Operational vulnerability indicator for prioritization and replacement of power transformers in substation (original) (raw)
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Risk Assessment Algorithm for Power Transformer Fleets Based on Condition and Strategic Importance
Algorithms
In every electric power system, power transformers (PT) play a critical role. Under ideal circumstances, PT should receive the utmost care to maintain the highest operative condition during their lifetime. Through the years, different approaches have been developed to assess the condition and the inherent risk during the operation of PT. However, most proposed methodologies tend to analyze PT as individuals and not as a fleet. A fleet assessment helps the asset manager make sound decisions regarding the maintenance scheduling for groups of PT with similar conditions. This paper proposes a new methodology to assess the risk of PT fleets, considering the technical condition and the strategic importance of the units. First, the state of the units was evaluated using a health index (HI) with a fuzzy logic algorithm. Then, the strategic importance of each unit was assessed using a weighting technique to obtain the importance index (II). Finally, the analyzed units with similar HI and II ...
Assessment of Power Transformers Conditions Based on Health Index
Power transformers are important assets in electrical power grids, in terms of both reliability and costs. The conditions of these assets have to be known, in order to avoid any possible outages and to choose the appropriate maintenance operation that could be done. The health index of a power transformer is one single overall indicator that represents its condition and is derived by a weighting process of all available indicators. This paper presents a case study on several power transformers from Romanian Electrical Grid, discussing the benefits of using health index and failure probability as overall diagnostic tools. Moreover, a remaining lifetime calculation based on the transformer failure probability is defined.
Power transformers are the most expensive and perhaps the most strategic assets in a substation. Accordingly, transformer operators both in the utilities and in industry are drawn to optimize their overall financial performance by maintaining a high reliability and extending lifetime at minimal costs. One obvious requirement for this performance improvement is knowledge about the current condition of the whole transformer fleet. This information is essential for the short-term, long-term, and strategic decisions of the transformer operator. In most companies, different funding sources (and departments) are responsible for the optimal fleet management: capital expenditures (CAPEX), operating expenditures (OPEX) and the grid operator.
Development of Indicators for Technical Condition Indexing of Power Transformers
Advances in Science, Technology and Engineering Systems Journal, 2018
Reliable operation of a power transformer with a certain load depends on the technical condition of individual construction parts and the ability to prevent defects that can cause a failure. During the lifecycle of a transformer, valuable data is constantly accumulated, which forms the basis for technical or risk assessment of the equipment. Therefore it also serves as a ground for the decisions on further operation, or repairs, or replacement. To achieve this goal, data need to be systematized. Since technical condition indexing allows combining various types of data including results of diagnostic tests is used within the framework of this research. As part of a larger risk assessment methodology, algorithms for two indicators are proposed in this paper, and they are based on results of electrical measurements and analysis of oil parameters, respectively. The novelty of the algorithms for indicators introduced in this paper is based on analysis of features specific to the power system in Latvia such as large proportion of aged transformers, low loading level, significant variation in oil volumes, and statistics on typical faults. Proposed limits of parameters are verified with data from operation history. Taking into account the differences in the measurement periodicity, the indicator that is based on electrical measurements assesses the individual constructive parts of the transformer (windings and core, bushing and onload tap changer) separately, whereas the other, indicator combines the results of oil parameters into a single assessment. These indicators were verified by using 30 transformers from the Latvian power system and the obtained results coincide well with the operation history.
Condition Assessment of Power Transformers Based on Health Index Value
Applied Sciences
In electric power systems, health index algorithms are mostly used for evaluation of the transformer population. In this method, some assessment criteria are insensitive when it comes to judging the technical state of the edges of the age spectrum. This paper presents a new health index calculation method that aims to improve the overall effectiveness of the assessment. The proposed algorithm is based on regularly conducted oil diagnostics and easily available maintenance data to enable estimation and updating of the device’s health status in short intervals from an operational point of view. This method is compared to another health index algorithm built from the same parameters, but with different weights and an alternative result assessment philosophy. The two health index calculation methods are tested on a population of 96 power transformers and then compared to results obtained with an expert system, which is based on much more advanced diagnostic tests to determine the techni...
Health Index for Power Transformer Condition Assessment: A Comparison of Three Different Techniques
Journal of Applied Research and Technology
In practice, the condition state of Power Transformers (PT) is quantified by using Health Index (HI). This paperanalyzes and compares three different state-of-the-art algorithms to compute HI. The first one uses a Weighted SumModel (WSM), the second is based on a Fuzzy Inference System (FIS), and the third combines both techniques, i.e.,WSM and FIS. These three approaches are tested in a PT fleet composed of 30 units. Results show that eachapproach produces different HI values for the same PTs. Therefore, decision making regarding the PT fleet willdepend on the selected approach for HI calculation. This work proposes merging the knowledge involved in eachanalyzed approach by using a K-means clustering technique to overcome this drawback. This solution could help theasset manager to make adequate decisions regarding the maintenance scheduling of PT when there is uncertaintyabout the appropriate approach to be selected.
Multicriteria Transformer Asset Management with Maintenance and Planning Perspectives
Strategic asset management of transformer fleets in electrical power systems is a critical aspect for distribution utilities. In this work an integrated framework for multicriteria asset management is presented. A multiobjective optimization model is deployed, simultaneously minimizing the maintenance costs and the predicted cost of unexpected failures, based on statistical estimates of failure probability and on the expected economic impact of failures. A multicriteria decision-support system is used for the selection of the recommended maintenance policy for a given time window. A criticality score for each transformer, which can assist planning engineers in defining replacement investments, is also provided. The application of the proposed framework is illustrated using the database of Brazilian power distribution utility CEMIG. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication in an issue of the journal. To cite the paper please use the doi provided on the Digital Library page.
Development of indicator based on oil analysis for estimating risk level of power transformers
2016 57th International Scientific Conference on Power and Electrical Engineering of Riga Technical University (RTUCON), 2016
Risk assessment for power transformers has long been an effective tool to analyze transformer conditions in order to prevent damage on transformers, extend transformer's life time and reduce maintenance costs. Various parameters can be evaluated, and decision can be made manually or with the help of mathematical model. A new mathematical risk-assessment model for power transformers is being developed for power system in Latvia, based on specific maintenance features and 4 indicators: dissolved gas analysis; oil analysis, electrical measurements and operation history. This paper specifies oil analysis as one of the indicators of regular risk assessment of power transformers. Development of this indicator is presented based on traditional binary evaluation algorithm combined with fuzzy logic, and as a case study results of oil parameters from different transformers are analyzed and discussed.