Unscheduled Outages Research Articles

Application of Artificial Neural Network for Automatic Contingency Analysis in Power Security Assessment

Several incidents that occurred around the world involving power failure caused by unscheduled line outages were identified as one of the main contributors to power failure and cascading blackout in electric power environment. With the advancement of computer technologies, artificial intelligence (AI) has been widely accepted as one method that can be applied to predict the occurrence of unscheduled disturbance. This paper presents the development of automatic contingency analysis and ranking algorithm for the application in the Artificial Neural Network (ANN). The ANN is developed in order to predict the post-outage severity index from a set of pre-outage data set. Data were generated using the newly developed automatic contingency analysis and ranking (ACAR) algorithm. Tests were conducted on the 24-bus IEEE Reliability Test Systems. Results showed that the developed technique is feasible to be implemented practically and an agreement was achieved in the results obtained from the tests. The developed ACAR can be utilised for further testing and implementation in other IEEE RTS test systems particularly in the system, which required fast computation time. On the other hand, the developed ANN can be used for predicting the post-outage severity index and hence system stability can be evaluated.

Application of Artificial Neural Network for Automatic Contingency Analysis in Power Security Assessment

Several incidents that occurred around the world involving power failure caused by unscheduled line outages were identified as one of the main contributors to power failure and cascading blackout in electric power environment. With the advancement of computer technologies, artificial intelligence (AI) has been widely accepted as one method that can be applied to predict the occurrence of unscheduled disturbance. This paper presents the development of automatic contingency analysis and ranking algorithm for the application in the Artificial Neural Network (ANN). The ANN is developed in order to predict the post-outage severity index from a set of pre-outage data set. Data were generated using the newly developed automatic contingency analysis and ranking (ACAR) algorithm. Tests were conducted on the 24-bus IEEE Reliability Test Systems. Results showed that the developed technique is feasible to be implemented practically and an agreement was achieved in the results obtained from the tests. The developed ACAR can be utilised for further testing and implementation in other IEEE RTS test systems particularly in the system, which required fast computation time. On the other hand, the developed ANN can be used for predicting the post-outage severity index and hence system stability can be evaluated.

Does Periodic Maintenance Cause Unscheduled Outages?

It has been suspected for some time that unscheduled outages of National Airspace System equipment increase during core working hours; to date, however, no research has been done to determine their cause. First, aggregate trends in scheduled periodic maintenance (PM) activities and unscheduled outages are examined for calendar years 2000 through 2004. The reported increase in unscheduled outages is postulated to be due to increased levels of maintenance activities that may occur during this period. A detailed analysis is presented, and the individual pieces of equipment that suffer unscheduled outages after receiving PM are examined. If PM activities have an effect on unscheduled outages, then higher levels of unscheduled outages would be expected to occur in the first hours after the completion of a PM task. Further data analysis shows evidence for this hypothesis.

Does Periodic Maintenance Cause Unscheduled Outages?: Investigation of National Airspace System Equipment Outages

It has been suspected for some time that unscheduled outages of National Airspace System equipment increase during core working hours; to date, however, no research has been done to determine their cause. First, aggregate trends in scheduled periodic maintenance (PM) activities and unscheduled outages are examined for calendar years 2000 through 2004. The reported increase in unscheduled outages is postulated to be due to increased levels of maintenance activities that may occur during this period. A detailed analysis is presented, and the individual pieces of equipment that suffer unscheduled outages after receiving PM are examined. If PM activities have an effect on unscheduled outages, then higher levels of unscheduled outages would be expected to occur in the first hours after the completion of a PM task. Further data analysis shows evidence for this hypothesis.

Procedural and Operational Consequences of Navigational Equipment Outages: Exploration of Airport Performance

This paper explores the impact of unscheduled navigational and surveillance equipment outages on airport performance during visual flight rules and instrument flight rules at San Francisco International Airport and Phoenix Sky Harbor International Airport. The following most common unscheduled short outages, which occurred during January 2000-December 2002, are analyzed in detail: very high frequency omnidirectional range (VOR), approach lighting system type 2 (ALSF-2), the secondary radar Mode S, and air traffic control radio beacon system (ATCRBS). We explore the air traffic control procedures and responses to unscheduled outages, and develop a methodology to examine the effects of unscheduled outages on airport performance. Two Federal Aviation Administration databases, maintenance management system and aviation system performance metrics, are used to construct censored regression models (i.e., Tobit models) to assess the airport throughput performance during such unscheduled outages. It is found that airport arrival and departure throughputs do not deteriorate with VOR and ALSF-2 outages due to availability of air traffic procedures that allow alternative approaches into the airport. However, the unscheduled outages of secondary radar Mode S and ATCRBS do cause airport throughput degradations.

