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Analysis of reliability improvements of transformers after application of dynamic rating
KTH, School of Electrical Engineering (EES). Kungliga Tekniska Högskola.
2017 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Analys av tillförlitlighet förbättringar av transformatorer efter tillämpning av dynamisk rating (Swedish)
Abstract [en]

In this project dynamic thermal rating for transformers and its effect on transformer reliability are investigated. A literature review is done on different thermal models used for this purpose and at the end differential equations model from IEC 60076-7 and bottom oil model from IEEE C57.91-1995 standard are selected to calculate hot spot temperature. A wind farm connected transformer is selected to implement the models. This transformer belongs to Ellevio AB and manufactured by ABB AB. Load data are gathered for every 5 minutes during 2016. Loss of life of transformer is calculated and it is concluded that by considering this factor, the transformer is overdesigned. The optimum size of transformer by utilizing dynamic rating is selected which results in a reduction in investment cost. This method can be used to select the appropriate size oft ransformer by taking advantages of ambient temperature variations and overload the transformer beyond nameplate ratings without exceeding transformer temperature limitations. Moreover, the risk of overloading the transformer at any time during 2016 is calculated. The risk of overloading is quantified as loss of life of transformer. It is shown that this risk is a function of ambient temperature and the duration of overloading. Finally, an economic analysis is done to demonstrate economic benefit of expanding wind farm by overloading the existing transformer by reducing the transformer life expectancy while keeping it in a safe limit.

Abstract [sv]

I detta projekt undersoks dynamisk varmeklassicering for transformatorer ochdess eekt pa transformatorns tillforlitlighet. En litteraturoversikt gors pa olikatermiska modeller som anvands for detta andamal och i slutet av dierentialekvationsmodellenfran IEC 60076-7 och bottenoljemodellen fran IEEE C57.91-1995 standard valjes for att berakna varmpunktstemperatur. En transformatormed vindkraftpark valjs for att genomfora modellerna. Denna transformatortillhor Ellevio AB och tillverkas av ABB AB. Lastdata samlas in for var 5: eminut under 2016. Transformatorns livslangd beraknas och det slutsatsen atttransformatorn ar overdesignad med hansyn till denna faktor. Den optimalastorleken pa transformatorn genom att anvanda dynamisk rating valjs vilket resulterari en minskning av investeringskostnaden. Denna metod kan anvandasfor att valja lamplig storlek for transformatorn genom att dra fordel av omgivandetemperaturvariationer och overbelasta transformatorn bortom markskyltarutan att overskrida transformatortemperaturbegransningar. Dessutomberaknas risken for overbelastning av transformatorn nar som helst under 2016.Risken for overbelastning kvantieras som forlust av livslangd for transformatorn.Det visas att denna risk ar en funktion av omgivande temperatur ochvaraktigheten av overbelastning. Slutligen gors en ekonomisk analys for attvisa ekonomisk nytta av att expandera vindkraftparken genom att overbelastaden bentliga transformatorn genom att minska transformatorens livslangd samtidigtsom den halls i en saker grans.

Place, publisher, year, edition, pages
2017.
Series
TRITA-EE, ISSN 1653-5146 ; 2017:121
Keyword [en]
Dynamic rating, Reliability, Transformer, Loss of life
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-217289OAI: oai:DiVA.org:kth-217289DiVA: diva2:1155097
External cooperation
ABB; Ellevio
Educational program
Master of Science - Electric Power Engineering
Supervisors
Examiners
Available from: 2017-11-07 Created: 2017-11-06 Last updated: 2017-11-07Bibliographically approved

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