| 1. |
- Arifianto, I., et al.
(författare)
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Investigation of transformer top-oil temperature considering external factors
- 2012
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Ingår i: Condition Monitoring and Diagnosis (CMD), 2012 International Conference on. - : IEEE. - 9781467310208 ; , s. 198-201
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Konferensbidrag (refereegranskat)abstract
- Standard estimation of top-oil temperature uses a thermal model related to load changes and variation of ambient temperature. Attempts have been done to improve the accuracy of top-oil temperature calculations by introducing internal properties into the model i.e. oil viscosity and winding resistance. The interest of this paper is to investigate the effect of external factors on top-oil temperature by looking into the weather, i.e. wind velocity. The results are compared with measurements on a 63MVA-ONAF 55/140 kV transformer unit, which is operated in ONAN cooling mode. The unit is located in subarctic climate, and it is equipped with a monitoring system and a weather station.
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| 2. |
- Babu, Sajeesh, et al.
(författare)
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On the status of reliability studies involving primary and secondary equipment applied to power system
- 2014
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Ingår i: 2014 International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2014 - Conference Proceedings. - : IEEE. - 9781479935611 ; , s. 6960653-
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Konferensbidrag (refereegranskat)abstract
- Growth in infrastructure and energy utilization consistently put forward the demand for added quality and quantity of electric power. Reliability concerns over power systems are widespread within its different associated divisions like 'primary' power system structure, protection system, control equipment, ICT (Information and Communication Technologies) etc. This paper is a review of the present status of practices regarding reliability analysis in these divisions and works towards collectively assessing some of the studies in the respective areas. The idea of integrating reliability analysis from the above areas is introduced along with pointing out the major challenges associated. A set of tools for operators to make use in these reliability evaluations and modelling are mentioned. The earlier attempts towards combined overall system reliability analysis are discussed and the approach in this regard with the help of 'control functions' is emphasised. The paper includes works dealing with theory, different methodologies and data associated with power system reliability.
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| 3. |
- Edström, Fredrik, et al.
(författare)
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Influence of Ambient Temperature on Transformer Overloading During Cold Load Pickup
- 2013
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Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 28:1, s. 153-161
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a method to investigate the socioeconomical aspects of transformer overloading during a cold load pickup (CLPU) in residential areas. The method uses customer damage functions to estimate the cost for their power interruption and a deterioration model to estimate the cost for transformer wear due to the CLPU. A thermodynamic model is implemented to estimate the peak and the duration of cold residential load. A stochastic differential equation is used to capture the volatility of the load and to estimate the probability for transformer overloading. In a numerical example, an optimal cold load pickup for a two-area system is demonstrated where transformer overloading is allowed. In this example, an ambient temperature threshold is identified, where transformer overloading is socioeconomically beneficial.
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| 4. |
- Edström, Fredrik, et al.
(författare)
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Modeling Impact of Cold Load Pickup on Transformer Aging Using Ornstein-Uhlenbeck Process
- 2012
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Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 27:2, s. 590-595
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Tidskriftsartikel (refereegranskat)abstract
- Thermostatically controlled devices, such as air conditioners, heaters, and heat pumps may cause cold load pickup (CLPU) problems after a prolonged blackout. This causes an increased load on the power components in the electrical grid. The result is unpredictable aging and increased risk of failure. Quantifying this risk is crucial for efficient asset management for cost-intensive components such as the transformer. This paper presents a new approach to model the loading profile of a CLPU using stochastic differential equations. The realization of the loading profile is used to determine the aging of a transformer. Two models for the deterioration of transformer solid insulation represent the loss of life due to the CLPU. A comparison between two models for the aging of the solid insulation in the transformer is made in a case study. Due to the stochastic behavior of the load, there is a probability for loading the transformer above the recommended ratings, and this probability is estimated with Monte Carlo simulations.
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| 5. |
- Ekstedt, Niklas, 1979-, et al.
(författare)
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Categorization and Review of Failure Rate Factors Used in Power Systems
- 2014
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Ingår i: 2014 International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2014 - Conference Proceedings, 2014. - : IEEE Press. - 9781479935611
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Konferensbidrag (refereegranskat)abstract
- To evaluate the reliability of power systems, good estimates of the failure rates of the included components are needed. Better predictions can be performed if relevant factors that affect the failure rates are used, and an increasing number of models that include different types of factors have been presented recently. This paper proposes a categorization of failure rate factors into seven categories, based on the type of information for the factors. The categorization can be used to map future studies in the context of similar work. Furthermore, the paper presents a review of a number of publications that uses different factors to model the failure rate of different power system components. The failure rate factors used in the reviewed publications are categorized into the proposed seven categories and a comprehensive summary table is included. The used models and methods to estimate the failure rate in the reviewed publications are also noted in the summary table.
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| 6. |
- Ekstedt, Niklas, et al.
(författare)
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Reliability Data : A Review of Importance, Use, and Availability
- 2014
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Konferensbidrag (refereegranskat)abstract
- For reliability studies of power distribution systems availability and collection of data on reliability is a key aspect. The acquirement of data can be challenging, because it endures effort and experience to know where to obtain accessible types of data. This paper gives the reader a guide to why input data to reliability analyses and asset management are useful, which data that can be obtained, and how to access the different types of data. Also, how to measure data accurately and the quality needed are discussed in the paper.After a general discussion on the benefits of data, we discuss the importance of knowing exactly what the data are measurements of. Furthermore, we argue that data from different contexts, even if seemingly similar, should be used with care. We also state and explain that the amount data restrict the type of analysis that can be conducted. The paper continues with a description of some examples of (to different degrees) open accessible data. Nationally collected reliability data from Swedish utilities, reported to authorities and interest organizations, are described and discussed. We discuss how Swedish weather data, which recently have become free and open, enable more studies on the weather related reliability effects, and some existing test systems are mentioned. A section follows that describes how failure and condition data are typically stored and utilized internally in organizations. Finally, we conclude that the paper is a potential guide and inspiration for anyone planning to conduct a reliability study in the future.