Creep Behavior of 2.25Cr-1Mo Steel Shield Metal Arc Weldment

In order to guarantee the safety of high temperature components and prevent unscheduled outage, remnant life assessment for creep is quite important. The experiences in actual components reveal that almost all the problems relating to creep are generated at the weldment, which contains microstructures with different creep properties from those presumed in the parent material. Nowadays, it is generally accepted that a terminal failure mode of low alloy ferritic steels or tempered martensitic steels become Type IV, taking place at the Intercritical HAZ or Fine Grained HAZ. However, in the present work using 2.25Cr-1Mo steel welds fabricated with basic coated Shield Metal Arc Weld (SMAW) consumables, the most prevalent failure mode was Type I in the center of weld metal rather than Type IV. And this tendency was more pronounced at low stresses, suggesting the possibility of Type I cracking in actual components. It was concluded that poor creep strength of 2.25Cr-1Mo weld metal was ascribed to its fully bainitic microstructure in which carbides evolution was accelerated and M 2 C depletion took place earlier than base metal.

Application of Adaptive Fuzzy Neural Network for Forecasting Coal Slagging in a Power Station

AbstractAsh related problems in coal‐fired power plants result in decreased efficiency, unscheduled outages, equipment failures and cleaning problems Assessing the potential impact of ash on power plant performance is extremely complicated and difficult due to coal variability, complexity of the ash behavior processes and changes in operating conditions involved This study introduces a new method of coal slagging forecast This method employs a hybrid‐learning rule composed of recursive least‐squares estimation and a gradient descent algorithm The forecast results are compared with measured data The comparison shows that the method based on adaptive fuzzy neural network for the prediction of coal slagging has the advantages of high precision, fast convergence and perfect adaptability

Applying fuel cell experience to sustainable power products

Fuel cell power plants have demonstrated high efficiency, environmental friendliness, excellent transient response, and superior reliability and durability in spacecraft and stationary applications. Broader application of fuel cell technology promises significant contribution to sustainable global economic growth, but requires improvement to size, cost, fuel flexibility and operating flexibility. International Fuel Cells (IFC) is applying lessons learned from delivery of more than 425 fuel cell power plants and 3 million h of operation to the development of product technology which captures that promise. Key findings at the fuel cell power plant level include: (1) ancillary components account for more than 40% of the weight and nearly all unscheduled outages of hydrocarbon-fuelled power plants; a higher level of integration and simplification is required to achieve reasonable characteristics, (2) hydrocarbon fuel cell power plant components are highly interactive; the fuel processing approach and power plant operating pressure are major determinants of overall efficiency, and (3) achieving the durability required for heavy duty vehicles and stationary applications requires simultaneous satisfaction of electrochemical, materials and mechanical considerations in the design of the cell stack and other power plant components. Practical designs must minimize application specific equipment. Related lessons for stationary fuel cell power plants include: (1) within fuel specification limits, natural gas varies widely in heating value, minor constituents such as oxygen and nitrogen content and trace compounds such as the odorant; (2) city water quality varies widely; recovery of product water for process use avoids costly, complicated and site-specific water treatment systems, but water treatment is required to eliminate impurities and (3) the embedded protection functions for reliable operation of fuel cell power conditioners meet or exceed those required for connection to the utility grid, but current standards do not recognize embedded protection functions, and, often, utilities mandate external protective devices. Consequently, current activity to develop such standards under IEEE auspices is important in eliminating the cost of extra protection equipment. Key fuel cell lessons learned from IFC's experience base along with the status of development for future vehicle and stationary power plants at IFC are discussed. These lessons have been applied to the 200 kW stationary fuel cell power plant as the information has become available. They are now being applied to a 50-kW, ambient pressure, polymer electrolyte membrane (PEM) fuel cell power plant that uses gasoline as the fuel. This power plant is intended for experimental bench testing demonstrations associated with vehicle power plant applications.

Optimum load-shedding technique to reduce the total customer interruption cost in a distribution system

In capacity deficiency conditions caused by unscheduled outages in a generation and transmission system, system operators have to shed load at selected feeders in the distribution system to maintain acceptable operating conditions. Different load-shedding schemes can result in quite different load point reliability performance. Conventionally, the objective is to shed the minimum load subject to system security constraints. An optimum load-shedding technique is presented that can be used to improve the reliability of a local distribution system. Customer concerns regarding interruption costs are considered in the load-shedding procedure. The objective is to minimise the total system interruption cost. Cost weight factors are used to determine the load-shedding priority among feeders, and an enumeration technique is used to divide the capacity deficiency between feeders. The unreliability cost indices of two representative distribution systems are evaluated to illustrate the technique.

