Scheduled Outages Research Articles

Design of a modular and versatile interlock system for ultrahigh vacuum machines: A crossed molecular beam setup as a case study

The design of a modular, versatile interlock system for ultrahigh vacuum machines is presented. This system can monitor the pressure (ultrahigh vacuum and high vacuum), the status of the power (power failure, power fluctuations, and scheduled power outages), the operation mode of the pumps (operation versus failure), the flow of cooling water, the humidity and temperature levels in the laboratory, as well as the concentration of toxic gases. If any of the set points is triggered, the vacuum machine is protected fully automatically. The interlock system is also interfaced to an automated paging system, thus transmitting a pager signal to the person on duty. Since the interlock system is modular in nature, it can be expanded and be adapted stepwise to incorporate additional safety and monitoring functions as needed.

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.

Extending the Life of Cast‐Iron Pipes

This article discusses the Village of Westfield, New York's experience of using chemical cleaning to rehabilitate their system's 4‐in.‐diameter cast‐iron pipes. Topics covered include: methods for determining the necessary cleaning solution strength and approximate cleaning time; methods of communicating with consumers about the project costs, provision of bottled water during periods when the water would be shut‐off, and scheduling of water outages; the mobile recirculation unit (MRU) used at each section of the system; easy disposal of the biodegradable chemical cleaning solution certified by Scientific Systems Certification as well as NSF/ANSI Standard 60; the different processes of the cleaning cycle; use of a passivating chemical to line the pipe to prevent flash corrosion; leak detection and rehabilitation; and, increased water pressure with costs being significantly less than pipe replacement as a result of using this cleaning process.

Prediction and real-time monitoring techniques for corrosion characterisation in furnaces

Combustion modifications to minimise NOx emissions have led to the existence of reducing conditions in furnaces. As regulations demand lower NOx levels, it is possible (to a degree) to continue to address these requirements with increased levels of combustion air staging. However, in most practical situations, a number of adverse impacts prevent the application of deep combustion air staging. One of the more important limitations is the increased corrosion that can occur on wall tubes exposed to fuel rich combustion environments. Current boiler corrosion monitoring techniques rely on ultrasonic tube wall thickness measurements typically conducted over 12 to 24 month intervals during scheduled outages. Corrosion coupons are also sometimes used; typically require considerable exposure time to provide meaningful data. The major drawback of these methods is that corrosion information is obtained after the damage has been done. Management of boiler waterwall loss and system optimisation therefore requires a real-time indication of corrosion rate in susceptible regions of the furnace. This paper describes the results of a program of laboratory trials and field investigations and considers the use of an on-line technology in combination with innovative applications, also modelling and precision metrology to better manage waterwall loss in fossil fuelled boilers while minimising NOx emissions.

The influence of the instantaneous fuel mix for electricity generation on the corresponding emissions

Since it would be unwise to apply an environmental measure before its impact is estimated, tools are needed to simulate the system to which the measure is applied. In this paper, a tool and a methodology are discussed in order to simulate scenarios for demand and supply side options and to quantify the emissions and the energy use related to electricity generation. To supply the electricity demand, the composition of the active power system evidently changes with the variations in demand. The instantaneous composition of the power system is determined by the activation order (set by a chosen criterion) of all power plants. Because of their specific nature, some problems are dealt with separately in the model. Pumping plants are both customer (pump-mode) and provider (turbine-mode) of electric power. Therefore, they are not modeled as other plants, but as an adaptation in the demand pattern for other plants. Outages are mostly unpredictable but very important for the instantaneous energy use and emissions. Therefore, the model contains a component in which an average outage schedule can be calculated. The possible deviation of this average result is dealt with in the calculation of the uncertainties. Also, other parameters, like accidental unavailability of plants, human decisions in activation and deactivation of plants and the unpredictable availability of cogeneration units, are included in the calculation of the uncertainties. A simulation tool is necessary, because a-priori “linear” estimates do not always appear to be accurate. Results are highly dependent on the composition of the power system and the activation order of the individual plants. Demand and supply side actions are therefore simulated. Simulations for Belgium have pointed out that variations in electricity-related greenhouse-gas emissions (per unit of electricity generated) can be larger than a factor two, depending on the time segment in which the electricity is consumed. For SO x and NO x emissions this variation can be even larger.

