usually different for different types of faults. However with multiple faults or different varieties of drive schemes, MCSA can become an onerous task as different types of faults and time harmonics may end up generating similar signatures. Thus other signals such as speed, torque, noise, vibration etc., are also explored for their frequency contents. Sometimes, altogether different techniques such as thermal measurements, chemical analysis, etc., are also employed to find out the nature and the degree of the fault. Human involvement in the actual fault detection decision making is slowly being replaced by automated tools such as expert systems, neural networks, fuzzy logic based systems to name a few. Keeping in mind the need for future research, this review paper describes different types of faults and the signatures they generate and their diagnostics' schemes.

Experience with an inverter-based dynamic voltage restorer

Abstract: The installation of the world's first dynamic voltage restorer (DVR) on a major US utility system to protect a critical customer plant load from power system voltage disturbances ushers in a new era of power quality problem solution on the utility side of the revenue billing meter. The prototype DVR built by Westinghouse for EPRI was installed in August, 1996 on the Duke Power Company (North Carolina) 12.47 kV system at an automated yarn manufacturing and weaving factory where it provides protection from disturbances coming from the utility distribution system that serves the plant. This paper describes the prototype DVR installation and presents early results from the demonstration project.

Behaviour of grounding systems excited by high impulse currents: the model and its validation

Abstract: The behaviour of grounding systems excited by high impulse currents (such as lightning strokes or phase to ground faults) considerably differs from that at low-frequency and at low-current: inductive behaviour can become more and more important with respect to resistive behaviour and, in addition, these currents can generate soil breakdown (which makes the impulse response typically nonlinear). Many experimental tests confirm these aspects. In order to obtain a correct design of electrical systems, with respect to the protection of installations against anomalous events, it is fundamental to predict the impulse characteristics of grounding systems. An efficient solution to this problem may be obtained by a mathematical model based on a circuit approach. The development of this model (which is able to simulate complex grounding systems when nonlinear ionization phenomena take place) is described in this paper. The model has been validated by comparing the numerical results both with experimental tests and with the simulations executed by various approaches.

Time coordination method for power system protection by evolutionary algorithm

Abstract: A typical industrial power network may consist of hundreds of pieces of equipment and even more protection relays to protect the system are required. Each protection relay in the power network needs to be coordinated with the relays protecting the adjacent equipment. The overall protection coordination is, thus, very complicated. A new concept of protection coordination by time is introduced in this paper to formulate all the system relays and system equipment operation into a set of optimization equations and constraints. Its purpose is to search for an optimal protection setting to minimize the system disturbance time as well as the time of interruption of the power supply. An evolutionary algorithm is applied as a constraint satisfaction optimization tool to search for the optimal relay setting. This method can find the best protection relay coordination, which cannot be achieved by traditional methods. This is the most significant achievement of the paper.

Application of a novel fuzzy neural network to real-time transient stability swings prediction based on synchronized phasor measurements

Abstract: The ability to rapidly acquire synchronized phasor measurements from around a power system opens up new possibilities for power system protection and control. In this paper, the authors develop a novel class of fuzzy hyperrectangular composite neural networks which utilize synchronized phasor measurements to provide fast transient stability swings prediction for use with high-speed control. Primary features of the method include constructing a fuzzy neural network for all fault locations, using a short window of realistic-precision post-fault phasor measurements for the prediction, and testing robustness to variations in the operating point. From simulation tests on a sample power system, it reveals that the proposed tool can yield a highly successful prediction rate in real-time.

C37.110 guide for the application of current transformers used for protective relaying purposes

Abstract: Relay engineers have had to rely on many sources to compile information on current transformer application. Typically, they have drawn on relay application and transformer textbooks, manufacturer publications, and standards. Recognizing the need for a comprehensive one source document, the power system relaying committee has produced the C37.110-1996 guide for the application of current transformers used for protective relay purposes.

