Failure Of Protection System Research Articles

Mortality in children registered in the Finnish child welfare registry: population based study

Studies have shown inverse associations between childhood social class and mortality,1 and others have shown higher mortality in children in care. 2 3 However, to our knowledge, only one study...

Solution for the crisis in electric power supply

New techniques for grid monitoring, protection, and control have been perfected, and their judicious application can help reduce the frequency and severity of catastrophic failures. This article describes the development of an innovative multiagent approach to prevent and control catastrophic failures in large power systems. The research has created understanding of the origin and nature of catastrophic failures. This is achieved by an analysis of hidden failures in protection systems. Vulnerabilities associated with the power system, the information network, and the communication network are also evaluated. The approach is characterized by the extensive use of real-time information from diverse sources, coupled with the development of an evolving dynamic decision event tree. A novel multiagent based platform is used to evaluate system vulnerability to catastrophic events taking in account the market environment and competing entities. Several new concepts associated with wide-area measurements and controls, networked sensors, and adaptive self healing are used to reconfigure the network to minimize the system vulnerability. Approaches developed in this research will provide important solutions for power systems and other interconnected networks of the future.

Defense-in-depth and diversity evaluation to cope with design bases events concurrent with common mode failure in digital plant protection system for KNGR

The Korean Next Generation Reactor (KNGR) has been evolved to adopt an advanced design feature, a digital Plant Protection System (PPS) as an effort of enhancing reliability and safety of the plant. Although the digital PPS can be designed with high reliability, it is considered to be vulnerable to the Common Mode Failure (CMF) in the system software resulting in a total loss of the built-in hardware redundancy. Therefore, a comprehensive evaluation has been performed to demonstrate the intrinsic capability of the KNGR design in coping with the design basis events concurrent with CMF in the digital PPS. Instead of the conservative bounding analysis methodology, a best-estimate analysis methodology has been developed and utilized since the design basis events accompanied by CMF in the digital PPS are categorized as beyond design bases events. A variety of diverse means such as Alternate Protection System (APS), process control systems, and timely operator actions have been verified to be effective in mitigating the design basis events with CMF in the digital PPS.

Nonlinear Behavior of Space Shuttle Superlightweight Tank Under Booster Ascent Loads

Results of linear-bifurcation and nonlinear analyses of the Space Shuttle superlightweight (SLWT) external liquid-oxygen (LO2) tank for an important early booster ascent loading condition are presented. These results for thin-walled linear elastic shells that are subjected to combined mechanical and thermal loads illustrate an important type of response mode that may be encountered in the design of other liquid-fuel launch vehicles. Linear-bifurcation analyses are presented that predict several nearly equal eigenvalues that correspond to local buckling modes in the forward ogive section of the LO 2 tank. In contrast, the nonlinear response phenomenon is shown to consist of short-wavelength bending deformations in the forward-ogive and barrel sections of the LO2 tank that grow in amplitude in a stable manner with increasing load. Imperfection sensitivity analyses are presented that show that the presence of several nearly equal eigenvalues does not lead to a premature general instability mode for the forward-ogive section. For the linear-bifurcation and nonlinear analyses, the results show that accurate predictions of the response of the shell generally require a large-scale, high-e delity, e nite element model, and that a design based on a linear-bifurcation buckling analysis and a buckling-load knockdown factor is overly conservative. Results are presented that show that the SLWT LO 2 tank can support loads in excess of approximately 2.6 timesthevaluesof theoperationalloads considered. In addition, results are presented that show that local bending deformations may cause failure of the thermal protection system (TPS) at load levels less than the load level corresponding to structural collapse. Results are presented that can be used to estimate the load level at which TPS failure is likely to occur.

Antioxidants and inflammatory cell response in preeclampsia.

