Impact of geomagnetic disturbances on power transformers: risk assessment of extreme events and data availability

Certain rare events can have a drastic impact on power systems. Such events are generally known as high-impact low-probability (HILP) events. It is challenging to predict the occurrence of a HILP event mainly due to lack of data or sparsity and scarcity of data points. Yet, it is essential to implement an evidence-driven asset management strategy. In this paper, event tree analysis is used to assess the risk of power transformer failure due to a geomagnetically induced currents (GIC). Those currents are caused by geomagnetic disturbances in Earth’s magnetic field due to solar activity. To assess the impact on power transformers, an understanding of the mechanism and sequence of sub-events that lead to failure is required to be able to construct an event tree. Based on the constructed event tree, mitigation actions can be derived. GIC blockers or reducers can be used. However, that would require extensive installation and maintenance efforts, and the impact on system reliability has to be studied. Also, such technology is still in its infancy and needs extensive validation. A suggested alternative is to combine early warning data from solar observatories with a load management plan to keep transformers below their rated operation point such that a DC offset due to GIC would not cause magnetic core saturation and overheating. Load management and the risk of early warning false positives can incur a negative effect on reliability. Nevertheless, the risk assessment performed in this paper show that incorporating load management in asset planning is a viable measure that would offset the probability of catastrophic failure.

Reliability of quantitative risk analysis through an industrial case study

PurposeThe purpose of this paper is to analyze the reliability of the quantitative risk model used for planning inspection and maintenance activities. The objective is to critically discuss the factors that contribute to the probability and consequence of failure calculations.Design/methodology/approachThe case study conducted using one of the most widely deployed risk models in the oil and gas industry where a full assessment was performed on an offshore gas producing platform.FindingsThe generic failure frequencies used as the basis for calculating the probability of failure are set at a value representative of the refining and petrochemical industry's failure data. This failure database does not cover offshore. The critical discussion indicated the lack of basis of the coefficient of variances, prior probabilities and conditional probabilities. Moreover, the risk model does not address the distribution of thickness measurements, corrosion rates and inspection effectiveness, whereas only overall deterministic values are used; this requires judgment to determine these values. Probabilities of ignition, probabilities of delayed ignition and other probabilities in Level 1 event tree are found selected based on expert judgment for each of the reference fluids and release types (i.e. continuous or instantaneous). These probabilities are constant and independent of the release rate or mass and lack of constructed model. Defining the release type is critical in the consequence of the failure methodology, whereas the calculated consequences differ greatly depending on the type of release, i.e. continuous or instantaneous. The assessment results show that both criteria of defining the type of release, i.e. continuous or instantaneous, do not affect the calculations of flammable consequences when the auto-ignition likely is zero at the storage temperature. While, the difference in the resulted toxic consequence was more than 31 times between the two criteria of defining the type of release.Research limitations/implicationsThere is a need to revamp this quantitative risk model to minimize the subjectivity in the risk calculation and to address the unique design features of offshore platforms.Originality/valueThis case study critically discuss the risk model being widely applied in the O&G industry and demonstrates to the end-users the subjectivity in the risk results. Hence, be vigilant when establishing the risk tolerance/target for the purpose of inspection and maintenance planning.

Causal Algebras on Chain Event Graphs with Informed Missingness for System Failure

Graph-based causal inference has recently been successfully applied to explore system reliability and to predict failures in order to improve systems. One popular causal analysis following Pearl and Spirtes et al. to study causal relationships embedded in a system is to use a Bayesian network (BN). However, certain causal constructions that are particularly pertinent to the study of reliability are difficult to express fully through a BN. Our recent work demonstrated the flexibility of using a Chain Event Graph (CEG) instead to capture causal reasoning embedded within engineers’ reports. We demonstrated that an event tree rather than a BN could provide an alternative framework that could capture most of the causal concepts needed within this domain. In particular, a causal calculus for a specific type of intervention, called a remedial intervention, was devised on this tree-like graph. In this paper, we extend the use of this framework to show that not only remedial maintenance interventions but also interventions associated with routine maintenance can be well-defined using this alternative class of graphical model. We also show that the complexity in making inference about the potential relationships between causes and failures in a missing data situation in the domain of system reliability can be elegantly addressed using this new methodology. Causal modelling using a CEG is illustrated through examples drawn from the study of reliability of an energy distribution network.

A TRIZ Approach to Reliable Megaproject Sustainability

Purposes: This article presents a recent research into megaproject sustainability with a particular focus on identifying a structure of its body of knowledge so as to establish the methodology of megaproject assessment on sustainability (MAS), which consists of a research roadmap toward megaproject sustainability and a system reliability analysis. In response to the research topic on “Reviews for Advanced Construction Management” at Frontiers in Built Environment, this article aims to make a contribution with the description about a generic approach to conducting literature review based on a whole range of relevant evidence in a systemic way.Methodology: The research described in this article is underpinned by the use of several methods. The nine-square process (NSP) of Theory of Inventive Problem Solving (TRIZ) is the method for facilitating a systemic evidence-based learning (EBL) process to identify further research into MAS. A normal process to establish research roadmap was then introduced to summarize what has been identified as specific research tasks alongside lifecycle processes on megaproject delivery, to which RIBA Plan of Work 2020 was adopted as the prototype. An event tree analysis (ETA) was eventually introduced by incorporating the novel measurements on system reliability to support quantitative MAS in terms of both practices and research.Findings: This article presents several findings from the described research, and these include that the use of NSP led to the formation of a systematic procedure for literature review, a procedure to support MAS, a research roadmap to facilitate efforts to be made for megaproject sustainability, and the feasibility of system reliability analysis to measure the status of sustainability underpinned by research and practices throughout megaproject lifecycle.Implications: The described research provides four modules to foster further research into megaproject sustainability, and these include a TRIZ-based module to facilitate systemic literature review for EBL, a lifecycle process module for MAS, a prototype research roadmap to guide research and development for megaproject sustainability, and an ETA module to support a system reliability analysis in the dynamic process of research and practices toward megaproject sustainability.Value: The research described in this article has made an initial effort to conduct a strategic review, development, analysis, and discussion about tactics for research and development toward megaproject sustainability. Research findings can be used for related research and practices with regard to technical guidance and best practices in megaproject delivery.