Thermal Analysis of Tap- Changers

Abstract: This thesis provides a way of mapping the temperature development of the tap-changer oil for some different standardized loading cases. The project was in collaboration with Hitachi Energy for one of their production cites situated in Ludvika, Sweden. The software used for the simulation environment was COMSOL 6.1 which is a finite element solver. Heat transfer from the tap-changer oil to the ambience is an important property to understand in order to be able to model the future tap-changers that can withstand harsch working environments. CAD files for the housing of a tap-changer model, as well as a mathematical model for the oil and heat transfer number, was made. Combined with COMSOLS inbuilt physics tools various temperature plots of the oil and housing could be made, following the creation of the user app that was shared with the company. The resulting temperature plots made it is possible to distinguish which models that operates below the temperature limits, and the ones passing the limit can then be adressed accordingly. Since it is a quite simple model, not including the fluidic dynamics of the oil and with a simple geometry, some errors is to be expected. An interesting finding in this project was the change of placement for the maximum temperature for one specific operation cycle. This could be of use for a future thermal management study that could be implemented into other operation cycles.