Dynamic thermal modelling of power transformers

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dc.contributor Aalto-yliopisto fi
dc.contributor Aalto University en
dc.contributor.author Susa, Dejan
dc.date.accessioned 2012-02-17T07:04:44Z
dc.date.available 2012-02-17T07:04:44Z
dc.date.issued 2005-08-26
dc.identifier.isbn 951-22-7742-5
dc.identifier.issn 1795-4584
dc.identifier.uri https://aaltodoc.aalto.fi/handle/123456789/2584
dc.description.abstract Power transformers represent the largest portion of capital investment in transmission and distribution substations. In addition, power transformer outages have a considerable economic impact on the operation of an electrical network. One of the most important parameters governing a transformer's life expectancy is the hot-spot temperature value. The classical approach has been to consider the hot-spot temperature as the sum of the ambient temperature, the top-oil temperature rise in tank, and the hot-spot-to-top-oil (in tank) temperature gradient. When fibre optic probes were taken into use to record local hot-spots in windings and oil ducts, it was noticed that the hot-spot temperature rise over top-oil temperature due to load changes is a function depending on time as well as the transformer loading (overshoot time dependent function). It has also been noticed that the top-oil temperature time constant is shorter than the time constant suggested by the present IEC loading guide, especially in cases where the oil is guided through the windings in a zigzag pattern for the ONAN and ONAF cooling modes. This results in winding hottest spot temperatures higher than those predicted by the loading guides during transient states after the load current increases, before the corresponding steady states have been reached. This thesis presents new and more accurate temperature calculation methods taking into account the findings mentioned above. The models are based on heat transfer theory, application of the lumped capacitance method, the thermal-electrical analogy and a new definition of nonlinear thermal resistances at different locations within a power transformer. The methods presented in this thesis take into account oil viscosity changes and loss variation with temperature. The changes in transformer time constants due to changes in the oil viscosity are also accounted for in the thermal models. In addition, the proposed equations are used to estimate the equivalent thermal capacitances of the transformer oil for different transformer designs and winding-oil circulations. The models are validated using experimental results, which have been obtained from a series of thermal tests performed on a range of power transformers. Most of the tested units were equipped with fibre optic sensors in the main windings. Some of them also had thermocouples in the core and structural parts. A significant advantage of the suggested thermal models is that they are tied to measured parameters that are readily available (i.e., data obtained from a normal heat run test performed by the transformer manufacturer). en
dc.format.extent 129
dc.format.mimetype application/pdf
dc.language.iso en en
dc.publisher Helsinki University of Technology en
dc.publisher Teknillinen korkeakoulu fi
dc.relation.ispartofseries TKK dissertations en
dc.relation.ispartofseries 9 en
dc.subject.other Electrical engineering en
dc.title Dynamic thermal modelling of power transformers en
dc.type G4 Monografiaväitöskirja fi
dc.description.version reviewed en
dc.contributor.department Department of Electrical and Communications Engineering en
dc.contributor.department Sähkö- ja tietoliikennetekniikan osasto fi
dc.subject.keyword power transformers en
dc.subject.keyword hot-spot temperature en
dc.subject.keyword top-oil temperature en
dc.subject.keyword bottom-oil temperature en
dc.subject.keyword non-linear thermal resistance en
dc.subject.keyword oil time constants en
dc.identifier.urn urn:nbn:fi:tkk-005380
dc.type.dcmitype text en
dc.type.ontasot Väitöskirja (monografia) fi
dc.type.ontasot Doctoral dissertation (monograph) en
dc.contributor.lab Power Systems and High Voltage Engineering en
dc.contributor.lab Sähköverkot ja suurjännitetekniikka fi

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