Design of experimenal setup to study factors affecting hot spot temperature in disc type winding transformers

Abstract

Oil immersed power transformers have complex structures for which electrical, mechanical and thermal considerations have to be taken into account during design. To produce a reliable transformer, the thermal profile in terms of temperature for windings is of interest because ageing of the transformer and its constituents is mainly affected by its operating temperature. The temperature profile is not uniform within a winding mainly because of the uneven loss distribution and the uneven flow distribution of the coolant within the winding structure. The Hot Spot Temperature (HST) is defined as the hottest temperature of the transformer which strongly affects the ageing of the transformer oil and the winding paper insulation near it. Understanding the HST helps utilize available assets for a utility in the longer term. Parameters affecting the location and the value of the HST can be split into geometrical and operational parameters. Geometrical parameters include horizontal cooling duct height, vertical cooling duct width and the number of discs per pass for a winding. Operational parameters include the inlet oil flow rate, the oils thermal properties and the loading level of the transformer. In this paper, the design and implementation of an experimental setup is presented which is used to study the effects of these parameters on the HST.