There is widespread evidence of inflammatory cell and antioxidant activity in preeclampsia. However, it is difficult to disentangle the pathological changes from the normal physiological responses to the pathological process. The site at which the measurements are taken, and the severity of disease, alter the results. The interaction between the mother and the fetus needs to be considered separately, especially when the genetics of preeclampsia is considered. It is clear that within the placenta, there is an increase in tumor necrosis factor-alpha (TNF-alpha) and lipid peroxide production. These changes are associated with a reduction in the various placental antioxidants. This suggests there may be a failure of the normal fetal protection systems. Lipid peroxidation is also increased in the peripheral blood, as well as IL-6, IL-8, and TNF-alpha, which are of monocytic origin. Stimulated monocytes produce free radicals, which can cause oxidative damage. Maternal cells protect themselves with both plasma and intracellular antioxidants. There is an imbalance between oxidant and antioxidant activity in preeclampsia. Changes in membrane oxidation can lead to changes in the membrane stability. Genetic difference in the production of TNF-alpha and nitric oxide may also modify the disease process, demonstrating the role for "moderator genes."

The Influence of Protection System Failures and Preventive Maintenance on Protection Systems in Distribution Systems

An electric power system comprises generation, transmission and distribution. Although distribution systems have received less attention than generating systems and composite generating and transmission systems, analysis of the customer failure statistics shows that distribution systems are responsible for as much as 90 percent of the unavailability of supply to a customer. Such statistics reinforce the need to be concerned with the reliability evaluation of distribution systems.

The influence of protection system failures and preventive maintenance on protection systems in distribution systems

Protection systems in power networks can fail either by not responding when they should (failure to operate) or by operating when they should not (false tripping). The former type of failure is particularly serious since it may result in the isolation of large sections of the power network. However, the probability of a failure to operate can be reduced by carrying out preventive maintenance on protection systems. This paper describes an approach to determine the impact of preventive maintenance on distribution network protection systems on the reliability of the power supply to customers. The proposed approach is based on Markov models.

Anatomy of power system blackouts: preventive relaying strategies

Major blackouts of electric power systems in which many customers are left without power are rare events. However, the effects of blackouts, for instance, can be catastrophic. It has been observed that protective system failures are a contributing factor in a large proportion of these blackouts. The most troublesome protection system failures are hidden failures, which remain dormant during normal system conditions, and are exposed during system disturbances. A study of hidden failures of the protective systems is undertaken to uncover their modes of failures, and to determine means of supervising their actions in times of highly stressed power system operations. The main contribution of this paper is to develop and document a method of quantitative analysis of the significance of hidden failures of protection systems. A complete protection system was designed for the New England 39-bus system and the hidden failure modes were used to develop regions of vulnerability and a vulnerability index. Through this analysis, critical protection systems, whose hidden failures would have a major impact on cascading failures or blackouts of the power system, can be identified These protection systems are candidates for increased monitoring and control, which would help alleviate the problems posed by hidden failures.

Best-Estimate Methodology for Analysis of Anticipated Transients Without Scram in Pressurized Water Reactors

Union Fenosa, a utility company in Spain, has performed research on pressurized water reactor (PWR) safety with respect to the development of a best-estimate methodology for the analysis of anticipated transients without scram (ATWS), i.e., those anticipated transients for which failure of the reactor protection system is postulated. A scientific and technical approach is adopted with respect to the ATWS phenomenon as it affects a PWR, specifically the Zorita nuclear power plant, a single-loop Westinghouse-designed PWR in Spain. In this respect, an ATWS sequence analysis methodology based on published codes that is generically applicable to any PWR is proposed, which covers all the anticipated phenomena and defines the applicable acceptance criteria. The areas contemplated are cell neutron analysis, core thermal hydraulics, and plant dynamics, which are developed, qualified, and plant dynamics, which are developed, qualified, and validated by comparison with reference calculations and measurements obtained from integral or separate-effects tests.

Searching for new approaches to solving technological and safety problems in fast reactors

Alternative solutions were developed for the technology and safety problems of fast reactors. Kinetic and design research for fast reactors based on modular construction was reviewed and assessed with specific attention given to the PRISM and SAFR reactors. Tradeoffs in power output and reactor safety for modular reactors, along with American interest in modular concepts, were also evaluated. The possibilities of using reactivity feedback to create passive reactor protection were discussed using the thermohydraulics and core kinetics of the EBR-II, the PRISM, the Phenix, the Rapsodie, the Superphenix-1, the British PFR, and the SAFR reactors under accident scenarios such as loss of flow, RCP shutoff, and protection system failure. The internally inherent safety characteristics of fast reactors and oxide versus metallic fuels were assessed. The implementation of internally inherent safety properties in fast reactor design, experimental research on high temperature reactor regimes, and the status of passive systems for accident heat removal were also reviewed.

