Showing papers on "Blackout published in 2002"

Critical points and transitions in an electric power transmission model for cascading failure blackouts

Abstract: From the analysis of a 15-year time series of North American electric power transmission system blackouts, we have found that the frequency distribution of the blackout sizes does not decrease exponentially with the size of the blackout, but rather has a power law tail. The existence of a power tail suggests that the North American power system has been operated near a critical point. To see if this is possible, here we explore the critical points of a simple blackout model that incorporates circuit equations and a process through which outages of lines may happen. In spite of the simplifications, this is a complex problem. Understanding the different transition points and the characteristic properties of the distribution function of the blackouts near these points offers a first step in devising a dynamical model for the power transmission systems.

Prevalence and correlates of alcohol-induced blackouts among college students: results of an e-mail survey.

Abstract: The authors conducted an e-mail survey of 772 college students to learn more about their experiences with blackouts. Approximately half (51%) of those who had ever consumed alcohol reported they had experienced a blackout at some point in their lives, and 40% had experienced 1 in the year before the survey. Among those who drank in the 2 weeks before the survey, nearly 1 in 10 (9.4%) had experienced a blackout during that period. Many later learned that, during the blackout, they had vandalized property, driven an automobile, had sexual intercourse, or engaged in other risky behaviors. Experiencing 3 or more blackouts was associated with a variety of other experiences, including heavier drinking, lower grades, an earlier age of drinking onset, and having others express concerns about their drinking. The female students who reported blackouts during the 2 weeks before the survey drank far less than male students did during this time period, supporting the use of gender-specific definitions of risk...

Examining criticality of blackouts in power system models with cascading events

Abstract: As power system loading increases, larger blackouts due to cascading outages become more likely. The authors investigate a critical loading at which the average size of blackouts increases sharply to examine whether the probability distribution of blackout sizes shows the power tails observed in real blackout data. Three different models are used, including two simulations of cascading outages in electric power transmission systems. They also derive and use a new, analytically solvable model of probabilistic cascading failure which represents the progressive system weakening as the cascade proceeds.

Application of a Wide Area Backup Protection Expert System to Prevent Cascading Outages

Abstract: A strategy to prevent cascading outages in power systems is proposed in this paper. The strategy employs wide-area back-up protection and artificial intelligence techniques to minimize the impact of a fault on a network. There are two ways in which wide-area backup protection can prevent cascading trips leading to a wide spread blackout: 1) Precise location of a fault so that only the circuit breakers necessary to isolate the fault are tripped; and 2) Avoidance of unnecessary trips, due to hidden failure or overloading, by blocking the trip signals of conventional back-up protection relays. The limitations of conventional back-up protection are examined and methods of improvement are presented.

Choice in a variable environment: effects of blackout duration and extinction between components.

Abstract: Pigeons were trained in a procedure in which sessions included seven four- or 10-reinforcer components, each providing a different reinforcer ratio that ranged from 27:1 to 1:27. The components were arranged in random order, and no signals differentiated the component reinforcer ratios. Each condition lasted 50 sessions, and the data from the last 35 sessions were analyzed. Previous results using 10-s blackouts between components showed some carryover of preference from one component to the next, and this effect was investigated in Experiment 1 by varying blackout duration from 1 s to 120 s. The amount of carryover decreased monotonically as the blackout duration was lengthened. Preference also decreased between reinforcers within components, suggesting that preference change during blackout might follow the same function as preference change between reinforcers. Experiment 2 was designed to measure preference change between components more directly and to relate this to preference change during blackout. In two conditions a 60-s blackout occurred between components, and in two other conditions a 60-s period of unsignaled extinction occurred between components. Preference during the extinction period progressively fell toward indifference, and the level of preference following extinction was much the same as that following blackout. Although these results are consistent with Davison and Baum's (2000) theory of the effects of reinforcers on local preference, other findings suggest that theory is incomplete: After a sequence of reinforcers from one alternative, some residual preference remained after 60 s of extinction or blackout, indicating the possibility of an additional longer term accumulation of reinforcer effects than originally suggested.