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| 7. |
- Grahn, Pia, et al.
(författare)
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A method for evaluating the impact of electric vehicle charging on transformer hotspot temperature
- 2011
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Ingår i: 2011 2nd IEEE PES International Conference and Exhibition on Innovative Smart Grid Technologies (ISGT Europe). - : IEEE.
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Konferensbidrag (refereegranskat)abstract
- The expected increasing market share of electric vehicles is a response to the combination of new technological developments, governmental financial control, and an attitude shift of residents to a more environmentally friendly lifestyle. The expected capacity required for charging, imposes changes in the load to the already existing components in the electric power grid. In order to continue managing these existing assets efficiently during this load change, it is important to evaluate the impact imposed by the battery charging.
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| 8. |
- Hilber, Patrik, et al.
(författare)
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Benefits of Reliability Centred Asset Management
- 2013
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Ingår i: 22nd International Conference and Exhibition on Electricity Distribution (CIRED 2013). - : Institution of Engineering and Technology. - 9781849197328 ; , s. 0668-
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Konferensbidrag (refereegranskat)abstract
- This paper provides an overview of risk and reliability assessment techniques, some which are available for distribution system operators, and others that are in the process of development. The main contribution of this paper is showing the possibilities and benefits of detailed risk and reliability analysis. Six samples of findings from research developed over the last decade within the RCAM group (Reliability Centred Asset Management) at the Royal Institute of Technology, Stockholm Sweden, are presented. The research is directly associated with risk and asset management applied to power systems. The first three examples are within developed research, followed by three areas where great potential is seen: 1) The value of accurate thermal models of transformers; 2) The impact of tariff regulation on asset management decisions; 3) Detailed interruption studies; 4) Dynamic rating; 5) Combined risk and reliability analysis of primary equipment and control equipment; 6) Systematic diagnostic measures for asset management.
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| 9. |
- Hilber, Patrik, 1975-
(författare)
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Cable Segment Replacement Optimization
- 2014. - 1
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Ingår i: Reliability Modeling and Analysis of Smart Power Systems. - New Delhi Heidelberg New York Dordrecht London : Springer London. - 9788132217978 - 9788132217985 ; , s. 195-202
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Bokkapitel (refereegranskat)
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| 10. |
- Hilber, Patrik, et al.
(författare)
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Potentiell användning av standardkostnader i regleringen av elnätsföretagens löpande påverkbara kostnader
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Potentiell användning av standardkostnader i regleringen av elnätsföretagens löpande påverkbara kostnader har utretts på uppdrag av Energimarknadsinspektionen (EI). Specifikt om mått baserade på Ekm kan användas i regleringen och hur dessa mått bör korrigeras. Ekm (Ekvivalent ledningslängd) är en standardkostnadsmodell där olika entiteter (t.ex. mängd av en komponentkategori) av elnät tilldelas en kvot för årlig drift- och underhållskostnad i förhållande till 1 km 0,4 kV luftledning. Projektets huvudslutsats är att existerande Ekm, tillhandahållna av Svensk Energi, inte kan användas utan rigorösa kontroller och omfattande utveckling, vilket entydigt styrks av utförda analyser. Emellertid finns det en potential att använda Ekm-liknande mått i kommande reglering. Vid ett eventuellt införande rekommenderas följande: Preliminära Ekm-liknande tal implementeras under första tillsynsperiod för en lägre andel av löpande påverkbara kostnader än ursprunglig plan (25%), förslagsvis så att de medel som omfördelas i genomsnitt blir väsentligt lägre än de medel som omfördelas på grund av kvalitetsregleringen. Noggrann utvärdering görs fortlöpande, vars resultat används för revidering av Ekm till nästkommande tillsynsperiod. Detaljerad analys och utveckling av Ekm liknande tal; förslag på handlingsplan tillhandahålls i appendix. Två enkäter har utformats, huvudenkäten har skickats ut till samtliga nätägare i Sverige. Svarsfrekvensen på denna blev 46 % (motsvarande ca 75 % av kundunderlaget). Uppföljande enkät skickades till de som angivit intresse för fördjupat deltagande (12st). Utöver enkäter bygger studien på material från EBR (del av Svensk Energi) och EI samt diskussioner med dessa och nätägare. Trots mängden empiriskt material har inga konkreta förslag på Ekm liknande mått kunnat tillhandahållas, dels på grund av stora variationer mellan svar och analyser och dels på grund av låg svarsfrekvens i enkäten för de delar som avser konkreta kostnader. I vissa fall ger enkätsvaren och analyserna indikationer på storleksordning för Ekm tal och hur dessa bör justeras. Ytterligare en osäkerhetsfaktor är huruvida nuvarande indelning är lämplig, dvs. om fler eller färre objektiva förutsättningar, t.ex. terräng, bör tas i beaktning. Detta är kopplat till den viktiga frågan om att kunna göra en analys av utfallet av ett införande, innan implementering (hur kommer intäkterna omfördelas). Detta har ej kunnat göras då företagen ännu ej rapporterat in sina nät-tillgångar. Studiens viktigaste resultat: Möjliggörande för samtliga parter att bidra med synpunkter innan eventuell skarp implementering. Inventering nuvarande förutsättningar avseende Ekm. Indikation på hur vissa mått bör modifieras. Metoder för utvärdering och bestämmande av nya mått. Ökad medvetenhet och kunskap hos myndighet och nätföretag. Handlingsplan för fortsatt arbete.
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