Failure analysis of plasma-sprayed thermal barrier coatings

In this work thermally induced failure processes of plasma-sprayed thermal barrier coatings were examined. Cracking processes give rise to noise which was monitored by acoustic emission techniques. The sequential failure of coatings was examined from samples which were thermally cycled. Coatings of yttria-stabilized zirconia with and without an Ni-Cr-Al-Zr bond coat were plasma sprayed onto a U 700 alloy rod. In some cases the substrate was intentionally overheated prior to deposition of the thermal protection system. In this way a qualitative appraisal of how process variables affect coating integrity could be made in terms of cracking behavior. Results from up to seven consecutive thermal cycles are reported here. Coating failure was observed in all cases. Failure of the thermal protection system is progressive, since cracking and crack growth have been observed prior to ultimate failure, and thus catastrophic failure occurs at some stage when there is a transformation from the microcrack to a macrocrack network.

Reliability Calculations for Electrical Transmission Systems on the Basis of Mean Failure Indices

In an electric power transmission network, a fault occurring on any one of its components sometimes causes an' active event' as a result of interaction between the power system and its protection system. An outage of sections adjacent to the faulted one for a small duration is characteristic of these events. In this paper, the mean failure indices (mean probability-of-failure and mean frequency-of-failure) of a network are defined as functions of the failure indices at various load points. Several types of active events including those caused by failure of protection system are considered and their contribution to the mean failure indices of the network evaluated. The effectiveness of providing normally open paths in reducing the mean failure indices of the network is explained. The points are illustrated by examples.

Composite Generation and Transmission System Adequacy Evaluation Including Protection System Failure Modes

Protection systems are normally considered to be perfectly reliable in composite system adequacy assessment. The effect on the calculated adequacy indices of neglecting these events can be quite significant in highly redundant configurations. This paper examines some protection system models and incorporates the results in a practical application of cmxposite systemtadequacy assessment.

Composite Generation and Transmission System Adequacy Evaluation Including Protection System Failure Modes

Composite Generation and Transmission System Adequacy Evaluation Including Protection System Failure Modes

Terminal Effects and Protection System Failures in Composite System Reliability Evaluation

Terminal Effects and Protection System Failures in Composite System Reliability Evaluation

Terminal Effects and Protection System Failures in Composite System Reliability Evaluation

This paper considers the effect of terminal station outages on the contingencies that should be studied in composite system reliability evaluation. It describes how these contingencies are affected by the operation and non-operation of the protection breakers in a terminal station. It also describes how the reliability indices of protection systems which contain commonly- shared components, redundancy and diversity can be evaluated using the event tree method and how these indicies are used to determine the associated indices of the contingency. The discussion illustrates that the effect of terminal station outages on the contingencies to be included in a composite system study can be severe and that it c-an be very important to model the protection system in a realistic manner.

Protection System Reliability Modeling: Unreadiness Probability and Mean Duration of Undetected Faults

A reliability model of a system and its associated protection system is described. The protection system detects the presence of faults and isolates the faulted equipment so as to prevent damage and minimize the effect of the faulted equipment on the operation of the rest of the system. If the protection system does not respond and the faulted component is not disconnected, a backup protection system comes into operation. The backup operation isolates a larger segment and disturbs the system more than if the designated protection system had responded appropriately. An example is the protective relay systems for electric power transmission and distribution systems. A measure of system unreadiness is defined and suitable expressions are derived for this index and the mean duration of undetected faults. The unreadiness probability is sensitive not only to the failure rate of the protection system but also to the failure rate of the system, the pdf of interval between inspections and its mean value. The unreadiness probability estimated from a given system cannot be used for another system having a similar protection system. The protection system failure rate can, however, be used to obtain the unreadiness probability.

A Cause-Consequence Chart of a Redundant Protection System

A cause-consequence chart is applied in analysing failures of a redundant protection system (a core spray system in a nuclear power plant). It is shown how the diagram provides a basis for calculating two probability measures for malfunctioning of the protection system. The test policy of components is taken into account. The possibility of using parameter variation as a basis for the choice of test policy is indicated.