A scheme for controlled islanding to prevent subsequent blackout

Abstract: The power systems operated by the utilities in developing countries suffer from a large gap between demand and generation, inadequate transmission capacity, and nonuniform location of the load centers and generating stations. Occurrences of faults in such systems, in most of the cases, end up with the worst consequences (i.e., complete blackout). This paper illustrates the way a blackout can be prevented in real time through controlled segregation of a system into a number of viable islands together with generation and/or load shedding. The nature and location of any fault that warrants such islanding can be ascertained in real time through monitoring the active-power (megawatt) flows at both ends of a number of prespecified lines. The blackout of June 20, 1998 in the Bangladesh Power Development Board system has been used as an example in the illustration. The philosophy of the proposed islanding scheme may be considered for implementation in other power systems also.

Dynamics, criticality and self-organization in a model for blackouts in power transmission systems

Abstract: A model has been developed to study the global complex dynamics of a series of blackouts in power transmission systems. This model included a simple level of self-organization by incorporating the growth of power demand and the engineering response to system failures. Two types of blackouts have been identified with different dynamical properties. One type of blackout involves loss of load due to lines reaching their load limits but no line outages. The second type of blackout is associated with multiple line outages. The dominance of one type of blackouts versus the other depends on operational conditions and the proximity of the system to one of its two critical points. The first critical point is characterized by operation with lines close to their line limits. The second critical point is characterized by the maximum in the fluctuations of the load demand being near the generator margin capability. The identification of this second critical point is an indication that the increase of the generator capability as a response to the increase of the load demand must be included in the dynamical model to achieve a higher degree of self-organization. When this is done, the model shows a probability distribution of blackout sizes with power tails similar to that observed in real blackout data,from North America.

Bilateral control with time-varying delay including communication blackout

Abstract: Yokokohji et al. (2000) proposed a bilateral control scheme with energy balance monitoring under time-varying communication delay. In this paper, experimental results using the proposed control scheme over a computer network are shown. In the above work, the authors dealt with a situation when the communication is in breakdown. However, they did not discuss how to recover the system after the communication line comes back. In this paper we also propose a way to recover the system from the communication blackout. Experimental results show the validity of the proposed methods.

The Spacecraft Communications Blackout Problem Encountered during Passage or Entry of Planetary Atmospheres

Abstract: During the Mars Pathfinder mission, there was a 30-second period in which the 8.4-GHz (X-band) communications link to Earth was lost during the atmospheric entry phase. An analysis of the Mars Pathfinder reconstructed flight profile using aero-thermodynamic tools provided estimates of the electron densities in the stagnation and wake regions of the spacecraft. For the wake region, where the low-gain antenna used to communicate with Earth was located, the electron-density estimates exceeded the critical X-band electron density during the first 20 seconds of the 30-second blackout period. High Doppler dynamics and low signal-to-noise ratio may have contributed to the blackout during the last 10 seconds. Thus, at least part of the Mars Pathfinder communications blackout during entry was possibly due to the sheath of charged particles generated by heating incurred by the shock. The upcoming Mars Exploration Rover (MER) missions, MER-A and MER-B, scheduled for 2003 launches, are not expected to experience communication blackouts due to charged particles during their entry phases into the Martian atmosphere in 2004. The estimated peak electron densities expected for MER lie about three orders of magnitude below the critical X-band electron density required for blackout.

Voltage stability assessment for real-time operation

Abstract: Network voltage stability is represented by nodal conditions associated with the maximum active and reactive power flow that can be transmitted from generators to loads. An analytical assessment tool is derived, based on a simple but sound mathematical background, modelling a straightforward physical characterisation of the phenomena. Comprehensive and meaningful indices are introduced. They indicate the MVA margin to the maximum, the region of operation, the relative importance among buses, the loading ranking of the buses, the sensitivity to control actions, and a measure of difficult for power transmission. Numerical results are presented for the Itaipu bulk transmission network in the S/SE of Brazil immediately before a voltage stability blackout in April 1997. Computational efficiency is no burden for real time operation including contingency analysis.