The TransAlta High-Energy Piping Program—A Five-Year History

In 1995, the High-Energy Piping Strategic Management Plan (HEPSMP) was initiated at TransAlta Utilities Corporation (TAU) for the three generating facilities. At that time, it was recognized that several of the piping systems were exhibiting signs of creep relaxation, with some hangers bottomed or topped out online and/or offline. Previous hanger adjustment attempts were not always adequate. The program workscope included: 1) hot and cold piping system walkdowns, 2) selection of high-priority girth weld inspection locations, 3) examination of critical weldments, 4) weld repairs where necessary, 5) adjustments or modifications of malfunctioning steam line hangers, and 6) recommended work for future scheduled outages. Prior to 1996, examination locations were limited to the traditional locations of the terminal points at the boiler and turbine, with reexaminations occurring at arbitrary intervals. Since the terminal points are not necessarily the most highly stressed welds causing service-related creep damage, service damage may not occur first at the pre-1996 examined locations. There was a need to maximize the safety and integrity of these lines by ensuring that the highest risk welds were identified and given the highest priority for examination. An engineering consulting company was selected to prioritize the highest risk weldments for each piping system. This risk-based methodology included the prediction and evaluation of actual sustained loads, thermal expansion loads, operating loads, multiaxial stresses, creep relaxation, and cumulative creep life exhaustion. The technical process included detailed piping system walkdowns and application of advanced analytical techniques to predict and rank creep/fatigue damage for each piping system. TAU has concluded that the program has met its objective of successfully prioritizing inspection locations. The approach has also resulted in reducing the scope and cost of reexaminations. Phases 1 and 2 evaluations and examinations have been completed for all units. Results of some of the important aspects of this program are provided as case history studies.

Generation maintenance scheduling considering transmission constraints

This paper describes a new approach for establishing power systems scheduled generators outages for maintenance purposes. The time frame considered refers to power systems short-term operations planning horizon (i.e. one month ahead). The paper's main contribution is focused on modeling grid operational constraints, which are dealt with by a DC optimal power flow. The resulting large-scale optimization problem is solved by mixed-integer programming techniques aided by Benders decomposition strategy. The obtained results clearly show that representing transmission influence is essential for the establishment of a sound set of scheduled outages for the system's generators, especially in the case of hydrothermal systems.

The evaluation of erosion/corrosion problems of carbon steel piping in Taiwan PWR nuclear power plant

Taiwan Pressurized Water Reactor (PWR), Maanshan nuclear power plant Units 1 and 2 implemented measurements of the wall thinning of the carbon steel piping under the request of regulation authority to prevent the events due to erosion/corrosion since 1989. At first, the licensee established the comprehensive inspection program by itself. Over 2000 components were inspected per unit and 300–500 pipe components were examined by ultrasonic testing per scheduled outage. The simple predictive methodology determined the operability of each individual piping component in the next fuel cycle. Based on the inspection results, the susceptible pipe components were established. Implementation of effective correction management and an improved inspection program can improve the safety, as well as the efficiency, of long-term reactor operations.

99/01509 Diagnostics based on thermodynamic analysis of performance of steam turbines: case histories : Tirone, G. et al. PWR (Am. Soc. Mech. Eng.), 1996, 30, (2), 415–421

The purpose of this paper is to describe some types of failures which have occurred with the ENEL stock of fossil-fuel steam turbines over the last 5--7 years. This paper also presents the corresponding thermodynamic analysis of turbine parameters which permitted failure diagnosis and pre-scheduled opening of the turbine. The examined failures concern: (1) in-service rupture of the bell seal retainer nut between a SH steam inlet sleeve and the inner HP/IP cylinder, on turbines with a main steam inlet system with bell seals; (2) incorrect assembly of pressure seal rings between steam inlet sleeves and the inner cylinder on turbines with a main steam inlet system with pressure seal rings during a scheduled outage; (3) steam flow path restriction in IP turbine inlet; (4) steam flow path restriction in 1st HP turbine stage nozzles; and (5) steam flow path restriction in 2nd HP turbine stage vanes. Thermodynamic failure analysis and the subsequent analysis of turbine damage (mechanical and financial) enabled condition-based maintenance operations to be carried out.

