Analysis of particle movement and partial discharge in the winding of power transformer using CFD

Power transformer is an important apparatus in electrical substation. It is therefore required that it should be protected against all types of undesirable events. It has been experienced that one of the reasons of failure of transformer is due to the presence of metal particles in the annular space between the windings. The particles during movement cause Partial Discharges (PD) due to the high voltage on the discs. The magnitude of PD depends on the particle nearness to the disk of transformer and stress developed on the metal particle. In order to determine the movement and stress on disc of transformer winding due to the presence of the particle, Computational Fluid Dynamics (CFD) analysis using FLUENT^TM software is carried out. The winding considered for calculation is the high voltage part of the 200 kV transformer. Since the transformer is a two group winding only one half is taken for analysis due to symmetry. A particle of length, L = 0.5 mm and hemispherical radius of 0.25 mm is allowed to move in oil with flow velocity of 0.5 m/sec. the stress is calculated at various discs during upward movement of particle. A typical electrical stress obtained on the particle close to HV winding is 0.556 kV / mm. The particle considered for analysis is of spherical nature. Stress on the spherical particle is presented in this paper