Control of Alkaline Stress Corrosion Cracking in Pressurized-Water Reactor Steam Generator Tubing

Abstract Outer-diameter stress corrosion cracking (ODSCC) of alloy 600 (UNS N06600) tubings in steam generators of the Kori-1 pressurized-water reactor (PWR) caused an unscheduled outage in 1994. Failure analysis and remedy development studies were undertaken to avoid a recurrence. Destructive examination of a removed tube indicated axial intergranular cracks developed at the top of sludge caused by a boiling crevice geometry. A high ODSCC propagation rate was attributed to high local pH and increased corrosion potential resulting from oxidized copper presumably formed during the maintenance outage and plant heatup. Remedial measures included: (1) crevice neutralization by crevice flushing with boric acid (H3BO3) and molar ratio control using ammonium chloride (NH4Cl), (2) corrosion potential reduction by hydrazine (H2NNH2) soaking and suppression of oxygen below 20 ppb to avoid copper oxide formation, (3) titanium dioxide (TiO2) inhibitor soaking, and (4) temperature reduction of 5°C. Since application o...

Prediction of Failures of Low-Pressure Steam Turbine Disks

Localized corrosion phenomena, including pitting corrosion, stress corrosion cracking, and corrosion fatigue, are the principal causes of corrosion-induced damage in electric power-generating facilities and typically result in more than 50 percent of the unscheduled outages. In this paper, we describe a deterministic method for predicting localized corrosion damage in low-pressure steam turbine disks downstream of the Wilson line, where a condensed, thin electrolyte layer exists on the steel disk surfaces. Our calculations show that the initiation and propagation of stress corrosion cracking (SCC) is not very sensitive to the oxygen content of the steam, but is sensitive to the conductivity of the condensed liquid layer and the stresses (residual and operational) that the disk experiences in service.

Review of temperature indicators and the use of duplex stainless steels for life assessment

Abstract This paper presents an overview of the recent development of life assessment techniques for high temperature plants, with special emphasis on a novel temperature-measuring technique, i.e. the ‘Feroplug’.Improved life assessment techniques will enable components to be replaced before failure, so reducing the risk of industrial accidents, as well as minimizing financial loss caused by unscheduled outages. The Feroplug is a new invention and has been patented by the US, UK and European patent bodies, with financial and legal support provided by the British Technology Group. It has been developed to supplement conventional temperature-measuring methods, such as the thermocouple, in extremely hostile environments, to provide information on the operating temperature, which is a major concern for life assessment. The principle of the Feroplug, which consists of piece of duplex (austenite + ferrite) stainless steel with specially designed composition, is based on the transformation of ferrite in the material on heating in the range 300–1000 °C. The extent of the transformation, being an indication of the temperature to which the Feroplug has been exposed, can be easily monitored using magnetic measurement techniques. The characteristics of the ferrite transformation are affected—in addition to the ageing temperature—by many metallurgical parameters, such as the composition of the alloy, thermomechanical pretreatments, etc. The recent progress of research in ferrite transformation is also reviewed in detail to provide the ground for understanding the principles of the Feroplug.

原子炉内リフレッシュ技術の開発

Japan has fifty nuclear power plants in operation and some of them has been operated more than twenty five years. It becomes more important to develop maintenance technologies to prevent unscheduled outage. We have developed wet shot peening system to change tensile stress to compressive stress around the weld preventing stress corrosion cracking (SCC).Together with the stress improvement technology, we have developed multipurpose remote handling equipment to execute the tasks required in a core area and an annulus area.

Complexity And Availability for Fusion Power Plants: The Potential Advantages of Inertial Fusion Energy

Probably the single largest advantage of the inertial route to fusion energy (IFE) is the perception that its power plant embodiments could achieve acceptable capacity factors. This is a result of its relative simplicity, the decoupling of the driver and reactor chamber, and the potential to employ thick liquid walls. We examine these issues in terms of the complexity, reliability, maintainability and, therefore, availability of both magnetic and inertial fusion power plants and compare these factors with corresponding scheduled and unscheduled outage data from present day fission experience. We stress that, given the simple nature of a fission core, the vast majority of unplanned outages in fission plants are due to failures outside the reactor vessel itself. Given we must be prepared for similar outages in the analogous plant external to a fusion power core, this puts severe demands on the reliability required of the fusion core itself. We indicate that such requirements can probably be met for IFE plants. We recommend that this advantage be promoted by performing a quantitative reliability and availability study for a representative IFE power plant and suggest that databases are probably adequate for this task.