Value-based reliability for short term operational planning

The paper presents a scheme for evaluating and optimally enhancing power system reliability for a short-time horizon operation of one week. Power system reliability can be efficiently enhanced by applying appropriate remedial actions (RAs). This paper investigates the impact of remedial actions on system reliability, the corresponding associated cost and the amount of unserved energy using the EPRI Transmission Reliability Evaluation for Large Scale System (TRELSS) program. The proposed scheme has been tested on a 27-bus example taken from the Northwest (NW) system. The method has the potential to be used for assessing the risks associated with near-term scheduled outages and other operational issues.

Probabilistic assessment of interconnection assistance between power systems

The interconnection assistance (IA) between power systems is a function of many variables such as the system installed capacity, generation dispatch, forced and scheduled outages of generating units, load duration characteristics, accuracy of load forecast, load diversity, capability of the interconnections and the operating limits imposed on the transmission network due to thermal, voltage and stability considerations. This paper describes a probabilistic approach for evaluating the IA that a system can provide at any selected location without affecting its level of reliability. The method considers most of the key factors affecting the level of power transfer and differentiates between two types of transfer, namely the economy transfer and the emergency transfer. The method calculates the expected value and the probability distribution of IA of each type. The proposed method is illustrated using the IEEE Reliability Test System.

Improving Lagrangian relaxation: an application to the scheduling of pressurized water reactor outages

This paper presents an improvement of Lagrangian relaxation techniques that are now widely used for optimizing the operational planning of power systems. It is a precise algorithm for maximizing the concave and nondifferentiable dual function: a proximal point algorithm. This algorithm is applied to an important operational planning problem: the scheduling of pressurized water reactor nuclear power plant outages. Compared to the more classical Uzawa algorithm, numerical examples show that the proximal algorithm significantly improves both the solutions and the indicators of their quality.

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.

Evaluation of Generator Maintenance Schedules at Entergy Electric System

Manual evaluation of the impact of detrimental events on outage schedules in electric power plants is both subjective and time-consuming. We developed a decision-tree-based methodology that converts the manual evaluation process into a computerized package. It uses a special statistic instead of the (less-useful) expected value analysis that typifies textbook presentations. It also provides a systematic procedure for determining the branches and probabilities of the decision tree based on historical data. The Entergy Electric System has used the new tool for over three years to enable the outage planner to isolate, high-risk time periods and to develop timely maintenance schedules in response to short-notice changes.

Distribution system feeder cold load pickup model

In order to maintain a balance between the generation and laod during service restoration, it is important to have mathematical voluminous feeder load measurement data collected duing larg-sclae reotating interruptions is presented in theis paper. REgression voluminous feeder load measurement data collected during large-scale rotating interruptions is presented in this paper. Regression models are proposed to estimate the feeder and substation cold load pickups after scheduled outages.

Modelling the partial planned outages in production costing simulation

Thus paper presents two ways of modelling such scheduled maintenance whose length is less than that of the simulation period (called partial planned or scheduled outages in the paper). The present author suggests using modified forced outage rate instead of derated capacity in this case. The effect of the different representations is shown on a very simple numerical example by comparing the loss-of-load probability, the energy not served and the expected energy generations of the units. The paper concludes that the modification of the forced outage parameter of units is more appropriate than derating the capacity.

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.

95/04747 List of scheduled outages at U.S. nuclear power plants

95/04747 List of scheduled outages at U.S. nuclear power plants

Probabilistic outage analysis of a combined-cycle power plant

Using the classical method of fault tree analysis, various reliability, availability and maintainability related characteristics of a package-engineered gas-fuelled combined-cycle power plant, comprising a GUD 2.94.3 block, were determined. The events of interest-top events of fault trees-are the power plant's losses in net power output due to forced outages. Additionally, exemplary losses due to scheduled outages were taken into account. The numerical findings of this RAM analysis reflect the high RAM performance of combined-cycle power plants.

List of scheduled outages at U.S. nuclear power plants

List of scheduled outages at U.S. nuclear power plants