Investigation of Operational and Design Parameters Affecting the Thermal Behaviour of Disc-Type Winding

Abstract

The lifetime and reliability of a power transformer are highly dependent on the lifetime of its insulation. Since excessive heat generation is the major cause of deteriorating insulation and aging, an optimal cooling design is necessary to avoid operating faults and material degradation. In this contribution, significant operational and geometrical parameters are considered and analyzed to predict their influences on the thermal behavior inside an oil-directed cooled winding model. This study presents 3D numerical Computational Fluid Dynamics results to determine the hot-spot temperature and its location by applying various boundary conditions, which are validated with measured temperatures from an experimental setup. The experimental setup consists of an oil feeding unit and a winding model consisting of 20 discs, which is equipped with fluid guides to obtain a zig-zag cooling mode. To account for the variations of the thermal characteristics of oil, its properties are changed by increasing the inlet oil temperature. The geometrical parameters can be divided into horizontal cooling channel height, vertical cooling channel width and number of discs per pass; whereas main operating parameters consist of inlet flow rate, inlet oil temperature and heat losses. The temperature profiles illustrate that reducing the height of horizontal channels, apart from making the transformer smaller, decreases the blockage caused by flow eddies and improves the oil flow distribution. Moreover, while the presence of fewer discs between two successive fluid guides aids in decreasing hot-spot and average oil temperature, it also leads to an increased drop in oil pressure. These results can be applied to optimize cooling aspects of disc-type windings.