Ethylene Producers Add Capacity To Buffer Cyclical Markets, Meet Demand

D escribing the ethylene market can be a simple rehash of macroeconomics—typical industry cycles subject to the swings of economic change, energy prices, supply and demand, and consumer spending. However, unexpected events—such as plant outages, shifts in feedstock availability, and tight supply—are keeping producers alert and open to creative ways to reduce their exposure to risk. Ethylene production is extremely capital intensive. Penny-per-pound price increases can mean the difference between being able to build new plants or not. And the current market situation is calling for new plants. To meet demand anticipated through the end of the decade, major ethylene producers have responded with plans for worldscale plants. In the first quarter of this year, U.S. ethylene inventories fell, although not to as low a point as in late 1994 and early 1995, when the industry experienced the effects of unscheduled plant outages. The National Petroleum Refiners Association reports inventories in the first quarter d...

Testing trnsformer oil

AbstractSuddenly, the unexpected happens—the power goes out—a critical transformer has failed. And just as suddenly, your plant is out of business. Since there are no visible moving parts there is a tendency to think that nothing can go wrong. But, preventive maintenance testing of transformers is not difficult to justify when you consider the high cost of repairs and the impact of an unscheduled outage of plant operation.

Power system planning — a reliability perspective

One of the basic objectives of power system planners is to determine the necessary generating capacity to satisfy the system demand in the presence of scheduled and unscheduled outages and unforeseen variations in the system load. A second important objective is the development of a suitable transmission network to transport the generated electrical energy to the bulk load centers. This aspect is dealt with in conjunction with the available and planned generation facilities. Lastly, adequate distribution facilities must be constructed in order to deliver the available energy from the bulk load centers to the actual customer premises. The reliability at which these three subsystems (namely, generation, transmission, and distribution) will function is of utmost importance. The power system engineer, therefore, must consider the reliability aspect right from the beginning, i.e. from the planning stage. This paper presents the basic concepts of power system reliability assessment and reviews the relability indices and methodologies from a planning viewpoint and also from an economic cost-benefit perspective. Some realistic data which can be used as a guide in the absence of any collected system data are also presented.

High-availability computer systems

The techniques used to build highly available computer systems are sketched. Historical background is provided, and terminology is defined. Empirical experience with computer failure is briefly discussed. Device improvements that have greatly increased the reliability of digital electronics are identified. Fault-tolerant design concepts and approaches to fault-tolerant hardware are outlined. The role of repair and maintenance and of design-fault tolerance is discussed. Software repair is considered. The use of pairs of computer systems at separate locations to guard against unscheduled outages due to outside sources (communication or power failures, earthquakes, etc.) is addressed. >

Monitoring Cable Systems

The existing underground transmission system in the United States is worth about $5 billion. To optimize the return on that investment and on further investment in the growing system, EPRI has sponsored research to develop periodic and continuous diagnostic procedures and methodologies for evaluating underground cables. By using monitoring results to support maintenance and cable management decisions, utilities will be able to improve maintenance planning, reduce unscheduled outages, increase system reliability, and extend cable life. At the same time, they will be able to operate systems more efficiently and closer to true ratings. The scope of this paper are the following projects: application of dissolved-gas analysis to the periodic monitoring of liquid-filled, paper-wrapped cables (RP7895-1) and also cables insulated with a laminate of cellulose paper, polypropylene film, and cellulose paper, or PPP-insulated cables (RP7910-1); development of a transmission cable diagnostic system based on periodic power factor measurements (RP7910-5); development of an integrated, multifaceted online diagnostic monitoring system known as the Dynamic Rating and Underground Monitoring System (DRUMS) (RP7900); development of a protocol for using perfluorocarbon tracers to locate leaks in high-pressure, liquid-filled cables (RP7905-1); and a long-term cable life evaluation and management project, comprising 10 research areas (RP7914).

The Power Production Operation of Solar One, the 10 MWe Solar Thermal Central Receiver Pilot Plant

Solar One, the 10 MWe Solar Thermal Central Receiver Pilot Plant near Barstow, Calif., completed a three-year period of power production testing in July 1987. During this period the plant’s capacity factor, system efficiency, and availability were studied to assess the operational capability of Solar One to reliably supply electrical power. The long-term performance of key plant components, such as the heliostats and the receiver, was also studied. During the three years of power production operation, Solar One achieved increases in capacity factor, system efficiency, and availability. Heliostat operation was reliable, and only small amounts of mirror corrosion were observed. Receiver tube leaks did occur, however, and were the main cause of the plant’s unscheduled outages. Solar One provided valuable lessons which will aid in the design of future solar central receiver plants.