Technical and economical benefits of superconducting fault current limiters in power systems

Abstract: There is no doubt that superconducting fault current limiters (SFCL) will be used if their technical and economical benefits are high enough. Up to now a number of studies have been carried out to show suitable applications of SFCL but very few reports have been published on their technical and economical benefits in existing networks. This paper shows favourable places of SFCL in an urban network up to a voltage of 110 kV, lists technical benefits and calculates the economical savings. In the investigated network it was found that feeder locations of power stations and wind generators are the most economical places for SFCL.

An innovative technique for packaging power electronic building blocks using metal posts interconnected parallel plate structures

Abstract: Power electronics building blocks (PEBBs) are envisioned as integrated power modules consisting of power semiconductor devices, power integrated circuits, sensors, and protection circuits for a wide range of power electronics applications, such as inverters for motor drives and converters for power processing equipment. At the Center for Power Electronics Systems, we developed a topology for a basic building block-a two-switch two-diode half-bridge converter in totem-pole configuration with built-in gate-driver and protection circuitry, fiber-optic receiver/transmitter interface, and soft-switching capability. Based on the topology, a series of prototype modules, with 600 V, 3.3 kW rating, were fabricated using an innovative packaging technique developed for the program-metal posts interconnected parallel plate structure (MPIPPS). This new packaging technique uses direct attachment of bulk copper, not wire-bonding of fine aluminum wires, for interconnecting power devices. Electrical performance data of the packaged devices show that an air-cooled 15 kW inverter, operating from 400 V dc bus with 20 kHz switching frequency can be constructed by integrating three prototype modules, which is almost double what could be achieved with commercially packaged devices of the same rating.

A stochastic study of hidden failures in power system protection

Abstract: Recent studies have shown that power systems protection mechanisms have played a major role in propagating disturbances. All of the last five major Western Systems Coordinating Council (WSCC) events (the North Ridge earthquake, December 14, 1994, July 2 and 3, 1996, and August 10, 1996), involved either false trips of line protection relays or generator protection equipment. Using an importance sampling based algorithm on the 179-bus WSCC equivalent system, we modeled the sequence of rare events involving generator trips and incorrect zone 3 relay operations. Due to possible loss of generation and load, frequencies were monitored for the necessary of load shedding. The algorithm uses the Newton–Raphson method for accuracy but reverts to DC load flow when the Newton–Raphson algorithm fails to converge within three iterations. The resulting sequence of rare events and its corresponding probability are used to detect weak links in the power system. This information can be beneficial not only in areas such as service and maintenance scheduling and in planning, but also in determining locations where an investment in improving the protection system is warranted.

Model reduction for analysis of cascading failures in power systems

Abstract: In this paper, we apply a principal-orthogonal decomposition based method to the model reduction of a hybrid, nonlinear model of a power network. The results demonstrate that the sequence of fault events can be evaluated and predicted without necessarily simulating the whole system.

Protecting power systems in the post-restructuring era

Abstract: Protective devices (relays) are the first line of defense against faults and other disturbances that could do extensive damage to power equipment as well as to power systems. They are the most important self-healing mechanisms of power systems. Modern protective systems have evolved into a highly reliable system over many years. As most of the evolution took place during the era of vertically integrated power companies (i.e., where the generation-transmission-distribution-load in a region were all under direct control of a single company), it is natural that protection philosophies in existence today have an in-built character that is well suited to such utility company structures. This paper is a free-flowing exploration of issues that seem to the authors to be significant in the post-restructuring era of the electricity supply industry. They raise many questions from the point of view of power system protection engineers.

Adaptive travelling wave protection algorithm using two correlation functions

Abstract: In this paper, the performance of the correlation function-based travelling wave protection algorithm for high resistance faults is investigated. The reason for its inaccuracies is revealed by the lattice diagram. To eliminate its limitation, an auxiliary cross-correlation function (CCF) is proposed to act as its complement, which takes advantage of the signal that causes the inaccuracies of the standard CCF. For high resistance faults, both the template and the desired signal of the auxiliary CCF have the same prominent feature, which makes them easy to be identified, and the fault location can be acquired from them correctly. An adaptive strategy is designed to select the correct result from the two CCFs so that it can deal with both low resistance and high resistance faults. Simulation results show that the reliability and accuracy of the travelling wave protection have improved significantly.

