Calculation of porosity values and flow analyzes of dry type transformer cabins with different ip classes

Since the heat caused by the losses in dry-type transformers with enclosures causes aging in the transformer, this heat must be effectively removed from the enclosure. Therefore, the design and efficiency of the cabin ventilation systems are crucial for extending the life of the transformer. In the heat transfer analyses of the designed transformers carried out with computational fluid dynamics (CFD) programs, porosity values of the ventilation grilles are needed to shorten the calculation process, which is quite long. In our study, the effect of different types of IP (Ingress Protection) protection classes used in dry-type transformer cabinet ventilation grilles on the flow was investigated experimentally and numerically and porosity values (1/α, viscous internal resistance factor and 𝐶2, inertial resistance factor) of these grilles were calculated. For this purpose, an experimental set was designed and manufactured to measure the air flow velocity passing through IP21, IP31, IPX3 and IP54 protection class grilles of dry-type transformer cabinets. For numerical results, a numerical model of the experimental set was created and CFD analyses were performed with Ansys Fluent software. In these analyses, k-ω SST turbulence model and Pressure-Velocity Coupling Simple solution algorithm were used to find the air outlet velocities and pressure drops. The obtained outlet velocities were compared with the experimental measurements and the numerical models were verified. According to the numerical results, it is seen that the highest pressure drop occurs in IP21 and the lowest pressure drop occurs in IPX3 when the fan operates at full capacity; the highest value in outlet velocities belongs to IPX3 and the lowest value belongs to IP31. Using the pressure drop values, the porosity values of the culverts were calculated as 𝐶2=1753,88, 1∕α=1,03x107 for IP21; 𝐶2=2958,94, 1/α=1,03x107for IP31 and 𝐶2=12602,45, 1∕α=9,00x105for IPX3. It is hoped that the porosity values obtained at the end of the study will be used in future transformer heat transfer analyses.