An initial complex systems analysis of the risks of blackouts in power transmission systems

Abstract: Electric power transmission systems are a keyinfrastructure and blackouts of these systems have major directand indirect consequences on the economy and nationalsecurity. In particular, electric power blackouts have cascadingeffects on other vital infrastructures. While it is useful toanalyze the detailed causes of individual blackouts, in thispaper we focus on the intrinsic dynamics of series of blackoutsand how this complex system dynamics impacts the assessmentand mitigation of blackout risk. Indeed, the mitigation offailures in complex systems needs to be approached with care.To motivate our work we consider the statistics of seriesof blackouts. The North American Electrical ReliabilityCouncil (NERC) has a documented list summarizing majorblackouts of the North American power transmission systemfrom 1984 to 1998 [NERC]. One might expect a probabilitydistribution of blackout sizes to fall off exponentially (as, forexample, in a Weibull distribution). However, analyses of theNERC data [Carreras00, Carreras01a, Chen01, CarrerasPES]show that the probability distribution of the blackout sizes doesnot decrease exponentially with the size of the blackout, butrather has a power law tail. For example, load shed is onemeasure of blackout size and Figure 1 plots on a log-log scalethe empirical probability distribution of load shed in the NorthAmerican blackouts. The fall-off with blackout size is close toa power dependence with an exponent of about -1.1. (Anexponent of -1 would imply that doubling the blackout sizeonly halves the probability.) Thus the NERC data suggests thatlarge blackouts are much more likely than might be expected.The NERC blackout data seems to be the best availablebut the statistics have limited resolution since the data is limitedto only 15 years. Thus the NERC data suggests rather thanproves the existence of the power tails. Modeling andsimulation of the complex system dynamics is indicated. Asdescribed below, progress has been made in modeling theoverall forces shaping the dynamics of series of blackouts.Simulations on artificial power networks using the OPA model[Dobson01, Carreras01b, Carreras02] can yield power tails thatare consistent with the NERC data as shown in Figure 1.

Vulnerability assessment and control of power system

Abstract: With power grids considered national security matters, the reliable operation of the system is of top priority to utilities. This concern is amplified by the utility's deregulation, which increases the system's openness while simultaneously decreasing the applied degree of control. Vulnerability Assessment (VA) deals with the power system's ability to continue to provide service in case of an unforeseen catastrophic contingency. Such contingencies may include unauthorized tripping, breaks in communication links, sabotage or intrusion by external agents, human errors, natural calamities and faults. These contingencies could lead to a disruption of service to part or all of the system. The service disruption is known as outage or blackout. The paper outlines an approach by which boundary tracking can be implemented to achieve on line vulnerability assessment.

Application of emergency and standby generation for distributed generation. 1

Abstract: Experience has shown that the demand for electricity imposes excessive peaks for short periods of time. On a yearly basis, these needle peaks exist for less than 200 hours cumulatively. However, meeting them has produced excessively high costs of electric energy or rolling blackouts when the additional energy was not available. A viable alternative to this excessive cost or blackout is the use of installed emergency and standby capacity for these short intervals of time. To meet the challenges of orchestrating a safe and acceptable interface of the varied power sources, utility companies and state regulators are struggling with the development of suitable interconnect requirements. While there are different strategies for bringing this installed base into service during such periods, this discussion centers on those issues concerned with the parallel operation and interconnection of emergency and standby synchronous generation resources with the electric power system.

Plasma telemetry in hypersonic flight

Abstract: Problems associated with telemetry blackout caused by the plasma sheath surrounding a hypersonic vehicle are addressed. In particular, the critical nature of overcoming this limitation for test and evaluation purposes is detailed. Since the telemetry blackout causes great concern for atmospheric cruise vehicles, ballistic missiles, and reentry vehicles, there have been many proposed approaches to solving the problem. This paper overviews aerodynamic design methodologies, for which the required technologies are only now being realized, which may allow for uninterrupted transmission through a plasma sheath. The severity of the signal attenuation is dependent on vehicle configuration, trajectory, flightpath, and mission.