Fault section estimation in electrical power systems using artificial neural network approach

Abstract: Fault section estimation is important for a power system to be restored to its normal state after a faulty section is isolated. In this study, an artificial neural network based approach is proposed to estimate the faulty section in power system by using the information from the protective relays and circuit breakers. The proposed approach is applied to a sample system where bus, transformer and line protection schemes are considered and the results are given.

Electric power system protection and control system

Abstract: A Power system protection and control system has protection and control terminals that perform protection and control of a power system by operation of a plurality of CBs in response to state variables input from power system; and a power system monitoring and control host mutually connected in a fashion to permit data exchange through a transmission system (communication network) with protection and control terminals and that performs monitoring and control of power system in accordance with data transmitted from protection and control terminals. Protection and control terminals each has a correlation circuit that performs correlation of an operated CB and the cause of its operation, using information sent from protective relay circuit, CB control circuit, re-closure circuit and CB state receiving circuit when at least one of a plurality of CBs is operated, and a correlation result transmission circuit that transmits the result obtained by the correlation processing of this correlation circuit to power system monitoring and control host through transmission system. The power system monitoring and control host includes a correlation result transmission unit that receives and displays the correlation result transmitted through transmission system from correlation result transmission circuit, associated message file storage unit and CB operation display unit.

A new method of network reconfiguration for service restoration in shipboard power systems

Abstract: The electric power systems of ships supply energy to sophisticated systems for weapons, communications, navigation and operation. Circuit breakers (CBs) and fuses are provided at different locations in order to remove faulted loads, generators or distribution systems from unfaulted portions of the system. These faults could be due to material causalities of individual loads or cables or due to widespread system fault due to battle damage. Because of the faults and after isolating the fault, there are unfaulted sections which are left without supply. It is required to quickly restore supply to these unfaulted sections of the shipboard power systems. This paper presents a new method to reconfigure the network to restore service to unfaulted sections of the system. The problem is formulated as a modification of the fixed charge network flow problem. The proposed method is illustrated using different case studies.

Neural network for current transformer saturation correction

Abstract: Current transformer (CT) saturation can cause protective relay misoperation or even prevent tripping. This paper presents use of artificial neural networks (ANN) to correct CT secondary waveform distortions. The ANN is trained to achieve the inverse transfer function of iron-core toroidal current transformers which are widely used in protective systems. The ANN provides a good estimate of the true (primary) current for a saturated transformer. The neural network is developed using MATLAB and trained using data from EMTP simulations, and data generated from actual CTs. In order to handle large dynamic ranges of fault currents, a technique of employing two sets of network coefficients is used. Different sets of network coefficients deal with different fault current ranges. The algorithm for running the network was implemented on an Analog Devices ADSP-2101 digital signal processor. The calculating speed and accuracy proved to be satisfactory in real-time application.

A recursive least-squares digital distance relaying algorithm

Abstract: A new digital distance relaying algorithm based on the well-known theory of least-squares is developed, and the results of testing it using numerical simulation are presented. The new technique estimates the distance to the fault and the fault resistance. To minimize the computational requirements of the digital relay, a recursive least-squares approach is used. Computer simulation results of the new least-squares algorithm seem promising, indicating that it should be considered for further testing and evaluation.

Automating the analysis of faults and power quality

Abstract: This article introduces an advanced system for power system automated fault analysis, accurate fault location and extensive power quality monitoring based on a digital fault recorder (DFR) infrastructure. Existing DFRs can be modified to provide the required data acquisition features. The existing communication network and processing power can be extended to accommodate the required data acquisition, processing and analysis. New software can be developed to accomplish the automated analysis.

Setting method of specific parameters of a superconducting fault current limiter considering the operation of power system protection-resistance-type and rectifier-type SFCLs in overhead transmission systems

Abstract: We have developed an EMTP model of a resistance-type and a rectifier-type super-conducting fault current limiter (SFCL) and defined their parameters which a user specifies when he plans to introduce an SFCL into a power system. Using these models, we propose the setting method of these parameters so as not to affect the response of protective relays when SFCLs operate.