Evaluation device for abnormality in blackout

Abstract: PROBLEM TO BE SOLVED: To resolve problems of availability of data acquisition only once at a timing of abnormality generation for evaluating blackout abnormality with a conventional evaluation device for abnormality in blackout, necessity of always monitoring the evaluation device for a measuring personnel and taking much time for the evaluation. SOLUTION: Provided 101 is a microcomputer voltage measuring means, 102 is an operation voltage recording means, 103 is a reset detection measuring means, 104 is an operation time recording means 1, 105 is a set power source on/off means, 106 is a time count means, 107 is an ON time setting means, 108 is an OFF time setting means 109 is a times count means and 110 is a times setting means.

Safety net design and implementation in taiwan power system

Abstract: The blackout event of July 29, 1999 in Taiwan power system has led to a thorough review of the current Taiwan power service reliability. An in-depth discussion of the incident causes through the analyses of load flow, transient stability (time domain), dynamic stability (frequency domain) and voltage stability is given in this paper. In order to avoid the wide spread incident to occur again, Taiwan Power Company (TPC) has designed and implemented a safety net for preventing extreme contingencies and unplanned events. This paper gives an overview of the safety net, including the design philosophy, action logic and Communication structure.

Emergency Diesel Generator System Surveillance Test Policy Optimization Through Genetic Algorithms Using Non-Periodic Intervention Frequencies and Seasonal Constraints

Abstract: Nuclear standby safety systems must frequently, be submitted to periodic surveillance tests. The main reason is to detect, as soon as possible, the occurrence of unrevealed failure states. Such interventions may, however, affect the overall system availability due to component outages. Besides, as the components are demanded, deterioration by aging may occur, penalizing again the system performance. By these reasons, planning a good surveillance test policy implies in a trade-off between gains and overheads due to the surveillance test interventions. In order maximize the systems average availability during a given period of time, it has recently been developed a non-periodic surveillance test optimization methodology based on genetic algorithms (GA). The fact of allowing non-periodic tests turns the solution space much more flexible and schedules can be better adjusted, providing gains in the overall system average availability, when compared to those obtained by an optimized periodic tests scheme. The optimization problem becomes, however, more complex. Hence, the use of a powerful optimization technique, such as GAs, is required. Some particular features of certain systems can turn it advisable to introduce other specific constraints in the optimization problem. The Emergency Diesel Generation System (EDGS) of a Nuclear Power Plant (N-PP) is a good example for demonstrating the introduction of seasonal constraints in the optimization problem. This system is responsible for power supply during an external blackout. Therefore, it is desirable during periods of high blackout probability to maintain the system availability as high as possible. Previous applications have demonstrated the robustness and effectiveness of the methodology. However, no seasonal constraints have ever been imposed. This work aims at investigating the application of such methodology in the Angra-II Brazilian NPP EDGS surveillance test policy optimization, considering the blackout probability growth during summer, due to the electrical power demand increase. Here, the model used penalizes test interventions by a continuous modulating function, which depends on the instantaneous blackout probability. Results have demonstrated the ability of the method in adapting the surveillance tests policy to seasonal behaviors. The knowledge acquired by the GA during the searching process has lead to test schedules that drastically minimize the test interventions at periods of high blackout probability. It is compensated by more frequent tests redistributed through the periods of low blackout probability, in order to provide improvement on the overall average availability at the system level.Copyright © 2002 by ASME

Information recovery system

Abstract: Technical Field. This invention concerns an information recovery system to provide information updates following periods of information blackout. These blackout periods may occur when a user is out of contact with their usual sources of information. In a further aspect it concerns a process for providing information recovery packages.

System for informing the stoppage of electric current by using telephone auto-dialing function

Abstract: PURPOSE: A service of informing a blackout by using an automatic dialing is provided to inform a telephone subscriber the blackout by quickly sensing the blackout and performing automatic telephone dialing. CONSTITUTION: The device includes a blackout sensing part(110) which senses an on/off state of a commercial ac power to output a sense signal to a central processing unit(120). A ROM(140) stores a telephone number input by a user. A voice storing part(160) stores a voice message to be reproduced at the blackout. The central processing unit(120) performs an automatic dialing operation using the telephone number stored in the ROM(140) when the blackout is sensed by the blackout sensing part(110) and controls the voice storing part so as to send the stored voice message.