Zone branch reliability methodology for analyzing industrial power systems

Abstract: There are many methods available for evaluating the frequency and duration of load point interruptions within a given industrial power system configuration. As systems become larger and more interconnected, these existing methods can become computationally bound and limited in their ability to assess the impact of unreliable protective equipment and unreliable protection-coordination schemes on individual load point reliability indexes within a given plant configuration. These methods also can often not account for complex isolation and restoration procedures within an industrial plant configuration. This paper presents a zone-branch methodology that overcomes many of these limitations and applies the methodology to a large industrial plant power system configuration. The primary advantage of the zone-branch methodology is that it can readily identify faulty protection schemes involving all the components of an industrial power system and evaluate load point reliability indexes.

Design and evaluation of a wind farm protection relay

Abstract: The paper describes the design and evaluation of a protection relay for wind farms with fixed-speed induction generators. The relay provides short-circuit protection for a medium-voltage collection circuit and the medium-voltage (MV) and low-voltage (LV) windings of the generator-transformers connected to it. The ability to protect the generator-transformers allows a significant reduction in wind farm construction cost, since the MV fuses normally used to protect the generator-transformers are not required. The authors discuss how the operating characteristic for the protection was designed, implemented in a processor-based relay and then tested using a wind farm simulator and test set. A selection of test results are to illustrate how the relay performs occur on the protected collection LV terminals of a generator-transformers or on the utility network. The paper also discusses how the relay performed when installed at the Cemmaes wind farm in Wales for a 12 month site trial.

Experimental examination of wide-area current differential backup protection employing broadband communications and time transfer systems

Abstract: Based on the authors' previously proposed wide-area current differential backup protection utilizing broadband packet communications and time synchronous systems for achieving better selectivity, smaller outage areas and faster operation times than conventional distance backup protection, experimental microprocessor-based protection devices have been examined with respect to both telecommunication and protection functions The experimental wide-area protection system consists of one central equipment (CE) unit and three terminal equipment (TE) units connected by a 155-Mbps ATM backbone network with a LAN interface and GPS time acquisition and features a simplified and effective method for expanding protection zones after primary or minimum-zone protection operation In an AC power system simulator configuring a busbar and a power line, each TE at a circuit breaker location transmits sampled current data to the CE and receives a tripping command initiated by it, and operate satisfactorily in various states of power system and telecommunications

Application of transformer ground differential protection relays

Abstract: Transformer ground differential protection relays (device 87G) have been used to protect the windings of resistance grounded transformers. A number of strategies have been utilized with electromechanical relays in the past. With the advent of the multifunction digital protective relay, these strategies can be adapted to continue this form of protection.

Integrated Modelling Environment: a platform for dynamic protection modelling and advanced functionality

Abstract: This paper summarises work undertaken in collaboration with The National Grid Company (NGC) to investigate the performance of dynamic models of the protection system. Models of commercially available relays have been developed, based on the manufacturers' specifications and algorithms. The concept of an Integrated Modelling Environment (IME) with an open architecture which can utilise (as input) primary power system simulation results obtained from the standard EMTP program, as well as actual fault records from the network, is presented. Case studies are presented to illustrate the capabilities of the IME, specifically involving the study of distance and unit protection scheme performance. Among other benefits, the paper also indicates the possible use of the IME as a Protection System Design Validation Tool. The outcome of this work has been validated by protection engineers and contributes to the improvement of the reliability and security of the protection system.

Development of a hybrid type assessment method for power system dynamic reliability

Abstract: The decision of the optimum scheme for preventing fault cascading is one of the most important tasks in power system planning. In order to make the above decision reasonably, it is indispensable to develop effective assessment methods for power system dynamic reliability. If the simulation or analysis method proposed up to this time is singly used, the calculation time becomes too large or the calculation error become too large. Considering this situation, we developed a hybrid type assessment method which can drastically decrease the degree of the above problem. The basic conception of this method is as follows. (1) Three kind of tasks (simulation of power plant dynamics, construction of event trees, reliability analysis of protection systems) are carried out alternately using previous results. (2) First, event trees are constructed assuming that all protection systems act normally. These trees are gradually extended considering multi-failures of protection systems. This method was applied to a model power system composed of 5 generators, 11 lines and 19 nodes. Results of application confirm that this method can exactly assess power system dynamic reliability. This method has the merit that the trade-off between the decrease of calculation time and error can easily carried out by adjusting the extension degree of event trees and the details degree of power plant dynamics models. We are confident that an assessment expert system for power system dynamic reliability constructed due to this method in the future will greatly contribute to the improvement of the planning for preventing fault cascading of power systems.

Fuzzy approach to fault classification for transmission line protection

Abstract: This paper presents a scheme for real time fault location and classification on transmission lines using fuzzy logic technique. The protection algorithm is based on the travelling waves present on major transmission lines after the incidence of a fault. The time interval between the initial travelling wave propagated from a fault and a later wave resulting from a reflection at the fault position is used to find the location of the fault. A possible application based on modal analysis to detect the type of fault is also proposed. This paper shows that a fuzzy approach can be useful in transmission line protection, whenever fuzzy decisions have to be undertaken. Simulation results are used to illustrate the basic features of the performance of the new scheme on a 220 kV transmission line.

Multipurpose overhead lines protection algorithm

Abstract: A numerical algorithm for multipurpose overhead lines protection, based on one terminal data and derived in the time domain, is presented. The fault location, direction and its nature (arcing or arcless fault) are estimated using the least squares error technique. The faulted phase voltage is modelled as a serial connection of fault resistance and arc voltage, offering more sophisticated line protection. The algorithm can be applied to both the ordinary and high-impedance fault detection, distance protection, intelligent autoreclosure, as well as for directional relaying. The new approach does not require the line zero-sequence resistance as an input datum. The algorithm is derived for the case of most frequent single-phase-to-ground asymmetrical faults. The results of algorithm testing through computer simulation are given. The influence of remote infeed, fault resistance, higher-order harmonics, power system frequency, network topology, line parameters and other factors are investigated and systematically presented.

Anticipatory load shedding scheme for loadability enhancement

Abstract: The paper presents a new anticipatory load shedding protection scheme implemented centrally from the energy control centre for loadability enhancement. Most of the schemes available in literature for this purpose are based on information at the current operating condition which are blind to load increase scenarios and the associated switchings in voltage controlled buses. The proposed scheme anticipates the danger of voltage instability in a time frame of interest by incorporating these effects. If the normal controls are exhausted, the algorithm based on successive application of LP restricts/sheds the required amount of low priority loads in advance so that the power system survives the voltage instability threat even during the worst power system period. Results for IEEE 30 bus and an Indian 91 bus power systems have been obtained to demonstrate the effectiveness of the proposed algorithm.

Protective relay setting of the tie line tripping and load shedding for the industrial power system

Abstract: This paper presents the proper underfrequency relay settings to enhance the operation of industrial power systems with cogeneration facilities. A cogeneration unit has been installed in the plant in 1996 to supply the power demand of the plant. The cogeneration unit always faces a shut down problem when there is a severe fault on the nearby Taipower network. It is therefore necessary to investigate the plant protective relay settings to prevent the whole plant blackout when the contingency occurs. The transient stability analysis has been performed by considering both the detail models of the cogenerators with the governor and exciter control systems and the external utility power system. The under frequency relay settings for tie line tripping and load shedding are designed to prevent the tripping of the cogeneration units so that the electricity service to the critical loads of the industrial customer can be maintained in case serious external disturbances such as short circuit faults occur. In this study, the scheme of underfrequency relay settings has been developed for the power system of a large synthetic rubber manufacturer with a large cogeneration unit. Three study cases have been selected for the transient stability analysis to verify the effectiveness of the proposed protective relay setting.

Trip and restore distribution circuits at transmission speeds

Abstract: In this paper, the authors show how to reduce tripping and restoration times for faults on distribution circuits. Using relays and/or controls with improved communications capabilities, linked together by optical fiber or other communication channels, one can detect faults and restore load to unaffected line sections faster.